Construction of Mungbean Genetic Linkage Map

Abstract

A high-density genetic linkage map with informative markers is essential for plant genome analyses, such as gene mapping, identification of quantitative trait loci, map-based cloning, and physical map construction. A genetic linkage map of mungbean ( Vigna radiata, 2 n = 2 x = 22) was constructed using a recombinant inbred line (RIL) population derived from an inter-subspecific cross between Berken (a bruchid-susceptible cultivar) and ACC41 (a bruchid-resistant genotype belonging to V. radiata subsp. s ublobata). For enhancing the density of the existing linkage map, 104 pairs of polymorphic simple sequence repeat (SSR) primer, were screened out. In combination with the data from other markers, a new genetic linkage map consisting of 179 markers was obtained. They included 97 SSR markers (91 of which were derived from mungbean close relatives), 76 RFLP markers, and 2 STS markers. These markers were assigned to 12 linkage groups with an average distance of 10.2 cM between markers. The transferability of the SSR markers from these relatives of mungbean, including azuki bean ( V. angularis), black gram ( V. mungo), common bean ( Phaseolus vulgaris), and cowpea ( V. unguiculata) was also evaluated. Approximately 65% of SSR markers form azuki bean, 72% from black gram, 42% from common bean, and 30% from cowpea could be effectively amplified in mungbean. These different ratios might reflect different levels of genomic homology between mungbean and the four close relatives. A total of 98 pairs of polymorphic SSR primers from these close relatives were effective in genetic analysis of mungbean. The new linkage map of mungbean was compared with a published linkage map of azuki bean based on 32 common SSR markers. The majority of these markers were mapped in similar orders between these 2 species and a few markers with different orders suggested relative rearrangements between the 2 genomes. As previously reported, a major locus resistant to bruchid was located on linkage group I (9). In this new map, the distances between the bruchid locus and its flanking markers were 8.0 cM (C78) and 2.7 cM (C220), respectively.