Genetic Analysis of Malus sieversii PI613981 for Resistance to Postharvest Apple Fruit Decay Caused by Penicillium expansum (blue mold)

Blue mold of apple caused by Penicillium expansum is one of the most important postharvest rots of apple fruit which can result in financial losses exceeding $4.5 million per year in the USA alone. P. expansum is also of great concern to fruit processing industries due to its production of patulin, a highly toxic mycotoxin.  Blue mold resistance is not currently of high priority in apple scion breeding programs due to the time required for seedlings to produce a sufficient number of fruit to phenotype the trait and the absence of resistance in commercial cultivars.  Malus sieversii PI613981 collected from the wild in Kazakhstan has previously been reported to be resistant to blue mold.  Fruit collected from a ‘Royal Gala’ X PI613981 mapping population (GMAL4593) in 2011 (145 individuals) and 2012 (115 individuals) were inoculated with P. expansum and evaluated for decay.  In 2011, 7 days post inoculation (dpi) the mean radius of decay ranged from 0-11 mm among individual progeny with an overall population mean of 7.5 mm.  Lesion diameters observed 7 dpi on 101 individuals evaluated for resistance in both years were significantly correlated (r=0.44, P<0.001).  Kruskal-Wallis analysis (MapQTL® 6.0, Kyazma) found a significant association between blue mold resistance and DNA markers on linkage group 4. Further analysis is underway to better define the putative QTL and identify molecular markers for use in MAS of blue mold resistance in apple.