Abstract
Optimal strategies for genetic improvement in crops depend on accurate assessments of the genetic architecture of traits. The overall objective of the present study was to determine the genetic architecture of anthracnose fruit rot (AFR) resistance caused by the fungus Colletotrichum acutatum in the University of Florida strawberry (Fragaria × ananassa) breeding germplasm. In 2016–2017, 33 full-sib families resulting from crosses between parents with varying levels of AFR resistance were tested. In 2017–2018, six full-sib families resulting from putative heterozygous resistant parents and homozygous susceptible parents were tested. Additionally, a validation population consisting of 77 advanced selections and ten cultivars was tested in the second season. Inoculation was performed using a mixture of three local isolates of the C. acutatum species complex. Phenotypes were scored weekly, and genotyping was performed using the IStraw35 Affymetrix Axiom® SNP array. A pedigree-based QTL analysis was performed using FlexQTL™ software. A major resistance locus, which we name FaRCa1, was detected in both seasons with a peak located at 55–56 cM on LG 6B and explaining at least 50% of the phenotypic variation across trials and seasons. The resistant allele exhibited partial dominance in all trials. The FaRCa1 locus is distinct from the previously discovered Rca2 locus, which mapped to LG 7B. While Rca2 is effective against European isolates from pathogenicity group 2, FaRCa1 appears to confer resistance to isolates of pathogenicity group 1.
Highlights
Optimal strategies for genetic improvement in allo-octoploid (2n = 8x = 56) strawberry (Fragaria × ananassa) depend on the genetic architecture of target traits (Whitaker et al 2012)
Loci associated with disease resistance in strawberry have been described using biparental populations, including for Verticilium wilt caused by Verticillium dahliae (Antanaviciute et al 2015), anthracnose caused by Colletotrichum acutatum (LerceteauKohler et al 2005), crown rot caused by Phytophthora cactorum (Denoyes-Rothan et al 2004) and red stele root rot caused by Phytophthora fragariae (Haymes et al 2000)
QTLs were detected for soluble solids content (SSC) (LG 6A), fruit size (LG 2BII), pH (LG 4CII), titratable acidity (LGs 2A and 5B) and perpetual flowering (LG 4A) in 23 pedigree-connected families obtained from 11 parents that represent the breeding populations included in the RosBREED project (Iezzoni et al 2017; Verma et al 2017b). These results have enabled a robust platform for marker-assisted selection for FaRXf1 and FaRPc2 and future applications for other QTLs present in the University of Florida (UF) strawberry breeding program and other strawberry breeding programs (Whitaker et al 2017)
Summary
Important fruit quality traits (LerceteauKohler et al 2012; Zorrilla-Fontanesi et al 2012) and flowering traits (Weebadde et al 2007) in strawberry have been described using biparental populations. Limitations inherent to biparental populations can restrict the applicability of these results in breeding programs (van de Weg et al 2004; Bink et al 2014). Traitassociated loci and their effects, while significant within a single cross, might not be relevant for broader germplasm. Most fruit breeding programs are characterized by many pedigree-connected clones, complex multi-generational
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