Morphological and Genetic diversity among farmers’ varieties of urdbean (Vigna mungo L.) Hepper of Andaman and Nicobar Islands Agro-Ecosystem

Urdbean [Vigna mungo (L.) Hepper- Fabeacae] is an important Asiatic species of the tropical, sub-tropical areas and has been identified as a potential crop in many countries (Girish et al., 2012). Urdbean is a widely cultivated pulse crop during kharif, rabi and summer seasons in India and other Asian countries. This crop is also popular due to their suitability in various crop rotation practices and well suited in both dry and irrigated conditions. The economic product of urdbean is seed grain, which provides significant inexpensive vegetable protein and iron, and is a good source to meet out the requirements of essential amino acids in daily diets of vegetarian diets. The yield of this crop is low because of the non-availability of high yielding and stable varieties. Evaluation and exploitation of farmers’ varieties for various yield and yield attributing traits is necessary for the development of improved varieties.
        
In an Andaman and Nicobar Islands, major area of the urdbean is cultivated using local varieties and/or farm saved seeds during rabi season mainly in rice fallow  marginal and sub marginal lands. In the process of such continuous minimal cultivation, the farmers’ varieties sustained low productivity and plant types have adapted to survival following natural selection against biotic and abiotic stresses. Genetic variability in available farmers’ varieties of urdbean is limited. Study of genetic resources is a critical factor for breeders to better understand the evolutionary and genetic relationship among accessions, to select farmers’ varieties in more systematic and effective way and to develop strategies to incorporate useful diversity in their breeding programme.
        
The existing varieties bred so far have low yield potential and are mostly vulnerable to abiotic stresses and diseases (Singh, et al., 2016). The inconsistency is that in order to enable to develop new cultivars for tomorrow, plant breeders will need to have access to the wealth of genes which exists now only in exotic and/or local genetic backgrounds. In this context, morphological characterization of farmers’ varieties may play a vital role in generating new desirable plant types that help in increasing crop production as well as quality of the produce. Therefore indigenous farmers’ varieties was used efficiently for research and breeding. In order to utilizing farmers’ varieties for the development of new varieties, an exhaustive characterization of the various farmers’ varieties holdings, advanced and cultivated farmers’ varieties that constitute the gene pool for the urdbean crop need to be characterized for identification of the useful genetic diversity.
        
In the present study, characterization of 56 farmers’ varieties on the basis of morphological descriptors was applied to determine their usefulness for analysing diversity in the urdbean gene pool. The goal of this study was to provide data useful to urdbean breeders and also to reveal insights into the evolution and dissemination of urdbean. The specific objectives were to determine the genetic diversity and relationships within and among farmers’ varieties and cultivated urdbean accessions under Andaman and Nicobar Islands conditions.

A set of 56 urdbean farmers’ varieties were analysed for characterization and evaluation on the basis of morphological markers on the basic information of the individual farmers’ varieties lines viz., source of farmers’ varieties. The experimental work was carried out on the experimental field of Garacharma Farm, Division of Field Crop Improvement and Protection, ICAR-Central Island Agricultural Research Institute, Port Blair, Andaman and Nicobar Islands, India during rabi season 2015-16 and 2016-17. The field trials were in a randomized block design. The climatic condition was hot and humid. Plants were grown in 3.0 m x 1.2 m small plots. Row to row distance was 30 cm and plant to plant distance was 10 cm. Data were collected from randomly selected 10 plants from each plant. The farmers’ varieties were described based on the descriptors for urdbean of PPV and FRA, New Delhi. Twenty one DUS parameters and 9 agronomic traits were recorded during the vegetative and reproductive stages. All the agronomical management practices were done as per the recommendation for the crop. Plants were harvested when 80% of the pods showed physiological maturity and turned brown and black colour.
        
Analysis of variance (ANOVA) was done to know the variations among the farmers’ varieties based on the 9 yields and yield attributing morphological traits. Before doing ANOVA in normality test all data showed a normal distribution, SAS statistical programme was used to analysis of genetic diversity. An unweighted pair-group method of the arithmetic average clustering procedure (UPGMA) was employed to construct dendrograms and to establish the importance of different traits in explaining the total variation.

The success of breeding programs is principally dependent on the availability of genetic variation in the breeding materials. The indigenous farmers’ varieties of urdbean are sources of important gene (s) for genetic diversity. Genetic diversity of farmers’ varieties and gene pools can increase the productivity of farming systems in a range of growing conditions and more diverse farming systems are also generally more resilient in the face of stress. It is an essential requirement for increasing crop productivity through breeding. Therefore, evaluation of local array of urdbean is an appropriate approach to seeking genes which are rare or absent in cultigens. The overall effect of plant breeding on genetic diversity has been a long standing concern in the evolutionary biology of crop improvements (Simmonds, 1962). Evaluating and understanding the extent of genetic diversity existing in the farmers’ varieties is important and leads to effective utilization of the farmers’ varieties. Hence, local farmers’ varieties collected from the different parts of the Andaman and Nicobar Islands of urdbean were analysed using morphological markers to understand the genetic diversity. The present study were in agreement with the previous studies revealed that urdbean genetic variability was sufficient in as urdbean farmers’ varieties to be exploited in breeding programs (Tickoo et al., 1988 and Tomooka et al., 2002).
        
Characterization of genotypes seeds of with regard to stable simple inherited characters is pre-requisite for varietal identification (Tripathi et al., 2011). A set of 56 accessions of urdbean representing farm saved seeds of farmers’ varieties were studied for 21 DUS parameters and stable morphological traits (Table 1 and 2). The farmers’ varieties showed enough range of variation for all nine quantitative traits. The analysis of variance (Table 3) showed significant differences among the farmers’ varieties for all the traits at 0.01 % level. In general, the farmers’ varieties with desirable characters were present in each trait group. However there were still some preferable characters such as high seed yield per plant, number of seeds per pod, number of pods per plant and seed weight which existed in rather low frequency in the set of farmers’ varieties. Seed size and seed yield per plant is one of the most limiting factors for productivity. The farmers’ varieties ANFVU-15-31 followed by ANFVU-15-38, ANFVU-16-08 and ANFVU-15-23 were shown large seeded (100 seed weight ranges 5.33 - 6.34 g) exhibited significantly different from other farmers’ varieties for seed yield per plant. In contrast, ANFVU-14-01 followed by ANFVU-15-22, ANFVU-16-10 and ANFVU-16-01 identified to have small seeded (100-seed weight ranges 2.75 - 2.96 g). Among the 56 farmers’ varieties accessions ANFVU-14-01 and ANFVU-15-34 had shown extra earliness with erect plant growth habit. However, the promising accessions ANFVU-14-07, ANFVU-14-11, ANFVU-15-21, ANFVU-15-23, ANFVU-15-31, ANFVU-15-38 and ANFVU-16-08 had shown erect plant growth habit with early and medium pod lengths. The farmers’ varieties ANFVU-15-31 followed by ANFVU-15-23, ANFVU-14-11, ANFVU-15-21, ANFVU-15-38 and ANFVU-16-08, while ANFVU-14-07 were significantly different from other farmers’ varieties for seed yield per plant. Twenty three accessions bears black seed coat colour while, 14 each exhibit green seed coat colour and mottled, 02 accessions bears greenish brown seed colour and 3 brown colour.
 

 

 

        
The hierarchical (UPGMA) cluster analysis conducted using standardized data classified the 56 farmers’ varieties were grouped into 9 groups. A dendogram based on average linkage distance for 56 urdbean farmers’ varieties was also calculated (Fig 1). Cluster I exhibits the largest, consisting of 26 accessions, while cluster VIII have only one accession (ANFVU-15-31) and had highest seed yield per plant showing earliness, erect plant growth habit and medium pod length. Mean values for each cluster were summarized (Table 4). Among them, cluster I consists of 26 farmers’ varieties is the most interesting, as its only 2 accessions (ANFVU-15-38 and ANFVU-16-50) had high seed yield per plant. However, cluster IX had only two farmers’ varieties in its group (ANFVU-14-11 and ANFVU-15-23) that had high seed yield per plant with erect plant growth habit, medium pod length and earliness.  Although Cluster I having 26 and cluster II having 5 distinct farmers’ varieties showed early flowering, erect plant growth habit and they also had high 100 seed weight. The outlier, ANFVU-15-31 was distinct from the other farmers’ varieties only for seed yield per plant, 100-seed weight, erect plant growth habit and number of pods per plant with black seed colour and dull seed lusture.
 

 

        
In the present study results revealed that the farmers’ varieties were grouped together on the basis of morphological performance rather than origin or source. Cluster analysis based on agriculturally important traits revealed that advance breeding lines and recommended cultivars were mostly characterized in Cluster I, which may be because of high selection pressure for high yield potential. This finding revealed that only a portion of genetic diversity has been exploited and it is suggested that selection of proper farmers’ varieties is playing a vital role for broaden genetic base of cultivated urdbean involving diverse parents for a successful breeding program. Parents with more genetic base can create higher genetic variation which can increase of genetic gain in selection. So depend on breeding objectives the result of cluster analysis can be applied for crossing program for urdbean improvement. In order to ensure the efficient and effective use of farmers’ varieties, its characterization is imperative and cluster analysis provides a good evaluation of farmers’ varieties by identifying those that should be further evaluated at the genetic level for future breeding programme. The findings were supported with the findings of Gantait et al., (2009), Singh et al., (2014), Tripathi et al., (2011) and Tripathi et al., (2016). Morphological characterizations as an important step in description of classification of crop farmers’ varieties because a breeding program mainly depends upon the magnitude of genetic variability. Tarika et al., (2009) and Abna et al., (2012) also evaluated and reported a wide range of diversity for most of the quantitative traits among mungbean diverse collection. These findings reflect that the tendency of each accession to emphasize agronomic traits as opposed to reproductive growth. Gafoor et al., (2001) evaluated different urdbean collections for quantitative traits and observed a wide range of diversity for most of the traits, along with some accessions of unique characters which could help to identify farmers’ varieties with suitable traits which can be used in direct selection and hybridization program for breeding to broaden genetic base. Abna et al., (2012) assess the genetic diversity among 20 farmers’ varieties of mungbean under Malaysian tropical environment for 8 quantitative characters and reported that morphological traits, which had more effects on diversity and three components explained 79% of the total variation among farmers’ varieties can be used for direct selection or for the hybridization programme for high yielding varieties.

Based on the present study, significant differences among urdbean farmers’ varieties were observed for most of the yield attributing traits except number of branches per plant and length of pods, which showed that there is sufficient variability to have an effective selection. Farmers’ varieties, AN-FVU-15-31 followed by AN-FVU-15-23 and AN-FVU-14-11 showed highest values seed yield and could be utilize in breeding programme for direct selection of high yielding urdbean genotypes. Based on the diversity analysis, it was concluded that more emphasis should be given on cluster I, II, VIII and IX for selecting farmers’ varieties as parents for crossing with the farmers’ varieties of cluster I which may produce new recombinants with desired traits will be useful in bringing new traits.