Genetic control for seedcoat darkening on carioca beans by natural and accelerated methods

The acceptability of a carioca common bean cultivars (Phaseolus vulgaris L.) by the producer market does not depend exclusively on high productivity, erect size, and resistance to diseases. Light and darkening tolerance grains are traits that determine the success of the breeding program since cultivars with light grains and slow darkening have greater acceptability by the consumers as it is associated to longer cooking time. The aim of the present study was to identify QTL (Quantitative Trait Loci) associated with the control of slow darkening. A carioca segregating population BC2F3 (AM) originated from the ‘AND 277’ x ‘IAC Milênio’ crossing and genotyped by GBS (Genotyping by Sequencing) was used. The population was sowed in an experimental field following the randomized complete block design, with 4 replications. After harvest, the seeds of each plot were used to measure the initial luminosity (L*) by the CIELAB system. Data was recorded using a colorimeter (Minolta CR-400) and then, two darkening methods were used to determine the degree of slow darkening: the natural darkening method under shelf conditions for 90 days (SDS) and accelerated one for 96 hours on UV (SDUV) chamber. The darkening values were determined by the difference between the initial L* and the L* after storage and expressed by the mean of five measurement repetitions for each sample. For QTL analysis, the genetic map previously constructed for the AM population was used and multiple interval mapping model (MIM) was adopted. Two QTL were identified: the first one at Pv03 chromosome associated with SDS with an estimated phenotypic effect of 18% and a second one for SDUV at Pv04 explaining 18% effect on phenotypic variance. The results showed a difference in the genetic control for both evaluated darkening methods, which were reported in the literature as equivalent. This is the first study involving QTL detection for seedcoat darkening on carioca beans and at least, for this bean class, natural darkening should be preferred in the routine of breeding programs as different QTL seem to be involved.