Abstract
Breeding for resistance against the destructive fire blight disease of apples is the most sustainable strategy to control the menace of this disease, and has become increasingly important in European apple breeding programs. Since most cultivars are susceptible, wild accessions have been explored for resistance with quantitative trait loci detected in a few wild species. Fire blight resistance of Malus fusca was described following phenotypic evaluations with a C-type strain of Erwinia amylovora, Ea222_JKI, and the detection of a major QTL on chromosome 10 (Mfu10) of this crabapple. The stability of the resistance of M. fusca and Mfu10 has been evaluated using two other strains, the highly aggressive Canadian S-type strain—Ea3049, and the avrRpt2EA mutant—ZYRKD3-1, both of which overcome the resistance of Malus ×robusta 5, a wild species accession with an already described fire blight resistance gene. To pave the way for positional cloning of the underlying fire blight resistance gene of M. fusca, we have fine mapped the QTL region on linkage group 10 using 1888 individuals and 23 newly developed molecular markers, thus delimiting the interval of interest to 0.33 cM between markers FR39G5T7xT7y/FR24N24RP and FRMf7358424/FR46H22. Tightly linked SSR markers are suitable for marker-assisted selection in breeding programs. Furthermore, a bacterial artificial chromosome (BAC) clone spanning FB_Mfu10 region was isolated and sequenced. One putative fire blight resistance candidate gene of M. fusca was predicted on the sequence of BAC 46H22 within the resistance region that encodes B-lectin and serine/threonine kinase domains.
Highlights
Apple (Malus domestica Borkh.) is one of the most economically important fruit crops worldwide
Markers were developed from sequences of paired end short reads of M. fusca as well as from sequenced T7 and RP ends of identified bacterial artificial chromosome (BAC) (Bacterial artificial chromosome) clones and from BAC sequences
Four markers were developed from BACends
Summary
Apple (Malus domestica Borkh.) is one of the most economically important fruit crops worldwide. One of the most serious threats to apple production is fire blight disease, caused by the bacterial pathogen, Erwinia amylovora (Burrill) (Winslow et al 1920). Fire blight is considered to be the most dreadful bacterial disease affecting pome fruit production. The T3SS deposits effector proteins into the host and enables the pathogen to cause disease in susceptible host plants. Some preventive measures employed by pome fruit growers include the use of antibiotics and antagonists. Rigid pruning of infected parts of a tree or the complete eradication of affected trees are curative measures. These control methods are not sustainable and cannot totally mitigate the disease in a season favorable to E. amylovora
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