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Identification, assessment of diseases and agronomic parameters of Curcuma amada Roxb (Mango ginger)
Current Plant Biology xxx (xxxx) xxx–xxx
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Identification, assessment of diseases and agronomic parameters of Curcuma amada Roxb (Mango ginger)☆ ⁎
Victor O. Ayodelea, , Olumayowa M. Olowea,c, Clement G. Afolabib, Iyabo A. Kehindea a
Department of Pure and Applied Botany, College of Bio-Sciences, Federal University of Agriculture Abeokuta, PMB, 2240, Abeokuta, Nigeria Department of Crop Protection, College of Plant Science and Crop Production, Federal University of Agriculture Abeokuta, PMB, 2240, Abeokuta, Nigeria c Department of Crop Science, College of Agriculture, Animal Science and Veterinary Medicine, University of Rwanda, Rwanda b
A R T I C LE I N FO
A B S T R A C T
Keywords: Mango ginger (Curcuma amada Roxb.) Leaf spot Leaf blight Rhizome rot Fungal diseases
Many diseases affect plants, causing physiological dysfunctions and structural deviation from normal. The effects of plant diseases on yield and quality of crops have been documented. Little, however, is known about the pathology and agronomy of Mango ginger (Curcuma amada Roxb.), an under-cultivated crop. The present study was carried out to assess disease incidence and severity of associated fungal diseases of Mango ginger; assess rhizome yield loss due to disease; isolate and identify fungal pathogens associated; evaluate growth parameters of Mango ginger. Mango ginger plants began showing symptoms of leaf spot and leaf blight at first week and at fifth week after emergence, respectively; at twenty-fourth week some rhizomes were visually observed to be affected with rot. Cercospora curcumae, Phyllosticta zingiberi and Colletotrichum capsici; C. gloeosporioides, Alternaria alternata and Rhizoctonia solani; R. solani, Fusarium solani and Pythium aphanidermatum were frequently found associated with leaf spot, leaf blight and rhizome rot, respectively. Correlation coefficient of: Spot Disease Incidence with plant height was −0.04 and −0.05 for 2016 and 2017, respectively; number of leaves in progression with age was significant at p < 0.01 in 2016 (0.63) but insignificant in 2017 (0.32). Also, correlation coefficient of Blight Disease Incidence: with plant height was significant at p < 0.01 in the year 2016 (0.94) and 2017 (0.92); with number of leaves as age progressed was 0.54 and 0.70 for 2016 and 2017, respectively, and significant at p < 0.01. Percentage losses of 3.25 and 3.02, at harvest, due to rhizome rot were recorded for 2016 and 2017, respectively. This study revealed the occurrence of diseases, associated with fungi and funguslike organisms, and their effect on Mango ginger plants.
1. Introduction Mango ginger (Curcuma amada Roxb.) is a common southern and eastern India perennial herb, but cultivated as annual crop mostly in India and Malaysia [6]. It is rhizomatous and aromatic, with leafy tuft and may grow 60–90 cm above ground level [25]. Its mango flavour is attributed to presence of car-3-ene and cis-ocimene among the 68 volatile aroma components present in the essential oil of its rhizomes [30]. The rhizomes are used in culinary preparations and in manufacture of pickles; also, Ayurveda and Unani medicinal systems use Curcuma amada as appetizer, alexteric, antipyretic, aphrodisiac, diuretic, emollient, expectorant and laxative and to cure biliousness, itching, skin diseases, bronchitis, asthma, hiccough and inflammation due to injuries [21]. Difurocumenonol, isolated from Mango ginger, is highly anti-
gram-positive and gram-negative bacteria [20]. Pre-treatment with Mango ginger significantly improved sperm count, and motility, and also declined cell phone radiation induced infertility in rats [8]. Mango ginger extract lowered, below normal level, the triglyceride in the blood of Triton-induced hyperlipidemic rats and also influenced liver synthesis and blood clearance [25]. Sivaprabha et al. [27] reported its cytotoxic activity against breast cancer cell lines MCF-7 and MDA MB 231. According to Sailendra et al. [24] labdane diterpene dialdehyde [labda-8(17), 12-diene-15, 16-dial]-an anti-tubercular agent was isolated and characterized from Mango ginger. Its ethanolic extract revealed presence of β-Sitosterol and Androstan-17-one, 3-ethyl-3-hydroxy-, β-Sitosterol - compounds with insecticidal activities [12]. Despite its uses and economic importance, little or no published pathological information exist about its agronomy. This created the assumption as to whether it is immune to disease or not. Also in view of
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This article is part of a special issue entitled “Plant Pathogens interactions”. Corresponding author. E-mail address: [email protected] (V.O. Ayodele).
https://doi.org/10.1016/j.cpb.2018.10.001 Received 23 March 2018; Received in revised form 9 October 2018; Accepted 10 October 2018 2214-6628/ © 2018 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/BY/4.0/).
Please cite this article as: AYODELE, V.O., Current Plant Biology, https://doi.org/10.1016/j.cpb.2018.10.001
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basis. Plants were randomly tagged for assessment in 2016 and 2017.
its benefits, an attempt was made towards its conservation, as an underutilized crop of which agronomy may be harnessed in the production of spice, food drinks, food colourings and food flavour and medicines. The present study, thus, investigated fungal diseases of Curcuma amada at field; and assessed some agronomic parameters with disease incidence and severity.
2.5.1.1. Plant height. This was done at seven (7) days interval, beginning from the seventh (7th) week of planting, to determine morphological growth of Mango-ginger. Plant height was measured from the surface soil level (base of plant) to peak/top (highest point attained at natural position above soil level). Measurements were taken with metre rule.
2. Materials and methods 2.1. Planting site
2.5.1.2. Leaf number per plant stand. Counting of leaves per tagged stand of plant was done at seven (7) days interval, beginning from the seventh (7th) week of planting, to determine morphological growth of Mango-ginger.
Two plantings were conducted at a maiden land (with no known history of cultivation) within The Federal University of Agriculture Abeokuta’s teaching and research farm of the botanical garden. The first planting was located at latitude 7.216463, longitude 3.441747 and altitude 66 m above sea level; the second planting at 7.215908 and 3.4238338 latitude and longitude, respectively and 66 m above sea level. The soil was dark brown and richly loamy. The first planting was in June 2016 and the second in April 2017; with minimum duration of six (6) months, from planting to harvest.
2.5.2. Assessment of disease incidence and severity 2.5.2.1. Description of diseases symptom. The approach to assess for disease involved determination of, and distinguishing between living and non-living causes of plant damage by looking for patterns, determining the development of the damage, and building a case history of the problem. Healthy plants made good identifier for diseased plants, as to what and how they should look like structurally and physiologically. Moreover, the non-uniform damages indicated living factor(s) as cause of disease. Symptoms were photographed and described based on visual appearance and compared with Plant Disease Compendia series of America Pathological Society (APS).
2.2. Planting materials Rhizomes for planting were collected from Department of Plant Physiology and Crop Production, College of Plant Science and Crop Production of the Federal University of Agriculture Abeokuta.
2.5.2.2. Calculation of disease incidence and severity. Percentage Disease Incidence (PDI) as used by Bdliya [5] and Jaydeep et al. [11] was calculated weekly, on the basis of infected plants divided by total number of plants assessed:
2.3. Experimental design and cultural practices The design was a Quasi-experimental design (natural experiment) which is fulcrumed as field observational study as described by Shadish et al. [26] and Harris et al. [10], to observe and measure variables at natural condition (without assigning treatment), with healthy plants serving as control. Hence, plot sizes of 20 m by 20 m and 15 m by 15 m were used to carry out the two plantings for the years 2016 and 2017, respectively. Intra- and inter-ridge spacings were 25 cm and 45 cm, respectively for a mono-culture planting of Mango ginger on parallel ridges. Planting of rhizomes was done 20th June 2016 and 11th April 2017; with emergence of 2006 and 240 plants, according to the order of the stated years. Plants were subjected only to the prevalent natural condition, with no chemical and no fertilizer application. General weeding was done at three weeks interval, beginning from the seventh (7th) week of planting.
PDI =
Number of infected plants × 100 Total number of plants assessed
The severity of the infected plants was assessed per week. Disease Severity Index (DSI) was calculated as applied by Bdliya [5] and Jaydeep et al. [11]:
DSI =
Sum of individual disease ratings Total number of plants rated × Highest score on the severity scale × 100
Disease was rated on a scale of 0–9, to calculate DSI, as used by Jaydeep et al. [11]. 2.5.3. Assessment of loss in rhizome yields Quality and commercial loss, as effect of disease on rhizome yields, was examined by comparison of rotted (Unmarketable Yield- UY) and clean (Marketable Yield- MY) rhizomes. Hence, sorting of harvested rhizomes was done immediately after harvest, to separate rhizomes infected with rots from clean rhizomes. Sorted rhizomes were weighed, fresh; and yields expressed in kilogramme per hectare and calculation as follows:
2.4. Source of weather data Weather data, for the planting months in 2016 and 2017, was sourced from Department of Agrometeorology and Water Management, Federal University of Agriculture Abeokuta. The weather parameters were: rainfall in millimetres, sunshine in hours, relative humidity in percent, evaporation in millimetres, soil temperature and atmospheric temperature in degree celcius.
UY = TY-MY 2.5. Agronomical parameters and disease assessment
Percentage Unmarketable Yield = Assessment of crop plants was done on weekly basis as follows:
UY × 100 TY
Where: TY is total yield; MY is marketable yield; UY is unmarketable yield.
1 Assessment of crop growth and development (plant height and number of leaves per tagged plant stand) 2 Assessment of disease incidence and severity 3 Assessment of losses in rhizome yield
2.6. Isolation and identification of phytopathogenic fungi Isolation was done on symptomatic plants and investigated fungi and fungus-like organisms were isolated from shoots, according to the method of Narayanasamy [18]. Mycelial growths were observed on PDA plates and then the organisms were viewed with microscope and identified based on their morphological characteristics as well as colony
2.5.1. Assessment of crop growth development Data of growth and development of plants were taken during the growing seasons. It described development from planting till harvest and also helped to monitor disease development in plants on weekly 2
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Colletotrichum capsici and Phyllosticta zingiberi were isolated, severally, from tissues with leaf spot of Curcuma amada.
growth as described by Narayanasamy [18]. Fungi identification was verified with literatures of fungi amongst which are Pictorial Atlas of Soil and Seed Fungi by Watanabe [31], and Illustrated Genera of Imperfect Fungi by Barnett and Hunter [4].
3.1.2. Leaf blight The disease was characterized first with chlorosis or yellowing of leaf tips, margins or blades; then the appearance of brown necrotic lesions within the yellow areas (Fig. 2a and b). The necrotic lesions enlarged and got dried into dark brown patches of varying sizes on blades; and sometimes covered more than half the surface of each diseased leaf, resulting in death of leaves (Fig. 2c). Older leaves were mostly affected by the disease, and infected leaves ended up dying. Alternaria alternata, Rhizoctonia solani and Colletotrichum gloeosporioideswere isolated from leaves infected with blight on more than two occasions.
2.7. Data presentation and analysis Pictures and charts were used to describe diseases symptom and ttest was used to determine significant difference between the evaluated growth and disease parameters, using SPSS version 20. 3. Results 3.1. Diseases of Curcuma amada
3.1.3. Rhizome rot Infection became clear on pseudostem as the base of the aerial shoot showed water-soaked soft lesions. Infection originated at the underground or ground level part of Mango ginger plant, and progressed to all directions. There was subsequent yellowing of leaves, beginning from lower leaves, followed by drooping and withering. Rhizomes rotted (Fig. 3) and became soft. Roots arising from infected rhizomes became rotted with brown discolouration. Pseudostems came off easily at gentle pull. Rhizomes size and production were reduced. Rotted rhizomes emitted foul smell, contrary to the characteristic raw mango smell. Pythium aphanidermatum, Rhizoctonia solani and Fusarium solani were observed associated with the disease in field.
The foliage diseases, by fungi, of Curcuma amada were spots and blights. Also, rhizome rot was observed at harvest. 3.1.1. Leaf spot Spots, which were observable beginning from a week after emergence, were white to grayish white on blades and surrounded by reddish brown, brown or yellow borders. The spots then turned papery and thinned out, leaving blades with holes. The spots, which were seen at first on the adaxial surface (Fig. 1a), became obvious also on the abaxial surface, before the formation of holes in the leaves (Fig. 1b and c). Holes in leaf blades were of varying sizes and shapes, and identical to initial created spots (of circular, elliptic or oblong shape). Irrespective of the age of plants, new and younger leaves were observed to be infected; and some tiny spots had widened with time, apart from the coalition of some spots into blotches. Few leaves also became shredded, at severe disease condition. Most infected leaves survived the disease.
3.2. Disease incidence and severity of associated fungi of Mango ginger Incidence of leaf blight disease was first observed in the 5th week
Fig. 1. Symptoms of leaf spot of Mango ginger plants. A- Early symptom of oval or circular white spots on blade; B and C -Advanced symptoms of coalition of spots, holes in blade and shredding of leaf. 3
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Fig. 3. (a) Freshly harvested Curcuma amada rhizomes (b) Sorted rhizomes affected with rots.
Fig. 2. a) Arrows point early blighting stage of leaf, first marked with yellowing, then obvious brown lesions (b) Progressive blight originated at leaf tip (c) Brown necrotic patches on blades, symptomatic of progressive leaf blight.
Fig. 4. Incidence of Blight Disease Observed in Mango ginger in 2016 and 2017. BDI is Blight Disease Incidence. Total sum of percent of Incidence was 135.1 and 315.2 for 2016 and 2017, respectively.
(0.38%) and 9th week of emergence in 2016 and 2017, respectively; and was highest in the 21st week (10.1%) and 20th week (36.2%) in 2016 and 2017, respectively (Fig. 4). Disease incidence of leaf spot was first observed in the 1st week (0.32%) and 2nd week (2.4%) of year 2016 and 2017, respectively; with maximum incidence of occurrence in the 12th week (12.1%) and 6th week (13.4%) of 2016 and 2017, in the order given (Fig. 5). There was highest severity of blight in the 18th week (78.9%) and 24th week (77.8%) of the years 2016 and 2017, correspondingly; and the total Blight Disease Severity for 2016 (810) was higher than 2017 (630.2) despite that severity increased steadily in 2017 (Fig. 6). Spot disease severity commenced higher in 2017 (3.3%) than in 2016 (2.3%) at week 2 and week 1, correspondingly; and there was highest severity in the 9th and 11th week (39.7%) in 2017 and in the 7th week (31%) in 2016. Severity, at total, was higher in 2017 than in 2016 (Fig. 7).
3.3. Loss of rhizomes to rot disease of Mango ginger plant Some rhizomes, at harvest, were observed to be affected with rot, thereby making them of lesser quality for use and for sale. Moreover, the loss due to rot disease was less than 5% in each year, though higher in 2016 (3.25%) than in 2017 (3.02%). The quantity evaluation of harvested rhizomes for the two years is given in Table 1.
3.4. Mean performance, relationship between characters and weather data Spot disease incidence and blight disease incidence showed significance (of 0.04 and 0.001, respectively, at p ≤ 0.05) between means evaluated in 2016 and 2017 (Table 2). Furthermore, the relationship between plant height and Blight Disease Incidence was positively linear and significant for 2016 4
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Table 2 Mean Performance of Mango ginger Evaluated in 2016 and 2017.
Fig. 5. Incidence of Spot Disease Observed with Mango ginger in 2016 and 2017. SDI is Spot Disease Incidence. Summation of percent of Incidence was 95.6 and 146.6 for 2016 and 2017, respectively.
Character
Mean ± StdErr (2016)
Mean ± StdErr (2017)
Sig. (2tailed)
Plant Height-A Plant Height-B Number of Leaves Spot Disease Incidence Blight Disease Incidence Spot Disease Severity Blight Disease Severity
34.83 ± 3.51 48.69 ± 5.37 5.42 ± 0.46 3.98 ± 0.74
43.48 ± 5.05 51.35 ± 6.01 6.63 ± 0.45 6.11 ± 0.71
0.17 0.74 0.07 0.04
5.63 ± 0.75
13.13 ± 2.24
0.00
15.80 ± 1.63
18.19 ± 2.25
0.39
33.75 ± 5.27
26.26 ± 5.62
0.34
Std Err = Standard Error; A-Mean Height (Measured from Soil Level to Tip of Youngest Leaf/Apical Bud); B-Mean Height (Measured from Ground Level to top of plant at natural standing). Means are significantly different at p-value ≤ 0.05. Table 3 Correlation Matrix of Characters Evaluated on Mango ginger Plants in 2016.
PH No. of L SDI BDI SDS BDS
PH
No. of L
SDI
BDI
SDS
BDS
1.00 0.47* −0.04 0.94** −0.23 0.87**
0.47* 1.00 0.63** 0.54** 0.45* 0.68**
−0.04 0.63** 1.00 0.20 0.58** 0.05
0.94** 0.54** 0.20 1.00 −0.22 0.81**
−0.23 0.45* 0.58** −0.22 1.00 −0.14
0.87** 0.68** 0.05 0.81** −0.14 1.00
** Correlation is significant at the 0.01 level (2-tailed). * Correlation is significant at the 0.05 level (2-tailed); PH = Plant Height; No. of L = Number of Leaves; SDI = Spot Disease Incidence; BDI = Blight Disease Incidence; SDS = Spot Disease Severity; BDS = Blight Disease Severity.
Fig. 6. Severity of blight observed in Mango ginger in 2016 and 2017. BDS is Blight Disease Severity. Total sum of percent severity was 810 and 630.2 for 2016 and 2017, respectively.
Table 4 Correlation Matrix of Characters Evaluated on Mango ginger Plants in 2017.
PH No. of L SDI BDI SDS BDS
PH
No. of L
SDI
BDI
SDS
BDS
1.00 0.76** −0.05 0.92** 0.07 0.93**
0.76** 1.00 0.32 0.70** 0.60** 0.48*
−0.05 0.32 1.00 −0.11 0.64** −0.27
0.92** 0.70** −0.11 1.00 0.04 0.88**
0.07 0.60** 0.64** 0.04 1.00 −0.25
0.93** 0.48* −0.27 0.88** −0.25 1.00
** Correlation is significant at the 0.01 level (2-tailed). * Correlation is significant at the 0.05 level (2-tailed); PH = Plant Height; No. of L = Number of Leaves; SDI = Spot Disease Incidence; BDI = Blight Disease Incidence; SDS = Spot Disease Severity; BDS = Blight Disease Severity.
(0.94**) and 2017 (0.92**) (Tables 3 and 4); also, Spot Disease Incidence reduced as plant height increased, in 2016 (-0.04) and 2017 (-0.05) (Tables 3 and 4); while Spot Disease Severity was insignificant, in 2016 (-0.23) and 2017 (0.07), with plant height, Blight Disease Severity was significant and positive with plant height for 2016 (0.87**) and 2017 (0.93**) (Table 3 and 4). Finally, relative humidity, soil and air temperature were slightly higher in 2017 than in 2016; and total rainfall was higher in 2016 than in 2017 (Table 5).
Fig. 7. Severity of spot disease observed in Mango ginger in 2016 and 2017. SDS is Spot Disease Severity. Total sum of percent severity was 379.3 and 436.6 for 2016 and 2017, respectively. Table 1 Marketable and Unmarketable Rhizome Yield of Mango ginger in 2016 and 2017. Yield Parameters
2016
2017
Total Yield(TY) Marketable Yield(MY) Unmarketable Yield(UY)
18,300 kg/ha (100%) 17,705 kg/ha (96.75%) 595 kg/ha (3.25%)
29,346.7 kg/ha (100%) 28,460 kg/ha (96.98%) 886.7 kg/ha (3.02%)
4. Discussion Disease symptoms of spots and blights as observed with leaves, and rhizome rot observed with some underground stems of Curcuma amada suggests the crop is not immune to infection. Lapin and Ackerveken [13] asserted that susceptibility to infectious diseases caused by adapted pathogens (that are able to elude or terminate host immunity)
Marketable yield is also valuable yield; unmarketable yield = less valuable yield.
5
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other parameters, in the correlation of growth parameters and disease assessment of potato. In addition, Sweet basil (Ocimum basilicum) was stated to be more susceptible to downy mildew, by Peronospora belbahrii, at 2–3 weeks old than at 4–7 weeks old [19]. Contrariwise, the correlation of Blight Disease Incidence with Plant Height, for the two years, strongly suggest that incidence of the disease increased as plant height increased with age. Thus, it may be explained that resistance to Blight Disease of Mango ginger plants, decreased as height increased with age. Millett et al. [17], correspondingly, reported preflowering plants of potato (Solanum bulbocastanum PT29 and S. tuberosum cv. Dark Red Norland) to have exhibited highest level of resistance to foliar late blight, followed by postflowering and near senescing plants. Highest anthracnose level caused by Colletotrichum truncatum were also observed on oldest plants of lentil (Lens culinaris), as elucidation of age dependent resistance by Vail and Vandenberg [29]. The association of plant age with resistance to Ascochyta Blight was, further, reported on chickpea (Cicer arietinum), by Chongo and Gossen [7], to decrease with age in partially resistant cultivars. This study, further, confirms soil borne disease, of rhizome rot, affecting Curcuma amada plants for which the causative pathogens might have penetrated the below ground tissues of stems or roots, to cause infection, and possibly had interfered with the leave’s water supply and economy by inhibiting the movement of water to the leaves and increasing the leaves’ transpiration, respectively, hence the drooping and withering symptoms that characterized rhizome rot. The water and nutrient starved leaves, being unable to function as photosynthetic organ, denied the plant system their food supply, resulting to death of entire plant. In quoting Agrios [1] ‘Many plant pathogens interfere in one or more ways with the translocation of water and inorganic nutrients through plants. Some pathogens cause roots to absorb less water as they affect their condition of completeness or function; other pathogens, by growing in the xylem vessels or by other means, interfere with the translocation of water through the stem; and, in some diseases, pathogens interfere with the water economy of the plant by causing excessive transpiration through their effects on leaves and stomata’. Curcuma amada crops below three weeks after emergence were observed symptomless to leaf blight unlike with leaf spot disease which was perceived with young and emerging leaves, irrespective of age of plant. According to Marie-Pierre et al. [16], induced resistance to disease at plant development is common in the plant kingdom, and appears at different stages of growth of host plant, varying with plant age or tissue maturity. Agrios [1] similarly stated that ‘pathogens differ… with respect to the organs and tissues that they can infect and with respect to the age of the organ or tissue of the plant on which they can grow’. Given the light from these authors, simply, the fungal pathogens affecting Curcuma amada are specific of tissue or organ and organ age of their host, due to host resistance which varies with age or maturity or type of tissue. Curcuma amada crops might be immune to blight at below three weeks after emergence of crops irrespective of environmental factors. Correspondingly, Curcuma amada crops become most resistant to leaf spot at maturity of organs and whole plant. The results of diseased rhizome of Curcuma amada plants may be considered in relation to yield of marketable rhizomes. On the basis of the record of Stirling et al. [28], Pythium myriotylum causes more than 50% and about 30% loss in rhizomes of ginger (Zingiber officinale) in Fiji and Australia, respectively. Loss of 70% in yield of Zingiber officinale was, in addition, reported by Li et al. [14] in China. Rhizome rot, also, is one of the most devastating crop diseases of Curcuma longa [3,22]. Incidence of rhizome rot disease, which is subject to crop susceptibility/ resistivity, environment and virulence factor of pathogen was low with Curcuma amada in comparison to reports on Curcuma longa and Zingiber officinale. Also, the observed higher increase of rhizome rot in the previous year as against 2017, in conjunction with the higher rainfall recorded in 2016 over 2017 suggests Pythium aphanidermatum, Rhizoctonia solani and Fusarium solani, as suspected causal organisms of the disease, to
Table 5 Mean Values of Weather Parameters from Planting Months to Harvest.
Rainfall total(mm) Sunshine (hour) Relative Humidity (%) Evaporation (mm) Soil Temp(oC) MeanTempMax/Min(oC)
10cm 20cm
2016
2017
95.7 3.9 67.7 2.9 27.4 27.8 26.2
89.4 3.9 70.5 2.6 27.7 28.0 26.9
Temp = temperature; Max = maximum; Min = minimum.
affects most plants in their natural habitat, resulting to yield losses in agriculture. The disintegration of leaf spots to creation of holes through blades and shredding of leaves of infected Curcuma amada plants may be explained from the idea of Agrios [1] on how plants defend themselves against pathogens. Genetically, Curcuma amada plants infected with spots were able to stop the disease from further developing by severing healthy tissues from diseased tissues, resulting into holes and shreds. This action creates an idea of Curcuma amada leaf spot as a local infection; and Curcuma amada plants may be said to be resistant to leaf spot disease. Again, Curcuma amada plants, at inoculation of the pathogens, might have recognized Leaf Spot Pathogen Elicitor (LSPE), leading to series of biochemical reactions and structural changes in leaves. Therefore, in an effort to fend-off the pathogen(s) and metabolites or to stop its further development, there was severing of diseased tissues from the rest organ(s), hence the holes and shreds of the leaves. This phenomenon, according to Ravichandra [23], is termed hypersensitivity. Leaf blight pathogens of Curcuma amada plants obtained feeding from leaves at expense of host plants. The pathogens conceivably interfered with the chloroplasts in the course of infection, by causing their degeneration and destroying the chlorophyll via metabolites and toxins released, which must have caused the chlorotic symptoms characteristic of emerging blight of Curcuma amada leaves. This explanation is in conformity with Agrios [1] who proposed that pathogens affecting plant photosynthesis secrete tentoxin and tabtoxin to inhibit some plant enzymes involved in photosynthesis. Succeeding the chlorosis was the brown necrosis which may be expounded as freshly dead tissues on which the pathogens were done feeding (where they are biotrophs) or were currently feeding on (as necrotrophs). In the absence of water, or where the tissues dried out to no water supply the necrotic tissues thus appeared obviously dark brown. The graphs of the disease progress reveals a polycyclic nature of the pathogens responsible for leaves spot and blight of Curcuma amada. Inconsistent increase and decrease (or rising and falling patterns of lines) portrayed multiple circles of development of the pathogens within one growth season (circle) of Curcuma amada plants. According to William [32], polycyclic pathogens, being responsible for most acute plant epidemics, complete many disease cycles per year, and are usually dispersed by air, and examples of which include leaf spots and blights. Environmental and genetic factors might have influenced incidences and severities of the diseases, for the two years. There must be environment, suitable for the virulency of the pathogen and encouraging host’s susceptibility, according to the disease triangle, for infection to occur; and this would have been the reason for the drastic increase in blight disease incidence and severity for the two years. Relationship of Spot Disease Incidence with Plant Height suggest that Curcuma amada plants were more susceptible to the disease at early age or were more resistant at later age, because as plant height increased with age, less symptoms were observed amongst species. Maan et al. [15] also reported incidence of Potato Apical Leaf-Curl Disease being significant and negatively associated with plant height, weight of leaves per hill, weight of foliage per hill and leaf area index among 6
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have thrived better in relatively increased soil moisture due to increased rainfall. P. aphanidermatum was stated to be ubiquitous in soil and water according to Al-Sheikh [2]. Disease of Root rot of wheat seedlings caused by R. solani was most severe at highest experimented soil moisture levels [9]. F. solani is also ubiquitous [33]. Again, the occurrence of a plant showing symptoms characteristic of more than a disease, such as spot and blight affecting Curcuma amada, could be expounded with the disease triangle, whereby for a disease to occur there is interaction of virulent pathogen and susceptible host in an environment favourable for the pathogen to initiate infection. Owing to this, the pathogens inoculum responsible for the diseases, under suitable moisture and temperature, attached to and penetrated the Curcuma amada host plants to initiate infections which were expressed by the plants as spots, blights and rots. Finally, these results do answer the hypothetical question: ‘Is Curcuma amada plant immune to disease?’ Contrary to the initial suggestive thought that Curcuma amada plant was immune to diseases, owing to the paucity of information about its pathology, it may be deduced that Curcuma amada plants are not immune to disease(s), but are resistant to disease(s). This suggestion indicates that all plant life are subject to infection, however some may be resistant. Agrios [1] states: ‘Plant diseases occur in all parts of the world where plants grow. They are more common and more severe, however, in humid to wet areas with cool, warm or tropical temperatures’.
[13]
Further studies
[19]
Pathogenicity test shall be done, as additional research, on the pathogens identified The identified pathogens shall be characterized, to provide valuable information on the formation of control strategies to curb the diseases. Control measures to curb the diseases shall be experimented, for adequate prescription to farmers.
[20]
[9]
[10]
[11]
[12]
[14]
[15]
[16]
[17]
[18]
[21]
[22]
Acknowledgements [23]
Special thanks to Prof. S. T. O. Lagoke through whom the planted rhizomes were gotten from Department of Plant Physiology and Crop Production, College of Plant Science and Crop Production of Federal University of Agriculture Abeokuta. Funding: This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
[24]
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Contents lists available at ScienceDirect
Current Plant Biology journal homepage: www.elsevier.com/locate/cpb
Identification, assessment of diseases and agronomic parameters of Curcuma amada Roxb (Mango ginger)☆ ⁎
Victor O. Ayodelea, , Olumayowa M. Olowea,c, Clement G. Afolabib, Iyabo A. Kehindea a
Department of Pure and Applied Botany, College of Bio-Sciences, Federal University of Agriculture Abeokuta, PMB, 2240, Abeokuta, Nigeria Department of Crop Protection, College of Plant Science and Crop Production, Federal University of Agriculture Abeokuta, PMB, 2240, Abeokuta, Nigeria c Department of Crop Science, College of Agriculture, Animal Science and Veterinary Medicine, University of Rwanda, Rwanda b
A R T I C LE I N FO
A B S T R A C T
Keywords: Mango ginger (Curcuma amada Roxb.) Leaf spot Leaf blight Rhizome rot Fungal diseases
Many diseases affect plants, causing physiological dysfunctions and structural deviation from normal. The effects of plant diseases on yield and quality of crops have been documented. Little, however, is known about the pathology and agronomy of Mango ginger (Curcuma amada Roxb.), an under-cultivated crop. The present study was carried out to assess disease incidence and severity of associated fungal diseases of Mango ginger; assess rhizome yield loss due to disease; isolate and identify fungal pathogens associated; evaluate growth parameters of Mango ginger. Mango ginger plants began showing symptoms of leaf spot and leaf blight at first week and at fifth week after emergence, respectively; at twenty-fourth week some rhizomes were visually observed to be affected with rot. Cercospora curcumae, Phyllosticta zingiberi and Colletotrichum capsici; C. gloeosporioides, Alternaria alternata and Rhizoctonia solani; R. solani, Fusarium solani and Pythium aphanidermatum were frequently found associated with leaf spot, leaf blight and rhizome rot, respectively. Correlation coefficient of: Spot Disease Incidence with plant height was −0.04 and −0.05 for 2016 and 2017, respectively; number of leaves in progression with age was significant at p < 0.01 in 2016 (0.63) but insignificant in 2017 (0.32). Also, correlation coefficient of Blight Disease Incidence: with plant height was significant at p < 0.01 in the year 2016 (0.94) and 2017 (0.92); with number of leaves as age progressed was 0.54 and 0.70 for 2016 and 2017, respectively, and significant at p < 0.01. Percentage losses of 3.25 and 3.02, at harvest, due to rhizome rot were recorded for 2016 and 2017, respectively. This study revealed the occurrence of diseases, associated with fungi and funguslike organisms, and their effect on Mango ginger plants.
1. Introduction Mango ginger (Curcuma amada Roxb.) is a common southern and eastern India perennial herb, but cultivated as annual crop mostly in India and Malaysia [6]. It is rhizomatous and aromatic, with leafy tuft and may grow 60–90 cm above ground level [25]. Its mango flavour is attributed to presence of car-3-ene and cis-ocimene among the 68 volatile aroma components present in the essential oil of its rhizomes [30]. The rhizomes are used in culinary preparations and in manufacture of pickles; also, Ayurveda and Unani medicinal systems use Curcuma amada as appetizer, alexteric, antipyretic, aphrodisiac, diuretic, emollient, expectorant and laxative and to cure biliousness, itching, skin diseases, bronchitis, asthma, hiccough and inflammation due to injuries [21]. Difurocumenonol, isolated from Mango ginger, is highly anti-
gram-positive and gram-negative bacteria [20]. Pre-treatment with Mango ginger significantly improved sperm count, and motility, and also declined cell phone radiation induced infertility in rats [8]. Mango ginger extract lowered, below normal level, the triglyceride in the blood of Triton-induced hyperlipidemic rats and also influenced liver synthesis and blood clearance [25]. Sivaprabha et al. [27] reported its cytotoxic activity against breast cancer cell lines MCF-7 and MDA MB 231. According to Sailendra et al. [24] labdane diterpene dialdehyde [labda-8(17), 12-diene-15, 16-dial]-an anti-tubercular agent was isolated and characterized from Mango ginger. Its ethanolic extract revealed presence of β-Sitosterol and Androstan-17-one, 3-ethyl-3-hydroxy-, β-Sitosterol - compounds with insecticidal activities [12]. Despite its uses and economic importance, little or no published pathological information exist about its agronomy. This created the assumption as to whether it is immune to disease or not. Also in view of
☆ ⁎
This article is part of a special issue entitled “Plant Pathogens interactions”. Corresponding author. E-mail address: [email protected] (V.O. Ayodele).
https://doi.org/10.1016/j.cpb.2018.10.001 Received 23 March 2018; Received in revised form 9 October 2018; Accepted 10 October 2018 2214-6628/ © 2018 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/BY/4.0/).
Please cite this article as: AYODELE, V.O., Current Plant Biology, https://doi.org/10.1016/j.cpb.2018.10.001
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basis. Plants were randomly tagged for assessment in 2016 and 2017.
its benefits, an attempt was made towards its conservation, as an underutilized crop of which agronomy may be harnessed in the production of spice, food drinks, food colourings and food flavour and medicines. The present study, thus, investigated fungal diseases of Curcuma amada at field; and assessed some agronomic parameters with disease incidence and severity.
2.5.1.1. Plant height. This was done at seven (7) days interval, beginning from the seventh (7th) week of planting, to determine morphological growth of Mango-ginger. Plant height was measured from the surface soil level (base of plant) to peak/top (highest point attained at natural position above soil level). Measurements were taken with metre rule.
2. Materials and methods 2.1. Planting site
2.5.1.2. Leaf number per plant stand. Counting of leaves per tagged stand of plant was done at seven (7) days interval, beginning from the seventh (7th) week of planting, to determine morphological growth of Mango-ginger.
Two plantings were conducted at a maiden land (with no known history of cultivation) within The Federal University of Agriculture Abeokuta’s teaching and research farm of the botanical garden. The first planting was located at latitude 7.216463, longitude 3.441747 and altitude 66 m above sea level; the second planting at 7.215908 and 3.4238338 latitude and longitude, respectively and 66 m above sea level. The soil was dark brown and richly loamy. The first planting was in June 2016 and the second in April 2017; with minimum duration of six (6) months, from planting to harvest.
2.5.2. Assessment of disease incidence and severity 2.5.2.1. Description of diseases symptom. The approach to assess for disease involved determination of, and distinguishing between living and non-living causes of plant damage by looking for patterns, determining the development of the damage, and building a case history of the problem. Healthy plants made good identifier for diseased plants, as to what and how they should look like structurally and physiologically. Moreover, the non-uniform damages indicated living factor(s) as cause of disease. Symptoms were photographed and described based on visual appearance and compared with Plant Disease Compendia series of America Pathological Society (APS).
2.2. Planting materials Rhizomes for planting were collected from Department of Plant Physiology and Crop Production, College of Plant Science and Crop Production of the Federal University of Agriculture Abeokuta.
2.5.2.2. Calculation of disease incidence and severity. Percentage Disease Incidence (PDI) as used by Bdliya [5] and Jaydeep et al. [11] was calculated weekly, on the basis of infected plants divided by total number of plants assessed:
2.3. Experimental design and cultural practices The design was a Quasi-experimental design (natural experiment) which is fulcrumed as field observational study as described by Shadish et al. [26] and Harris et al. [10], to observe and measure variables at natural condition (without assigning treatment), with healthy plants serving as control. Hence, plot sizes of 20 m by 20 m and 15 m by 15 m were used to carry out the two plantings for the years 2016 and 2017, respectively. Intra- and inter-ridge spacings were 25 cm and 45 cm, respectively for a mono-culture planting of Mango ginger on parallel ridges. Planting of rhizomes was done 20th June 2016 and 11th April 2017; with emergence of 2006 and 240 plants, according to the order of the stated years. Plants were subjected only to the prevalent natural condition, with no chemical and no fertilizer application. General weeding was done at three weeks interval, beginning from the seventh (7th) week of planting.
PDI =
Number of infected plants × 100 Total number of plants assessed
The severity of the infected plants was assessed per week. Disease Severity Index (DSI) was calculated as applied by Bdliya [5] and Jaydeep et al. [11]:
DSI =
Sum of individual disease ratings Total number of plants rated × Highest score on the severity scale × 100
Disease was rated on a scale of 0–9, to calculate DSI, as used by Jaydeep et al. [11]. 2.5.3. Assessment of loss in rhizome yields Quality and commercial loss, as effect of disease on rhizome yields, was examined by comparison of rotted (Unmarketable Yield- UY) and clean (Marketable Yield- MY) rhizomes. Hence, sorting of harvested rhizomes was done immediately after harvest, to separate rhizomes infected with rots from clean rhizomes. Sorted rhizomes were weighed, fresh; and yields expressed in kilogramme per hectare and calculation as follows:
2.4. Source of weather data Weather data, for the planting months in 2016 and 2017, was sourced from Department of Agrometeorology and Water Management, Federal University of Agriculture Abeokuta. The weather parameters were: rainfall in millimetres, sunshine in hours, relative humidity in percent, evaporation in millimetres, soil temperature and atmospheric temperature in degree celcius.
UY = TY-MY 2.5. Agronomical parameters and disease assessment
Percentage Unmarketable Yield = Assessment of crop plants was done on weekly basis as follows:
UY × 100 TY
Where: TY is total yield; MY is marketable yield; UY is unmarketable yield.
1 Assessment of crop growth and development (plant height and number of leaves per tagged plant stand) 2 Assessment of disease incidence and severity 3 Assessment of losses in rhizome yield
2.6. Isolation and identification of phytopathogenic fungi Isolation was done on symptomatic plants and investigated fungi and fungus-like organisms were isolated from shoots, according to the method of Narayanasamy [18]. Mycelial growths were observed on PDA plates and then the organisms were viewed with microscope and identified based on their morphological characteristics as well as colony
2.5.1. Assessment of crop growth development Data of growth and development of plants were taken during the growing seasons. It described development from planting till harvest and also helped to monitor disease development in plants on weekly 2
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Colletotrichum capsici and Phyllosticta zingiberi were isolated, severally, from tissues with leaf spot of Curcuma amada.
growth as described by Narayanasamy [18]. Fungi identification was verified with literatures of fungi amongst which are Pictorial Atlas of Soil and Seed Fungi by Watanabe [31], and Illustrated Genera of Imperfect Fungi by Barnett and Hunter [4].
3.1.2. Leaf blight The disease was characterized first with chlorosis or yellowing of leaf tips, margins or blades; then the appearance of brown necrotic lesions within the yellow areas (Fig. 2a and b). The necrotic lesions enlarged and got dried into dark brown patches of varying sizes on blades; and sometimes covered more than half the surface of each diseased leaf, resulting in death of leaves (Fig. 2c). Older leaves were mostly affected by the disease, and infected leaves ended up dying. Alternaria alternata, Rhizoctonia solani and Colletotrichum gloeosporioideswere isolated from leaves infected with blight on more than two occasions.
2.7. Data presentation and analysis Pictures and charts were used to describe diseases symptom and ttest was used to determine significant difference between the evaluated growth and disease parameters, using SPSS version 20. 3. Results 3.1. Diseases of Curcuma amada
3.1.3. Rhizome rot Infection became clear on pseudostem as the base of the aerial shoot showed water-soaked soft lesions. Infection originated at the underground or ground level part of Mango ginger plant, and progressed to all directions. There was subsequent yellowing of leaves, beginning from lower leaves, followed by drooping and withering. Rhizomes rotted (Fig. 3) and became soft. Roots arising from infected rhizomes became rotted with brown discolouration. Pseudostems came off easily at gentle pull. Rhizomes size and production were reduced. Rotted rhizomes emitted foul smell, contrary to the characteristic raw mango smell. Pythium aphanidermatum, Rhizoctonia solani and Fusarium solani were observed associated with the disease in field.
The foliage diseases, by fungi, of Curcuma amada were spots and blights. Also, rhizome rot was observed at harvest. 3.1.1. Leaf spot Spots, which were observable beginning from a week after emergence, were white to grayish white on blades and surrounded by reddish brown, brown or yellow borders. The spots then turned papery and thinned out, leaving blades with holes. The spots, which were seen at first on the adaxial surface (Fig. 1a), became obvious also on the abaxial surface, before the formation of holes in the leaves (Fig. 1b and c). Holes in leaf blades were of varying sizes and shapes, and identical to initial created spots (of circular, elliptic or oblong shape). Irrespective of the age of plants, new and younger leaves were observed to be infected; and some tiny spots had widened with time, apart from the coalition of some spots into blotches. Few leaves also became shredded, at severe disease condition. Most infected leaves survived the disease.
3.2. Disease incidence and severity of associated fungi of Mango ginger Incidence of leaf blight disease was first observed in the 5th week
Fig. 1. Symptoms of leaf spot of Mango ginger plants. A- Early symptom of oval or circular white spots on blade; B and C -Advanced symptoms of coalition of spots, holes in blade and shredding of leaf. 3
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Fig. 3. (a) Freshly harvested Curcuma amada rhizomes (b) Sorted rhizomes affected with rots.
Fig. 2. a) Arrows point early blighting stage of leaf, first marked with yellowing, then obvious brown lesions (b) Progressive blight originated at leaf tip (c) Brown necrotic patches on blades, symptomatic of progressive leaf blight.
Fig. 4. Incidence of Blight Disease Observed in Mango ginger in 2016 and 2017. BDI is Blight Disease Incidence. Total sum of percent of Incidence was 135.1 and 315.2 for 2016 and 2017, respectively.
(0.38%) and 9th week of emergence in 2016 and 2017, respectively; and was highest in the 21st week (10.1%) and 20th week (36.2%) in 2016 and 2017, respectively (Fig. 4). Disease incidence of leaf spot was first observed in the 1st week (0.32%) and 2nd week (2.4%) of year 2016 and 2017, respectively; with maximum incidence of occurrence in the 12th week (12.1%) and 6th week (13.4%) of 2016 and 2017, in the order given (Fig. 5). There was highest severity of blight in the 18th week (78.9%) and 24th week (77.8%) of the years 2016 and 2017, correspondingly; and the total Blight Disease Severity for 2016 (810) was higher than 2017 (630.2) despite that severity increased steadily in 2017 (Fig. 6). Spot disease severity commenced higher in 2017 (3.3%) than in 2016 (2.3%) at week 2 and week 1, correspondingly; and there was highest severity in the 9th and 11th week (39.7%) in 2017 and in the 7th week (31%) in 2016. Severity, at total, was higher in 2017 than in 2016 (Fig. 7).
3.3. Loss of rhizomes to rot disease of Mango ginger plant Some rhizomes, at harvest, were observed to be affected with rot, thereby making them of lesser quality for use and for sale. Moreover, the loss due to rot disease was less than 5% in each year, though higher in 2016 (3.25%) than in 2017 (3.02%). The quantity evaluation of harvested rhizomes for the two years is given in Table 1.
3.4. Mean performance, relationship between characters and weather data Spot disease incidence and blight disease incidence showed significance (of 0.04 and 0.001, respectively, at p ≤ 0.05) between means evaluated in 2016 and 2017 (Table 2). Furthermore, the relationship between plant height and Blight Disease Incidence was positively linear and significant for 2016 4
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Table 2 Mean Performance of Mango ginger Evaluated in 2016 and 2017.
Fig. 5. Incidence of Spot Disease Observed with Mango ginger in 2016 and 2017. SDI is Spot Disease Incidence. Summation of percent of Incidence was 95.6 and 146.6 for 2016 and 2017, respectively.
Character
Mean ± StdErr (2016)
Mean ± StdErr (2017)
Sig. (2tailed)
Plant Height-A Plant Height-B Number of Leaves Spot Disease Incidence Blight Disease Incidence Spot Disease Severity Blight Disease Severity
34.83 ± 3.51 48.69 ± 5.37 5.42 ± 0.46 3.98 ± 0.74
43.48 ± 5.05 51.35 ± 6.01 6.63 ± 0.45 6.11 ± 0.71
0.17 0.74 0.07 0.04
5.63 ± 0.75
13.13 ± 2.24
0.00
15.80 ± 1.63
18.19 ± 2.25
0.39
33.75 ± 5.27
26.26 ± 5.62
0.34
Std Err = Standard Error; A-Mean Height (Measured from Soil Level to Tip of Youngest Leaf/Apical Bud); B-Mean Height (Measured from Ground Level to top of plant at natural standing). Means are significantly different at p-value ≤ 0.05. Table 3 Correlation Matrix of Characters Evaluated on Mango ginger Plants in 2016.
PH No. of L SDI BDI SDS BDS
PH
No. of L
SDI
BDI
SDS
BDS
1.00 0.47* −0.04 0.94** −0.23 0.87**
0.47* 1.00 0.63** 0.54** 0.45* 0.68**
−0.04 0.63** 1.00 0.20 0.58** 0.05
0.94** 0.54** 0.20 1.00 −0.22 0.81**
−0.23 0.45* 0.58** −0.22 1.00 −0.14
0.87** 0.68** 0.05 0.81** −0.14 1.00
** Correlation is significant at the 0.01 level (2-tailed). * Correlation is significant at the 0.05 level (2-tailed); PH = Plant Height; No. of L = Number of Leaves; SDI = Spot Disease Incidence; BDI = Blight Disease Incidence; SDS = Spot Disease Severity; BDS = Blight Disease Severity.
Fig. 6. Severity of blight observed in Mango ginger in 2016 and 2017. BDS is Blight Disease Severity. Total sum of percent severity was 810 and 630.2 for 2016 and 2017, respectively.
Table 4 Correlation Matrix of Characters Evaluated on Mango ginger Plants in 2017.
PH No. of L SDI BDI SDS BDS
PH
No. of L
SDI
BDI
SDS
BDS
1.00 0.76** −0.05 0.92** 0.07 0.93**
0.76** 1.00 0.32 0.70** 0.60** 0.48*
−0.05 0.32 1.00 −0.11 0.64** −0.27
0.92** 0.70** −0.11 1.00 0.04 0.88**
0.07 0.60** 0.64** 0.04 1.00 −0.25
0.93** 0.48* −0.27 0.88** −0.25 1.00
** Correlation is significant at the 0.01 level (2-tailed). * Correlation is significant at the 0.05 level (2-tailed); PH = Plant Height; No. of L = Number of Leaves; SDI = Spot Disease Incidence; BDI = Blight Disease Incidence; SDS = Spot Disease Severity; BDS = Blight Disease Severity.
(0.94**) and 2017 (0.92**) (Tables 3 and 4); also, Spot Disease Incidence reduced as plant height increased, in 2016 (-0.04) and 2017 (-0.05) (Tables 3 and 4); while Spot Disease Severity was insignificant, in 2016 (-0.23) and 2017 (0.07), with plant height, Blight Disease Severity was significant and positive with plant height for 2016 (0.87**) and 2017 (0.93**) (Table 3 and 4). Finally, relative humidity, soil and air temperature were slightly higher in 2017 than in 2016; and total rainfall was higher in 2016 than in 2017 (Table 5).
Fig. 7. Severity of spot disease observed in Mango ginger in 2016 and 2017. SDS is Spot Disease Severity. Total sum of percent severity was 379.3 and 436.6 for 2016 and 2017, respectively. Table 1 Marketable and Unmarketable Rhizome Yield of Mango ginger in 2016 and 2017. Yield Parameters
2016
2017
Total Yield(TY) Marketable Yield(MY) Unmarketable Yield(UY)
18,300 kg/ha (100%) 17,705 kg/ha (96.75%) 595 kg/ha (3.25%)
29,346.7 kg/ha (100%) 28,460 kg/ha (96.98%) 886.7 kg/ha (3.02%)
4. Discussion Disease symptoms of spots and blights as observed with leaves, and rhizome rot observed with some underground stems of Curcuma amada suggests the crop is not immune to infection. Lapin and Ackerveken [13] asserted that susceptibility to infectious diseases caused by adapted pathogens (that are able to elude or terminate host immunity)
Marketable yield is also valuable yield; unmarketable yield = less valuable yield.
5
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other parameters, in the correlation of growth parameters and disease assessment of potato. In addition, Sweet basil (Ocimum basilicum) was stated to be more susceptible to downy mildew, by Peronospora belbahrii, at 2–3 weeks old than at 4–7 weeks old [19]. Contrariwise, the correlation of Blight Disease Incidence with Plant Height, for the two years, strongly suggest that incidence of the disease increased as plant height increased with age. Thus, it may be explained that resistance to Blight Disease of Mango ginger plants, decreased as height increased with age. Millett et al. [17], correspondingly, reported preflowering plants of potato (Solanum bulbocastanum PT29 and S. tuberosum cv. Dark Red Norland) to have exhibited highest level of resistance to foliar late blight, followed by postflowering and near senescing plants. Highest anthracnose level caused by Colletotrichum truncatum were also observed on oldest plants of lentil (Lens culinaris), as elucidation of age dependent resistance by Vail and Vandenberg [29]. The association of plant age with resistance to Ascochyta Blight was, further, reported on chickpea (Cicer arietinum), by Chongo and Gossen [7], to decrease with age in partially resistant cultivars. This study, further, confirms soil borne disease, of rhizome rot, affecting Curcuma amada plants for which the causative pathogens might have penetrated the below ground tissues of stems or roots, to cause infection, and possibly had interfered with the leave’s water supply and economy by inhibiting the movement of water to the leaves and increasing the leaves’ transpiration, respectively, hence the drooping and withering symptoms that characterized rhizome rot. The water and nutrient starved leaves, being unable to function as photosynthetic organ, denied the plant system their food supply, resulting to death of entire plant. In quoting Agrios [1] ‘Many plant pathogens interfere in one or more ways with the translocation of water and inorganic nutrients through plants. Some pathogens cause roots to absorb less water as they affect their condition of completeness or function; other pathogens, by growing in the xylem vessels or by other means, interfere with the translocation of water through the stem; and, in some diseases, pathogens interfere with the water economy of the plant by causing excessive transpiration through their effects on leaves and stomata’. Curcuma amada crops below three weeks after emergence were observed symptomless to leaf blight unlike with leaf spot disease which was perceived with young and emerging leaves, irrespective of age of plant. According to Marie-Pierre et al. [16], induced resistance to disease at plant development is common in the plant kingdom, and appears at different stages of growth of host plant, varying with plant age or tissue maturity. Agrios [1] similarly stated that ‘pathogens differ… with respect to the organs and tissues that they can infect and with respect to the age of the organ or tissue of the plant on which they can grow’. Given the light from these authors, simply, the fungal pathogens affecting Curcuma amada are specific of tissue or organ and organ age of their host, due to host resistance which varies with age or maturity or type of tissue. Curcuma amada crops might be immune to blight at below three weeks after emergence of crops irrespective of environmental factors. Correspondingly, Curcuma amada crops become most resistant to leaf spot at maturity of organs and whole plant. The results of diseased rhizome of Curcuma amada plants may be considered in relation to yield of marketable rhizomes. On the basis of the record of Stirling et al. [28], Pythium myriotylum causes more than 50% and about 30% loss in rhizomes of ginger (Zingiber officinale) in Fiji and Australia, respectively. Loss of 70% in yield of Zingiber officinale was, in addition, reported by Li et al. [14] in China. Rhizome rot, also, is one of the most devastating crop diseases of Curcuma longa [3,22]. Incidence of rhizome rot disease, which is subject to crop susceptibility/ resistivity, environment and virulence factor of pathogen was low with Curcuma amada in comparison to reports on Curcuma longa and Zingiber officinale. Also, the observed higher increase of rhizome rot in the previous year as against 2017, in conjunction with the higher rainfall recorded in 2016 over 2017 suggests Pythium aphanidermatum, Rhizoctonia solani and Fusarium solani, as suspected causal organisms of the disease, to
Table 5 Mean Values of Weather Parameters from Planting Months to Harvest.
Rainfall total(mm) Sunshine (hour) Relative Humidity (%) Evaporation (mm) Soil Temp(oC) MeanTempMax/Min(oC)
10cm 20cm
2016
2017
95.7 3.9 67.7 2.9 27.4 27.8 26.2
89.4 3.9 70.5 2.6 27.7 28.0 26.9
Temp = temperature; Max = maximum; Min = minimum.
affects most plants in their natural habitat, resulting to yield losses in agriculture. The disintegration of leaf spots to creation of holes through blades and shredding of leaves of infected Curcuma amada plants may be explained from the idea of Agrios [1] on how plants defend themselves against pathogens. Genetically, Curcuma amada plants infected with spots were able to stop the disease from further developing by severing healthy tissues from diseased tissues, resulting into holes and shreds. This action creates an idea of Curcuma amada leaf spot as a local infection; and Curcuma amada plants may be said to be resistant to leaf spot disease. Again, Curcuma amada plants, at inoculation of the pathogens, might have recognized Leaf Spot Pathogen Elicitor (LSPE), leading to series of biochemical reactions and structural changes in leaves. Therefore, in an effort to fend-off the pathogen(s) and metabolites or to stop its further development, there was severing of diseased tissues from the rest organ(s), hence the holes and shreds of the leaves. This phenomenon, according to Ravichandra [23], is termed hypersensitivity. Leaf blight pathogens of Curcuma amada plants obtained feeding from leaves at expense of host plants. The pathogens conceivably interfered with the chloroplasts in the course of infection, by causing their degeneration and destroying the chlorophyll via metabolites and toxins released, which must have caused the chlorotic symptoms characteristic of emerging blight of Curcuma amada leaves. This explanation is in conformity with Agrios [1] who proposed that pathogens affecting plant photosynthesis secrete tentoxin and tabtoxin to inhibit some plant enzymes involved in photosynthesis. Succeeding the chlorosis was the brown necrosis which may be expounded as freshly dead tissues on which the pathogens were done feeding (where they are biotrophs) or were currently feeding on (as necrotrophs). In the absence of water, or where the tissues dried out to no water supply the necrotic tissues thus appeared obviously dark brown. The graphs of the disease progress reveals a polycyclic nature of the pathogens responsible for leaves spot and blight of Curcuma amada. Inconsistent increase and decrease (or rising and falling patterns of lines) portrayed multiple circles of development of the pathogens within one growth season (circle) of Curcuma amada plants. According to William [32], polycyclic pathogens, being responsible for most acute plant epidemics, complete many disease cycles per year, and are usually dispersed by air, and examples of which include leaf spots and blights. Environmental and genetic factors might have influenced incidences and severities of the diseases, for the two years. There must be environment, suitable for the virulency of the pathogen and encouraging host’s susceptibility, according to the disease triangle, for infection to occur; and this would have been the reason for the drastic increase in blight disease incidence and severity for the two years. Relationship of Spot Disease Incidence with Plant Height suggest that Curcuma amada plants were more susceptible to the disease at early age or were more resistant at later age, because as plant height increased with age, less symptoms were observed amongst species. Maan et al. [15] also reported incidence of Potato Apical Leaf-Curl Disease being significant and negatively associated with plant height, weight of leaves per hill, weight of foliage per hill and leaf area index among 6
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have thrived better in relatively increased soil moisture due to increased rainfall. P. aphanidermatum was stated to be ubiquitous in soil and water according to Al-Sheikh [2]. Disease of Root rot of wheat seedlings caused by R. solani was most severe at highest experimented soil moisture levels [9]. F. solani is also ubiquitous [33]. Again, the occurrence of a plant showing symptoms characteristic of more than a disease, such as spot and blight affecting Curcuma amada, could be expounded with the disease triangle, whereby for a disease to occur there is interaction of virulent pathogen and susceptible host in an environment favourable for the pathogen to initiate infection. Owing to this, the pathogens inoculum responsible for the diseases, under suitable moisture and temperature, attached to and penetrated the Curcuma amada host plants to initiate infections which were expressed by the plants as spots, blights and rots. Finally, these results do answer the hypothetical question: ‘Is Curcuma amada plant immune to disease?’ Contrary to the initial suggestive thought that Curcuma amada plant was immune to diseases, owing to the paucity of information about its pathology, it may be deduced that Curcuma amada plants are not immune to disease(s), but are resistant to disease(s). This suggestion indicates that all plant life are subject to infection, however some may be resistant. Agrios [1] states: ‘Plant diseases occur in all parts of the world where plants grow. They are more common and more severe, however, in humid to wet areas with cool, warm or tropical temperatures’.
[13]
Further studies
[19]
Pathogenicity test shall be done, as additional research, on the pathogens identified The identified pathogens shall be characterized, to provide valuable information on the formation of control strategies to curb the diseases. Control measures to curb the diseases shall be experimented, for adequate prescription to farmers.
[20]
[9]
[10]
[11]
[12]
[14]
[15]
[16]
[17]
[18]
[21]
[22]
Acknowledgements [23]
Special thanks to Prof. S. T. O. Lagoke through whom the planted rhizomes were gotten from Department of Plant Physiology and Crop Production, College of Plant Science and Crop Production of Federal University of Agriculture Abeokuta. Funding: This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
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