Genome-wide association mapping reveals new loci associated with light-colored seed coat at harvest and slow darkening in carioca beans

Background Common bean (Phaseolus vulgaris L.) is a legume whose grain can be stored for months, a common practice among Brazilian growers. Over time, seed coats become darker and harder to cook, traits that are undesirable to consumers, who associate darker-colored beans with greater age. Like commercial pinto and cranberry bean varieties, carioca beans that have darker seeds at harvest time and after storage are subject to decreased market values. Results The goal of our study was to identify the genetic control associated with lightness of seed coat color at harvest (HL) and with tolerance to post-harvest seed coat darkening (PHD) by a genome-wide association study. For that purpose, a carioca diversity panel previously validated for association mapping studies was used with 138 genotypes and 1,516 high-quality SNPs. The panel was evaluated in two environments using a colorimeter and the CIELAB scale. Shelf storage for 30 days had the most expressive results and the L* (luminosity) parameter led to the greatest discrimination of genotypes. Three QTL were identified for HL, two on chromosome Pv04 and one on Pv10. Regarding PHD, results showed that genetic control differs for L* after 30 days and for the Delta L* (final L*-initial L*); only Delta L* was able to properly express the PHD trait. Four phenotypic classes were proposed, and five QTL were identified through six significant SNPs. Conclusions Lightness of seed coat color at harvest showed an oligogenic inheritance corroborated by moderate broad-sense heritability and high genotypic correlation among the experiments. Only three QTL were significant for this trait - two were mapped on Pv04 and one on Pv10. Considering the Delta L, six QTL were mapped on four different chromosomes for PHD. The same HL QTL at the beginning of Pv10 was also associated with Delta L* and could be used as a tool in marker-assisted selection. Several candidate genes were identified and may be useful to accelerate the genetic breeding process.

Automated summary

This study identified the genetic control associated with lightness of seed coat color at harvest and tolerance to post-harvest seed coat darkening through a genome-wide association study. The results showed oligogenic inheritance for lightness of seed coat color with moderate broad-sense heritability. Only three QTL were significant for lightness of seed coat color, while six QTL were mapped for post-harvest seed coat darkening on different chromosomes, with Delta L* being a key parameter for this trait. Several candidate genes were identified, showing potential for accelerating the genetic breeding process.