Abstract
Bloom time in sweet cherry (Prunus avium L.) is a highly heritable trait that varies between genotypes and depends on the environmental conditions. Bud-break occurs after chill and heat requirements of each genotype are fulfilled, and dormancy is released. Bloom time is a critical trait for fruit production as matching cultivar adaptation to the growing area is essential for adequate fruit set. Additionally, low chilling cultivars are of interest to extend sweet cherry production to warmer regions, and for the crop adaptation to increasing winter and spring temperatures. The aim of this work is to investigate the genetic control of this trait by analyzing multiple families derived from the low chilling and extra-early flowering local Spanish cultivar ‘Cristobalina’ and other cultivars with higher chilling requirements and medium to late bloom times. Bloom time evaluation in six related sweet cherry populations confirmed a high heritability of this trait, and skewed distribution toward late flowering, revealing possible dominance of the late bloom alleles. SNP genotyping of the six populations (n = 406) resulted in a consensus map of 1269 SNPs. Quantitative trait loci (QTL) analysis using the Bayesian approach implemented by FlexQTL™ software revealed two major QTLs on linkage groups 1 and 2 (qP-BT1.1m and qP-BT2.1m) that explained 47.6% of the phenotypic variation. The QTL on linkage group 1 was mapped to a 0.26 Mbp region that overlaps with the DORMANCY ASSOCIATED MADS-BOX (DAM) genes. This finding is consistent with peach results that indicate that these genes are major determinants of chilling requirement in Prunus. Haplotype analysis of the linkage group 1 and 2 QTL regions showed that ‘Cristobalina’ was the only cultivar tested that contributed early bloom time alleles for these two QTLs. This work contributes to knowledge of the genetic control of chilling requirement and bloom date and will enable marker-assisted selection for low chilling in sweet cherry breeding programs.
Highlights
Bloom time (BT) is an important horticultural trait in temperate fruit tree species like sweet cherry (Prunus avium L.)
Castède et al (2014) reported the same Quantitative trait locus (QTL) region for two of three years for a ‘Regina’ × ‘Garnet’ population, with similar additive effect (1.4 days) and mean percentage of variation explained (PVE) (8%). This QTL represented 32.4 of PVE and has an additive effect of 7.4 Julian Days (JD). These results indicate that BT of our plant material, in our environmental conditions, was determined by this QTL in a larger proportion than in earlier works in sweet cherry
Two major QTLs located on Linkage group (LG) 1 and 2 were identified that explained 47.6% of total phenotype variation
Summary
Bloom time (BT) is an important horticultural trait in temperate fruit tree species like sweet cherry (Prunus avium L.). Cultivar adaptation to climatic conditions in the growing area is essential for flower production and fruit set. Blooming cultivars are susceptible to spring frost damage in cold regions (Luedeling, 2012), while late blooming cultivars can exhibit irregular floral development and low fruit set due to warm temperatures during the flowering period (Mahmood et al, 2000; Atkinson et al, 2013). Fruit trees like sweet cherry require a period of chilling temperatures followed by a period of warm temperatures to induce blooming (Lang et al, 1987). In Prunus species, several studies indicate that BT is more dependent on chilling than on heat requirement and that there is large variation in these requirements among individuals of the same species (Campoy et al, 2011; Okie and Blackburn, 2011; Sánchez-Pérez et al, 2012; Castède et al, 2014)
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