Abstract
Angular leaf spot (ALS) is a disease that causes major yield losses in the common bean crop. Studies based on different isolates and populations have already been carried out to elucidate the genetic mechanisms of resistance to ALS. However, understanding of the interaction of this resistance with the reproductive stages of common bean is lacking. The aim of the present study was to identify ALS resistance loci at different plant growth stages (PGS) by association and linkage mapping approaches. An BC2F3 inter-gene pool cross population (AND 277 × IAC-Milênio – AM population) profiled with 1,091 SNPs from genotyping by sequencing (GBS) was used for linkage mapping, and a carioca diversity panel (CDP) genotyped by 5,398 SNPs from BeadChip assay technology was used for association mapping. Both populations were evaluated for ALS resistance at the V2 and V3 PGSs (controlled conditions) and R8 PGS (field conditions). Different QTL (quantitative trait loci) were detected for the three PGSs and both populations, showing a different quantitative profile of the disease at different plant growth stages. For the three PGS, multiple interval mapping (MIM) identified seven significant QTL, and the Genome-wide association study (GWAS) identified fourteen associate SNPs. Several loci validated regions of previous studies, and Phg-1, Phg-2, Phg-4, and Phg-5, among the 5 loci of greatest effects reported in the literature, were detected in the CDP. The AND 277 cultivar contained both the Phg-1 and the Phg-5 QTL, which is reported for the first time in the descendant cultivar CAL143 as ALS10.1UC. The novel QTL named ALS11.1AM was located at the beginning of chromosome Pv11. Gene annotation revealed several putative resistance genes involved in the ALS response at the three PGSs, and with the markers and loci identified, new specific molecular markers can be developed, representing a powerful tool for common bean crop improvement and for gain in ALS resistance.
Highlights
Common bean (Phaseolus vulgaris L.) is the most important grain that is directly consumed in the human diet, corresponding to half of the grain legumes consumed in the world
Angular leaf spot (ALS) resistance is modulated by different QTL throughout the plant growth stage, corroborating the results shown phenotypically by Pereira R. et al (2019)
The markers associated with the resistance loci represent a powerful tool for crop breeding, which can be applied in studies on germplasm bank screening, selection of parents holding resistance alleles, and marker-assisted and backcross selection (Rocha et al, 2012; Rezene et al, 2019; Almeida et al, 2020b). This is the first mapping study to identify loci associated with ALS resistance at different plant growth stages of diverse genotypes from different genetic backgrounds using two mapping approaches
Summary
Common bean (Phaseolus vulgaris L.) is the most important grain that is directly consumed in the human diet, corresponding to half of the grain legumes consumed in the world. The expressive consumption of the grain is mainly due to its nutritional attributes. As it is a legume, common bean associates with nitrogen-fixing bacteria, leading to significantly higher protein concentration than in other species (Broughton et al, 2003). Brazil is the largest consumer of beans in the world and has the estimated production of the last year around 3.1 million tons (CONAB, 2021), with commercial carioca beans accounting for 70% of the total varieties consumed (Silva et al, 2014). The carioca variety belongs to the Mesoamerican gene pool (Almeida et al, 2020a) and the first cultivar was launched in 1971 by the Instituto Agronômico (IAC, Campinas, SP, Brazil). The new cream-striped cultivar quickly became widely cultivated in Brazil because of its excellent technological qualities and high productivity (Almeida et al, 1971)
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