Genetic control of the resistance of the common bean plant to white mold using the reaction to oxalic acid / Controle genÃtico da resistÃncia do feijoeiro ao mofo branco e seleÃÃo assistida por marcadores moleculares

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

The use of genetically resistant cultivars is the most efficient method to diminish risks of epidemics and damage by white mold (Sclerotinia sclerotiorum (Lib.) by Bary). As the best known sources of resistance are not adapted it is necessary to do the backcross using elite lines. So the breeding will be easy if we understand the genetic control of the reaction of the common bean to white mold. Besides, evaluations of resistance to white mold in the field are hindered by environmental conditions and avoidance mechanisms that confound the expression and detection of physiological resistance mechanisms. The use of indirect methods that do not use the pathogen to cause disease are preferred. The objectives of this study were to identify the genetic control of the resistance of common bean to white mold through the reaction of seedling without roots to oxalic acid, and promote early selection with molecular marker linked to QTL of resistance to the disease in a backcrossed population. The line VC3 (susceptible) and G122 (resistant) were crossed and the F1, F2, F3 and F1RC1 were used. The reaction to white mold was indirectly evaluated by means of a visual score given after treatment of the seedling with oxalic acid. The evaluations were done both on individual plants and on families. In the former case, the plants of the populations P1, P2, F1, F2 and within F3 family were evaluated in a completely random design with two replications. In the second case, variances among F2:3 families were estimated. The randomized complete block design was adopted with two replications, and the family means were adjusted based on the parents performance. Additionally the F1RC1 (F1 x VC3) was evaluated for resistance to white mold by means of the SCAR Phs developed specifically for this type of resistance. Fifty three F1RC1 plants were obtained, and only the plants with the marker were selected for the next backcross. The oxalic acid test was efficient to detect genetic differences among genotypes. It was found that there was a predominance of the additive effects characterized by partial dominance (d/a = 0.47). Only one resistance gene is involved in the control of the trait although it is highly influenced by the environment. Estimates of the broad-sense heritability at the level of family means (0.47) was higher than the estimates based on individual plants (0.33) indicating that selection should be done using means of progenies. The marker was efficient in identifying the plants that have the QTL in the RC1 population.

ASSUNTO(S)

sclerotini sclerotiorum, phaseolus vulgares, Ãcido oxÃlico melhoramento vegetal sclerotinia sclerotiorum, oxalic acid, phaseolus vulgaris,

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