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Genetic variability and trait association studies in cashew (Anacardium occidentale L.)
Scientia Horticulturae 255 (2019) 108–114
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Genetic variability and trait association studies in cashew (Anacardium occidentale L.)
T
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Paul K.K. Adu-Gyamfia, , Mustapha Abu Dadziea, Michael Barnora, Abraham Akperteya, Alfred Arthura, Seth Osei-Akotob, Atta Oforia, Francis Padia a b
Cocoa Research Institute of Ghana P. O. Box 8 New Tafo Akim E/R, Ghana Ministry of Food and Agriculture P. O. Box M 37 Accra, Ghana
A R T I C LE I N FO
A B S T R A C T
Keywords: Germplasm Trunk cross-sectional area Genotype × environment interaction Heritability
High seedling mortality during the establishment phase together with low nut yield limit cashew productivity in Ghana. The survival and nut yield of 20 cashew germplasm clones were evaluated at two locations, Wenchi in the Forest Transition and Bole in the Guinea Savannah agro - ecological zones in Ghana. A randomized completeblock design with four replications was used to evaluate the clones for the following traits: seedling survival, vigour (estimated as trunk cross-sectional area, TCSA), height, nut yield, nut size and yield outturn. There were significant (p < 0.05) clone × environment interaction effects for nut yield. The best three highest yielding clones in Bole were SG 266, BE 575 and BE 203 whereas in Wenchi SG 224, SG 266 and SG 014 were the highest yielding clones. Genotypic co-efficient of variation (GCV) of nut yield (24.5%), TCSA (15.9%) and height (14.9%) were higher than those of other traits (3.0–4.5%). Height, TCSA, nut yield and outturn were found to be under moderate genetic control for the two locations combined whereas survival and nut size were under low genetic control. Broad sense heritability ranged from 0.56 ± 0.04 - 0.11 ± 0.01 for height and nut size respectively. Genetic correlation estimates suggest that selection for TCSA and height might lead to a large increment in seedling survival and early nut yield. Multivariate clustering identified clones with complementary traits. Our results, suggest that there is considerable genetic variability that could be exploited to develop superior cashew hybrids.
1. Introduction Recently, cashew (Anacardium occidentale L.) became the leading agricultural non - traditional export commodity crop in the Forest Savanna Transitional agro-ecological zone of Ghana. In 2016, cashew exports alone contributed over US$ 197 million in foreign exchange earnings to the Ghanaian economy (GEPA, 2018). Cashew has similarly attained the status of a cash crop in other Sub - Saharan African countries, including Benin, Togo, Ivory Coast, and Nigeria. Cashew originated from North-Eastern Brazil (Mitchell and Mori, 1987), and was introduced into Ghana by the early Portuguese settlers and begun as sporadic plantings across the country in the 1960′s, under the Savannah Afforestation Programme (Addaquay and Nyamekye-Boamah, 1998). Since then, cashew germplasm plots have been formally established (2004–2006) with seeds from Benin, Brazil, Mozambique, Tanzania and Ghana (Local collections) at the Wenchi and Bole research substations (Dadzie et al., 2014) to augment the cashew breeding program in Ghana.The cashew tree grows well in both tropical and sub-
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tropical regions of the world (Ohler, 1979). It is reputed for being drought tolerant requiring an annual rainfall range of 1500–2000 mm (Sys et al., 1993) and a temperature range of 25–28 ᵒC (Dendena and Corsi, 2014) with a pronounced dry period of 5–6 months (Dedzoe et al., 2001) for optimum productivity. It grows best on well drained, deep, light to medium textured soils (Dedzoe et al., 2001) with a pH range of 4.5–6.5 (Dendena and Corsi, 2014). The potential of cashew as a cash crop for poverty alleviation in the West African sub- region has previously been described (Dendena and Corsi, 2014; Chivandi et al., 2015). However, high seedling mortality at the establishment phase, low nut yields and quality constitute a major constraint to cashew production in Ghana (Dadzie et al., 2014). This has been attributed to the use of unimproved planting materials (Oliveira et al., 2006; Dadzie et al., 2014) and drought (Armah et al., 2011). The harmful effect of climate change at several levels of plant functions, leading to a drastic reduction in growth rates and yield traits has been highlighted. In leaves, the photosynthetic form is recognized as sensitive to elevated temperatures (Ceylan et al., 2018; Okatan,
corresponding author at: Cocoa Research Institute of Ghana P. O. Box 8 New Tafo Akim E/R, Ghana. E-mail address: [email protected] (P.K.K. Adu-Gyamfi).
https://doi.org/10.1016/j.scienta.2019.05.023 Received 27 February 2019; Received in revised form 7 May 2019; Accepted 8 May 2019 Available online 18 May 2019 0304-4238/ © 2019 Elsevier B.V. All rights reserved.
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2. Materials and methods
2018). Photosynthesis may be inhibited as a result of the loss of chlorophyll and reduced carbon fixation and assimilation. In addition, the reproductive tissues and their functions are highly sensitive to heat stress, and a few degrees rise in temperature during flowering can lead to loss of entire plant cycles (Mehmet et al. 2018; Okatan et al., 2015; Usanmaz et al., 2018). The low nut yields observed from farmers fields therefore suggest that the increasing incomes for the majority of smallscale farmers could be attributed to the increasing cashew nut prices over the past decades. Besides, the cashew clones currently given to farmers as an interim variety were recommended based on single tree nut yield performance of local germplasm collections established from seed sources and evaluated at a single site (Wenchi) where environmental conditions were considered optimal. The heterogeneity and out crossing tendency of cashew suggest that, such recommendations were not repeatable across the transition - savannah agro-ecological zones which holds the largest concentration of commercial cashew production in Ghana. Multi-location evaluation of germplasm clones has enabled breeders to identify superior parents and varieties for specific environments and the introduction of high yielding food crops with a short growing season in the crop pattern is considered to be an effective means for narrowing the food gap in the world (Okatan et al., 2016; Lateef et al., 2018). Currently, very few cashew clones in Ghana have been evaluated, moreover, the evaluations were carried out at a single location. The first evaluation consisted of ten cashew clones assessed for nut yield and yield efficiency (Dadzie et al., 2014). In Tanzania, Masawe et al. (1999) and Madeni (2016) reported a significant genotype × location interaction effects on the growth and yield of cashew respectively. Similarly, a significant genotype × environment interaction effects on nut yield of cashew have been reported in Nigeria (Aliyu et al., 2014). The usefulness of both local and exotic germplasm in identifying genotypes with rare alleles or allele combination conferring adaptation to specific environment, increased yield stability, food quality, and an advantage of reduced dependence on agronomic inputs have been noted for many crops (Palmgren et al., 2015; Castañeda-Álvarez et al., 2016; Dwivedi et al., 2016; Wang et al., 2017). Therefore, a comprehensive evaluation of germplasm clones from both local and exotic sources across defined ecologies for survival, vigour and yield is crucial to the cashew breeding program for an effective comparison and determination of clones for future breeding efforts. In tree crop breeding, key agronomic traits including juvenile growth traits (plant height and stem diameter increments) and yield efficiency (the ratio of cumulative yield to stem diameter increments) has gained interest in selecting high and early yielding genotypes (Padi et al., 2012; Ofori et al., 2015). In Ghana, cashew breeding research is still at its infancy (< 20yrs) and Dadzie et al. (2014) have utilized canopy area and yield efficiency to identify potentially high yielding cashew clones. The magnitude of genetic variation of key agronomic traits is important for effective utilisation and selection of cashew germplasm clones as parents in breeding programs. However, information on genetic parameters such as variance, heritability as well as correlation among agronomic traits in cashew germplasm clones in Ghana is limited. The utilisation of such information is critical if cashew breeders want to identify potential parents for breeding improved cultivars with broad genetic base. The objectives of the present study were (i) to assess the performance of cashew germplasm clones for seedling survival, vigour (estimated as Trunk - Cross - Sectional Area), plant height, nut size, outturn and nut yield (ii) to estimate the heritability for seedling survival, vigour, plant height, nut size, outturn and nut yield (iii) to assess the phenotypic and genotypic correlations between vigour and yield and it's component traits in cashew clones in Ghana.
2.1. Plant materials Twenty cashew germplasm clones were selected and clonally propagated by grafting scions harvested from mother trees onto 2.5 months old rootstocks raised from open pollinated seeds. This selection comprised of fifteen (15) high yielding (≥7 kg/tree) local germplasm clones SG 266, SG 224, SG 273, SG 004, SG 014, IDDM 29, KT 1, KT 2, SB 9, BAME 7, AKD, AKC, BAMBOI 7, KT 4 and KT 5 and five (5) high yielding (≥7 kg/tree) exotic germplasm clones ; BE 203, BE 627, BE 739, BE 204 and BE 575 from Benin. The selected clones were part of the local and exotic germplasm collections assembled at the Wenchi Agricultural Research Station under the cashew development project which was funded by the African Development Bank (Dadzie et al., 2014). 2.2. Field evaluation and plant culture The experiments were conducted at the Wenchi Agricultural Research Station in the Forest Transition agro - ecological zone (N 09ᵒ 00.561′, W002° 32.237′) and at Bole, a Substation of Cocoa Research Institute of Ghana in the Guinea Savannah agro - ecological zone (N 07ᵒ 45.171′ W002°05.803′). At the vegetative phase, total/mean rainfall amounts within the dry season were consistently higher at Wenchi (466 mm/78.9 mm) than at Bole (203.1 mm/42.3 mm) whereas mean maximum temperatures were relatively lower at Wenchi (32.8 °C) than Bole (36.1 °C) (Figure A1). At the reproductive phase (2012–2014), total/mean annual rainfall amounts were similarly, higher at Wenchi (1633 mm/93.3 mm) than Bole (1083 mm/56.7 mm) whereas annual maximum temperatures were consistently higher at Bole (33.3 °C) compared to Wenchi (31.2 ᵒC) (Figure A2). Comparatively, the weather conditions at Wenchi appeared favourable than Bole. Soil samples randomly collected from both sites at a depth of 0–15 and 15–30 cm did indicate that, the soils were of acidic reaction with pH values of 6.2 and 5.9 at Wenchi and 6.09 and 5.98 at Bole respectively (Table A1). At both soil depths, Wenchi consistently recorded high contents of organic carbon, nitrogen, phosphorus, potassium, magnesium and calcium than Bole. Indeed, at a soil depths of 0–15 cm, the total available phosphorus content was three fold higher at Wenchi (14.6 ppm) than Bole (5.06 ppm). Based on the soil chemical composition, the soils appeared to be more fertile at Wenchi than Bole. The trial was laid out in a randomized complete block design with four (4) replications involving 12 trees per clone per replication and clones were transplanted in June 2009 at a spacing of 10 m × 10 m (100 plants per hectare). In July 2009, each cashew plant was fertilized with nitrogen supplied as ammonium sulphate because of the low levels of fertility of the soil used for the experiment. The application of agro-pesticides followed recommended agronomic practices for cashew production in Ghana. Essentially, cyperderm (active ingredient - cypermethrin) @ 150 mL ha−1 was used to control insect pest from August - October annually. 2.3. Data collection Agronomic traits evaluated in this study included seedling survival (%), plant height (m), trunk cross-sectional area (mm2), nut size (g), outturn or shelling (%) and nut yield (kg ha−1). The stem diameter of young cashew plants was measured at 15 cm above the graft union with electronic callipers at yearly intervals from June 2009 to June 2011. Survival was estimated by determining the percentage of surviving plants after one year (2009–2010) of establishment in each plot. Data on yield per plot per annum were estimated from the weight of nuts collected from each clone throughout the fruiting season between 2012–2014 cropping years. Nut sizes (g) were estimated as the weight of 1 kg of raw cashew nuts divided by the number of nuts and out-turn (%) was estimated as (weight of healthy kernels divided by the weight 109
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two locations. The highest survival rate (≥90%) were observed with clone BE 203, BE 204, BE 627 KT 4 and SG 224 at Wenchi whilst BE 575, BE 739 and KT 5 were outstanding at Bole (Table 2). Across the two environments, survival rates were significantly lower by 12.8% at Bole than Wenchi. At Bole, TCSA increments ranged from 300 in BE 627 to 816 (mm2) in BAME 7 whilst at Wenchi an increment of 1360 in AKC to 3224 (mm2) in SG 266 was observed. The three best clones with the highest TCSA were observed with clone SG 266, BE 739 and SG 224 at Wenchi and BAME 7, SG 266 and BE 575 and at Bole respectively. Clone SG 266 was consistently vigorous ranking 1st in Bole and 2nd in Wenchi. Relatively, TCSA increments was three fold higher at Wenchi compared to Bole. Plant height increments also ranged from 0.49 in BE 627 to 1.07 m in SG 266 at Bole but at Wenchi a range of 0.77 in AKD to 1.58 m in SG 014 was recorded. Clones SG 266, BE 203 and KT 4 at Bole were the top three best clones with highest plant height increments whereas at Wenchi, clones SG 014, BE 204 and SG 266 were the best. In comparing the two locations, a relative reduction of 52.7% in plant height was observed at Bole. Nut yields at Bole, ranged from 37.2 in SB 9 to 391 kg ha −1yr in SG 266 whilst at Wenchi, a range of 210.4 in AKD to 625.8 kg ha −1 in SG 244 was observed (Table 3). Clones SG 224, SG 266, SG 014, SG 004 and BE 204 were the best five highest yielding clones at Wenchi whereas at Bole SG 266, BE 575, BE 203, BE 739 and BAME 7 was the best. Again, SG 266 appeared to be consistently high yielding, ranking 2nd in Wenchi and 1st at Bole. Across the two locations a relative nut yield reduction of 170% was observed. The location effects on nut yield was highly significant (p < 0.001), Wenchi (387.8 kg ha −1) gave higher nut yields than Bole (143.9 kg ha −1 ). At Bole, the best five clones with the largest nut size (≥5.1 g) included BE 739, KT 5, SG 273, BAME 7 and BE 575 whereas at Wenchi BAMBOI 7, BE 739, KT 4, KT 5 and IDDM 29 were outstanding (nut sizes ≥ 6.3 g). Across the two locations, a relative mean nut size reduction of 21% was observed at Bole compared with Wenchi. At Bole, the best five clones with the highest outturn (≥28%) were IDDM 29, SG 224, SB 9, BE 203 and BAMBOI 7, but in Wenchi KT 2, BAMBOI 7, BAME 7, SG 014, and BE 203 were superior (outturn ≥ 30%). A relative outturn reduction of 6.4% was observed when Bole was compared to Wenchi. In comparing the two locations, Bole could be relatively marginal. This was evident from the relatively low rainfall amount and distribution, low soil fertility and higher temperatures stress observed (Table A1 and Figure A1 & A2). Accordingly, TCSA, plant height, nut yield, nut size and outturn estimates of the clones tested were lower in Bole than Wenchi.
of raw nuts) × 100 for each clone. Plant height was measured by placing a meter rule against the plant and measuring from the base of the plant (soil surface) to the apex of the plant. Trunk cross-sectional area (TCSA) was estimated from the tree trunk diameter measurements using the formula: (πd2)/4 Where, d is the stem/trunk diameter. 2.4. Statistical analysis Analysis of variance based on best linear unbiased prediction (BLUP) was carried out with META - R (Multi-Environment Trial Analysis with R for Windows) statistical package (Alvarado et al., 2018), with environments considered a random effect and germplasm clones as a fixed effects. The following model was used for combined location analysis. Yijk = μ + Bj + Gj + Lk + GLjk+ Ɛijk Where, Yijk = observed trait value of genotype j in block i of Environment k, μ=grand mean, Bi=block effect, Gj=effect of genotype, Lk= Environmental effect, GLjk = the interaction effect of genotype j with Environment k and Ɛijk = error (residual) effect of genotype j in block i of environment k. The differences among means were tested by least significant difference (LSD) at the 5% probability level. Heritability, phenotypic and genetic correlations among traits across environments were estimated using META-R (Alvarado et al., 2018). The standard errors of heritability were calculated according to the formula suggested by Singh et al. (1993). The analyses on yield utilized 3-year yield data (2012–2014), whereas the analysis on the growth (trunk crosssectional area and plant height) utilized the difference between the initial and final recordings from 2009 to 2011. Multivariate analyses were conducted using the procedure of principal component analysis and hierarchical cluster analysis to bring out the patterns of similarity among the 20 clones. Genotypic and phenotypic coefficient of variation were estimated following (Burton, 1952) as,
GCV = √σG M and PCV = √σP M Where, GCV, PCV, σG, σP and M are genotypic coefficient of variation, phenotypic coefficient of variation, genotypic variance, phenotypic variance and trait mean respectively.
3.2. Genotypic and phenotypic coefficient of variation and heritability of traits
3. Results
Generally, the phenotypic coefficient of variation (PCV) was higher than the genotypic coefficient of variation (PCV) for all the traits evaluated (Table 4). Nut yield had the highest genotypic coefficient of variation (GCV) of 24.5% and outturn had the lowest (3.6%) compared with the other traits. Phenotypic coefficient of variation (PCV) likewise, followed a similar trend with nut yield having the highest (40.0%) and outturn being the lowest (5.1%). Heritability estimates across locations were generally moderate to low. The highest heritability estimate was
3.1. Clone × environment interaction effect for traits The analysis of variance revealed significant clone, environment and clone x environment interaction effects (p < 0.05) for survival, trunk cross-sectional area, plant height, nut yield, nut size and outturn (Table 1). Differences in ranking among the clones were evident at the
Table 1 Mean sum of squares for percent survival, trunk cross sectional area (TCSA), plant height, nut yield, nut size and outturn of 20 cashew germplasm clones evaluated at Bole and Wenchi.from 2009 to 2014. Source
df
Survival (%)
TCSA (mm2)
Height (m)
Yield (kg/ha)
Nut size (g)
Outturn (%)
Block Clone Environment Clone × Environment Error
3 19 1 19 117
612.1 1585.3*** 2331.7* 1100.2* 618.2
97926* 779,733** 123,358,474* 383,741* 228627
0.032* 0.260* 6.11** 0.113* 0.065
433,308* 57,712*** 2,380,586** 23,613** 12153
0.1377 0.794*** 54.05*** 1.079** 0.2253
2.26 15.54*** 124.96*** 10.32** 4.93
*, **, ***Significantly different at p ≤ 0.05 p ≤ 0.01and p ≤ 0.001, respectively. 110
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Table 2 Mean survival, TCSA and height of 20 cashew germplasm clones at 24 months after planting at Bole and Wenchi. Wenchi
Bole 2
Clones
Survival (%)
TCSA(mm )
Height(m)
Clone
Survival (%)
TCSA (mm2)
Height (m)
BE 203 BE 204 BE 627 KT 4 SB 9 SG 224 BE 575 IDDM 29 KT 2 SG 273 KT 1 SG 004 SG 014 BE 739 KT 5 BAMBOI 7 SG 266 AKC BAME 7 AKD Mean SED (C × E)
100.0 (90.0) 100.0 (90.0) 100.0 (90.0) 100.0 (90.0) 100.0 (90.0) 100.0 (90.0) 87.5 (75.0) 87.5 (69.3) 87.5 (69.3) 87.5 (69.3) 81.2 (64.7 81.2 (64.7) 75.0 (60.0) 81.2 (59.0) 81.2 (59.0) 75.0 (54.3) 75.0 (54.3) 68.8 (44.0) 56.2 (35.4) 56.2 (34.7) 84.1(67.7 ± 4.1) 17.58
2637 1749 1830 2610 2533 2917 2647 2779 2024 1891 1962 1868 2401 3089 2138 1965 3224 1360 2265 1596 2274.3 ± 115 338.1
1.40 1.48 0.99 0.96 1.2 1.41 0.95 0.91 0.94 0.93 0.89 1.43 1.58 1.18 1.19 1.33 1.44 0.85 0.81 0.77 1.13 ± 0.05 0.18
BE 575 BE 739 BAME 7 IDDM 29 KT 2 KT 5 BE 203 KT 4 BE 204 BAMBOI 7 SB 9 SG 224 SG 266 SG 004 SG 014 BE 627 KT 1 AKD AKC SG 273
100.0 (90.1) 100.0 (90.0) 87.5 (75.0) 87.5 (75.0) 87.5 (75.0) 100.0 (75.0) 81.2 (71.1) 81.2 (71.1) 81.2 (64.7) 87.5 (60.0) 75.0 (60.0) 68.8 (60.0) 87.5 (60.0) 75.0 (49.7) 68.8 (45.8) 56.2 (41.1) 56.2 (41.1) 56.2 (34.7) 56.1 (34.6) 43.8 (26.1) 76.9 (60.1 ± 4.0)
780 568 816 556 343 548 646 647 572 455 457 437 782 470 487 300 510 312 350 327 518.2 ± 35.2
0.88 0.83 0.77 0.71 0.61 0.77 1.04 0.9 0.77 0.85 0.53 0.65 1.07 0.74 0.78 0.49 0.55 0.58 0.61 0.7 0.74 ± 0.03
C - Clones, E-Environment,TCSA - Trunk cross-sectional area, SED - Standard error of difference. Figures in parenthesis are transformed values. Table 3 Mean nut yield, nut size and outturn of 20 cashew germplasm clones evaluated at Wenchi and Bole from 2012–2014. Wenchi
Bole
Clone
Nut yield (kg ha−1)
Nut size (g)
Outturn (%)
Clone
Nut yield (kg ha−1)
Nut size (g)
Outturn (%)
SG 224 SG 266 SG 014 SG 004 BE204 BE203 BE627 KT 5 BE575 SB 9 SG 273 IDDM29 BAME 7 KT 2 BAMBOI 7 BE739 KT 4 KT 1 AKC AKD Mean SED (0.05) C × E
625.8 561.4 555 536.7 469.4 469.2 403.3 372.5 370.1 369.2 368.3 361.7 342.5 342.5 316.6 314.2 299.8 256.7 211.2 210.4 387.8 ± 25.9 60.8
6.1 5.8 5.2 5.9 5.3 5.2 6.0 6.3 5.9 6.2 5.4 6.3 6.0 5.3 6.3 6.3 6.3 5.3 5.9 5.9 5.8 ± 0.90 0.34
29.9 30 31.7 29.8 25.7 31.3 30.9 30.1 29.3 30.4 28.8 30.6 31.6 34 31.8 29.2 30.7 28.4 28.7 30.1 30.1 ± 0.37 1.6
SG 266 BE575 BE203 BE739 BAME 7 BE204 SG 014 KT 1 KT 5 SG 004 IDDM29 BAMBOI 7 KT 4 SG 224 BE627 KT 2 SG 273 AKD AKC SB 9
391 250.7 208.8 206.3 178.3 177 171.5 170.8 156.7 148.2 123.4 114.9 102.7 100.8 92.5 87.1 72.9 44.9 42.4 37.2 143.9 ± 18.6
3.5 5.2 4.2 5.6 5.3 4.6 4.5 4.8 5.6 4.8 4.6 4.6 4.6 4.7 4.4 4.8 5.3 4.8 5.1 4.4 4.8 ± 0.11
25.3 26.4 27.9 30.2 27.4 25.5 28.9 27.5 28.5 29.5 32.3 27.5 29.2 31.6 28.5 27.3 29.3 28.6 25.8 30.6 28.3 ± 0.43
C - Clones, E-Environment, SED - Standard error of difference.
observed in plant height ( h2bs = 0.56) followed by outturn ( h2bs = 0.52), TCSA ( h2bs = 0.51), survival ( h2bs = 0.14) whilst the least was observed with nut size ( h2bs = 0.11).
(rg = 0.90, p < 0.001; rp = 0.80, p < 0.001) at both the genotypic and phenotypic level whilst a significant genotypic correlation with survival (rg = 0.96, p < 0.001) was similarly only observed at Bole. A negative significant correlation between nut yield and nut size (rg = − 0.48, p < 0.05;) and outturn (rg = − 0.40, p < 0.05) only at the genotypic level was observed. Generally genotypic correlation coefficient estimates were higher than phenotypic estimates for most traits.
3.3. Genotypic and phenotypic correlation among traits A positive genotypic (rg) and phenotypic (rp) correlation were observed between TCSA increments versus yield (rg = 0.94, p < 0.001; rp = 0.76, p < 0.001) in Bole and (rg = 0.41, p < 0.05; rp = 0.35ns) in Wenchi (Table 5). However, for survival, a significant correlation (rg = 0.98, p < 0.001; rp = 0.66, p < 0.01) with TCSA was only observed at Bole. Plant height increments likewise correlated with yield at Bole (rg = 0.93, p < 0.001; rp = 0.74, p < 0.001) and at Wenchi
3.4. Multivariate analysis The output of the principal component analysis based on six morphological traits; survival, plant height, TCSA, nut size, outturn and nut yield of the 20 cashew clones demonstrated that in Bole, at a similarity 111
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Table 4 Estimates of mean, range and genetic variability components for survival, TCSA, height, nut yield, nut size and outturn of 20 cashew germplasm clones evaluated at Bole and Wenchi. Genetic parameters
Survival (%)
TCSA (mm2)
Height (m)
Nut yield (Kg/ha)
Nut size (g)
Outturn (%)
Mean Range Vg Vp Vg x Ve GCV PCV Vg/Ve h2bs
65.4 35 - 82.5 25.49 182.2 171.22 3.0 20.6 4.9 0.14 ± 0.03
1396.2 855 - 2003 49498.93 97056.6 41210.18 15.9 22.3 3.1 0.51 ± 0.06
0.94 0.70 - 1.3 0.02 0.033 0.01 14.5 19.4 4.05 0.56 ± 0.04
265.86 126.8 - 476.2 4260.44 11211.6 2007.34 24.5 40 6.8 0.38 ± 0.02
5.22 4.7 - 6.0 0.056 1.4 0.17 4.5 22.6 12.04 0.11 ± 0.01
29.4 25.6 - 31.5 1.17 2.28 0.82 3.6 5.1 1.1 0.52 ± 0.03
Vg - genotypic variance, Vp - phenotypic variance, GCV - genotypic coefficient of variation, PCV - phenotypic coefficient of variation, h2bs – broad sense heritability and its standard errors and Ve - environmental variance.
coefficient of 0.85 three clusters were formed (Fig. 1). The first cluster comprised of eight clones; AKC, AKD, BAMBOI 7, KT 2, BE627, IDDM 29, SG 224 and SB 9 which had relatively lower nut yield (80.4 kg ha−1), with corresponding low survival rates (55%), TCSA (401.25 mm2), plant height (0.63 m) and nut sizes (4.7 g) but higher outturns (29.0%). The second cluster consisted of eleven clones; BAME 7, BE 203, BE 204, BE 575, BE 739, KT 1, KT 4, KT 5, SG 004, SG 014, SG 273 which also had comparatively moderate nut yields (167.6 kg ha−1) and survival rates (63.6%) together with medium plant height (0.79 m), TCSA (579.18 mm2) and nut sizes (5 g). The third cluster included only a single clone SG 266 which was extremely higher yielding (391 kg ha−1) with higher plant heights (1.07 m), TCSA (782 mm2), moderate survival rates (60%) with extremely lower nut sizes (3.5 g) and outturns (25.3%). In Wenchi, at the same similarity coefficient value of 0.85, four clusters were formed (Fig. 2). The first cluster comprised of AKC, AKD, BAME 7, KT 1, SG 273 and KT 2 which typically had the lowest survival rates (52.9%), yield (288.6 kg ha−1), plant height (0.86 m) and TCSA (1849.6 mm2). The second cluster, also comprised of BAMBOI 7, SB 9, BE 575, BE 627, BE 739, IDDM29, KT 4, KT 5, and SG 004. This group was characterized by relatively largest nut sizes (6.1 g), moderate survival rates (72.6%), TCSA (2384.33 mm2), plant height (1.1 m) and nut yields (371.56 kg ha−1). The third cluster which was made up of only two clones SG 224 and SG 266 were the most vigorous, TCSA (3070.5 mm2) with corresponding relatively highest nut yields (593.6 kg ha −1) and plant height (1.4 m) but moderate survival rates (72.15%). The fourth cluster was characteristically taller plants (1.5 m) with higher TCSA (2262.33 mm2), moderate nut yields (497.86 kg ha−1) and relatively higher survival rates (80%). This cluster involved three clones; SG 014, BE 203 and BE 204.
Fig. 1. Dendrogram constructed on first two principal components for 20 cashew germplasm clones evaluated at Bole over 5 year period.
selecting parental clones for yield improvement. In this study, we report on the responses of cashew germplasm clones to two contrasting locations; Wenchi and Bole. The significant clone × environment interaction variation observed for survival, TCSA, height, nut yield, nut size and outturn indicated that the germplasm clones exhibited differences in ecological variation under the different growth conditions observed at the two locations. It therefore suggest that, trait expressions among the germplasm clones were largely influenced by the environment and selecting genotypes that are best adapted to specific environments could be the best breeding strategy for cashew improvement, if high genetic and economic gains are expected. This observation is consistent with other authors who found significant genotype × environment (G × E)
4. Discussion The level of genetic variation present in germplasm collections and the genetic relationship among key agronomic traits could be vital in
Table 5 Genotypic and phenotypic correlation coefficients for survival, TCSA, height, nut yield, nut size and outturn of 20 cashew germplasm clones evaluated at Bole and Wenchi. TCSA (mm2)
Traits
Survival (%) Nuts sizes (g) Outturn (%) Nut yield (kg/ha)
Height (m)
Survival (%)
Nut size (g)
Outturn (%)
Genotypic /Phenotypic
Bole
Wenchi
Bole
Wenchi
Bole
Wenchi
Bole
Wenchi
Bole
Wenchi
Genotypic Phenotypic Genotypic Phenotypic Genotypic Phenotypic Genotypic Phenotypic
0.98*** 0.66** −0.09 −0.02 −0.27 −0.27 0.94*** 0.76**
0.33 0.16 0.37 0.34 0.20 0.10 0.41* 0.35
0.96*** 0.58** −0.22 −0.18 −0.20 −0.19 0.93*** 0.74***
0.35 0.27 −0.30 −0.22 −0.23 −0.14 0.90*** 0.80***
−0.26 −0.04 0.23 −0.05 0.89*** 0.49*
−0.12 −0.10 −0.19 −0.20 0.45* 0.33
0.01 0.04 −0.48* −0.30
0.06 0.09 −0.27 −0.23
−0.40* −0.32
0.01 −0.51*
*: P < 0.05, **: P < 0.01, ***P < 0.001. TCSA - Trunk cross sectional area. 112
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tolerance to high temperature stress. They could, therefore, be utilized as donors to develop superior cashew hybrids with higher tolerance to drought stress. The significant positive (genotypic and phenotypic) correlations observed between nut yield and the other yield related component indicate that direct selection for any of those characters could improve nut yield. The significant positive genotypic and phenotypic correlation observed survival and TCSA (rg = 0.98, p < 0.001; rp = 0.66, p < 0.01) and plant height (rg = 0.96, p < 0.001) in Bole implies that TCSA and plant height could be a better indicator for determining survival especially under marginal environmental conditions as evidenced in other studies (Hutcheon, 1973; Ofori et al., 2017). The reports on cashew seedling survival rate is rare, however, in many tree crops, seedling survival is related to vigour (TCSA), thus more vigorous genotypes had a higher survival rate than less vigorous genotypes especially under drought stress conditions (Hutcheon, 1973; Ofori et al., 2017). This finding also suggest that, cashew clones may employ faster growth rate to evade moisture deficit and ensure survival. On the other hand, a significant correlation was observed between nut yield and TCSA (vigour) at Bole (rg = 0.94, p < 0.001; rp = 0.76, p < 0.001) and TCSA at Wenchi (rg = 0.41, p < 0.05; rp = 0.35ns). Subsequently, nut yield also correlated with plant height at Bole (rg = 0.93, p < 0.001; rp = 0.74, p < 0.001) and at Wenchi (rg = 0.90, p < 0.001; rp = 0.80, p < 0.001). Similar correlations in cashew have been reported but at the phenotypic level (Masawe et al., 1999; Sethi and PCLSK, 2016). Although both TCSA and plant height could be indicators in determining nut yield, TCSA is a better indicator in determining early nut yield in cashew under marginal conditions. This concurs with other reports emphasizing the effectiveness of TCSA in predicting nut yields in Cola nitida (Akpertey et al., 2017) and Theobroma Cacao (Padi et al., 2012). The negative significant correlation between nut yield and nut size (rg = − 0.48, p < 0.05;) and outturn (rg = − 0.40, p < 0.05) indicates that the smaller the nut size and outturn, the higher the corresponding nut yield. Although, both positive and negative correlations between nut yield and nut size have been reported in cashew (Sena et al., 1994; Aliyu, 2006), the conflicting reports on these relationships been attributed to differences in the advanced stage of the population utilized and the nature of the previous selection method employed in the previous yield improvement programme (Sundararaju et al., 2006; Paikra, 2016). Their use as a selection criterion in the breeding program under all ecologies have therefore demonstrated significant indirect effects on yield through the number of nuts per tree without any adverse compensation effects (Madeni, 2016). The analysis of the relatedness among the germplasm clones in our study demonstrated that clusters were of mixed origin which suggested that geographical diversity among the germplasm clones evaluated did not significantly influence genetic diversity of the traits studied. The development of superior cashew hybrids with higher seedling survival rates and higher nut yield and quality may involve hybridization of germplasm clones with complimentary traits among clusters. This is in concurrence with Aliyu (2006) who emphasized that hybridization and recurrent selection approach could improve cashew productivity without compromising quality.
Fig. 2. Dendrogram constructed on first two principal components for 20 cashew germplasm clones evaluated at Wenchi over 5 year period.
interactions effects for growth and nut yield in cashew (Aliyu et al., 2014). Moreover, the relatively faster growth rate and higher nut yield observed at Wenchi compared with Bole where environmental conditions were relatively marginal suggest that, cashew productivity at a given location could partly depend on rainfall amount, soil fertility status and temperature stress during the cropping season. This concurs with the findings of other researchers who emphasized that agro-climatic differences, genetic make and interaction of both are responsible for the reported differences in the yield of many crops (Datta, 2013; Balogoun et al., 2016; Madeni, 2016). Burton (1952) opined that the genetic coefficients of variation (GCV) provides a scale for comparing genetic variability in quantitative traits and in combination with heritability estimates, determine the extent of heritable variation. In this study, the correspondingly higher heritabilities estimates in combination with higher genotypic coefficient of variation values observed for plant height (0.56; 14.5%), TCSA (0.51 had 13.5%) and nut yield (0.38 had 3.1%) could indicate an equivalent genetic potential for the improvement of growth traits as that for yield traits. The relatively high heritability estimates observed for plant height compared with TCSA suggest that plant height has higher genetic control than TCSA and more genetic gain can be expected from the selection of plant height than for TCSA. Besides, the observed heritability estimates for TCSA and plant heights in our study were quiet comparable to earlier reported range of 0.30 - 0.85 for stem diameter increment and 0.46–0.80 for plant height (Sethi et al., 2016) respectively. The low heritability estimate for survival and nut size suggest that, these traits have low genetic control and low genetic gain as it's expression is largely influenced by the environment which is evident from the high environmental variance of 4.9 and 12.04 respectively. Although heritability estimates for survival in cashew is rare, heritability estimates of 0.78 for nut size has been reported but this estimates were obtained from field trials conducted at a single location only (Sankaranarayanan et al., 2011). The relatively low heritability estimates observed for survival and nut size suggest that significant genetic improvement in this trait is achievable if progeny testing and phenotypic recurrent selection approaches employed since they have demonstrated significant genetic gains for traits with low heritabilities but high economic importance (Jansky, 2009). In addition, the advantage using more efficient statistical methods in the identification of superior families and individuals using best linear unbiased prediction (BLUP) have produced significant genetic improvement in many crops (Slater et al., 2014). The superior performance observed in clones BE 575, BE 739, KT 5, SG 266 for survival, BE 575, BE 203, BE 739 for nut yield and BAMBOI 7, BE 739, IDDM 29 and KT 4 for nut size in Bole where environmental conditions were relatively marginal suggest that these clones could possibly posses alleles that ensures higher water and nutrient-use efficiency with better
5. Conclusions The variation existing in germplasm collection could be associated with the genetic history, origin, and selection of the desired trait by farmers (Chipojola et al., 2009). In this study, we assessed the genetic variability and relationship among key agronomic traits for growth and yield attributes of 20 diverse juvenile cashew clones from both local and exotic sources in two contrasting agro - ecological locations in Ghana. We estimated some genetic parameters mainly, heritability, genotypic variance, genotypic and phenotypic co-efficient of variation, genotypic and phenotypic correlation and our study revealed significant environment, clone and clone × environment interaction 113
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effects for survival, TCSA, height, nut yield, nut size and outturn. The significant clone × environment interaction observed might be a reflection of the varied responses observed among the clones to the agroclimatic differences observed at the two locations. The differences in the amount of rainfall, soil nutrient levels and high temperature stress at the two locations might possibly be the main drivers of this interaction. The moderate to high GCV observed for height, TCSA and nut yield suggest the presence of considerable genetic variability for these traits. Again, the moderate to high broad sense heritabilities estimate for nut yield, outturn, TCSA, heights and low for survival and nut size for the two sites combined indicated moderate to high environmental influence in the expression of these traits respectively. The significant genetic correlations estimates between TCSA, plant height with nut yield and survival were moderate to strong, suggesting that selection for TCSA and height traits might lead to increment in survival and nut yield, and genetic factors act concurrently to increase nut yield, TCSA and height. The high yielding clones could be selected at this stage for further breeding programs. The results from our study indicated that there is considerable genetic variation among the germplasm clones for growth and yield related traits. The identified clones that are complimentary for survival, vigour, nut yield, nut size and outturn could be utilized as parental clones to for the cashew hybridization program without further evaluation for these traits.
Castañeda-Álvarez, N.P., Khoury, C.K., Achicanoy, H.A., Bernau, V., Dempewolf, H., Eastwood, R.J., Guarino, L., Harker, R.H., Jarvis, A., Maxted, N., 2016. Global conservation priorities for crop wild relatives. Nat. Plants 2, 16022. Ceylan, F., Akpınar, M.G., Cherciov, A.-M., Özkan, B., Gül, M., 2018. Consumer preferences of organic products for Romania. Int. J. Agric. For. Life Sci. 2, 47–55. Chipojola, F.M., Mwase, W.F., Kwapata, M.B., Bokosi, J.M., Njoloma, J.P., Maliro, M.F., 2009. Morphological characterization of cashew (Anacardium occidentale L.) in four populations in Malawi. Afr. J. Biotechnol. 8. Chivandi, E., Mukonowenzou, N., Nyakudya, T., Erlwanger, K.H., 2015. Potential of indigenous fruit-bearing trees to curb malnutrition, improve household food security, income and community health in Sub-Saharan Africa: a review. Food Res. Int. 76, 980–985. Dadzie, A.M., Adu-Gyamfi, P.K.K., Opoku, S.Y., Yeboah, J., Akpertey, A., Opoku-Ameyaw, K., Assuah, M., Gyedu-Akoto, E., Danquah, W.B., 2014. Evaluation of potential cashew clones for utilization in Ghana. Adv. Biol. Chem., vol.04 (8) No. 04. Datta, S., 2013. Impact of climate change in Indian horticulture-a review. Int. J. Sci. Environ. Technol. 2, 661–671. Dedzoe, C., Senayah, J., Asiamah, R., 2001. Suitable agro-ecologies for cashew (Anacardium occidetale L) production in Ghana. West Afr. J. Appl. Ecol. 2. Dendena, B., Corsi, S., 2014. Cashew, from seed to market: a review. Agron. Sustain. Dev. 34, 753–772. Dwivedi, S.L., Ceccarelli, S., Blair, M.W., Upadhyaya, H.D., Are, A.K., Ortiz, R., 2016. Landrace germplasm for improving yield and abiotic stress adaptation. Trends Plant Sci. 21, 31–42. GEPA, 2018. Cashew Export. Available at https://www.gepaghana.org/market-report/ cashew-nut-shell-competitor-analysis-2017/ [Accessed 30/5/2018]. . Hutcheon, W., 1973. Breeding for Tolerance of Exposure and the Ability to Respond to Increased radiation Annual Report 1971. Jansky, S., 2009. Breeding, genetics, and cultivar development. Advances in Potato Chemistry and Technology. Elsevier, pp. 27–62. Lateef, E.A., Salam, M.A., Selim, M., Tawfik, M., Mohamad, Farrag A., 2018. Effect of climate change on mungbean growth and productivity under egyptian conditions. Int. J. Agric. For. Life Sci. 2, 16–23. Madeni, J.P., 2016. Genotype X Environment Interaction on Performance of Selected Cashew (Anacardium Occidentale L.) Hybrids in Tanzania. MSc. Thesis. Sokoine University of Agriculture. Masawe, P., Cundall, E., Caligari, P., 1999. Studies on genotype-environment interaction (GxE) in half-sib progenies of cashew (Anacardium occidentale L.) in Tanzania. Tanzania J. Agric. Sci. 2. Mehmet, K.O.Ç., Çetinkaya, H., Yildiz, K., 2018. A research on recent developments and determination of the potential of olive in kilis. Int. J. Agric. For. Life Sci. 2 (2), 185–188. Mitchell, J.D., Mori, S.A., 1987. The cashew and its relatives. Mem. New York Bot. Gard 42. Ofori, A., Padi, F., Acheampong, K., Lowor, S., 2015. Genetic variation and relationship of traits related to drought tolerance in cocoa (Theobroma cacao L.) under shade and no-shade conditions in Ghana. Euphytica 201, 411–421. Ofori, A., Padi, F., Akpertey, A., Adu-Gyamfi, P., Dadzie, M., Amoah, F., 2017. Variability of survival and yield traits in cacao (Theobroma cacao L.) clones under marginal field conditions in Ghana. J. Crop. Improv. 31, 847–861. Ohler, J.G., 1979. ’Cashew.’ (Koninklijk Instituut Voor De Tropen: Koninklijk Instituut Voor De Tropen. Department of agricultural, research, Amsterdam. Okatan, V., 2018. Phenolic compounds and phytochemicals in fruits of black mulberry (Morus nigra L.) genotypes from the Aegean region in Turkey. Folia Hortic. 30, 93–101. Okatan, V., Polat, M., Așkın, M., Çolak, A., 2015. Determination of Some Physical Properties of Currant (Ribes Spp.), Jostaberry (Ribes× Nidigrolaria Bauer) and Goosberry (Ribes Grossularia L.) Cultivars 10. Ziraat Fakültesi Dergisi-Süleyman Demirel Üniversitesi, pp. 83–89. Okatan, V., Polat, M., AŞKIN, M.A., 2016. Some Physico-chemical characteristics of Black mulberry (morus nigra l.) in bitlis. Sci. Papers-Series B, Horticult. 27–30. Oliveira, V.H., Miranda, F.R., Lima, R.N., Cavalcante, R.R.R., 2006. Effect of irrigation frequency on cashew nut yield in Northeast Brazil. Sci. Hortic. 108, 403–407. Padi, F.K., Opoku, S.Y., Adomako, B., Adu-Ampomah, Y., 2012. Effectiveness of juvenile tree growth rate as an index for selecting high yielding cocoa families. Sci. Hortic. 139, 14–20. Paikra, M.S., 2016. Studies On Genetic Divergence In Cashew (Anacardium Occidentale L.). Indirra Gandhi Krishi Vishwavidyalaya, Raipur Research thesis PhD Thesis. Palmgren, M.G., Edenbrandt, A.K., Vedel, S.E., Andersen, M.M., Landes, X., Østerberg, J.T., Falhof, J., Olsen, L.I., Christensen, S.B., Sandøe, P., 2015. Are we ready for back-to-nature crop breeding? Trends Plant Sci. 20, 155–164. Sankaranarayanan, R., Ahmad Shah, H., Sekar, V., 2011. Genetic Analysis in Cashew, I International Symposium on Cashew Nut 1080. Sena, D., Lenka, P., Jagadev, P., Beura, S., 1994. Genetic variability and character association in cashewnut (Anacardium occidentale L.). Indian J. Genet. Plant Breed. 54, 304–309. Sethi, K., PCLSK, Tripathy, 2016. Correlation and path coefficient analysis of nut yield and ancillary component traits in cashew. J. Plant. Crop. 44, 119–123. Sethi, K., Tripathy, P., Mohapatra, K., 2016. Variability and heritability of important quantitative. Environment & Ecology 34, 1795–1798. Singh, M., Ceccarelli, S., Hamblin, J., 1993. Estimation of heritability from varietal trials data. Theor. Appl. Genet. 86, 437–441. Slater, A.T., Wilson, G.M., Cogan, N.O., Forster, J.W., Hayes, B.J., 2014. Improving the analysis of low heritability complex traits for enhanced genetic gain in potato. Theor. Appl. Genet. 127, 809–820. Sundararaju, D., Yadukumar, N., Bhat, P.S., Raviprasad, T., 2006. Yield performance of “Bhaskara” cashew variety. J. Plant. Crop. 34, 216–219. Sys, C., Van Ranst, E., FB, JD, 1993. Land Evaluation Part 3: Crop Requirements Agricultural Publications n° 7. G.A.D.C., Brussels, Belgium. Usanmaz, S., Öztürkler, F., Helvaci, M., Alas, T., Kahramanoğlu, I., Aşkin, M., 2018. Effects of periods and altitudes on the phenolic compounds and oil contents of olives, cv. Ayvalik. Int. J. Agric. For. Life Sci. 2, 32–39. Wang, C., Hu, S., Gardner, C., Lübberstedt, T., 2017. Emerging avenues for utilization of exotic germplasm. Trends Plant Sci. 22, 624–637.
Disclosure statement The authors declare no potential conflict of interest. Acknowledgement This work was supported by Cocoa Research Institute of Ghana (CRIG) with funding from the African Development Bank (AfDB) through the erstwhile Cashew Development Project (CDP). Our appreciation goes to Mr Gabriel Boahen and staff of the Wenchi Agricultural Research Station for their invaluable assistance in the establishment and maintenance of this trial at Wenchi and Bole. This manuscript is published with the permission of the executive director This paper is published with the permission of the Executive Director of the Cocoa Research Institute of Ghana as manuscript number CRIG/011/2019/ 035/003. Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.scienta.2019.05.023. References Addaquay, J., Nyamekye-Boamah, K., 1998. The Ghana cashew industry study. Report Prepared for Ministry of Food and Agriculture Under the Agricultural Diversification Project. World Bank. Akpertey, A., Dadzie, A.M., Adu-Gyamfi, P.K.K., Ofori, A., Padi, F.K., 2017. Effectiveness of juvenile traits as selection criteria for yield efficiency in kola. Sci. Hortic. 216, 264–271. Aliyu, O., 2006. Phenotypic correlation and path coefficient analysis of nut yield and yield components in cashew (Anacardium occidentale L.). Silvae Genet. 55, 19–24. Aliyu, O.M., Adeigbe, O.O., Lawal, O.O., 2014. Phenotypic stability analysis of yield components in cashew (Anacardium occidentale L.) using additive main effect and multiplicative interaction (AMMI) and GGE biplot analyses. Plant Breed. Biotechnol. 2, 354–369. Alvarado, G., López, M., Vargas, M., Pacheco, Á, Rodríguez, F., Burgueño, J., Crossa, J., 2018. META-R (Multi Environment Trail Analysis with R for Windows) Version 6.03. CIMMYT Research Data & Software Repository Network. Armah, F.A., Odoi, J.O., Yengoh, G.T., Obiri, S., Yawson, D.O., Afrifa, E.K., 2011. Food security and climate change in drought-sensitive savanna zones of Ghana. Mitig. Adapt. Strateg. Glob. Chang. 16, 291–306. Balogoun, I., Ahoton, E.L., Saïdou, A., Bello, O.D., Ezin, V., 2016. Effect of climatic factors on cashew (Anacardium occidentale L.) productivity in Benin (West Africa). J. Earth Sci. Clim. Chang. 7 (1). Burton, G.W., 1952. Quantitative inheritance in grasses. Pro. VI Int. Grassl. Cong. 1952, 277–283.
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Scientia Horticulturae journal homepage: www.elsevier.com/locate/scihorti
Genetic variability and trait association studies in cashew (Anacardium occidentale L.)
T
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Paul K.K. Adu-Gyamfia, , Mustapha Abu Dadziea, Michael Barnora, Abraham Akperteya, Alfred Arthura, Seth Osei-Akotob, Atta Oforia, Francis Padia a b
Cocoa Research Institute of Ghana P. O. Box 8 New Tafo Akim E/R, Ghana Ministry of Food and Agriculture P. O. Box M 37 Accra, Ghana
A R T I C LE I N FO
A B S T R A C T
Keywords: Germplasm Trunk cross-sectional area Genotype × environment interaction Heritability
High seedling mortality during the establishment phase together with low nut yield limit cashew productivity in Ghana. The survival and nut yield of 20 cashew germplasm clones were evaluated at two locations, Wenchi in the Forest Transition and Bole in the Guinea Savannah agro - ecological zones in Ghana. A randomized completeblock design with four replications was used to evaluate the clones for the following traits: seedling survival, vigour (estimated as trunk cross-sectional area, TCSA), height, nut yield, nut size and yield outturn. There were significant (p < 0.05) clone × environment interaction effects for nut yield. The best three highest yielding clones in Bole were SG 266, BE 575 and BE 203 whereas in Wenchi SG 224, SG 266 and SG 014 were the highest yielding clones. Genotypic co-efficient of variation (GCV) of nut yield (24.5%), TCSA (15.9%) and height (14.9%) were higher than those of other traits (3.0–4.5%). Height, TCSA, nut yield and outturn were found to be under moderate genetic control for the two locations combined whereas survival and nut size were under low genetic control. Broad sense heritability ranged from 0.56 ± 0.04 - 0.11 ± 0.01 for height and nut size respectively. Genetic correlation estimates suggest that selection for TCSA and height might lead to a large increment in seedling survival and early nut yield. Multivariate clustering identified clones with complementary traits. Our results, suggest that there is considerable genetic variability that could be exploited to develop superior cashew hybrids.
1. Introduction Recently, cashew (Anacardium occidentale L.) became the leading agricultural non - traditional export commodity crop in the Forest Savanna Transitional agro-ecological zone of Ghana. In 2016, cashew exports alone contributed over US$ 197 million in foreign exchange earnings to the Ghanaian economy (GEPA, 2018). Cashew has similarly attained the status of a cash crop in other Sub - Saharan African countries, including Benin, Togo, Ivory Coast, and Nigeria. Cashew originated from North-Eastern Brazil (Mitchell and Mori, 1987), and was introduced into Ghana by the early Portuguese settlers and begun as sporadic plantings across the country in the 1960′s, under the Savannah Afforestation Programme (Addaquay and Nyamekye-Boamah, 1998). Since then, cashew germplasm plots have been formally established (2004–2006) with seeds from Benin, Brazil, Mozambique, Tanzania and Ghana (Local collections) at the Wenchi and Bole research substations (Dadzie et al., 2014) to augment the cashew breeding program in Ghana.The cashew tree grows well in both tropical and sub-
⁎
tropical regions of the world (Ohler, 1979). It is reputed for being drought tolerant requiring an annual rainfall range of 1500–2000 mm (Sys et al., 1993) and a temperature range of 25–28 ᵒC (Dendena and Corsi, 2014) with a pronounced dry period of 5–6 months (Dedzoe et al., 2001) for optimum productivity. It grows best on well drained, deep, light to medium textured soils (Dedzoe et al., 2001) with a pH range of 4.5–6.5 (Dendena and Corsi, 2014). The potential of cashew as a cash crop for poverty alleviation in the West African sub- region has previously been described (Dendena and Corsi, 2014; Chivandi et al., 2015). However, high seedling mortality at the establishment phase, low nut yields and quality constitute a major constraint to cashew production in Ghana (Dadzie et al., 2014). This has been attributed to the use of unimproved planting materials (Oliveira et al., 2006; Dadzie et al., 2014) and drought (Armah et al., 2011). The harmful effect of climate change at several levels of plant functions, leading to a drastic reduction in growth rates and yield traits has been highlighted. In leaves, the photosynthetic form is recognized as sensitive to elevated temperatures (Ceylan et al., 2018; Okatan,
corresponding author at: Cocoa Research Institute of Ghana P. O. Box 8 New Tafo Akim E/R, Ghana. E-mail address: [email protected] (P.K.K. Adu-Gyamfi).
https://doi.org/10.1016/j.scienta.2019.05.023 Received 27 February 2019; Received in revised form 7 May 2019; Accepted 8 May 2019 Available online 18 May 2019 0304-4238/ © 2019 Elsevier B.V. All rights reserved.
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2. Materials and methods
2018). Photosynthesis may be inhibited as a result of the loss of chlorophyll and reduced carbon fixation and assimilation. In addition, the reproductive tissues and their functions are highly sensitive to heat stress, and a few degrees rise in temperature during flowering can lead to loss of entire plant cycles (Mehmet et al. 2018; Okatan et al., 2015; Usanmaz et al., 2018). The low nut yields observed from farmers fields therefore suggest that the increasing incomes for the majority of smallscale farmers could be attributed to the increasing cashew nut prices over the past decades. Besides, the cashew clones currently given to farmers as an interim variety were recommended based on single tree nut yield performance of local germplasm collections established from seed sources and evaluated at a single site (Wenchi) where environmental conditions were considered optimal. The heterogeneity and out crossing tendency of cashew suggest that, such recommendations were not repeatable across the transition - savannah agro-ecological zones which holds the largest concentration of commercial cashew production in Ghana. Multi-location evaluation of germplasm clones has enabled breeders to identify superior parents and varieties for specific environments and the introduction of high yielding food crops with a short growing season in the crop pattern is considered to be an effective means for narrowing the food gap in the world (Okatan et al., 2016; Lateef et al., 2018). Currently, very few cashew clones in Ghana have been evaluated, moreover, the evaluations were carried out at a single location. The first evaluation consisted of ten cashew clones assessed for nut yield and yield efficiency (Dadzie et al., 2014). In Tanzania, Masawe et al. (1999) and Madeni (2016) reported a significant genotype × location interaction effects on the growth and yield of cashew respectively. Similarly, a significant genotype × environment interaction effects on nut yield of cashew have been reported in Nigeria (Aliyu et al., 2014). The usefulness of both local and exotic germplasm in identifying genotypes with rare alleles or allele combination conferring adaptation to specific environment, increased yield stability, food quality, and an advantage of reduced dependence on agronomic inputs have been noted for many crops (Palmgren et al., 2015; Castañeda-Álvarez et al., 2016; Dwivedi et al., 2016; Wang et al., 2017). Therefore, a comprehensive evaluation of germplasm clones from both local and exotic sources across defined ecologies for survival, vigour and yield is crucial to the cashew breeding program for an effective comparison and determination of clones for future breeding efforts. In tree crop breeding, key agronomic traits including juvenile growth traits (plant height and stem diameter increments) and yield efficiency (the ratio of cumulative yield to stem diameter increments) has gained interest in selecting high and early yielding genotypes (Padi et al., 2012; Ofori et al., 2015). In Ghana, cashew breeding research is still at its infancy (< 20yrs) and Dadzie et al. (2014) have utilized canopy area and yield efficiency to identify potentially high yielding cashew clones. The magnitude of genetic variation of key agronomic traits is important for effective utilisation and selection of cashew germplasm clones as parents in breeding programs. However, information on genetic parameters such as variance, heritability as well as correlation among agronomic traits in cashew germplasm clones in Ghana is limited. The utilisation of such information is critical if cashew breeders want to identify potential parents for breeding improved cultivars with broad genetic base. The objectives of the present study were (i) to assess the performance of cashew germplasm clones for seedling survival, vigour (estimated as Trunk - Cross - Sectional Area), plant height, nut size, outturn and nut yield (ii) to estimate the heritability for seedling survival, vigour, plant height, nut size, outturn and nut yield (iii) to assess the phenotypic and genotypic correlations between vigour and yield and it's component traits in cashew clones in Ghana.
2.1. Plant materials Twenty cashew germplasm clones were selected and clonally propagated by grafting scions harvested from mother trees onto 2.5 months old rootstocks raised from open pollinated seeds. This selection comprised of fifteen (15) high yielding (≥7 kg/tree) local germplasm clones SG 266, SG 224, SG 273, SG 004, SG 014, IDDM 29, KT 1, KT 2, SB 9, BAME 7, AKD, AKC, BAMBOI 7, KT 4 and KT 5 and five (5) high yielding (≥7 kg/tree) exotic germplasm clones ; BE 203, BE 627, BE 739, BE 204 and BE 575 from Benin. The selected clones were part of the local and exotic germplasm collections assembled at the Wenchi Agricultural Research Station under the cashew development project which was funded by the African Development Bank (Dadzie et al., 2014). 2.2. Field evaluation and plant culture The experiments were conducted at the Wenchi Agricultural Research Station in the Forest Transition agro - ecological zone (N 09ᵒ 00.561′, W002° 32.237′) and at Bole, a Substation of Cocoa Research Institute of Ghana in the Guinea Savannah agro - ecological zone (N 07ᵒ 45.171′ W002°05.803′). At the vegetative phase, total/mean rainfall amounts within the dry season were consistently higher at Wenchi (466 mm/78.9 mm) than at Bole (203.1 mm/42.3 mm) whereas mean maximum temperatures were relatively lower at Wenchi (32.8 °C) than Bole (36.1 °C) (Figure A1). At the reproductive phase (2012–2014), total/mean annual rainfall amounts were similarly, higher at Wenchi (1633 mm/93.3 mm) than Bole (1083 mm/56.7 mm) whereas annual maximum temperatures were consistently higher at Bole (33.3 °C) compared to Wenchi (31.2 ᵒC) (Figure A2). Comparatively, the weather conditions at Wenchi appeared favourable than Bole. Soil samples randomly collected from both sites at a depth of 0–15 and 15–30 cm did indicate that, the soils were of acidic reaction with pH values of 6.2 and 5.9 at Wenchi and 6.09 and 5.98 at Bole respectively (Table A1). At both soil depths, Wenchi consistently recorded high contents of organic carbon, nitrogen, phosphorus, potassium, magnesium and calcium than Bole. Indeed, at a soil depths of 0–15 cm, the total available phosphorus content was three fold higher at Wenchi (14.6 ppm) than Bole (5.06 ppm). Based on the soil chemical composition, the soils appeared to be more fertile at Wenchi than Bole. The trial was laid out in a randomized complete block design with four (4) replications involving 12 trees per clone per replication and clones were transplanted in June 2009 at a spacing of 10 m × 10 m (100 plants per hectare). In July 2009, each cashew plant was fertilized with nitrogen supplied as ammonium sulphate because of the low levels of fertility of the soil used for the experiment. The application of agro-pesticides followed recommended agronomic practices for cashew production in Ghana. Essentially, cyperderm (active ingredient - cypermethrin) @ 150 mL ha−1 was used to control insect pest from August - October annually. 2.3. Data collection Agronomic traits evaluated in this study included seedling survival (%), plant height (m), trunk cross-sectional area (mm2), nut size (g), outturn or shelling (%) and nut yield (kg ha−1). The stem diameter of young cashew plants was measured at 15 cm above the graft union with electronic callipers at yearly intervals from June 2009 to June 2011. Survival was estimated by determining the percentage of surviving plants after one year (2009–2010) of establishment in each plot. Data on yield per plot per annum were estimated from the weight of nuts collected from each clone throughout the fruiting season between 2012–2014 cropping years. Nut sizes (g) were estimated as the weight of 1 kg of raw cashew nuts divided by the number of nuts and out-turn (%) was estimated as (weight of healthy kernels divided by the weight 109
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two locations. The highest survival rate (≥90%) were observed with clone BE 203, BE 204, BE 627 KT 4 and SG 224 at Wenchi whilst BE 575, BE 739 and KT 5 were outstanding at Bole (Table 2). Across the two environments, survival rates were significantly lower by 12.8% at Bole than Wenchi. At Bole, TCSA increments ranged from 300 in BE 627 to 816 (mm2) in BAME 7 whilst at Wenchi an increment of 1360 in AKC to 3224 (mm2) in SG 266 was observed. The three best clones with the highest TCSA were observed with clone SG 266, BE 739 and SG 224 at Wenchi and BAME 7, SG 266 and BE 575 and at Bole respectively. Clone SG 266 was consistently vigorous ranking 1st in Bole and 2nd in Wenchi. Relatively, TCSA increments was three fold higher at Wenchi compared to Bole. Plant height increments also ranged from 0.49 in BE 627 to 1.07 m in SG 266 at Bole but at Wenchi a range of 0.77 in AKD to 1.58 m in SG 014 was recorded. Clones SG 266, BE 203 and KT 4 at Bole were the top three best clones with highest plant height increments whereas at Wenchi, clones SG 014, BE 204 and SG 266 were the best. In comparing the two locations, a relative reduction of 52.7% in plant height was observed at Bole. Nut yields at Bole, ranged from 37.2 in SB 9 to 391 kg ha −1yr in SG 266 whilst at Wenchi, a range of 210.4 in AKD to 625.8 kg ha −1 in SG 244 was observed (Table 3). Clones SG 224, SG 266, SG 014, SG 004 and BE 204 were the best five highest yielding clones at Wenchi whereas at Bole SG 266, BE 575, BE 203, BE 739 and BAME 7 was the best. Again, SG 266 appeared to be consistently high yielding, ranking 2nd in Wenchi and 1st at Bole. Across the two locations a relative nut yield reduction of 170% was observed. The location effects on nut yield was highly significant (p < 0.001), Wenchi (387.8 kg ha −1) gave higher nut yields than Bole (143.9 kg ha −1 ). At Bole, the best five clones with the largest nut size (≥5.1 g) included BE 739, KT 5, SG 273, BAME 7 and BE 575 whereas at Wenchi BAMBOI 7, BE 739, KT 4, KT 5 and IDDM 29 were outstanding (nut sizes ≥ 6.3 g). Across the two locations, a relative mean nut size reduction of 21% was observed at Bole compared with Wenchi. At Bole, the best five clones with the highest outturn (≥28%) were IDDM 29, SG 224, SB 9, BE 203 and BAMBOI 7, but in Wenchi KT 2, BAMBOI 7, BAME 7, SG 014, and BE 203 were superior (outturn ≥ 30%). A relative outturn reduction of 6.4% was observed when Bole was compared to Wenchi. In comparing the two locations, Bole could be relatively marginal. This was evident from the relatively low rainfall amount and distribution, low soil fertility and higher temperatures stress observed (Table A1 and Figure A1 & A2). Accordingly, TCSA, plant height, nut yield, nut size and outturn estimates of the clones tested were lower in Bole than Wenchi.
of raw nuts) × 100 for each clone. Plant height was measured by placing a meter rule against the plant and measuring from the base of the plant (soil surface) to the apex of the plant. Trunk cross-sectional area (TCSA) was estimated from the tree trunk diameter measurements using the formula: (πd2)/4 Where, d is the stem/trunk diameter. 2.4. Statistical analysis Analysis of variance based on best linear unbiased prediction (BLUP) was carried out with META - R (Multi-Environment Trial Analysis with R for Windows) statistical package (Alvarado et al., 2018), with environments considered a random effect and germplasm clones as a fixed effects. The following model was used for combined location analysis. Yijk = μ + Bj + Gj + Lk + GLjk+ Ɛijk Where, Yijk = observed trait value of genotype j in block i of Environment k, μ=grand mean, Bi=block effect, Gj=effect of genotype, Lk= Environmental effect, GLjk = the interaction effect of genotype j with Environment k and Ɛijk = error (residual) effect of genotype j in block i of environment k. The differences among means were tested by least significant difference (LSD) at the 5% probability level. Heritability, phenotypic and genetic correlations among traits across environments were estimated using META-R (Alvarado et al., 2018). The standard errors of heritability were calculated according to the formula suggested by Singh et al. (1993). The analyses on yield utilized 3-year yield data (2012–2014), whereas the analysis on the growth (trunk crosssectional area and plant height) utilized the difference between the initial and final recordings from 2009 to 2011. Multivariate analyses were conducted using the procedure of principal component analysis and hierarchical cluster analysis to bring out the patterns of similarity among the 20 clones. Genotypic and phenotypic coefficient of variation were estimated following (Burton, 1952) as,
GCV = √σG M and PCV = √σP M Where, GCV, PCV, σG, σP and M are genotypic coefficient of variation, phenotypic coefficient of variation, genotypic variance, phenotypic variance and trait mean respectively.
3.2. Genotypic and phenotypic coefficient of variation and heritability of traits
3. Results
Generally, the phenotypic coefficient of variation (PCV) was higher than the genotypic coefficient of variation (PCV) for all the traits evaluated (Table 4). Nut yield had the highest genotypic coefficient of variation (GCV) of 24.5% and outturn had the lowest (3.6%) compared with the other traits. Phenotypic coefficient of variation (PCV) likewise, followed a similar trend with nut yield having the highest (40.0%) and outturn being the lowest (5.1%). Heritability estimates across locations were generally moderate to low. The highest heritability estimate was
3.1. Clone × environment interaction effect for traits The analysis of variance revealed significant clone, environment and clone x environment interaction effects (p < 0.05) for survival, trunk cross-sectional area, plant height, nut yield, nut size and outturn (Table 1). Differences in ranking among the clones were evident at the
Table 1 Mean sum of squares for percent survival, trunk cross sectional area (TCSA), plant height, nut yield, nut size and outturn of 20 cashew germplasm clones evaluated at Bole and Wenchi.from 2009 to 2014. Source
df
Survival (%)
TCSA (mm2)
Height (m)
Yield (kg/ha)
Nut size (g)
Outturn (%)
Block Clone Environment Clone × Environment Error
3 19 1 19 117
612.1 1585.3*** 2331.7* 1100.2* 618.2
97926* 779,733** 123,358,474* 383,741* 228627
0.032* 0.260* 6.11** 0.113* 0.065
433,308* 57,712*** 2,380,586** 23,613** 12153
0.1377 0.794*** 54.05*** 1.079** 0.2253
2.26 15.54*** 124.96*** 10.32** 4.93
*, **, ***Significantly different at p ≤ 0.05 p ≤ 0.01and p ≤ 0.001, respectively. 110
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Table 2 Mean survival, TCSA and height of 20 cashew germplasm clones at 24 months after planting at Bole and Wenchi. Wenchi
Bole 2
Clones
Survival (%)
TCSA(mm )
Height(m)
Clone
Survival (%)
TCSA (mm2)
Height (m)
BE 203 BE 204 BE 627 KT 4 SB 9 SG 224 BE 575 IDDM 29 KT 2 SG 273 KT 1 SG 004 SG 014 BE 739 KT 5 BAMBOI 7 SG 266 AKC BAME 7 AKD Mean SED (C × E)
100.0 (90.0) 100.0 (90.0) 100.0 (90.0) 100.0 (90.0) 100.0 (90.0) 100.0 (90.0) 87.5 (75.0) 87.5 (69.3) 87.5 (69.3) 87.5 (69.3) 81.2 (64.7 81.2 (64.7) 75.0 (60.0) 81.2 (59.0) 81.2 (59.0) 75.0 (54.3) 75.0 (54.3) 68.8 (44.0) 56.2 (35.4) 56.2 (34.7) 84.1(67.7 ± 4.1) 17.58
2637 1749 1830 2610 2533 2917 2647 2779 2024 1891 1962 1868 2401 3089 2138 1965 3224 1360 2265 1596 2274.3 ± 115 338.1
1.40 1.48 0.99 0.96 1.2 1.41 0.95 0.91 0.94 0.93 0.89 1.43 1.58 1.18 1.19 1.33 1.44 0.85 0.81 0.77 1.13 ± 0.05 0.18
BE 575 BE 739 BAME 7 IDDM 29 KT 2 KT 5 BE 203 KT 4 BE 204 BAMBOI 7 SB 9 SG 224 SG 266 SG 004 SG 014 BE 627 KT 1 AKD AKC SG 273
100.0 (90.1) 100.0 (90.0) 87.5 (75.0) 87.5 (75.0) 87.5 (75.0) 100.0 (75.0) 81.2 (71.1) 81.2 (71.1) 81.2 (64.7) 87.5 (60.0) 75.0 (60.0) 68.8 (60.0) 87.5 (60.0) 75.0 (49.7) 68.8 (45.8) 56.2 (41.1) 56.2 (41.1) 56.2 (34.7) 56.1 (34.6) 43.8 (26.1) 76.9 (60.1 ± 4.0)
780 568 816 556 343 548 646 647 572 455 457 437 782 470 487 300 510 312 350 327 518.2 ± 35.2
0.88 0.83 0.77 0.71 0.61 0.77 1.04 0.9 0.77 0.85 0.53 0.65 1.07 0.74 0.78 0.49 0.55 0.58 0.61 0.7 0.74 ± 0.03
C - Clones, E-Environment,TCSA - Trunk cross-sectional area, SED - Standard error of difference. Figures in parenthesis are transformed values. Table 3 Mean nut yield, nut size and outturn of 20 cashew germplasm clones evaluated at Wenchi and Bole from 2012–2014. Wenchi
Bole
Clone
Nut yield (kg ha−1)
Nut size (g)
Outturn (%)
Clone
Nut yield (kg ha−1)
Nut size (g)
Outturn (%)
SG 224 SG 266 SG 014 SG 004 BE204 BE203 BE627 KT 5 BE575 SB 9 SG 273 IDDM29 BAME 7 KT 2 BAMBOI 7 BE739 KT 4 KT 1 AKC AKD Mean SED (0.05) C × E
625.8 561.4 555 536.7 469.4 469.2 403.3 372.5 370.1 369.2 368.3 361.7 342.5 342.5 316.6 314.2 299.8 256.7 211.2 210.4 387.8 ± 25.9 60.8
6.1 5.8 5.2 5.9 5.3 5.2 6.0 6.3 5.9 6.2 5.4 6.3 6.0 5.3 6.3 6.3 6.3 5.3 5.9 5.9 5.8 ± 0.90 0.34
29.9 30 31.7 29.8 25.7 31.3 30.9 30.1 29.3 30.4 28.8 30.6 31.6 34 31.8 29.2 30.7 28.4 28.7 30.1 30.1 ± 0.37 1.6
SG 266 BE575 BE203 BE739 BAME 7 BE204 SG 014 KT 1 KT 5 SG 004 IDDM29 BAMBOI 7 KT 4 SG 224 BE627 KT 2 SG 273 AKD AKC SB 9
391 250.7 208.8 206.3 178.3 177 171.5 170.8 156.7 148.2 123.4 114.9 102.7 100.8 92.5 87.1 72.9 44.9 42.4 37.2 143.9 ± 18.6
3.5 5.2 4.2 5.6 5.3 4.6 4.5 4.8 5.6 4.8 4.6 4.6 4.6 4.7 4.4 4.8 5.3 4.8 5.1 4.4 4.8 ± 0.11
25.3 26.4 27.9 30.2 27.4 25.5 28.9 27.5 28.5 29.5 32.3 27.5 29.2 31.6 28.5 27.3 29.3 28.6 25.8 30.6 28.3 ± 0.43
C - Clones, E-Environment, SED - Standard error of difference.
observed in plant height ( h2bs = 0.56) followed by outturn ( h2bs = 0.52), TCSA ( h2bs = 0.51), survival ( h2bs = 0.14) whilst the least was observed with nut size ( h2bs = 0.11).
(rg = 0.90, p < 0.001; rp = 0.80, p < 0.001) at both the genotypic and phenotypic level whilst a significant genotypic correlation with survival (rg = 0.96, p < 0.001) was similarly only observed at Bole. A negative significant correlation between nut yield and nut size (rg = − 0.48, p < 0.05;) and outturn (rg = − 0.40, p < 0.05) only at the genotypic level was observed. Generally genotypic correlation coefficient estimates were higher than phenotypic estimates for most traits.
3.3. Genotypic and phenotypic correlation among traits A positive genotypic (rg) and phenotypic (rp) correlation were observed between TCSA increments versus yield (rg = 0.94, p < 0.001; rp = 0.76, p < 0.001) in Bole and (rg = 0.41, p < 0.05; rp = 0.35ns) in Wenchi (Table 5). However, for survival, a significant correlation (rg = 0.98, p < 0.001; rp = 0.66, p < 0.01) with TCSA was only observed at Bole. Plant height increments likewise correlated with yield at Bole (rg = 0.93, p < 0.001; rp = 0.74, p < 0.001) and at Wenchi
3.4. Multivariate analysis The output of the principal component analysis based on six morphological traits; survival, plant height, TCSA, nut size, outturn and nut yield of the 20 cashew clones demonstrated that in Bole, at a similarity 111
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Table 4 Estimates of mean, range and genetic variability components for survival, TCSA, height, nut yield, nut size and outturn of 20 cashew germplasm clones evaluated at Bole and Wenchi. Genetic parameters
Survival (%)
TCSA (mm2)
Height (m)
Nut yield (Kg/ha)
Nut size (g)
Outturn (%)
Mean Range Vg Vp Vg x Ve GCV PCV Vg/Ve h2bs
65.4 35 - 82.5 25.49 182.2 171.22 3.0 20.6 4.9 0.14 ± 0.03
1396.2 855 - 2003 49498.93 97056.6 41210.18 15.9 22.3 3.1 0.51 ± 0.06
0.94 0.70 - 1.3 0.02 0.033 0.01 14.5 19.4 4.05 0.56 ± 0.04
265.86 126.8 - 476.2 4260.44 11211.6 2007.34 24.5 40 6.8 0.38 ± 0.02
5.22 4.7 - 6.0 0.056 1.4 0.17 4.5 22.6 12.04 0.11 ± 0.01
29.4 25.6 - 31.5 1.17 2.28 0.82 3.6 5.1 1.1 0.52 ± 0.03
Vg - genotypic variance, Vp - phenotypic variance, GCV - genotypic coefficient of variation, PCV - phenotypic coefficient of variation, h2bs – broad sense heritability and its standard errors and Ve - environmental variance.
coefficient of 0.85 three clusters were formed (Fig. 1). The first cluster comprised of eight clones; AKC, AKD, BAMBOI 7, KT 2, BE627, IDDM 29, SG 224 and SB 9 which had relatively lower nut yield (80.4 kg ha−1), with corresponding low survival rates (55%), TCSA (401.25 mm2), plant height (0.63 m) and nut sizes (4.7 g) but higher outturns (29.0%). The second cluster consisted of eleven clones; BAME 7, BE 203, BE 204, BE 575, BE 739, KT 1, KT 4, KT 5, SG 004, SG 014, SG 273 which also had comparatively moderate nut yields (167.6 kg ha−1) and survival rates (63.6%) together with medium plant height (0.79 m), TCSA (579.18 mm2) and nut sizes (5 g). The third cluster included only a single clone SG 266 which was extremely higher yielding (391 kg ha−1) with higher plant heights (1.07 m), TCSA (782 mm2), moderate survival rates (60%) with extremely lower nut sizes (3.5 g) and outturns (25.3%). In Wenchi, at the same similarity coefficient value of 0.85, four clusters were formed (Fig. 2). The first cluster comprised of AKC, AKD, BAME 7, KT 1, SG 273 and KT 2 which typically had the lowest survival rates (52.9%), yield (288.6 kg ha−1), plant height (0.86 m) and TCSA (1849.6 mm2). The second cluster, also comprised of BAMBOI 7, SB 9, BE 575, BE 627, BE 739, IDDM29, KT 4, KT 5, and SG 004. This group was characterized by relatively largest nut sizes (6.1 g), moderate survival rates (72.6%), TCSA (2384.33 mm2), plant height (1.1 m) and nut yields (371.56 kg ha−1). The third cluster which was made up of only two clones SG 224 and SG 266 were the most vigorous, TCSA (3070.5 mm2) with corresponding relatively highest nut yields (593.6 kg ha −1) and plant height (1.4 m) but moderate survival rates (72.15%). The fourth cluster was characteristically taller plants (1.5 m) with higher TCSA (2262.33 mm2), moderate nut yields (497.86 kg ha−1) and relatively higher survival rates (80%). This cluster involved three clones; SG 014, BE 203 and BE 204.
Fig. 1. Dendrogram constructed on first two principal components for 20 cashew germplasm clones evaluated at Bole over 5 year period.
selecting parental clones for yield improvement. In this study, we report on the responses of cashew germplasm clones to two contrasting locations; Wenchi and Bole. The significant clone × environment interaction variation observed for survival, TCSA, height, nut yield, nut size and outturn indicated that the germplasm clones exhibited differences in ecological variation under the different growth conditions observed at the two locations. It therefore suggest that, trait expressions among the germplasm clones were largely influenced by the environment and selecting genotypes that are best adapted to specific environments could be the best breeding strategy for cashew improvement, if high genetic and economic gains are expected. This observation is consistent with other authors who found significant genotype × environment (G × E)
4. Discussion The level of genetic variation present in germplasm collections and the genetic relationship among key agronomic traits could be vital in
Table 5 Genotypic and phenotypic correlation coefficients for survival, TCSA, height, nut yield, nut size and outturn of 20 cashew germplasm clones evaluated at Bole and Wenchi. TCSA (mm2)
Traits
Survival (%) Nuts sizes (g) Outturn (%) Nut yield (kg/ha)
Height (m)
Survival (%)
Nut size (g)
Outturn (%)
Genotypic /Phenotypic
Bole
Wenchi
Bole
Wenchi
Bole
Wenchi
Bole
Wenchi
Bole
Wenchi
Genotypic Phenotypic Genotypic Phenotypic Genotypic Phenotypic Genotypic Phenotypic
0.98*** 0.66** −0.09 −0.02 −0.27 −0.27 0.94*** 0.76**
0.33 0.16 0.37 0.34 0.20 0.10 0.41* 0.35
0.96*** 0.58** −0.22 −0.18 −0.20 −0.19 0.93*** 0.74***
0.35 0.27 −0.30 −0.22 −0.23 −0.14 0.90*** 0.80***
−0.26 −0.04 0.23 −0.05 0.89*** 0.49*
−0.12 −0.10 −0.19 −0.20 0.45* 0.33
0.01 0.04 −0.48* −0.30
0.06 0.09 −0.27 −0.23
−0.40* −0.32
0.01 −0.51*
*: P < 0.05, **: P < 0.01, ***P < 0.001. TCSA - Trunk cross sectional area. 112
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tolerance to high temperature stress. They could, therefore, be utilized as donors to develop superior cashew hybrids with higher tolerance to drought stress. The significant positive (genotypic and phenotypic) correlations observed between nut yield and the other yield related component indicate that direct selection for any of those characters could improve nut yield. The significant positive genotypic and phenotypic correlation observed survival and TCSA (rg = 0.98, p < 0.001; rp = 0.66, p < 0.01) and plant height (rg = 0.96, p < 0.001) in Bole implies that TCSA and plant height could be a better indicator for determining survival especially under marginal environmental conditions as evidenced in other studies (Hutcheon, 1973; Ofori et al., 2017). The reports on cashew seedling survival rate is rare, however, in many tree crops, seedling survival is related to vigour (TCSA), thus more vigorous genotypes had a higher survival rate than less vigorous genotypes especially under drought stress conditions (Hutcheon, 1973; Ofori et al., 2017). This finding also suggest that, cashew clones may employ faster growth rate to evade moisture deficit and ensure survival. On the other hand, a significant correlation was observed between nut yield and TCSA (vigour) at Bole (rg = 0.94, p < 0.001; rp = 0.76, p < 0.001) and TCSA at Wenchi (rg = 0.41, p < 0.05; rp = 0.35ns). Subsequently, nut yield also correlated with plant height at Bole (rg = 0.93, p < 0.001; rp = 0.74, p < 0.001) and at Wenchi (rg = 0.90, p < 0.001; rp = 0.80, p < 0.001). Similar correlations in cashew have been reported but at the phenotypic level (Masawe et al., 1999; Sethi and PCLSK, 2016). Although both TCSA and plant height could be indicators in determining nut yield, TCSA is a better indicator in determining early nut yield in cashew under marginal conditions. This concurs with other reports emphasizing the effectiveness of TCSA in predicting nut yields in Cola nitida (Akpertey et al., 2017) and Theobroma Cacao (Padi et al., 2012). The negative significant correlation between nut yield and nut size (rg = − 0.48, p < 0.05;) and outturn (rg = − 0.40, p < 0.05) indicates that the smaller the nut size and outturn, the higher the corresponding nut yield. Although, both positive and negative correlations between nut yield and nut size have been reported in cashew (Sena et al., 1994; Aliyu, 2006), the conflicting reports on these relationships been attributed to differences in the advanced stage of the population utilized and the nature of the previous selection method employed in the previous yield improvement programme (Sundararaju et al., 2006; Paikra, 2016). Their use as a selection criterion in the breeding program under all ecologies have therefore demonstrated significant indirect effects on yield through the number of nuts per tree without any adverse compensation effects (Madeni, 2016). The analysis of the relatedness among the germplasm clones in our study demonstrated that clusters were of mixed origin which suggested that geographical diversity among the germplasm clones evaluated did not significantly influence genetic diversity of the traits studied. The development of superior cashew hybrids with higher seedling survival rates and higher nut yield and quality may involve hybridization of germplasm clones with complimentary traits among clusters. This is in concurrence with Aliyu (2006) who emphasized that hybridization and recurrent selection approach could improve cashew productivity without compromising quality.
Fig. 2. Dendrogram constructed on first two principal components for 20 cashew germplasm clones evaluated at Wenchi over 5 year period.
interactions effects for growth and nut yield in cashew (Aliyu et al., 2014). Moreover, the relatively faster growth rate and higher nut yield observed at Wenchi compared with Bole where environmental conditions were relatively marginal suggest that, cashew productivity at a given location could partly depend on rainfall amount, soil fertility status and temperature stress during the cropping season. This concurs with the findings of other researchers who emphasized that agro-climatic differences, genetic make and interaction of both are responsible for the reported differences in the yield of many crops (Datta, 2013; Balogoun et al., 2016; Madeni, 2016). Burton (1952) opined that the genetic coefficients of variation (GCV) provides a scale for comparing genetic variability in quantitative traits and in combination with heritability estimates, determine the extent of heritable variation. In this study, the correspondingly higher heritabilities estimates in combination with higher genotypic coefficient of variation values observed for plant height (0.56; 14.5%), TCSA (0.51 had 13.5%) and nut yield (0.38 had 3.1%) could indicate an equivalent genetic potential for the improvement of growth traits as that for yield traits. The relatively high heritability estimates observed for plant height compared with TCSA suggest that plant height has higher genetic control than TCSA and more genetic gain can be expected from the selection of plant height than for TCSA. Besides, the observed heritability estimates for TCSA and plant heights in our study were quiet comparable to earlier reported range of 0.30 - 0.85 for stem diameter increment and 0.46–0.80 for plant height (Sethi et al., 2016) respectively. The low heritability estimate for survival and nut size suggest that, these traits have low genetic control and low genetic gain as it's expression is largely influenced by the environment which is evident from the high environmental variance of 4.9 and 12.04 respectively. Although heritability estimates for survival in cashew is rare, heritability estimates of 0.78 for nut size has been reported but this estimates were obtained from field trials conducted at a single location only (Sankaranarayanan et al., 2011). The relatively low heritability estimates observed for survival and nut size suggest that significant genetic improvement in this trait is achievable if progeny testing and phenotypic recurrent selection approaches employed since they have demonstrated significant genetic gains for traits with low heritabilities but high economic importance (Jansky, 2009). In addition, the advantage using more efficient statistical methods in the identification of superior families and individuals using best linear unbiased prediction (BLUP) have produced significant genetic improvement in many crops (Slater et al., 2014). The superior performance observed in clones BE 575, BE 739, KT 5, SG 266 for survival, BE 575, BE 203, BE 739 for nut yield and BAMBOI 7, BE 739, IDDM 29 and KT 4 for nut size in Bole where environmental conditions were relatively marginal suggest that these clones could possibly posses alleles that ensures higher water and nutrient-use efficiency with better
5. Conclusions The variation existing in germplasm collection could be associated with the genetic history, origin, and selection of the desired trait by farmers (Chipojola et al., 2009). In this study, we assessed the genetic variability and relationship among key agronomic traits for growth and yield attributes of 20 diverse juvenile cashew clones from both local and exotic sources in two contrasting agro - ecological locations in Ghana. We estimated some genetic parameters mainly, heritability, genotypic variance, genotypic and phenotypic co-efficient of variation, genotypic and phenotypic correlation and our study revealed significant environment, clone and clone × environment interaction 113
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Disclosure statement The authors declare no potential conflict of interest. Acknowledgement This work was supported by Cocoa Research Institute of Ghana (CRIG) with funding from the African Development Bank (AfDB) through the erstwhile Cashew Development Project (CDP). Our appreciation goes to Mr Gabriel Boahen and staff of the Wenchi Agricultural Research Station for their invaluable assistance in the establishment and maintenance of this trial at Wenchi and Bole. This manuscript is published with the permission of the executive director This paper is published with the permission of the Executive Director of the Cocoa Research Institute of Ghana as manuscript number CRIG/011/2019/ 035/003. Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.scienta.2019.05.023. References Addaquay, J., Nyamekye-Boamah, K., 1998. The Ghana cashew industry study. Report Prepared for Ministry of Food and Agriculture Under the Agricultural Diversification Project. World Bank. Akpertey, A., Dadzie, A.M., Adu-Gyamfi, P.K.K., Ofori, A., Padi, F.K., 2017. Effectiveness of juvenile traits as selection criteria for yield efficiency in kola. Sci. Hortic. 216, 264–271. Aliyu, O., 2006. Phenotypic correlation and path coefficient analysis of nut yield and yield components in cashew (Anacardium occidentale L.). Silvae Genet. 55, 19–24. Aliyu, O.M., Adeigbe, O.O., Lawal, O.O., 2014. Phenotypic stability analysis of yield components in cashew (Anacardium occidentale L.) using additive main effect and multiplicative interaction (AMMI) and GGE biplot analyses. Plant Breed. Biotechnol. 2, 354–369. Alvarado, G., López, M., Vargas, M., Pacheco, Á, Rodríguez, F., Burgueño, J., Crossa, J., 2018. META-R (Multi Environment Trail Analysis with R for Windows) Version 6.03. CIMMYT Research Data & Software Repository Network. Armah, F.A., Odoi, J.O., Yengoh, G.T., Obiri, S., Yawson, D.O., Afrifa, E.K., 2011. Food security and climate change in drought-sensitive savanna zones of Ghana. Mitig. Adapt. Strateg. Glob. Chang. 16, 291–306. Balogoun, I., Ahoton, E.L., Saïdou, A., Bello, O.D., Ezin, V., 2016. Effect of climatic factors on cashew (Anacardium occidentale L.) productivity in Benin (West Africa). J. Earth Sci. Clim. Chang. 7 (1). Burton, G.W., 1952. Quantitative inheritance in grasses. Pro. VI Int. Grassl. Cong. 1952, 277–283.
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