Identification of Quantitative Trait Loci Associated with Fructose, Glucose, and Sucrose Concentration in Snap Bean Pods

Sugars, including fructose, glucose, and sucrose, contribute significantly to the flavor and consumer acceptance of snap beans (Phaseolus vulgaris L.). Differences between dry and snap bean cultivars and among snap bean cultivars in the patterns of accumulation of sugars have been observed. In 'Eagle', a white-seeded, large-sieve snap bean cultivar, fructose and glucose concentrations in developing pods decreased while sucrose concentration increased with increasing pod size. In contrast, fructose and glucose concentrations increased while sucrose remained unchanged with increasing pod size in Puebla 152, a black-seeded dry bean landrace from Mexico. A population derived from the cross Eagle x Puebla 152 consisting of 75 F-9:10 recombinant inbred lines (RILs) was developed by single seed descent. Significant differences in fructose, glucose, and sucrose concentrations of sieve size 4 (8.33-9.52 mm) pods were observed among RILs. No significant genotype x year interactions were observed. Heritability estimates for fructose, glucose, and sucrose were 0.85 +/- 0.16, 0.81 +/- 0.16, and 0.85 +/- 0.16, respectively. A single quantitative trait locus (QTL) on linkage group B1 was identified that is closely linked to random amplified polymorphic DNA (RAPD) marker W9.1050 and explains 28.8 and 26.6% of the variation in pod fructose and sucrose concentration, respectively. A two-QTL model, including W9.1050 and RAPD marker F8.500 on linkage group B6, explained 36.4% of the variation in glucose concentration in pods.