1a. Objectives (from AD-416):
The objectives of this project are: 1) identify potential effector genes in P. expansum that play a role in pathogenicity; and 2) identify QTLs for disease resistance in apple using a segrating mapping population of Malus sieversii x 'Royal Gala' (GMAL4593).
1b. Approach (from AD-416):
Comparative secretome analysis and BLAST sequence similarity searches will be used to identify putative effectors in the sequenced genome of P. expansum. Transcriptomic analysis using Illumina technology will be used to examine differential gene expression in resistant and susceptible apple genotypes of M. sieversii in response to P. expansum. QTL analysis will be performed independently and combined for both parents in the GMAL4593 population to identify loci affecting P. expansum. Marker density in the QTLs will be increased using additional SNPs and DIPs. Identification of candidate resistance genes located in the QTL will be done by examining the sequenced genome of 'Golden Delicious'.
3. Progress Report:
Blue mold of apple caused by Penicillium expansum is a major postharvest disease. Selection for postharvest disease resistance in breeding programs has been ignored in favor of fruit quality traits such as size, color, taste, etc. The identification of resistance as a heritable trait would represent a significant accomplishment and has not been attempted in apple. Furthermore, insight into the biology of pathogenicity of P. expansum in apple could provide new approaches to postharvest decay management in apple. The objectives of the project are: 1) identify potential effector genes in P. expansum that play a role in pathogenicity; 2) conduct a transcriptomic study of the response of susceptible (‘Royal Gala’) and resistant (PI613981) fruit to P. expansum; and 3) identify QTLs for postharvest disease resistance in apple using a segrating mapping population of Malus sieversii x ‘Royal Gala’ (GMAL4593). Two years of phenotyping a mapping population of apple for postharvest disease resistance have been completed and a preliminary QTL on linkage group 4 of apple has been identified. Additionally, transcriptomic data have been collected within the mapping population on the response of susceptible and resistant genotypes of apple to blue mold infection. Lastly, the genome of the blue mold pathogen, P. expansum, has been sequenced, and a number of effector genes have been identified and characterized.