Abstract
The bacterium, Erwinia amylovora, deposits effector proteins such as AvrRpt2EA into hosts through the type III secretion pathogenicity island to cause fire blight in susceptible Malus genotypes. A single nucleotide polymorphism in the AvrRpt2EA effector plays a key role in pathogen virulence on Malus hosts by exchanging one cysteine to serine in the effector protein sequence. Fire blight resistance quantitative trait loci (QTLs) were detected in a few apple cultivars and wild Malus genotypes with the resistance of wild apples generally found to be stronger than their domestic relatives. The only candidate and functionally analyzed fire blight resistance genes proposed are from wild apple genotypes. Nevertheless, the aforementioned AvrRpt2EA SNP and a couple of effector mutants of E. amylovora are responsible for the breakdown of resistance from a few Malus donors including detected QTLs and underlying R-genes. This review summarizes a key finding related to the molecular basis underpinning an aspect of virulence of E. amylovora on Malus genotypes, as well as mechanisms of host recognition and specificity, and their implications on the results of genetic mapping and phenotypic studies within the last 5–6 years. Although the knowledge gained has improved our understanding of the Malus–E. amylovora system, more research is required to fully grasp the resistance mechanisms in this genus especially as they pertain to direct interactions with pathogen effectors.
Highlights
Economic Importance of Fire Blight and Host ImmunityErwinia amylovora (Burrill) (Winslow et al, 1920) incites fire blight disease in the genus Malus as it does other genera belonging to the Rosaceae family
This review focuses on works that have contributed to our understanding as it pertains to Malus–Erwinia amylovora (Ea) interaction and host resistance mechanisms since 2013 till date
Vogt and colleagues proved that strains encoding for the S-allele were more aggressive for different apple cultivars, and Malus ×robusta 5 (Mr5) itself - a major source of fire blight resistance, but not on other wild apple accessions of Malus fusca and Malus baccata
Summary
Economic Importance of Fire Blight and Host ImmunityErwinia amylovora (Burrill) (Winslow et al, 1920) incites fire blight disease in the genus Malus as it does other genera belonging to the Rosaceae family. Vogt and colleagues proved that strains encoding for the S-allele were more aggressive for different apple cultivars, and Mr5 itself - a major source of fire blight resistance, but not on other wild apple accessions of Malus fusca and Malus baccata. The suspicion that the fire blight resistance QTL of Mr5 on linkage group 3 (LG3) is broken down by the highly aggressive S-allele encoding Canadian strain Ea3049 (Peil et al, 2011), was confirmed by Wöhner et al (2014).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
