Resumen de Phenology and fruit quality in sweet cherry (prunus avium l.). Genetics, qtl analysis and marker assisted selection
Sweet cherry (Prunus avium L.) is a very appreciated fruit, with a high nutritional value and economic interest, which cultivation has increased during last years. In order to provide new cultivars adapted to producer and consumer demands, and that confront challenges like global warming, is necessary to develop tools that can help optimizing the breeding process. For this purpose, the objective of this work is to investigate the genetics of some relevant phenology and fruit quality traits of sweet cherry and to advance in the understanding of the biological mechanisms that regulate them. To achieve this goal, seven sweet cherry intraspecific populations that derive from cross- and self-pollinations of local plant material (‘Cristobalina’ and ‘Ambrunés’), and that provide additional phenotypic variation for these traits, were used. These populations were genotyped with the whole genome RosBREED cherry 6K and/or 15K Illumina® Infinium SNP arrays, which allowed developing five high-density genetic maps that were then used for analyzing synteny between sweet cherry and peach (P. persica) and for QTL analyses. The seven populations were also phenotyped for phenology traits (bloom time, fruit development period and maturity date), and for fruit quality traits [firmness, size, color, solid soluble content, titratable acidity and polyphenols (anthocyanins and phenolic acids) content]. These data were used to perform single and/or multi-year QTL analysis, using different mapping strategies, which included single bi-parental analysis with MapQTL®, or combined multi-parental populations using FlexQTL™. These analyses allowed identifying major and minor QTLs for all the traits investigated, validating some QTLs previously reported for the same traits, reporting new QTLs for newly investigated traits, and identifying new QTLs variants of breeding interest. Major QTLs were identified on linkage groups (LGs) 1 and 2 for bloom time, on LG4 for fruit development period and maturity date, on LGs 1 and 2 for fruit size, on LGs 1 and 4 for fruit firmness, on LG4 for solid soluble content, on LG6 for titratable acidity, on LG3 for fruit color and anthocyanins content, and on LG1 for phenolic acids content. Relevant QTL haplotypes for breeding purposes were identified in these major QTLs in some cultivars, like for low chilling and early blooming in ‘Cristobalina’ LGs 1 and 2, for short development period and early maturity date in ‘Cristobalina’ and ‘Burlat’ LG4, and in ‘Ambrunés’ LG1 for size and firmness. Fruit development period reveal itself as an essential trait for phenology and fruit quality, as maturity date, firmness and soluble solids contents were correlated with fruit development and were associated to the same QTLs. The identification of major QTLs allowed proposing and confirming candidate genes for these traits at these QTLs, and candidate genes for bloom time were investigated. Using the ‘Regina’ sweet cherry genome sequence, candidate genes for chilling requirements and bloom time, PavDAM genes, orthologous to P. persica and P. mume DAM genes, were identified and characterized in the major bloom time QTL on LG1. Sequence comparison of PavDAM genes of various sweet cherry cultivars with different chilling requirements and bloom times allowed detecting sequence polymorphisms that may be associated to their phenotypic differences, and a deletion in the ‘Cristobalina’ PavDAM promoter (DPD) that is associated to early blooming. A DNA marker for this mutation, that can be used for marker-assisted selection of early blooming from ‘Cristobalina’, was also developed.
