| Chilling requirement (CR), together with heat requirement (HR), determines bloom date (BD), which impacts climatic distribution of genotypes of temperate tree species. The molecular basis of floral bud CR is poorly understood despite its importance to fruit tree adaptation and production. A peach F2 populations developed from two genotypes with contrasting CR values was used for QTL mapping for CR, HR and BD. Using the Contender x Fla.92-2c population, 20 QTLs with additive effects were identified for three traits including one major QTL for CR and two major QTLs for BD. Particularly, one genomic region of 2cM pleiotropic for the three traits overlaps with the sequenced peach evg region. Association approaches and candidate-gene approaches were used to explore and refine the detected QTL regions. Seven Polycomb group and their associated protein encoding genes in/close to QTL regions and three genes (including DAM4 and DAM6 ) in evg locus were identified as potential candidate genes regulating CR and BD. In addition, we established the use of plum as transgenic system to test peach candidate genes for CR and BD. Transgenic plums overexpressing DAM6 showed dwarfing and more branching phenotype. |
