Amy Iezzoni, Project Director, Michigan State University

Phytophthora crown rot of strawberry, caused by Phytophthora cactorum, is a major contributor to root and crown rot on strawberries in wet and humid production regions, such as the major strawberry production area in central Florida. The fungus produces zoospores dispersed by water that can enter the strawberry root and crown tissues, leading to decay, leaf wilt, whole plant collapse, and death. No effective cultural practices are available to mitigate losses and the most effective chemical control — soil fumigation with methyl bromide — is no longer allowed.

Developing cultivars with reduced susceptibility to Phytophthora crown rot is a high priority for the University of Florida strawberry breeding program. Fortunately, there is genetic variation in susceptibility to this disease within the breeding program’s elite germplasm; however, phenotyping for the pathogen is a labor-intensive, lengthy process. Good news again: a genetic study undertaken by the University of Florida strawberry team revealed the presence of a locus named Pc-1, located on strawberry linkage group 7D, position 63 cM, that explained 20% of the phenotypic variation disease susceptibility (1, submitted). Two particular alleles at this locus conferred reduced susceptibility. These alleles acted in a partially dominant manner, whereby individuals carrying even one allele had a significantly slower rate of pathogen infection and colonization. Development of DNA tests to detect the presence of these desirable alleles is currently underway.

Therefore, because knowledge of this genetic region will lead to the more effective breeding of strawberry cultivars, it is a RosBREED “Jewel in the Genome”.


1. Mangandi J, Verma S, Osorio L, Peres NA, van de Weg E, Whitaker V. 201x. Pedigree-based discovery and validation of a major QTL for resistance to crown rot caused by Phytophthora cactorum in octoploid strawberry. Theoretical and Applied Genetics (submitted).