Advances in Greengram and Blackgram Genomics

Abstract

Greengram [Vigna radiata (L.) Wilczek] and blackgram [V. mungo (L.) Hepper] (both 2n = 2x = 22) are important legume crops in Asia, where it is a major source of dietary protein for its predominantly vegetarian population. Various genomic resources have been developed to accelerate the marker assisted selection in these crops. Different types of markers such as RFLPs, RAPDs, AFLPs, SSRs and ISSRs have been used in discerning genetic diversity and developing linkage maps in these crops. In greengram, eight genetic linkage maps have been developed so far but no map contained enough markers to resolve all the 11 linkage groups, while the two linkage maps constructed in blackgram resolved all 11 linkage groups. Markers have been used for tagging and mapping of genes and QTLs for resistance against mungbean yellow mosaic virus, powdery mildew and Cercospora leaf spot diseases, bruchids and for seed traits. Comparative genome mapping between greengram and several other legumes including azuki bean, common bean, cowpea, soybean and lablab revealed various levels of macrosynteny depending on species, with the greatest upon common bean. Comparison between blackgram and azuki bean maps revealed high degree of genome colinearity. Efforts have been made in developing BAC libraries in greengram to facilitate map based cloning of genes and QTLs. High throughput sequencing technologies have led to the partial nuclear genome sequencing (100 Mb) and complete sequencing of chloroplast and mitochondrial genomes of greengram. Annotation of transcriptome sequences for functional genes has been carried out in greengram. The ESTs and genomic data base from closely related legumes will be helpful in developing high throughput markers such as SSRs and SNPs. These resources have the potential to accelerate gene discovery, mapping and assist molecular breeding in these crops.