Morphological variation and characterization of local mungbean germplasm

Sixty one mungbean (green gram) accessions were evaluated for 12 agro morphological traits under field conditions during 2011 Yala seasons at the Grain Legumes and Oil Crops Research and Development Centre at Angunakolapelessa, Sri Lanka. Data were collected on quantitative agronomic characteristics, yield and yield parameters including days to first flowering, days to 50% flowering, days to first pod maturity, days to maturity, plant height, pod length, number of seeds per pod, pod length, number of seeds per plant, thousand seed weight, first yield, second yield, total yield and yield per plant. All the traits were analyzed using the SPSS version 20 software. The principal component analysis sorted the accessions into three principal components within cluster similarities and inter-cluster variations. Over 70% of the total variance was explained by the resulted principal components. At rescaled cluster distance of five, 61 mungbean accessions were made into seven clusters. The first and second clusters contained similar number of genotypes (nine) and three recommended varieties ‘MI-05’, ‘MI-06’ and ‘Ari’ were grouped into cluster II. The cluster VII was the largest and most diverse consisting 18 mungbean genotypes with the variety ‘Harsha’. This clustering pattern can be used for the selection of parental materials with diverse characteristics for the effective utilization, conservation of the genetic recourses and also be useful in variety development in future mungbean breeding programmes.


Introduction
Wilczek] is one of the most important food legumes in south and south-east Asia. Presently about 11,095 ha in Sri Lanka are cultivated under mungbean and the annual production is about 14,130 mt (Ag Stat, 2014). However, Sri Lanka imports about 7,000 mt of mungbean, which accounts for 33% of domestic requirement, from Australia, Myanmar, Thailand and India. The productivity of mungbean was about 1.27 mt/ha in 2013. The grain is consumed as dhal, in soup, as bean sprout or processed into high value products. Mungbean is a cheap source of dietary protein with high levels of folate and iron compared to many other legumes (Nair et al., 2012). Farmers prefer to cultivate mungbean as it does not need much water and other inputs while it helps restoring soil fertility through symbiotic nitrogen fixation (Malik et al., 1997). Proteins of grain legumes contain relatively more essential amino acids such as Lysine and Tryptophan and thus, compliment the amino acids supplied by cereals. Moreover, they contain relatively small proportions of Sulphur-containing amino acids such as Methionine and Cysteine and, also a useful source of Thiamine, Niacin and Calcium. Therefore, mungbean has a tremendous market potential than any other grain legume crop. Improved accessions and old cultivars of mungbean are important and useful genes that can be used in breeding programmes. However, landraces and accessions are heterogeneous and include several genotypes within a population. The only way to ensure genetic variations of future generations is to exploit the present day genetic diversity of the crop and to identify the promising one for breeding programmes. Variation of mungbean accessions is important to maintain genetic diversity of gene pool. Estimation of genetic distance is one of the appropriate tools for parental selection in breeding programme. This is also important in identification of the diversity, crop evolution and the centre of origin (Mohammadi and Prasanna, 2003). The present study was conducted to evaluate the genetic diversity of mungbean accessions using quantitative agro-morphological traits in order to identify the superior parental genotypes to be used in future breeding programmes.

Materials and Methods
Seeds of 61 accessions of mungbean germplasm were collected from the Plant Genetic Resources Center (PGRC) at Gannoruwa, Sri Lanka and from various parts of the country during 2010. The plants were grown during the Yala season (March-August) 2011 at the Grain Legumes and Oil Crops Research and Development Centre at Angunakolapelessa, Sri Lanka in a complete randomized design. Two rows, each at 3 m length was planted to each accession with 50 cm and 10 cm inter-and intrarow spacing, respectively. Four varieties namely, 'MI-05', 'MI-05', 'Harsha' and 'Ari' were used as check varieties for visual comparison of lines. Recommended cultural practices were followed. The plants were evaluated for various morphological traits under field conditions.

Results and Discussion
The total yield was recorded with the highest deviation from the population mean (Table 1) while the other attribute traits such as first and second yield, thousand seed weight, and number of seeds per plant also deviated considerably from the mean. The Pearson's correlation coefficients among agronomic and yield attributing characters for 61 mungbean accessions, including the four varieties, are shown in Table 2. The extent of relationship between yield and its various components is important for the plant breeders to select plants which consist of desirable characteristics (Divyaramakrishnan and Savithramma, 2014). The total yield was significantly correlated with first yield and second yield r-0.661 and r=0.889, respectively (p<0.05). Ganguly et al. (2012) reported that most of the variables were not dependent on each other but only few of them show a considerable relation. In the present study, the pod length and seeds per pods showed positive and significant (p<0.05) correlations with seeds per plant. The results are in agreement with those of Ganguly et al. (2012). Number of days to first flowering, 50% flowering and first pod maturity exhibited a significant positive relationship with the number of days taken to maturity. Most of the other variables were not dependent on each other. Our results also agree with Siddique et al. (1996) who reported an inverse correlation between seed yield and number of days to 50% flowering and maturity.

Principal component analysis
The progress in breeding programme for economic characters often depends on the availability of a large germplasm representing a diverse genetic variation. In order to ensure an efficient and effective use of crop germplasm, its characterization is imperative and multivariate analysis provides a good evaluation of land races. After identifying variation of morphological traits that should be further evaluated at a genetic level (Rabhani et al., 1998), PCA has extracted three principal components (PCs) in this study with an Eigen value more than 1.0, and expressed 70% of the among the traits studied (Table 3).   The first PC always describes variation of the population (Guei et al., 2005). The first components were extracted with the relatively large amounts of variance, while the later components accounted for relatively smaller amounts. Among the first three PCs, PC1 accounted for high proportions of the total variance (42%) and remaining two principal components PC2 and PC3 recorded 17% and 10% of variance from the total variance, respectively.
The first PC was more related to total yield, yield per plant, second yield, first yield and thousand seeds weight (Table 4). This implies that the yield related characteristics are close together when the second principal component seeds per plant, seeds per pod and pod length were more related traits. The third principle component exhibited negative effects on seeds per plant, seeds per pod and pod length. Three PCs extracted from the 13 characteristics by PCA were used for clustering the accessions. Similar genotypes were classified into the same cluster based on their various agronomic and yield parameters. The single Dendrogram represented four clusters at 10 re-scaled distances. Basnet et al. (2014) reported that the multivariate analysis involving the qualitative traits clearly show the alignment of the different genotypes into different clusters according to the similarity indices. Cluster analysis grouped genotypes together with greater genetics similarity; the clusters did not necessarily include all genotypes from the same origin (Figure 1). Some clusters consisted only of the local or exotic genotypes while in others, genotypes of both were found together. This was primarily due to the similarity in the different genotypes for the qualitative traits observed. Our results also showed the same pattern with some-sub clusters consisted only of the recommended varieties while in others, both accessions and variety were found together. By incision, the dendrogram at 5 rescaled distance, the genotypes were categorized into 7 clusters (Figure 1). The number of accessions per cluster varied from three accessions in the sixth cluster to 18 in the last cluster. The first cluster contained 9 genotypes and those were separated into two sub groups. Most of the genotypes in the first cluster were large-seeded, high yielding and had a high thousand seed weight. Long-seeded variety "Ari", which was grouped into one of the sub groups, was distinct from the other genotypes in the cluster II. The three recommended varieties were separated into cluster II with two sub groups. The most popular mungbean varieties 'MI-05' and 'MI-06' were clearly separated to the same sub group under cluster II with three other accessions. Those lines were high yield with similar maturity periods.
Five large-seeded accessions with the same days to maturity grouped into the cluster III, while the cluster IV consisted of 12 accessions with three subgroups. These genotypes had medium seed size and the same maturity period. The subgroup MB 53 and MB 59 were grouped separately from other germplasm, where these genotypes had same thousand seed weight, yield per plant, number of seeds per plant and similar pod length. Three genotypes were grouped into the second sub group of cluster V with similar number of days to 50% flowering and maturity, and number of seeds per pod. The smallest cluster (Cluster VI) categorized the accessions with little number of seeds per plants, green purple hypocotyls, and days to first flowering, days to 50% flowering and days to maturity. The cluster VII was the largest and most diverse consisting 18 mungbean genotypes. This cluster was made into four sub groups. Most of the genotypes grouped into this cluster had small seed size, similar number of flowering days and maturity days. The variety 'Harsha' was grouped with two other accessions under cluster VII with same characteristics of 50% flowering, number of days taken to maturity, plant height pod length, number of seeds per pod and yield per plant.
The scatter plot ( Figure. 2) consisting of four quadrants illustrated the distribution of mungbean genotypes according to the diversity of their morphological characteristics. Most of the genotypes felt into the third and fourth quadrants and few were in the first quadrant. The variety 'Ari' of cluster II was clearly seen to be diverged greatly from the other clusters. Most of the genotypes were concentrated in forth quadrant none of them in the second quadrant.

Conclusion
Results of the study revealed that the agronomic characteristics and yield parameters can be effectively used to group mungbean accessions. The principal component analysis grouped these accessions into three principal components that were within cluster similarities and inter-cluster variations. Sixty one mungbean genotypes were grouped into VII divergent groups at the rescaled cluster distance of 5. This clustering pattern can be used for the selection of parental materials with diverse characteristics for the effective utilization, conservation of the genetic recourses and useful in development of varieties in the future mungbean breeding programmes.