No abstract

Yam bean (Pachyrhizus erosus Rich. Ex DC.) is an underutilized leguminous crop which has been used as a food source across central America and Asia. It is adapted to a range of environments and is closely related to major leguminous food crops, offering the potential to understand the genetic basis of environmental adaptation, and it may be used as a source of novel genes and alleles for the improvement of other legumes. Here, we assembled a draft genome of P. erosus of 460 Mbp in size containing 37,886 gene models. We used this assembly to compare three cultivars each of P. erosus and the closely related P. tuberosus and identified 10,187,899 candidate single nucleotide polymorphisms (SNPs). The SNP distribution reflects the geographic origin and morphology of the individuals.

Cytological understanding is an important parameter to understand the genetic architecture of yam bean. The ploidy level and genome size of two cultivated species of yam bean (Pachyrhizus erosus and P. tuberosus) were estimated using flow cytometric analysis of young leaf tissue, with propidium iodide as a fluorescent dye. Six genotypes of P. erosus and three genotypes of P. tuberosus were analysed. Rice (Oryza sativa cv. Nipponbare) and Mung bean (Vigna radiata cv Berken) were used as internal reference standards. Variation of 2C nuclear DNA content among the six P. erousus lines was 4.18%, ranging from 1.17 to 1.22 pg, whereas only 1.8% variation was observed among the three P. tuberosus lines, which ranged from 1.07 to 1.09 pg. Moreover, it was found that the nuclear DNA content of P. tuberosus was lower than that of P. erosus. The result of the flow cytometric analysis showed that all the species were diploid (2n = 2x) and coefficient of variation (CV%) of all the accessions of the two species was less than 3.5%. This is the first report of ploidy analysis and genome size estimation of the leguminous underutilized tuber crop yam bean using flow cytometry. This result will be helpful for yam bean genome sequencing and crop improvement programmes.