Introduction
Jackfruit (Artocarpus heterophyllus Lam.) is grown primarily as a fruit crop and is an important component of Asian home gardens and agroforestry systems (Narasimham, Reference Narasimham, Nagy, Shaw and Wardowski1990; Reddy et al., Reference Reddy, Patil, Shashikumar and Govindaraju2004). Jackfruit has been recognized as a crop with the potential to improve food security and reduce malnutrition in India, Bangladesh, Sri Lanka, Pakistan and others (Mohri et al., Reference Mohri, Lahoti, Saito, Mahalingam, Gunatilleke, Hitinayake, Takeuchi and Herath2013; Shajib et al., Reference Shajib, Kawser, Miah, Begum, Bhattacharjee, Hossain, Fomsgaard and Islam2013; Sau et al., Reference Sau, Sarkar, Deb and Ghosh2016). It produces large compound cauliflorous fruits with high yields and high levels of minerals and carotenoid contents (Salunkhe and Kadam, Reference Salunkhe and Kadam1995; Ranasinghe et al., Reference Ranasinghe, Maduwanthi and Marapana2019). The tender (unripe) jackfruit is also used in curry and pickle preparations. The seeds are generally boiled/roasted, salted or dried, and used in powder form. The ripe fruit is usually eaten raw as fruit and processed to make jam, juice and candies. The species grown in the wild forests of India's Western Ghats have been identified as the crop's origin (Muralidharan et al., Reference Muralidharan, Ganapathy, Velayudhan and Amalraj1997; Reddy et al., Reference Reddy, Patil, Shashikumar and Govindaraju2004). The Western Ghats and southern and north-eastern parts of India represent diverse wild jackfruit sites. Jackfruit is also widely distributed in the wild and cultivated in countries such as Nepal, Sri Lanka, Burma, Brazil, Pakistan, the Philippines, Thailand and Malaysia (Soepadmo, Reference Soepadmo, Verheiji and Coronel1991; Wangchu et al., Reference Wangchu, Singh and Mitra2013).
Jackfruit has innumerable types or forms due to the high cross-pollination, and is mostly propagated through seeds. Several jackfruit genotypes have been collected throughout the tropics over the past few decades for their conservation, study and improvement (Rai et al., Reference Rai, Visha, Das and Kumar2003; Azad et al., Reference Azad, Jones and Haq2007; Jagadeesh et al., Reference Jagadeesh, Reddy, Basavaraj, Swamy, Gorbal, Hegde, Raghavan and Kajjidoni2007; Wangchu et al., Reference Wangchu, Singh and Mitra2013). Jackfruit collections made for evaluation and selection in India, Indonesia, Nepal, Malaysia, Thailand, the Philippines, Sri Lanka, Vietnam and Bangladesh are limited (IPGRI, 2000; Haq and Hughes, Reference Haq and Hughes2002), and therefore, the information available on the performance of the genotypes is also limited. Reddy et al. (Reference Reddy, Patil, Shashikumar and Govindaraju2004) and Jagadeesh et al. (Reference Jagadeesh, Reddy, Basavaraj, Swamy, Gorbal, Hegde, Raghavan and Kajjidoni2007) studied the physio-chemical characteristics of jackfruit clones and found diversity in several traits such as the fruit weight, flake weight, total soluble solid (TSS), acidity, etc. Traits such as the fruit size, pulp content, acidity and TSS are important for selecting jackfruit genotypes for table and processing purposes. A higher edible portion (in the tender stage), softness after boiling (pressure in lbs), earliness and palatability are the important traits for selecting jackfruit genotypes for culinary purposes. A moderate level of genetic diversity erosion of jackfruit has been reported in Bangladesh (Haque et al., Reference Haque, Rahman and Bhuiya2004; Khan et al., Reference Khan, Zerega, Hossain and Zuberi2010), and India is no exception. Jackfruit is hardly regarded as a commercial fruit crop, although it is extensively cultivated (Bose and Mitra, Reference Bose and Mitra1990). This is due to the lack of superior varieties, wide variation in fruit quality, long gestation period (8–10 years) and high vulnerability to borer attacks. However, jackfruit has been gaining commercial importance in recent years, with increasing recognition of its nutritional value in the human diet and its diverse uses. The current research work was conducted to evaluate and describe the variation in the fruit and seeds of a genetically diverse group of jackfruit growing in a single location.
Materials and methods
The Jackfruit germplasm repository
The Indian Council of Agricultural Research, Research Complex for Eastern Region (ICAR-RCER) has the National Germplasm Repository of Sub-tropical Fruit Crops at its regional centre ‘Farming System Research Centre for Hill and Plateau Region, Ranchi, India’. The jackfruit germplasm repository collection includes 134 individual jackfruit genotypes. The seeds from promising jackfruit collections were collected during the years 1990–1992 from important jackfruit growing regions in the Bihar (Muzaffarpur – 26° 11′ N, 85° 39′ E & Patna – 25° 59′ N, 85° 13′ E) and Jharkhand (Deoghar – 24° 48′ N, 85° 27′ E & Dumka – 23° 81′ N, 90° 41′ E) states of India and are conserved ex situ (on farm) in the jackfruit germplasm repository at Ranchi, Jharkhand (23° 25′ N, 85° 20′ E). The germplasm repository is situated at an altitude of 620 m, with a mean maximum temperature of 30.5°C and an average minimum temperature of 19.5°C, and it receives an average annual rainfall of 1386 mm over the course of a year. The soil within the studied area is alfisol classified as sandy loam in texture, well-drained and acidic in nature with pH values ranging from 5.1 to 5.6.
Data collection
The data were collected during 2017–18 from a total of 28 jackfruit genotypes planted from seed at a spacing of 10 × 10 m and maintained in a square system. The 28 genotypes were selected based on their superior yields (>150 kg/tree/year) during the last 10 years. The jackfruit genotypes were healthy and trained as free-bush with minimum pruning during their >25 years of age. Each of the genotypes received similar cultural treatments throughout their growth period to avoid any variations based on differences in environmental factors. In total, 27 fruit traits (Table 1) were measured and recorded based on the jackfruit descriptors of the International Plant Genetic Resources Institute (IPGRI, 2000). The dessert-type fruits were harvested at the mature stage and were judged by a low spine density, moderate spreading of spines, the presence of a distinct hollow metallic sound, and moderately flattened fruit stalks. The fruits were then transported to the laboratory to study the fruit parameters at the edible ripe stage. For each genotype, the minimum sample size was three fruits, and each fruit was considered a replication. Observations were recorded for the fruit weight, fruit length, fruit width, peel weight, number of seeds, seed weight, pulp weight, pulp %, peel thickness, TSS, acidity, reducing sugar and total sugar of the fruits by following standard procedures. The weight of the fruit, skin, pulp and seed was measured by an analytical balance (Mettler Toledo, PB403-S). The length and width of the fruit were measured at the maximum point with a digital Vernier calliper (RSK™, 150 mm, 0.01 mm reading capacity). The rind thickness was measured at five different positions of each fruit using a digital Vernier calliper. The TSSs were estimated in degrees Brix with a digital refractometer (ATAGO PAL-1, Japan, range 0–53°Brix). The titratable acidity was estimated by titrating a known amount of juice against 0.1 N NaOH using phenolphthalein as an indicator (Ranganna, Reference Ranganna1984). The reducing sugars and total sugars were determined by volumetric methods, as suggested by Lane and Eynon (Reference Lane and Eynon1923).
Table 1. Summary statistics of fruit traits of jackfruit genotypes
Data analysis
PAST 3 (Palaeontological Statistics; Hammer et al., Reference Hammer, Harper and Ryan2001) computer software was used for principal component analysis (PCA). PCA was used to identify the patterns of physicochemical variation of the fruit characteristics within the jackfruit genotypes and as a tool for genotype characterization. A biplot was used to study the correlations among fruit parameters. To determine the principal components (PCs) that accounted for the greatest amount of variation for each trait, the eigenvectors of the PCs were compared for each trait. The trait being considered was ascribed to the PC having the largest absolute value. Within the genotypes, the similarity was analysed using tree clustering analysis. The tree diagram was constructed using the unweighted pair-group average method [unweighted pair-group method with arithmetic mean (UPGMA)] with the squared Euclidean distance. In the UPGMA method, the distance between two clusters is calculated as the average distance between all pairs of objects in two different clusters.
Results
Evaluation of jackfruit genotypes based on fruit traits
A wide range of variability in fruit traits was observed among the 28 selected genotypes (Table 1 & online Supplementary Table 1). The jackfruit genotypes had high variability in traits such as the fruit weight, core diameter, core weight and pulp weight (coefficient of variation (CV) = 44.63–67.97%). There was a 4.81-fold range (from 3.84 to 18.50 kg) in fruit weights among the studied jackfruit genotypes. The core diameter ranged from 36.71 to 175.95 mm, the core weight ranged from 0.20 to 1.16 kg, and the pulp weight ranged from 0.43 to 10.07 kg. The fruit pulp percent is an important parameter for determining the value of genotypes for table and processing purposes. The highest fruit pulp percent was recorded in JS 6/3 (60.26%), and the lowest was recorded in JS 6/1 (5.39%), with a 13.01 standard deviation and a 33.89% CV. Similarly, the maximum fruit length was recorded in JS 5/6 (59.54 cm), and the minimum was recorded in JS 1/8 (25.28 cm). The fruit diameter ranged between 17.43 and 35.35 cm, with a standard deviation of 4.70 and a CV of 20.53%. The fruit rind thickness ranged from 7.40 to 17.76 mm, and the highest fruit volume was recorded in JS 7/8, with the least in JS 1/7. The fruit rind weight varied from 1.42 (JS 1/8) to 7.29 kg (JS 4/2). The core length ranged from 19.30 (JS 7/4) to 45.30 cm (JS 5/6). The skewness and kurtosis were also measured for further studying the genetic divergence among the selected genotypes. A positive skewness was recorded for traits such as the fruit weight, fruit length, fruit diameter, rind weight, core length, core diameter, core weight and pulp weight, whereas a negative skewness was recorded for the rind thickness and pulp percentage. Kurtosis indicates the weights of the tails of a distribution. In the present set of data, a platykurtic distribution (positive) pattern was recorded for the fruit weight, fruit length, fruit diameter, core length, core diameter, core weight, pulp weight and pulp %. A leptokurtic distribution (negative) was recorded for traits such as the rind thickness and rind weight.
Evaluation of jackfruit genotypes based on flake characteristics
The flake characteristics are a major trait that determines the pulp yield, fruit quality and consumer preference. In the studied jackfruit genotypes, low to high variation (CV = 14.47–61.28%) was found for the number of bulbs, flake weight, flake length and flake diameter. There was an 11-fold range (from 48.00 to 533.00) in the number of bulbs among the jackfruit genotypes in our study. The average flake weight ranged from 14.25 to 46.85 g, and the maximum value was registered in JS 3/4, followed by JS 8/3. The average flake length varied between 46.44 and 86.03 mm. The JS 8/3 genotype has a larger flake, which is a desirable trait for the acceptability by consumers and from a market perspective. The average flake diameter ranged from 23.48 to 42.72 mm. The highest flake diameter was measured in JS 3/4, and the lowest was recorded in JS 8/5. Positive skewness was recorded for traits such as the number of bulbs, average flake weight, average flake length and average flake diameter. In the present set of data, a platykurtic distribution (positive) pattern was recorded for the number of bulbs and average flake length, whereas a leptokurtic distribution (negative) was recorded for the average flake weight and average flake diameter (Table 1 & online Supplementary Table 2).
Evaluation of jackfruit genotypes based on seed characteristics
The average seed weight ranged from 1.24 (JS 8/5) to 8.44 g (JS 7/7), the total seed weight/fruit ranged from 0.21 (JS 7/4) to 2.34 kg/fruit (JS 3/8), the average seed length ranged from 21.88 (JS 6/5) to 36.62 mm (JS 3/8) and the average seed diameter ranged from 12.27 (JS 1/10) to 22.17 mm (JS 3/4). The coefficients of variation for seed characteristics ranged from 13.56 to 64.83%. Positive skewness was recorded for the average seed weight, total seed weight (kg/fruit) and average seed length, while a platykurtic distribution (positive) pattern was recorded for the average seed weight and total seed weight. For traits such as the average seed length and average seed diameter, a leptokurtic (negative) distribution was recorded (Table 1 & online Supplementary Table 3).
Jackfruit quality characteristics
An essential criterion for assessing the quality of the fruit is the TSSs. The TSSs varied from 17.40 to 26.60°Brix. Four genotypes (JS 1/3, 2/1, 4/4 and 8/5) had a TSS in excess of 25°Brix among the genotypes tested. The highest TSS was found in the JS 1/3 (26.60°Brix) genotype, and the minimum was found in JS 2/4 (17.40°Brix), with a standard deviation of 2.74 and a 12.56% coefficient of variance. The acidity ranged from 0.08 (JS 6/1) to 0.21% (JS 8/5), with a standard deviation of 0.03 and a CV of 23.09%. The reducing sugars varied from 2.36 to 5.38 (%), with a standard deviation of 0.81 and a CV of 19.59%. The maximum non-reducing sugars and total sugars were found in genotype JS 1/3 (9.60 and 14.71%, respectively). Positive skewness was recorded for the TSS, acidity, reducing sugar and total sugar, whereas negative skewness was recorded for non-reducing sugars. In the present set of data, a platykurtic distribution (positive) pattern was recorded for traits such as the TSS, reducing sugars and total sugars, and a leptokurtic distribution (negative) was recorded for the acidity and non-reducing sugars (Tables 1 and 2).
Table 2. Quality characteristics of different jackfruit genotypes
Cluster analysis
The Pearson similarity correlation coefficient-based cluster analysis categorized the 28 studied jackfruit genotypes into four main clusters (Fig. 1). Table 3 shows the traits that defined each cluster. Cluster III consisted of the largest number of jackfruit genotypes (18) and was characterized by a smaller fruit size, a high average flake weight, average seed diameter and TSS, and a lower total seed weight/fruit. Cluster II, which had four genotypes, was characterized by medium-sized fruit and high core weight, core diameter, average flake length, average seed weight, average seed length, acidity and non-reducing sugars values. Cluster IV contained five genotypes and had high core length, reducing sugars and total sugars values and a lower average seed weight. Cluster I had only one genotype, which was characterized by a high fruit weight, fruit length, fruit diameter, rind thickness and rind weight (also see online Supplementary Table 4).
Fig. 1. Dendrogram of jackfruit genotypes obtained by the average distance between cluster analyses based on fruit traits.
Table 3. Means of the traits for the four clusters of 28 jackfruit genotypes
Principal component analysis
Variations among the fruit characteristics were also assessed using PCA for 28 jackfruit genotypes (Table 4). The first PC explained 80.22% of the variation among the genotypes and recorded an eigenvalue of 7.12, which explained 30.94% of the total variation within the associated traits such as fruit weight, fruit length, fruit diameter, rind weight, core diameter, core weight, pulp weight, number of bulbs, average flake length, total seed weight/fruit and average seed length. PC2 explained 21.37% of the variation, with an eigenvalue of 4.92. The variations in the core length, average flake weight, average flake diameter, average seed weight, average seed diameter, TSS and total sugar were accounted for by PC2. PC3, PC4 and PC5 explained 12.75, 8.97 and 6.20% of the total variation, with eigenvalues of 2.93, 2.06 and 1.42, respectively. The biplot between PC1 and PC2, which separates the genotypes on the basis of multiple traits, showed that the genotypes in each of the groups are superior in certain traits (Fig. 2). More interesting genotypes were ICAR-RCER JS 1/3 (higher TSS), JS 8/5 (lowest average seed weight), 7/7 (highest fruit weight and lowest core weight), 3/8 (higher fruit weight and total seed weight per fruit) and 7/8 (higher rind thickness), which were disposed in gaps and were the most diverse. The genotypes scattered in all the quarters showed a diverse pattern among the studied jackfruit.
Fig. 2. Segregation of the jackfruit genotypes according to fruit traits determined by PCA.
Table 4. The first five PC loadings for fruit variables of the jackfruit genotypes
Discussion
The set of jackfruit genotypes was evaluated at a single place to avoid variation caused by environmental factors. Jagadeesh et al. (Reference Jagadeesh, Reddy, Basavaraj, Swamy, Gorbal, Hegde, Raghavan and Kajjidoni2007) also emphasized the importance of growing promising jackfruit types to be evaluated for performance in a common field. This would essentially separate genetically caused variations from environmentally caused variations before the selection strategies can be developed. The relative contributions of the traits reflected that the pulp weight per fruit contributed the most towards the CV (67.97%), followed by the total seed weight (kg) per fruit (64.83%), number of bulbs per fruit (61.28%), core weight (48.02%) and core diameter (45.73%). The maximum relative contribution to the total diversity being exhibited by the pulp weight per fruit and total seed weight confirms the ample amount of diversity with respect to these traits. The variability noticed in the present study is the manifestation of the cross-pollinated progeny of jackfruit. Variation in jackfruit fruit traits has also been reported by Jagadeesh et al. (Reference Jagadeesh, Reddy, Basavaraj, Swamy and Hegde2010) and Balamaze et al. (Reference Balamaze, Muyonga and Byaruhanga2019).
The TSS, acidity and sugar content play important roles in determining the quality of jackfruit.
The CV was the least for traits such as the TSS (12.56%) and average seed length (13.56%). Therefore, the TSS and seed size may also be given priority when conducting surveys for promising genotypes and in operating selection procedures for crop improvement in jackfruit. In our study, four genotypes (ICAR-RCER JS 1/3, 2/1, 4/4 and 8/5) had a TSS of more than 25°Brix. Mitra and Mani (Reference Mitra and Mani2000) also reported that jackfruit with a TSS of more than 25°Brix was suitable for table purposes. Genotypes with a high TSS coupled with other fruit traits such as fair fruit size, high pulp content and low seed content should be considered for the selection of superior genotypes. Jackfruit seeds also play an important role in the livelihood of tribal farmers in India. The seeds are used for culinary purposes, as well as for the production of starch. Roasted and/or boiled jackfruit seeds are consumed by the tribal farmers as food. The presence of large seeds coupled with superior-quality fruit is also an important criterion for the selection of genotypes suitable for tribal homesteads. In our study, genotype JS 10/2 was recorded as a bold-seeded type (8.44 g) with a desirable TSS (22.30°Brix) of the pulp. Alam et al. (Reference Alam, Islam, Uddin, Hossain and Bashir2011) also reported the AH009 and AH010 genotypes as the most seeded cultivars. Hence, based on the overall performance (medium fruit size, pulp >50% and TSS >20°Brix), genotypes ICAR-RCER JS 6/3 and 10/3 were found to be the most promising for table purposes, whereas genotype ICAR-RCER JS 7/7, with its large fruit size, pulp >50% and TSS >20°Brix, was found to be suitable for processing purposes. Earlier studies by Maiti et al. (Reference Maiti, Wangchu and Mitra2002) in jackfruit, Dhakar et al. (Reference Dhakar, Das, Nath, Sarkar and Singh2019) in bael and Divakara (Reference Divakara2008) in tamarind attempted to classify superior types by considering a few important traits.
The clustering of the genotypes in the four major groups is an indication of diversity among the studied jackfruit genotypes. Maiti et al. (Reference Maiti, Wangchu and Mitra2002) reported similar clustering of jackfruit genotypes on the basis of fruit traits. An overview of clusters in the context of the means of different fruit traits in the present study reveals that all economically important traits were not found to be the highest in any single cluster, indicating the vast diversity that exists in the studied jackfruit genotypes. Cluster III has the highest concentration of fruit traits with economic importance, such as the average flake weight, average flake diameter, TSS and small to medium fruit size, compared to the other clusters. The evidence indicates that these clusters may be utilized to select the traits of interest for selection or crop improvement in jackfruit. The reflection of the genotypes in all the quarters of the biplot suggests a high level of genetic diversity among the jackfruit genotypes evaluated. In the biplot, an acute angle between two parameters represents a positive correlation, and a wide angle means a negative correlation across the tested jackfruit genotypes for the traits (Fig. 2). The length, weight and diameter of the flake and seeds showed positive correlations among each other, whereas these parameters were negatively correlated to fruit quality parameters viz. TSS, acidity, reducing sugars, non-reducing sugars and total sugars. Priority should be given to the traits that were defined in PC1 (fruit weight, fruit length, fruit diameter, rind weight, core diameter, core weight, pulp weight, number of bulbs, average flake length, total seed weight/fruit and average seed length) and PC2 (core length, average flake weight, average flake diameter, average seed weight, average seed diameter, TSS and total sugars) for the characterization and varietal development of jackfruit. PCA showed that genotypes ICAR-RCER JS 1/3 (higher TSS), JS 8/5 (lowest average seed weight), 7/7 (highest fruit weight and lowest core weight), 3/8 (higher fruit weight and total seed weight per fruit) and 7/8 (higher rind thickness) were very diverse, so they can be employed as distinct parents for future breeding programmes. The studied fruit traits (fruit, flake and seed characteristics) will be helpful for studying the wide range of variation existing in nature and for the selection of superior desirable jackfruit wild types in future exploration programmes.
Supplementary material
The supplementary material for this article can be found at https://doi.org/10.1017/S1479262120000325.
Acknowledgements
This work was supported by the ICAR – Research Complex for Eastern Region, Patna, India and project under the Indian Council of Agricultural Research (ICAR) (ICAR-RCER/HARP/2001/03).
Conflict of interest
The authors declare that they have no conflict of interest.
Ethical standards
Accepted principles of ethical and professional conduct have been followed. This paper does not contain any studies involving animals performed by any of the authors.
