![]() ![]() noted that reduced susceptibility mechanisms for defense against E. Breeding resistant apple cultivars could complement current unsustainable control methods (e.g., antibiotics), as discussed in several book chapters and reviews. commercial apple production systems have become more vulnerable to fire blight epidemics due to production of highly susceptible apple cultivars (e.g., Gala, Fuji), the shift towards high-density planting systems, and lack of sustainable control methods that are effective against all disease phases. apple crop is produced, resulted in estimated direct costs of over $37 million from chemical sprays, tree removal, and tree replacement. For example, in 2018, severe fire blight infections in Washington State, where approximately 66% of the U.S. Fire blight, which has been reported in over 40 countries, can result in significant economic costs. The bacterium, which infects the flowers, fruits, shoots, and rootstock of the tree, can cause severe structural damage and tree death ( Figure 1). Clonally Propagated Apple Orchards Are Vulnerable to Fire Blight Epidemicsīreeding for resistance offers a potential long-term solution to fire blight, a devastating bacterial disease in apple ( Malus domestica Borkh) caused by Erwinia amylovora. Here we discuss (1) considerations and challenges associated with phenotyping resistance/susceptibility to fire blight (2) sources of resistance that have been identified for use as parents and (3) our perspective on short and long-term strategies to breed apple cultivars with durable resistance to fire blight with emphasis on the potential contributions of reduced susceptibility alleles to achieve this goal.ġ. Although resistance to fire blight is an attractive target for DNA-informed breeding, relatively few trait-predictive DNA tests for breeding relevant fire blight QTLs are available. ![]() Several QTLs have been identified in populations derived from cultivars and reduced-susceptibility alleles have been characterized in multiple important breeding parents. Most resistance alleles at fire blight QTLs have been identified in wild Malus germplasm with poor fruit quality, which limits their breeding utility. Several quantitative trait loci (QTLs) associated with resistance/susceptibility to fire blight have been detected throughout the apple genome. ![]() Inheritance of resistance/susceptibility to fire blight is complex and phenotypic information alone is insufficient to guide breeding decisions targeting resistance. amylovora strain virulence, differential host × strain interactions, quantitative host resistance, environmental influences on disease, and impacts of tree vigor on susceptibility. However, phenotyping resistance/susceptibility to fire blight is challenging due to E. Breeding apple cultivars with durable genetic resistance is a potential long-term solution to fire blight, a devastating bacterial disease caused by Erwinia amylovora. ![]()
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