Genomic Studies on a Highly Complex Trait in Sweet Cherry: Tolerance to Rain-Induced Fruit Cracking

Rain-induced fruit cracking is one of the major agronomic problems for cherry producers. It is a highly complex phenomenon that depends on four different types of factors: genetic, physiological, climatic and agronomic. Searching for tolerant varieties is one of the most economic and ecological solutions. At INRA Bordeaux, studies aimed at deciphering the genetic determinism of tolerance to fruit cracking were initiated at the end of the 90’s. Three different bi-parental populations were used for QTL detection studies. Phenotypic data was recorded from 2008 until 2014. Tolerance to cracking was evaluated by visually analyzing 100 fruits harvested at physiological maturity and by differentiating three types of cracking, at the pistillar end, on the fruit side and at the stem cavity. QTLs were detected on many linkage groups, confirming the high complexity of this trait. However, few of them were stable over years and the percentage of phenotypic variance explained by the QTLs was relatively low. Hence, complementary studies aimed at characterizing different fruit parameters, which could be correlated to cracking tolerance, were recently initiated. Metabolomic analyses were conducted: the main sugars and acids within mature fruits were quantified as well as the composition of the cell walls. Finally, collaboration was initiated with the University of Chile to study candidate genes (CG) involved in cracking tolerance. Transcriptomic analyses conducted in Chile allowed identifying differentially expressed genes between cracking-tolerant and susceptible varieties. A subset of these genes will be mapped onto the INRA mapping progenies in order to search for QTL/GC co-localizations.