Associação genômica ampla para resistência a bacteriose em germoplasma de pessegueiro com base em SNPs

Abstract

Peach (Prunus persica) is one of the best genetically characterized deciduous trees and the third most important temperate fruit crop worldwide. This crop is vulnerable to bacterial spot caused by Xanthomonas arboricola pv. pruni (Xap) and breeding for resistance has been the main choice to control the disease. With the aim to contribute with breeding for more resistant cultivars, and perform genome-wide association analysis (GWAS), we explored the use of genotyping by sequencing (GBS) for large-scale SNP discovery and simultaneous genotyping and performed high quality phenotyping for Xap response, among a panel with 220 peach genotypes, representative of the Brazilian breeding germplasm. A total of 93,353 SNP markers were discovered, and after filtering 18,373 high quality SNPs were used in analyses. Thirty-four percent of selected SNPs were located in genic regions and 70% of these in the coding sequence. Strong population genetic structure was detected, with the distribution of genotypes within subpopulations based mainly on fruit-related traits: melting and non-melting flesh. Linkage disequilibrium (LD) patterns suggested a medium LD level, with the extent of LD highly dependent on the subpopulations and genome regions. Field evaluation and detached leaf assessments were reliable and complementary methods to identify Xap resistant sources. The genotypes ‘Norman’, ‘Cristal Taquari’, ‘La Feliciana’ and ‘Precocinho’ were considered highly resistant sources and may be effective alternatives to improve Xap resistance in peach. Overall, the germplasm evaluated showed great variability for response to Xap, allowing the identification of contrasting genotypes for the trait of interest. Genotypes with resistance could be preferred for peach production areas more subjected to disease occurrence, or used as parents by the breeding program to improve resistance. GWAS analysis validated and defined more accurately the known genomic regions underlying Xap resistance, as well as identified novel candidate genes that provide useful targets for further investigation. Several informative SNPs were functionally annotated in genes involved in defense mechanisms against pathogen infection, highlighting two genomic regions, located on chromosome 1 (2.59 Mbp) and 2 (2.85 Mbp), respectively, both housing several R genes. Our results provide new insights into breeding for Xap resistance in peach, with great potential for subsequent application of marker-assisted selection.