Project Number: 8080-21000-026-02-T
Project Type: Trust Fund Cooperative Agreement
Start Date: Apr 1, 2015
End Date: Mar 30, 2019
The objectives for this project will be to: 1) determine the best sources of fire blight resistance in Malus sieversii for future use in the Washington State University Apple Breeding Program (WABP); 2) determine fire blight resistance levels in RosBREED reference germplasm for current WABP use; and 3) develop DNA tests to enable the fire blight resistance of ‘Enterprise’ and ‘Splendour’ to be efficiently evaluated in seedlings and to evaluate genetic resistance in current elite selections.
Fire blight is a devastating disease affecting the Washington apple industry. Breeding for resistance to fire blight offers a sustained genetic solution to the problem. Unfortunately, elite cultivars only carry some genetic tolerance to the pathogen and are not yet combined into single cultivars for stronger resistance. Furthermore, genes for stronger resistance are known to exist in the wild ancestral species, Malus sieversii, but are not yet residing in cultivars or parents with superior fruit quality. In a 2012-2014 project with the Washington Tree Fruit Research Commission (PIs Norelli and Evans), 20 highly resistant individuals were identified from evaluation of 194 Malus sieversii accessions for resistance to fire blight shoot infection. These 20 accessions will be evaluated for fruit quality and blossom blight resistance to identify the best one to three lines to use in the WABP as parents for strong resistance (Obj. 1). The previous project also established a grafted replication planting of the RosBREED apple reference germplasm set (elite cultivars and their seedlings, n=3,500) for future fire blight evaluation. This set will be ready for evaluation of resistance to fire blight shoot infection in 2016 (Obj. 2). A vast dataset was developed for this germplasm in the previous RosBREED project, including comprehensive fruit quality evaluations, high-resolution genome scans, and predictive genotypes at fruit quality-influencing loci. Some elite parents in the WABP are already known to be tolerant to fire blight. Recent research in the USA and Europe, including our preliminary data, is identifying genomic regions influencing the fire blight resistance in two WABP parents, ‘Enterprise’ and ‘Splendour’. The resistance of these two cultivars is thought to be controlled by distinct mechanisms. Combining the genetic factors underlying these two mechanisms (Obj. 3) should make it more difficult for the pathogen to overcome resistance and thereby, increase resistance durability.