P-385 - Florida’s Blueberry Leaf Rust Pathogen and Screening for Resistance in Southern Highbush Blueberry Germplasm

Blueberry leaf rust, caused by Thekopsora minima, is one of the most significant diseases affecting the commercial production of blueberries in Florida. High prevalence of this disease leads to severe defoliation, resulting in reduced yields and compromised fruit quality. Its impact has grown as Florida growers increasingly adopt an evergreen production system, which allows for larger quantities of surviving urediniospores through the winter. Currently, all varieties cultivated are susceptible and require multiple fungicide applications for effective rust management; however, resistance has been observed in the germplasm of the University of Florida Blueberry Breeding Program. We confirmed the presence of a single species of rust pathogen across multiple blueberry genotypes, spanning from Florida’s northernmost to southernmost regions, and from both deciduous and evergreen production systems. Comparisons of conserved internal transcribed spacer (ITS) and large subunit (LSU) sequences revealed limited variation and confirmed the identity of T. minima in every sample collected. To reliably phenotype two genetically mapped populations of blueberries planted in north-central and south Florida, a categorical disease severity rating scale was developed. Preliminary results have identified consistent heritable resistance phenotypes, ranging from apparent immunity to high susceptibility. Ongoing work aims to associate resistance with specific genetic loci and to develop molecular markers to assist in the selection of these traits for use in future resistant blueberry varieties.