Discovery of Novel Fusarium Wilt Resistance Genes in Heirloom Strawberry Cultivars

The soil-borne pathogen Fusarium oxysporum f. sp. Fragariae infects the vascular system of strawberry (Fragaria x ananassa) plants through their root system. Symptoms of infections commonly referred to as Fusarium wilt are chlorosis, wilting, and death in susceptible plants. This pathogen threatens production in many parts of the world including California. The development of Fusarium wilt resistant cultivars is important to prevent production losses caused by this pathogen. Genotypes resistant to the most virulent race of the pathogen found in California (AMP132) have been identified. These include heirloom and modern cultivars, most of which carry Fw1, a dominant gene that confers resistance to AMP132 and has been physically and genetically mapped to chromosome 2-4. DNA markers in linkage disequilibrium with Fw1 accurately predict Fw1 haplotypes in most resistant and susceptible cultivars. However, earlier studies identified two resistant cultivars (Wiltguard and Guardian) with DNA marker haplotypes different from resistant cultivars known to carry Fw1. Here, we show these cultivars carry novel dominant Fusarium wilt resistance genes. The Guardian gene (Fw2) mapped to a 2.7 Mb region on chromosome 2-4. The Wiltguard gene (Fw3) mapped to a 3.6 Mb on chromosome 1-4. The Fw2 gene was found to be equal in strength to the Fw1 gene, both of which confer immunity. The resistance conferred by the Fw3 gene, while statistically significant, was weaker than Fw1 and Fw2. Our results demonstrate evidence of novel resistance genes carried by the heirlooms Guardian and Wiltguard. We anticipate that the discovery of these two novel resistance genes loci will provide the necessary information for development of KASP assays. With the development of KASP assays the ability to pyramid Fusarium wilt resistance genes will be possible. The combination of multiple resistance genes into a single genetic background will result in improved Fusarium wilt resistance