QTL detection for fruit weight, fruit firmness and fruit cracking tolerance in sweet cherry

Rain-induced fruit cracking is one of the most limiting factors of cherry cultivation in many growing regions. Thus, breeders seek cracking-tolerant varieties. INRA has recently started a breeding program aimed at applying multi-trait marker-assisted strategies, which have to be preceded by the study of the genetic determinism of agronomic traits of interest. Hence, five-year (2006, 2008, 2009, 2010 and 2011) QTL detection studies were conducted at INRA-Bordeaux (France) on a sweet cherry F1 progeny derived from the cross between varieties ‘Regina’ and ‘Lapins’. ‘Regina’ is a late ripening variety with a low fruit cracking susceptibility while ‘Lapins’ has an intermediate maturity period and is relatively susceptible to fruit cracking. The progeny is composed of 124 hybrids planted on their own roots in orchard and grafted on Tabel Edabriz and planted in pots. A map was constructed separately for each parent, ‘Regina’ and ‘Lapins’, with primarily SNP markers (453 and 348 respectively) as well as SSR markers (89 and 72 respectively). Fruit cracking was evaluated according to different tests, based on the observation of 100 randomly selected fruits (% of cracked fruits). Three different types of cracking were considered: apical end, stem end and fruit side. Fruit weight and fruit firmness were also evaluated. The strongest and most stable QTLs were found for the following traits: fruit weight (LG2 and LG3), and fruit firmness (LG2). QTLs for cracking susceptibility were relatively weak and variable across years. However, a QTL on LG5, with a maximum explained phenotypic variance of 15%, was detected during 4 years.