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Potential correlation between growth habit and yield of Spanish pomegranate cultivars
Scientia Horticulturae 144 (2012) 168–171
Contents lists available at SciVerse ScienceDirect
Scientia Horticulturae journal homepage: www.elsevier.com/locate/scihorti
Potential correlation between growth habit and yield of Spanish pomegranate cultivars Fca. Hernández, P. Melgarejo, P. Legua, R. Martínez ∗ , J.J. Martínez Plant Science and Microbiology Department, Universitas Miguel Hernandez, Ctra Beniel 3.2, 03312 Orihuela (Alicante), Spain
a r t i c l e
i n f o
Article history: Received 21 January 2012 Received in revised form 27 June 2012 Accepted 3 July 2012 Keywords: Growth Mixed shoots Prompt lateral shoots Fruit Pomegranate Punica granatum
a b s t r a c t The vegetative growth habit as well as the yield of seven pomegranate varieties native to Southeastern Spain was studied. The evaluated cultivars were: Mollar de Elche 14 and 15 (“ME14” and “ME15”), Pi˜ nón tierno de Ojós 2, 4, 7 and 8 (“PTO2”, “PTO4”, “PTO7” and “PTO8”) and Casta del Reino 1 (“CRO1”). Very short vegetative shoots bearing a rosette of leaves behave as photosynthetic units. These units were abundant in all evaluated varieties; approximately 50% of all buds yielded this type of shoot unit. The other 50% were either mixed shoots or shoots with apical flower buds. Moreover, there appeared to be a tendency of the “PTO” varietal group and the “CRO1” cultivar to produce a higher number of mixed shoots than the ME varietal group. The Mollar de Elche varieties yielded longer mixed shoots than prompt lateral ones. The “PTO” varietal group and the “CRO1” cultivar approximately produced from 2 to 4 length units of prompt lateral shoots per each mixed shoot unit. An inversely proportional relationship was established between the length of prompt lateral shoots and each variety’s fruit yield. © 2012 Elsevier B.V. All rights reserved.
1. Introduction Pomegranate is a species that grows in a mild climate and requires high summer temperatures to ripen properly. Therefore, Southeastern Spain offers a suitable climate for it to grow in and to produce good quality fruit. The Mediterranean basin is one of the areas to which pomegranate growing best adapts, although it also grows in South Asia, North Africa, and in some countries of North and South America. This species has dispersed as it has adapted well to the Mediterranean climate, which has given rise over time to new individuals that are occasionally grouped under the same name. This is precisely the case of the Mollar de Elche or the Pi˜ nón Tierno de Ojós variety, among others (Melgarejo, 1993). Growing interest has been shown in this fruit not only because it is pleasant to eat, but also because it is considered a functional fruit of great interest for the human diet. Indeed several groups of substances that are useful in the prevention of certain diseases have been described (Andreu Sevilla et al., 2008; Legua et al., 2012; Tehranifar et al., 2010; Tzulker et al., 2007). In recent years, pomegranates have gone from being a fruit that was practically eaten only as a fresh product to be in great demand by the processing industry to obtain different products (juice, jam etc.). Because of these industrial applications and the increase in the consumption of pomegranates as a fresh fruit, it is essential to characterise the
different varieties to obtain a quality product in commercial terms and one that is most interesting in economic terms. Expansion possibilities are extraordinary for the arid and semiarid areas of our planet, especially those areas where salinity and lack of water are limiting factors to grow many other fruit crops. Therefore pomegranate production is a new and interesting fruit alternative for these areas. To date, most literature has focused on fruit characteristics (Al-Maiman and Ahmad, 2002; Barone et al., 2001; Fadavi et al., 2005; Gözlekc¸i and Kaynak, 1998; Martínez, 1999; Martínez et al., 2006a,b; Sharma et al., 2005; Padmavathamma and Hulmani, 2007), floral biology (Mars and Marrakchi, 2004; Martínez et al., 2006a,b) and growing techniques (El Khawaga, 2007; Melgarejo et al., 2004). Yet few or no publications have related plant growth habit and the yields of the different cultivars. Therefore, it is most important to know the growth habits of the varieties of interest as they definitively condition growing techniques, plant spacing and orchard management in general. The current study aims to acknowledge the growth patterns of seven pomegranate varieties native to Southeastern Spain by relating their growth habits to fruit yields. 2. Material and methods 2.1. Plant material
∗ Corresponding author. Tel.: +34 966749644; fax: +34 966749693. E-mail address: [email protected] (R. Martínez). 0304-4238/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.scienta.2012.07.001
Seven new pomegranate cultivars were evaluated: Mollar de nón tierno de Ojós Elche 14 (“ME14”), Mollar de Elche 15 (“ME15”), Pi˜
Fca. Hernández et al. / Scientia Horticulturae 144 (2012) 168–171
169
2 (“PTO2”), Pi˜ nón tierno de Ojós 4 (“PTO4”), Pi˜ nón tierno de Ojós 7 (“PTO7”), Pi˜ nón tierno de Ojós 8 (“PTO8”) and Casta del Reino de Ojós 1 (“CRO1”). There were four pomegranate trees per accession. The evaluated plant material is part of the main EU pomegranate germplasm bank, located at the experimental field station of the Miguel Hernandez University (UMH) in the province of Alicante, Eastern Spain: 02◦ 03 50 E, 38◦ 03 50 N, and 25 masl. The trees were propagated by rooted wood cuttings and grown under homogeneous conditions. All accessions were 6 years-old when the study began. The studied varieties were selected in accordance with four basic criteria: most were sweet varieties and one sour-sweet; they produced arils with soft kernels as well as good-sized fruit. In accordance with these criteria, individuals were selected from the most important population varieties in Spain, the world’s main pomegranate exporter (Spain exports more than 55% of the world’s pomegranate production). The “ME14” and “ME15” varieties were selected from the Mollar de Elche (ME) population variety because of their abundant fruits of excellent organoleptic quality (sweet taste and easy to chew). The “PTO2”, “PTO4”, “PTO7”, “PTO8” and “CRO1” varieties were selected as they present good-sized fruit despite belonging to less important population varieties than the “ME” varieties. “PTO” means pi˜ nón tierno de Ojós, which refers to the low degree of hardness of the edible part of the fruit (arils with soft kernels) and the population to which it belongs. Varieties 2, 4 and 8 were selected for their large-sized fruits, while variety 7 was chosen because of its slightly sour-sweet flavour and large size. Likewise, cultivar “CRO1” was chosen for its large-sized fruit and its sweet, soft arils.
conditions. This constant may be interpreted as the length of prompt shoots growing from each primary shoot unit. By means of the K2 constant, and with the 24 initially labelled buds per tree, the total length of prompt shoots growing from these buds was estimated. To do this, the sum of the lengths of the mixed labelled shoots per variety was multiplied by its K2 constant. The data used for this study were those obtained until July 16th, by which time the vegetative growth ceased because of summer temperatures. Shoot lengths were annually assessed for the 3-year study (period 2006–08).
2.2. Plant growth
Productivity (kg cm−2 ) was determined from the yield and the mid section of the trunk. The trunk mid section was calculated with the two trunk perimeters measured at 10 cm and 30 cm from the soil.
The buds that were beginning to grow on the 28 trees included in this study were labelled. Labels were placed next to the buds, and were chosen uniformly from the whole tree. Eight areas per tree were distinguished and corresponded to the 4 basic orientations (north, south, east and west) and to 2 heights (high and low canopy), depending on whether the shoot was located in the upper or the lower half of the tree canopy. Three buds were selected from all 8 areas; therefore, 24 shoots were studied per tree. The lengths of the shoots were measured every 7 days. The absolute and relative frequencies of the types of shoot units produced (very short vegetative shoots bearing a rosette of leaves and the fructiferous formations, long mixed shoots (>10 cm) and short mixed ones (<10 cm) with a single apical flower bud) were obtained from the 24 labelled buds on each tree per variety. In order to study the incidence of prompt lateral shoots, 5 mixed shoots were selected from the mid part of each tree canopy to represent each variety, and the prompt shoots growing on each one were counted. Then both the main and lateral (anticipated) shoots were measured. These data were used to calculate the proportion of each shoot type in the varieties studied. Furthermore, the performance of the typical mixed shoot of each variety was calculated with the pool of labelled mixed shoots per variety. As regards prompt shoots, the field data were used to calculate for each variety the mean length of a primary shoot, the mean number of lateral shoots it supports and their mean length. With these data, the total length of prompt shoots that each primary one supports was established. Then this calculated length was divided by the mean primary shoot length to obtain a constant called K2 . This constant defines the rate at which prompt shoots had grown per variety and in comparison with primary shoots. This figure represents the habit of each variety, which obviously depends on genetic and environmental factors, although all pomegranate accessions in this study were grown under homogeneous
2.3. Yield and productivity Yield was determined for all seven varieties and for the years 2006, 2007 and 2008. The fruits of the 4 trees of each variety were counted and weighed, thus indicating the number of fruits obtained in each harvest. These data may compare perfectly with each other because they were obtained under homogeneous conditions. All the cultivars in this study had a similar maturation period, and have been catalogued as mid-season (Melgarejo, 1993; Martínez, 1999); that is, between September the 20th and the end of October, since this fruit tree has a staggered blooming period. The criterion followed to pick fruits was determined by the fruits’ external colour. Fruits were picked when their external colour was no longer green, and when the typical yellow-red colours of each variety were showing. The harvest dates of the three years were as follows: Year
First harvesting date
Second harvesting date
2006 2007 2008
First week of October Last week of September Last week of September
Last week of October Third week of October Last week of October
2.4. Relationship between plant growth habit and yield In order to gain in-depth knowledge of the varieties under study, plant growth was related with yield to assess the extent of the effect of growing habits on these varieties’ yield capacity. To do this, the mean yield per tree (kg) was related with the coefficient K2 = Lsl Lsp−1 (lateral shoots growth/primary shoots growth), in an attempt to find a relationship showing the influence between plant growth habit and fructification. 2.5. Statistical analysis Firstly, a basic descriptive statistics was performed, followed by an analysis of variance (ANOVA). Then varieties were classified by performing the LSD multiple range test with a 95% confidence level. Finally, graphs were prepared to show the relationship between plant growth habit and productivity. 3. Results and discussion 3.1. Plant growth Table 1 shows the mean absolute and relative frequencies per variety of the types of shoot units annually produced for the 3year study (period 2006–08): very short vegetative shoots bearing a rosette of leaves and the fructiferous formations, long mixed shoots and short mixed ones with a single apical flower bud. The short woody units present leaves in a rosette form and appeared upon sprouting. After a few weeks, they no longer grew
Fca. Hernández et al. / Scientia Horticulturae 144 (2012) 168–171
Table 1 The mean absolute and relative frequencies of the shoot units produced from the 24 labelled buds per tree of each variety. Period 2006–08. Variety
PTO4 PTO7 PTO8 PTO2 CRO1 ME14 ME15
Short vegetative shoots with a rosette of leaves
Long mixed shoots
Number
%
Number
%
Number
%
11 a 12 a 12 a 15 b 15 b 12 a 11 a
45.83 50.00 50.00 62.50 62.50 50.00 45.83
7 ab 8 ab 9b 6a 6a 6a 6a
29.17 33.33 37.50 25.00 25.00 25.00 25.00
6a 4b 3b 3b 3b 6a 7a
25.00 16.67 12.50 12.50 12.50 25.00 29.17
Short mixed shoots
Table 2 Mean length of the primary (Lmp) and lateral (prompt) shoots (Lml), mean number of lateral shoots per primary shoot (Nl), mean total length of lateral shoots growing from a primary one (Ltml), and the K2 = Ltml Lmp−1 relationship among the varieties under study. Period 2006–08. Variety
Lmp (mm)
Nl
Lml (mm)
Ltml (mm)
K2 = Ltml Lmp−1
PTO4 PTO7 PTO8 PTO2 CRO1 ME14 ME15
585 ac 871 b 797 b 786 b 673 ab 428 c 469 c
15 a 19 a 16 a 15 a 14 a 3c 3c
152 ab 186 b 137 ab 155 ab 142 ab 119 a 126 a
2252 a 3541 b 2250 a 2387 a 2011 a 358 c 351 c
3.85 a 4.06 a 2.82 b 3.04 ab 2.99 ab 0.84 c 0.75 c
and became the numerous sources that provide photosynthates to elongate shoot tips and nourish flowers and fruits. These are the structures that appear in higher numbers. And according to this, cultivars can be classified into two homogeneous groups: the “PTO2” and “CRO1” varieties showed the highest frequencies of short woody units (62.5% each), whereas the “PTO4”, “PTO7”, “PTO8”, “ME14” and “ME15” significantly showed lower and similar rates for these short structures (45.83%, 50%, 50%, 50% and 45.83%, respectively). The fructiferous formations are the short mixed shoots with a single apical flower bud and the long mixed ones. The “PTO8” variety yielded a number of long mixed units similar to other cultivars of the “PTO” group but the “PTO2”. Still this number was significantly higher than those yielded by cultivars “ME14”, “ME15” and “CRO1”. The quantities of short mixed shoots shown by the “ME14”, “ME15” and “PTO4” varieties were considerably the highest of all evaluated pomegranate cultivars (Table 1). With the data obtained, and with the considerations made in Section 2, Tables 2 and 3 were calculated. The “ME” varietal group significantly showed the lowest numbers of lateral units per primary shoot (Nl) and total lengths of prompt shoots that each primary one supports (Ltml), as well as the lowest total shoot growth. Mollares de Elche varieties showed K2 coefficients lower than 1, which means that the primary mixed shoots grow longer Table 3 Importance of primary shoots growth (Lsp) and lateral (prompt or secondary) shoots growth (Lsl) on the varieties included in this study. Period 2006–08. Variety
Primary shoots growth (Lsp) (m)
Lateral shoots growth (Lsl) (m)
K2 = Lsl Lsp−1
Total growth (Lsp + Lsl) (m)
PTO4 PTO7 PTO8 PTO2 CRO1 ME14 ME15
3.40 a 5.80 b 8.40 c 3.10 a 5.60 b 1.70 d 3.10 a
13.00 a 23.50 b 23.60 b 9.30 c 16.60 a 1.40 d 2.30 e
3.85 a 4.06 a 2.82 b 3.04 a 2.99 a 0.84 c 0.75 c
16.40 a 29.20 b 32.00 b 12.40 a 22.20 ab 3.10 c 5.30 d
0,8
Mean Prouctivity (kg.cm -2)
170
ME15
0,7 0,6
y = -0,3279Ln(x) + 0,6003 R 2 = 0,9201
ME14
0,5 0,4 CRO1
0,3 0,2
PTO8 PTO2
0,1 0 0,00
PTO7
1,00
2,00
K2
3,00
PTO4
4,00
5,00
Fig. 1. Relationship between the mean productivity (kg cm−2 ) and plant growth habit (lateral shoots growth/primary shoots growth; K2 = Lsl Lsp−1 ).
than the lateral ones. This growth rate varied in the rest of varieties by between approximately 2 and 4 length units of lateral shoots growing from each primary shoot unit (Tables 2 and 3). According to Melgarejo et al. (1996), sprouting may commence at the end of February, but it normally starts halfway through March. The sprouting dates noted in this study coincide with those indicated by these authors. In a study conducted in India, Josan et al. (1979) reported that the Bedana cultivar commenced sprouting in February the 27th, while that of the Kali-Shirin cultivar began in March the 20th. 3.2. Yield and productivity Table 4 shows the mean value, the standard deviation and the analyses of some of the main productive parameters of the varieties under study. Melgarejo (1993) established three yield levels (high: >40 kg tree−1 , average: 20–40 kg tree−1 and low: <20 kg tree−1 ). Classification in terms of this criterion is as follows: - High yield (>40 kg tree−1 ): “ME14” and “ME15”. - Average yield (20–40 kg tree−1 ): “CRO1” and “PTO7”. - Low yield (10–20 kg tree−1 ): “PTO2”, “PTO4” and “PTO8”. The “ME14” and “ME15” varieties yielded appropriate mean fruit weights but significantly lower than the other varieties, owing to the number of fruits produced by them being considerably higher (Table 4). Larger-sized fruits for the “ME14” and “ME15” varieties could be obtained by thinning fruits just when they start to grow. Both “ME” cultivars still scored the highest productivities (kg cm−2 ) among the varieties under study (from 2.5 to 5 times higher). 3.3. Correlation between plant growth and fruit yields Next the growth habit of each tree per variety was related with its mean productivity. Fig. 1 shows this relationship for the cultivars under study. Table 3 and Fig. 1 show how the Mollares de Elche cultivars presented K2 coefficients lower than 1. This means they produce longer primary mixed shoots than the lateral or prompt kind. It can be also stated how these two varieties are significantly more productive than the remaining ones, which is probably due to less competition for photosynthates between flowering and vegetative growth. The period in which lateral shoots grow plainly coincides with both blooming and fruit set stages. The K2 constant for the rest of varieties varied between 2.82 and 4.06 units of length for the lateral shoots growing from each primary unit, these being less productive. This reveals an inversely proportional relationship between
Fca. Hernández et al. / Scientia Horticulturae 144 (2012) 168–171
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Table 4 Mean yield per tree (kg), mean productivity (kg cm−2 ), mean number of fruits per tree and mean fruit weight (g). Period 2006–08. Variety
Mean yield (kg tree−1 )
Mean productivity (kg cm−2 )
Mean fruit number tree−1
Mean fruit weight (g)
PTO4 PTO7 PTO8 PTO2 CRO1 ME14 ME15
15.41 ± 1.23 b 25.97 ± 2.60 c 16.56 ± 1.82 b 13.64 ± 1.36 b 20.50 ± 3.49 c 44.00 ± 4.40 a 46.70 ± 5.60 a
0.17 ± 0.03 b 0.25 ± 10.03 c 0.19 ± 0.03 b 0.15 ± 0.01 b 0.25 ± 0.03 b 0.63 ± 0.06 a 0.75 ± 0.08 a
35.75 ± 5.36 b 72.50 ± 1.16 c 42.75 ± 7.70 bd 32.25 ± 6.13 b 49.50 ± 6.93 d 173.75 ± 31.28 a 195.75 ± 33.28 a
419.27 ± 58.70 b 358.26 ± 28.66 c 387.45 ± 46.49 cb 423.07 ± 55.00 b 414.18 ± 66.27 b 253.22 ± 25.32 a 238.59 ± 21.47 a
Each value is expressed by its mean ± standard deviation. Those values within a column followed by the same letter do not differ significantly (p ≤ 0.05).
the length of the prompt shoots generated and the fruit yield of each variety. The K2 coefficients and productivities of the cultivars under study are highly correlated (R2 = 0.92). The growth habits of these varieties have an intense effect on their yielding potentials; the higher the number of lateral shoots produced and their growth, the lower the productivity is (Fig. 1). Likewise, other researchers confirm the negative correlation between plant growth habit and production. An inversely proportional relationship between the vegetative growth of lychee trees and their production was described by Menzel and Simpson (1992). In other study dealing with apples, Larsen et al. (1992) evaluated the influence of nine rootstocks on the growth habit and production of several cultivars grafted onto them. They observed that the apple rootstock M26, the least vigorous one of those tested, induced higher productivities on the varieties grafted onto it. Furthermore, Nishizawa (1993) corroborated the positive effect of paclobutrazol applications on increasing strawberry yields. Moreover, Padi et al. (2012) studied the vegetative growth and production of cocoa, concluding that both factors were closely correlated. Similarly, the contrary relationship between vegetative growth and productivity was evidenced in many studies on regulated deficit irrigation regimes (RDI). Bedbabis et al. (2010) and Egea et al. (2010) stated that it is possible to obtain similar yields with lower vegetative growths. Therefore, and in view of the results, farming techniques as pruning, irrigation regimes, fertilization programs, etc. should be tailored to each of these pomegranate varieties in order to increase their productivity. 4. Conclusions The short woody units with leaves appear among the varieties studied in higher numbers, and approximately 50% of buds gave rise to this formation type. The “ME” cultivars produce longer primary mixed shoots than lateral (secondary) ones. The “PTO” varietal group and the “CRO1” cv. produce between approximately 2 and 4 units of length of lateral shoots per primary unit. Of all the varieties studied, the “ME14” and “ME15” are the most productive. Therefore the fruits of “ME14” and “ME15” have lower mean weights. There is indeed an inversely proportional relationship between the length of the lateral shoots generated and the fruit yield of each variety. References Al-Maiman, Salah A., Ahmad, Dilshad, 2002. Changes in physical and chemical properties during pomegranate (Punica granatum L.) fruit maturation. Food Chem. 76, 437–441. Andreu Sevilla, A.J., Signes Pastor, A.J., Carbonell Barrachina, A.A., 2008. Pomegranate and pomegranate juices. Alimentacion, Equipos y Tecnologia 234, 36–39.
Bedbabis, S., Ferrara, G., Rouina, B.B., Boukhris, M., 2010. Effects of irrigation with treated wastewater on olive tree growth, yield and leaf mineral elements at short term. Sci. Hortic. 126, 345–350. Barone, E., Caruso, T., Mara, F.P., Sottile, F., 2001. Preliminary observations on some sicilian pomegrante (Punica granatum L.) varieties. J. Am. Pomol. Soc. 55 (1), 4–7, 2001. Egea, G., Nortes, P.A., González-Real, M.M., Baille, A., Domingo, R., 2010. Agronomic response and water productivity of almond trees under contrasted deficit irrigation regimes. Agric. Water Manage. 97 (1), 171–181. El-Khawaga, A.S., 2007. Reduction in fruit cracking in Manfaluty pomegranate following a foliar application with paclobutrazol and zinc sulphate. J. Appl. Sci. Res. (September), 837–840. Fadavi, A., Barzegar, M., Azizi, M.H., Bayat, M., 2005. Physico-chemical composition of ten pomegranate cultivars (Punica granatum L.) grown in Iran. Food Sci. Technol. Int. 11 (2), 113–119. Gözlekc¸i, S., Kaynak, L., 1998. Physical and chemical chances during fruit development and flowering in pomegranate (Punica granatum L.) cultivar Hicaznar grown in Antaya region. In: I Symposium Internacional sobre el granado, Orihuela. Alicante (Spain). Josan, J.S., Jawanda, J.S., Uppal, D.K., 1979. Studies on the floral biology of pomegranate. I. Sprouting of vegetative buds, flower bud development, flowering habit, time and duration of flowering & floral morphology. Punjab Hortic. J., 59–65, Department of Horticulture, Punjab Agricultural University, Ludhiana 141004. India. Larsen, F.E., Higgins, S.S., Dolph, C.A., 1992. Rootstock influence over 25 years on yield, yield efficiency and tree growth of cultivars ‘delicious’ and ‘golden delicious’ apple (Malus domestica Borkh.). Sci. Hortic. 49 (1–2), 63–70. Legua, P., Melgarejo, P., Abdelmajid, H., Martínez, J.J., Martínez-Font, R., Ilham, H., Habida, H., Hernández, Fca., 2012. Total phenols and antioxidant capacity in 10 moroccan pomegranate varieties. J. Food Sci. 71 (1), 115–120. Martínez, J.J., 1999. Biología floral y varietal del granado (Punica granatum L). Tesis Doctoral. Escuela Politécnica Superior de Orihuela (Universidad Miguel Hernández), Spain, 616 pp. Martínez, J.J., Melgarejo, P., Hernández, Fa ., Legua, P., Martínez, R., 2006a. Pomegranate (Punica granatum L.) flower biology, pistil receptiveness and effective pollination time. Adv. Hortic. Sci. 20 (4), 281–284. Martínez, J.J., Melgarejo, P., Hernández, Fa ., Salazar, D.M., Martínez, R., 2006b. Seed characterization of five new pomegranate (Punica granatum L.) varieties. Sci. Hortic. 110, 241–246. Melgarejo, P., 1993. Selección y tipificación varietal de granado (Punica granatum L.). Tesis Doctoral. U.P.V. (Valencia), Spain. Melgarejo, P., Martínez, J.J., Hernández, Fca., Martínez-Font, R., Erez, A., Barrows, P., 2004. Kaolin treatments to reduce pomegranate sunburn. Sci. Hortic. 100, 349–353. Melgarejo, P., Martínez-Valero, R., Guillamón, J.M., Miró, M., Amorós, A., 1996. Phenological Stages of pomegranate tree (Punica granatum L.). Ann. Appl. Biol. 130, 135–140. Menzel, C.M., Simpson, D.R., 1992. Growth, flowering and yield of lychee cultivars. Sci. Hortic. 49 (3–4), 243–254. Nishizawa, T., 1993. The effect of paclobutrazol on growth and yield during first year greenhouse strawberry production. Sci. Hortic. 49 (4), 267–274. 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. Padmavathamma, A.S., Hulmani, N.C., 2007. Studies on physico-chemical characters of Pomegranate (Punica granatum L.) var. Jyoti. J. Res. ANGRAU. 35 (3), 24–29, 5 ref. Sharma, N., Bist, H.S., Rajesh Kumar, 2005. Studies on physico-chemical characteristics of some pomegranate (Punica granatum L.) cultivars in Himachal Pradesh. J. Hortic. 18 (2), 71–74. Tehranifar, A., Zarei, M., Nemati, Z., Esfandiyari, B., Vasifeshenas, M.R., 2010. Investigation of physico-chemical properties and antioxidant activity of twenty Iranian pomegranate (Punica granatum L.) cultivars. Sci. Hortic. 126, 180–185. Tzulker, R., Glazer, I., Bar-Ilan, I., Holland, D., Aviram, M., Amir, R., 2007. Antioxidant activity, polyphenol content and related compounds in different fruit juices and homogenates prepared from 29 different pomegranate accessions. J. Agric. Food Chem. 55, 9559–9570.
Contents lists available at SciVerse ScienceDirect
Scientia Horticulturae journal homepage: www.elsevier.com/locate/scihorti
Potential correlation between growth habit and yield of Spanish pomegranate cultivars Fca. Hernández, P. Melgarejo, P. Legua, R. Martínez ∗ , J.J. Martínez Plant Science and Microbiology Department, Universitas Miguel Hernandez, Ctra Beniel 3.2, 03312 Orihuela (Alicante), Spain
a r t i c l e
i n f o
Article history: Received 21 January 2012 Received in revised form 27 June 2012 Accepted 3 July 2012 Keywords: Growth Mixed shoots Prompt lateral shoots Fruit Pomegranate Punica granatum
a b s t r a c t The vegetative growth habit as well as the yield of seven pomegranate varieties native to Southeastern Spain was studied. The evaluated cultivars were: Mollar de Elche 14 and 15 (“ME14” and “ME15”), Pi˜ nón tierno de Ojós 2, 4, 7 and 8 (“PTO2”, “PTO4”, “PTO7” and “PTO8”) and Casta del Reino 1 (“CRO1”). Very short vegetative shoots bearing a rosette of leaves behave as photosynthetic units. These units were abundant in all evaluated varieties; approximately 50% of all buds yielded this type of shoot unit. The other 50% were either mixed shoots or shoots with apical flower buds. Moreover, there appeared to be a tendency of the “PTO” varietal group and the “CRO1” cultivar to produce a higher number of mixed shoots than the ME varietal group. The Mollar de Elche varieties yielded longer mixed shoots than prompt lateral ones. The “PTO” varietal group and the “CRO1” cultivar approximately produced from 2 to 4 length units of prompt lateral shoots per each mixed shoot unit. An inversely proportional relationship was established between the length of prompt lateral shoots and each variety’s fruit yield. © 2012 Elsevier B.V. All rights reserved.
1. Introduction Pomegranate is a species that grows in a mild climate and requires high summer temperatures to ripen properly. Therefore, Southeastern Spain offers a suitable climate for it to grow in and to produce good quality fruit. The Mediterranean basin is one of the areas to which pomegranate growing best adapts, although it also grows in South Asia, North Africa, and in some countries of North and South America. This species has dispersed as it has adapted well to the Mediterranean climate, which has given rise over time to new individuals that are occasionally grouped under the same name. This is precisely the case of the Mollar de Elche or the Pi˜ nón Tierno de Ojós variety, among others (Melgarejo, 1993). Growing interest has been shown in this fruit not only because it is pleasant to eat, but also because it is considered a functional fruit of great interest for the human diet. Indeed several groups of substances that are useful in the prevention of certain diseases have been described (Andreu Sevilla et al., 2008; Legua et al., 2012; Tehranifar et al., 2010; Tzulker et al., 2007). In recent years, pomegranates have gone from being a fruit that was practically eaten only as a fresh product to be in great demand by the processing industry to obtain different products (juice, jam etc.). Because of these industrial applications and the increase in the consumption of pomegranates as a fresh fruit, it is essential to characterise the
different varieties to obtain a quality product in commercial terms and one that is most interesting in economic terms. Expansion possibilities are extraordinary for the arid and semiarid areas of our planet, especially those areas where salinity and lack of water are limiting factors to grow many other fruit crops. Therefore pomegranate production is a new and interesting fruit alternative for these areas. To date, most literature has focused on fruit characteristics (Al-Maiman and Ahmad, 2002; Barone et al., 2001; Fadavi et al., 2005; Gözlekc¸i and Kaynak, 1998; Martínez, 1999; Martínez et al., 2006a,b; Sharma et al., 2005; Padmavathamma and Hulmani, 2007), floral biology (Mars and Marrakchi, 2004; Martínez et al., 2006a,b) and growing techniques (El Khawaga, 2007; Melgarejo et al., 2004). Yet few or no publications have related plant growth habit and the yields of the different cultivars. Therefore, it is most important to know the growth habits of the varieties of interest as they definitively condition growing techniques, plant spacing and orchard management in general. The current study aims to acknowledge the growth patterns of seven pomegranate varieties native to Southeastern Spain by relating their growth habits to fruit yields. 2. Material and methods 2.1. Plant material
∗ Corresponding author. Tel.: +34 966749644; fax: +34 966749693. E-mail address: [email protected] (R. Martínez). 0304-4238/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.scienta.2012.07.001
Seven new pomegranate cultivars were evaluated: Mollar de nón tierno de Ojós Elche 14 (“ME14”), Mollar de Elche 15 (“ME15”), Pi˜
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2 (“PTO2”), Pi˜ nón tierno de Ojós 4 (“PTO4”), Pi˜ nón tierno de Ojós 7 (“PTO7”), Pi˜ nón tierno de Ojós 8 (“PTO8”) and Casta del Reino de Ojós 1 (“CRO1”). There were four pomegranate trees per accession. The evaluated plant material is part of the main EU pomegranate germplasm bank, located at the experimental field station of the Miguel Hernandez University (UMH) in the province of Alicante, Eastern Spain: 02◦ 03 50 E, 38◦ 03 50 N, and 25 masl. The trees were propagated by rooted wood cuttings and grown under homogeneous conditions. All accessions were 6 years-old when the study began. The studied varieties were selected in accordance with four basic criteria: most were sweet varieties and one sour-sweet; they produced arils with soft kernels as well as good-sized fruit. In accordance with these criteria, individuals were selected from the most important population varieties in Spain, the world’s main pomegranate exporter (Spain exports more than 55% of the world’s pomegranate production). The “ME14” and “ME15” varieties were selected from the Mollar de Elche (ME) population variety because of their abundant fruits of excellent organoleptic quality (sweet taste and easy to chew). The “PTO2”, “PTO4”, “PTO7”, “PTO8” and “CRO1” varieties were selected as they present good-sized fruit despite belonging to less important population varieties than the “ME” varieties. “PTO” means pi˜ nón tierno de Ojós, which refers to the low degree of hardness of the edible part of the fruit (arils with soft kernels) and the population to which it belongs. Varieties 2, 4 and 8 were selected for their large-sized fruits, while variety 7 was chosen because of its slightly sour-sweet flavour and large size. Likewise, cultivar “CRO1” was chosen for its large-sized fruit and its sweet, soft arils.
conditions. This constant may be interpreted as the length of prompt shoots growing from each primary shoot unit. By means of the K2 constant, and with the 24 initially labelled buds per tree, the total length of prompt shoots growing from these buds was estimated. To do this, the sum of the lengths of the mixed labelled shoots per variety was multiplied by its K2 constant. The data used for this study were those obtained until July 16th, by which time the vegetative growth ceased because of summer temperatures. Shoot lengths were annually assessed for the 3-year study (period 2006–08).
2.2. Plant growth
Productivity (kg cm−2 ) was determined from the yield and the mid section of the trunk. The trunk mid section was calculated with the two trunk perimeters measured at 10 cm and 30 cm from the soil.
The buds that were beginning to grow on the 28 trees included in this study were labelled. Labels were placed next to the buds, and were chosen uniformly from the whole tree. Eight areas per tree were distinguished and corresponded to the 4 basic orientations (north, south, east and west) and to 2 heights (high and low canopy), depending on whether the shoot was located in the upper or the lower half of the tree canopy. Three buds were selected from all 8 areas; therefore, 24 shoots were studied per tree. The lengths of the shoots were measured every 7 days. The absolute and relative frequencies of the types of shoot units produced (very short vegetative shoots bearing a rosette of leaves and the fructiferous formations, long mixed shoots (>10 cm) and short mixed ones (<10 cm) with a single apical flower bud) were obtained from the 24 labelled buds on each tree per variety. In order to study the incidence of prompt lateral shoots, 5 mixed shoots were selected from the mid part of each tree canopy to represent each variety, and the prompt shoots growing on each one were counted. Then both the main and lateral (anticipated) shoots were measured. These data were used to calculate the proportion of each shoot type in the varieties studied. Furthermore, the performance of the typical mixed shoot of each variety was calculated with the pool of labelled mixed shoots per variety. As regards prompt shoots, the field data were used to calculate for each variety the mean length of a primary shoot, the mean number of lateral shoots it supports and their mean length. With these data, the total length of prompt shoots that each primary one supports was established. Then this calculated length was divided by the mean primary shoot length to obtain a constant called K2 . This constant defines the rate at which prompt shoots had grown per variety and in comparison with primary shoots. This figure represents the habit of each variety, which obviously depends on genetic and environmental factors, although all pomegranate accessions in this study were grown under homogeneous
2.3. Yield and productivity Yield was determined for all seven varieties and for the years 2006, 2007 and 2008. The fruits of the 4 trees of each variety were counted and weighed, thus indicating the number of fruits obtained in each harvest. These data may compare perfectly with each other because they were obtained under homogeneous conditions. All the cultivars in this study had a similar maturation period, and have been catalogued as mid-season (Melgarejo, 1993; Martínez, 1999); that is, between September the 20th and the end of October, since this fruit tree has a staggered blooming period. The criterion followed to pick fruits was determined by the fruits’ external colour. Fruits were picked when their external colour was no longer green, and when the typical yellow-red colours of each variety were showing. The harvest dates of the three years were as follows: Year
First harvesting date
Second harvesting date
2006 2007 2008
First week of October Last week of September Last week of September
Last week of October Third week of October Last week of October
2.4. Relationship between plant growth habit and yield In order to gain in-depth knowledge of the varieties under study, plant growth was related with yield to assess the extent of the effect of growing habits on these varieties’ yield capacity. To do this, the mean yield per tree (kg) was related with the coefficient K2 = Lsl Lsp−1 (lateral shoots growth/primary shoots growth), in an attempt to find a relationship showing the influence between plant growth habit and fructification. 2.5. Statistical analysis Firstly, a basic descriptive statistics was performed, followed by an analysis of variance (ANOVA). Then varieties were classified by performing the LSD multiple range test with a 95% confidence level. Finally, graphs were prepared to show the relationship between plant growth habit and productivity. 3. Results and discussion 3.1. Plant growth Table 1 shows the mean absolute and relative frequencies per variety of the types of shoot units annually produced for the 3year study (period 2006–08): very short vegetative shoots bearing a rosette of leaves and the fructiferous formations, long mixed shoots and short mixed ones with a single apical flower bud. The short woody units present leaves in a rosette form and appeared upon sprouting. After a few weeks, they no longer grew
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Table 1 The mean absolute and relative frequencies of the shoot units produced from the 24 labelled buds per tree of each variety. Period 2006–08. Variety
PTO4 PTO7 PTO8 PTO2 CRO1 ME14 ME15
Short vegetative shoots with a rosette of leaves
Long mixed shoots
Number
%
Number
%
Number
%
11 a 12 a 12 a 15 b 15 b 12 a 11 a
45.83 50.00 50.00 62.50 62.50 50.00 45.83
7 ab 8 ab 9b 6a 6a 6a 6a
29.17 33.33 37.50 25.00 25.00 25.00 25.00
6a 4b 3b 3b 3b 6a 7a
25.00 16.67 12.50 12.50 12.50 25.00 29.17
Short mixed shoots
Table 2 Mean length of the primary (Lmp) and lateral (prompt) shoots (Lml), mean number of lateral shoots per primary shoot (Nl), mean total length of lateral shoots growing from a primary one (Ltml), and the K2 = Ltml Lmp−1 relationship among the varieties under study. Period 2006–08. Variety
Lmp (mm)
Nl
Lml (mm)
Ltml (mm)
K2 = Ltml Lmp−1
PTO4 PTO7 PTO8 PTO2 CRO1 ME14 ME15
585 ac 871 b 797 b 786 b 673 ab 428 c 469 c
15 a 19 a 16 a 15 a 14 a 3c 3c
152 ab 186 b 137 ab 155 ab 142 ab 119 a 126 a
2252 a 3541 b 2250 a 2387 a 2011 a 358 c 351 c
3.85 a 4.06 a 2.82 b 3.04 ab 2.99 ab 0.84 c 0.75 c
and became the numerous sources that provide photosynthates to elongate shoot tips and nourish flowers and fruits. These are the structures that appear in higher numbers. And according to this, cultivars can be classified into two homogeneous groups: the “PTO2” and “CRO1” varieties showed the highest frequencies of short woody units (62.5% each), whereas the “PTO4”, “PTO7”, “PTO8”, “ME14” and “ME15” significantly showed lower and similar rates for these short structures (45.83%, 50%, 50%, 50% and 45.83%, respectively). The fructiferous formations are the short mixed shoots with a single apical flower bud and the long mixed ones. The “PTO8” variety yielded a number of long mixed units similar to other cultivars of the “PTO” group but the “PTO2”. Still this number was significantly higher than those yielded by cultivars “ME14”, “ME15” and “CRO1”. The quantities of short mixed shoots shown by the “ME14”, “ME15” and “PTO4” varieties were considerably the highest of all evaluated pomegranate cultivars (Table 1). With the data obtained, and with the considerations made in Section 2, Tables 2 and 3 were calculated. The “ME” varietal group significantly showed the lowest numbers of lateral units per primary shoot (Nl) and total lengths of prompt shoots that each primary one supports (Ltml), as well as the lowest total shoot growth. Mollares de Elche varieties showed K2 coefficients lower than 1, which means that the primary mixed shoots grow longer Table 3 Importance of primary shoots growth (Lsp) and lateral (prompt or secondary) shoots growth (Lsl) on the varieties included in this study. Period 2006–08. Variety
Primary shoots growth (Lsp) (m)
Lateral shoots growth (Lsl) (m)
K2 = Lsl Lsp−1
Total growth (Lsp + Lsl) (m)
PTO4 PTO7 PTO8 PTO2 CRO1 ME14 ME15
3.40 a 5.80 b 8.40 c 3.10 a 5.60 b 1.70 d 3.10 a
13.00 a 23.50 b 23.60 b 9.30 c 16.60 a 1.40 d 2.30 e
3.85 a 4.06 a 2.82 b 3.04 a 2.99 a 0.84 c 0.75 c
16.40 a 29.20 b 32.00 b 12.40 a 22.20 ab 3.10 c 5.30 d
0,8
Mean Prouctivity (kg.cm -2)
170
ME15
0,7 0,6
y = -0,3279Ln(x) + 0,6003 R 2 = 0,9201
ME14
0,5 0,4 CRO1
0,3 0,2
PTO8 PTO2
0,1 0 0,00
PTO7
1,00
2,00
K2
3,00
PTO4
4,00
5,00
Fig. 1. Relationship between the mean productivity (kg cm−2 ) and plant growth habit (lateral shoots growth/primary shoots growth; K2 = Lsl Lsp−1 ).
than the lateral ones. This growth rate varied in the rest of varieties by between approximately 2 and 4 length units of lateral shoots growing from each primary shoot unit (Tables 2 and 3). According to Melgarejo et al. (1996), sprouting may commence at the end of February, but it normally starts halfway through March. The sprouting dates noted in this study coincide with those indicated by these authors. In a study conducted in India, Josan et al. (1979) reported that the Bedana cultivar commenced sprouting in February the 27th, while that of the Kali-Shirin cultivar began in March the 20th. 3.2. Yield and productivity Table 4 shows the mean value, the standard deviation and the analyses of some of the main productive parameters of the varieties under study. Melgarejo (1993) established three yield levels (high: >40 kg tree−1 , average: 20–40 kg tree−1 and low: <20 kg tree−1 ). Classification in terms of this criterion is as follows: - High yield (>40 kg tree−1 ): “ME14” and “ME15”. - Average yield (20–40 kg tree−1 ): “CRO1” and “PTO7”. - Low yield (10–20 kg tree−1 ): “PTO2”, “PTO4” and “PTO8”. The “ME14” and “ME15” varieties yielded appropriate mean fruit weights but significantly lower than the other varieties, owing to the number of fruits produced by them being considerably higher (Table 4). Larger-sized fruits for the “ME14” and “ME15” varieties could be obtained by thinning fruits just when they start to grow. Both “ME” cultivars still scored the highest productivities (kg cm−2 ) among the varieties under study (from 2.5 to 5 times higher). 3.3. Correlation between plant growth and fruit yields Next the growth habit of each tree per variety was related with its mean productivity. Fig. 1 shows this relationship for the cultivars under study. Table 3 and Fig. 1 show how the Mollares de Elche cultivars presented K2 coefficients lower than 1. This means they produce longer primary mixed shoots than the lateral or prompt kind. It can be also stated how these two varieties are significantly more productive than the remaining ones, which is probably due to less competition for photosynthates between flowering and vegetative growth. The period in which lateral shoots grow plainly coincides with both blooming and fruit set stages. The K2 constant for the rest of varieties varied between 2.82 and 4.06 units of length for the lateral shoots growing from each primary unit, these being less productive. This reveals an inversely proportional relationship between
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Table 4 Mean yield per tree (kg), mean productivity (kg cm−2 ), mean number of fruits per tree and mean fruit weight (g). Period 2006–08. Variety
Mean yield (kg tree−1 )
Mean productivity (kg cm−2 )
Mean fruit number tree−1
Mean fruit weight (g)
PTO4 PTO7 PTO8 PTO2 CRO1 ME14 ME15
15.41 ± 1.23 b 25.97 ± 2.60 c 16.56 ± 1.82 b 13.64 ± 1.36 b 20.50 ± 3.49 c 44.00 ± 4.40 a 46.70 ± 5.60 a
0.17 ± 0.03 b 0.25 ± 10.03 c 0.19 ± 0.03 b 0.15 ± 0.01 b 0.25 ± 0.03 b 0.63 ± 0.06 a 0.75 ± 0.08 a
35.75 ± 5.36 b 72.50 ± 1.16 c 42.75 ± 7.70 bd 32.25 ± 6.13 b 49.50 ± 6.93 d 173.75 ± 31.28 a 195.75 ± 33.28 a
419.27 ± 58.70 b 358.26 ± 28.66 c 387.45 ± 46.49 cb 423.07 ± 55.00 b 414.18 ± 66.27 b 253.22 ± 25.32 a 238.59 ± 21.47 a
Each value is expressed by its mean ± standard deviation. Those values within a column followed by the same letter do not differ significantly (p ≤ 0.05).
the length of the prompt shoots generated and the fruit yield of each variety. The K2 coefficients and productivities of the cultivars under study are highly correlated (R2 = 0.92). The growth habits of these varieties have an intense effect on their yielding potentials; the higher the number of lateral shoots produced and their growth, the lower the productivity is (Fig. 1). Likewise, other researchers confirm the negative correlation between plant growth habit and production. An inversely proportional relationship between the vegetative growth of lychee trees and their production was described by Menzel and Simpson (1992). In other study dealing with apples, Larsen et al. (1992) evaluated the influence of nine rootstocks on the growth habit and production of several cultivars grafted onto them. They observed that the apple rootstock M26, the least vigorous one of those tested, induced higher productivities on the varieties grafted onto it. Furthermore, Nishizawa (1993) corroborated the positive effect of paclobutrazol applications on increasing strawberry yields. Moreover, Padi et al. (2012) studied the vegetative growth and production of cocoa, concluding that both factors were closely correlated. Similarly, the contrary relationship between vegetative growth and productivity was evidenced in many studies on regulated deficit irrigation regimes (RDI). Bedbabis et al. (2010) and Egea et al. (2010) stated that it is possible to obtain similar yields with lower vegetative growths. Therefore, and in view of the results, farming techniques as pruning, irrigation regimes, fertilization programs, etc. should be tailored to each of these pomegranate varieties in order to increase their productivity. 4. Conclusions The short woody units with leaves appear among the varieties studied in higher numbers, and approximately 50% of buds gave rise to this formation type. The “ME” cultivars produce longer primary mixed shoots than lateral (secondary) ones. The “PTO” varietal group and the “CRO1” cv. produce between approximately 2 and 4 units of length of lateral shoots per primary unit. Of all the varieties studied, the “ME14” and “ME15” are the most productive. Therefore the fruits of “ME14” and “ME15” have lower mean weights. There is indeed an inversely proportional relationship between the length of the lateral shoots generated and the fruit yield of each variety. References Al-Maiman, Salah A., Ahmad, Dilshad, 2002. Changes in physical and chemical properties during pomegranate (Punica granatum L.) fruit maturation. Food Chem. 76, 437–441. Andreu Sevilla, A.J., Signes Pastor, A.J., Carbonell Barrachina, A.A., 2008. Pomegranate and pomegranate juices. Alimentacion, Equipos y Tecnologia 234, 36–39.
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