Mapeamento de genes de resistência a diferentes isolados de Colletotrichum lindemuthianum e seleção recorrente visando à resistência a antracnose do feijoeiro

Abstract

The large variability of Colletotrichum lindemuthianum fungus, the causal agent of anthracnose in the common bean, has made it difficult to obtain cultivars with durable resistance to this pathogen. Variability within races has been reported in addition to the variability of identified physiological races. In this context, the objectives of this study were to i) identify genomic regions associated with the resistance to different C. lindemuthianum strains, one of the most significant races of this fungus in Brazil; and ii) develop and evaluate the efficiency o f a recurrent selection program as an alternative to obtain durable resistance to anthracnose in common bean. To reach the first objective, we employed two mapping approaches: the traditional mapping by linkage analysis, using an F2 population derived from the cross between BRS Estilo x Ouro Vermelho common bean cultivars, which are contrasting regarding the reaction to two different C. lindemuthianum strains of race 65; and the association mapping, using a panel of 189 accessions of the common bean germplasm bank of the Universidade Federal de Lavras, with phenotypic variation for five different strains of the same race. We genotyped the 189 common bean lines of the germplasm bank and 400 individuals from the F 2 population of the cross between BRS Estilo x Ouro Vermelho, as well as the parental, using the BARCBEAN6K_3 Illumina SNP chip with 5398 SNPs. For the development of the recurrent selection program, we used a mixture of seeds from 45 F2 populations (S0 population) derived from the diallelic cross among ten common bean lines to form the base population (Cycle 0).. These common bean lines present variability regarding different C. lindemuthianum strains. From cycle 0, we performed five evaluation, selection and recombination cycles among the S 0 plants most resistant to strains of races 65, 73, 81 and 89, obtaining approximately 40 S0:2 progenies in each cycle. The result of the mapping using the biparental population derived from the cross between BRS Estilo x Ouro Vermelho and two different strains of C. lindemuthianum, race 65, revealed the presence of markers completely linked to genomic regions associated with resistance to each of the two strains used, on the Pv04 chromosome, distant 1.8cM from each other. Through the association mapping, we identified significant Quantitative Trait Loci (QTLs) associated with the resistance to both strains this same position as well as in other positions of the Pv04. Furthermore, we identified QTLs associated with resistance to three other strains of race 65 on chromosomes Pv04, Pv05, Pv10, and Pv11. This is the first study about mapping of resistance genes in Phaseolus vulgaris using different strains belonging to the same race of C. lindemuthianum. The results indicate that the genomic regions that control resistance to C. lindemuthianum, race 65, vary according to the strain used. Some common bean lines with, already identified resistance alleles to C. lindemuthianum, race 65, were also evaluated regarding the reaction to the five strains of race 65 used in the present study, presenting a different reaction to each of these strains. Concerning the recurrent selection, we were able to perform three selective cycles per year using this method. After five selective cycles, we observed genetic progress of 7.4% and 10.7% for two different strains of race 65 and 9.0%, 9.0%, and 8.0% for the strains of races 73, 81, and 89, respectively. Moreover, there was an increase in the number of progenies resistant to a higher number of C. lindemuthianum strains during the selective cycles, demonstrating the efficiency of the method. If the progenies derived from this program are conducted by the bulk method within S0 progenies, the progenies will be composed of mixtures of pure common bean lines at the end of the process. If the breeder chooses to use this mixture of pure lines as a cultivar, it will present pyramided resistance alleles among and within the pure lines that compose the mixture, which can provide higher stability and durability of the resistance against the large variability among and within C. lindemuthianum races.