Mapping Snap Bean Pod and Color Traits, in a Dry Bean × Snap Bean Recombinant Inbred Population

Abstract

Snap bean (Phaseolus vulgaris L.) breeding programs are tasked with developing cultivars that meet the standards of the vegetable processing industry and ultimately that of the consumer, all the while matching or exceeding the field performance of existing cultivars. While traditional breeding methods have had a long history of meeting these requirements, genetic marker technology, combined with the knowledge of important quantitative trait loci (QTL), can accelerate breeding efforts. In contrast to dry bean, snap bean immature pods and seeds are consumed as a vegetable. Several pod traits are important in snap bean including: reduced pod wall fiber, absence of pod suture strings, and thickened, succulent pod walls. In addition, snap bean pods are selected for round pod cross section, and pods tend to be longer with cylindrical seed shape. Seed color is an important trait in snap bean, especially those used for processing, as processors prefer white-seeded cultivars. The objective of this study was to investigate the genetic control of traits important to snap bean producers and processors. RR6950, a small seeded brown indeterminate type IIIA dry bean accession, was crossed to the Oregon State University (OSU) breeding line OSU5446, a type I Blue Lake four-sieve breeding line to produce the RR138 F4:6 recombinant inbred (RI) mapping population. We evaluated the RR138 RI population for processing and morphological traits, especially those affecting pods. The RR138 population was genotyped with the BARCBean6K_3 Beadchip, and single nucleotide polymorphisms (SNPs) were used to assemble a linkage map, and identify QTL for pod traits. The linkage map produced from this study contained 1689 SNPs across 1196cM. The map was populated with an average of one SNP per 1.4 cM, spanning 11 linkage groups. Seed and flower color genes B and P were located on Pv02 and Pv07, respectively. A QTL for string:pod length (PL) ratio was found on Pv02 controlling 32% of total genetic variation. QTL for a suite of important processing traits including pod wall fiber, pod height, pod width, and pod wall thickness were found clustering on Pv04 and controlled 21%, 26%, 18%, and 16% of genetic variation for each of these respective traits. A QTL for PL was found on Pv09 controlling 5% of genetic variation.