Patterns of Accumulation and Genetic Mapping of Fructose, Glucose, and Sucrose in Snap Beans

Sugars, including fructose, glucose, and sucrose contribute significantly to the flavor and consumer acceptance of snap beans (Phaseolus vulgaris). Little is known regarding differences between and within dry bean and snap bean cultivars, the patterns of sugar development with increasing pod size, or the presence of quantitative trait loci associated with sugar concentration. This study consists of two experiments. In experiment one, alcohol-soluble sugar content of five snap bean cultivars and one dry bean cultivar planted in field trials were assayed throughout pod development over two years using high-performance liquid chromatography. Significant differences in sugar accumulation patterns were observed among cultivars. In general, fructose and glucose levels decreased while sucrose levels increased with increasing pod size in the snap bean cultivars. In contrast, fructose and glucose levels increased in the dry bean cultivar while sucrose levels remained unchanged with increasing pod size. No year by genotype interactions were observed for sugar accumulation patterns.  Results indicate that differences among cultivars can be sampled at commercial sieve size 3 (7.34 to 8.33 mm) or 4 (8.33 to 9.52 mm). In the second experiment, a recombinant inbred line population consisting of 75 F2:10 recombinant inbred lines (RIL) developed from a cross between ‘Eagle’ and ‘Puebla 152’ by single seed descent was utilized to identify putative QTL. A previously published random amplification of polymorphic DNA (RAPD) linkage map of the ‘Eagle’ x ‘Puebla 152’ RIL (EP-RIL) population was used to scan for putative QTL associated with sugar concentration levels. Significant differences were observed among the EP-RIL genotypes, with no significant genotype by environment interactions. Heritability estimates for fructose, glucose, and sucrose were 0.85, 0.81, and 0.85, respectively. A single QTL was mapped to linkage group B1 and was closely linked to marker W9.1050 for fructose and sucrose concentration levels. Marker W9.1050 explained 28.8% of the variation in fructose and 26.6% in sucrose. A two-QTL model with associated markers W9.1050 on linkage group B1 and F8.500 on linkage group B6 was mapped for glucose and explained 36.4% of the variation in glucose concentration levels.