Effector gene suites in some soil isolates of Fusarium oxysporum are not sufficient predictors of vascular wilt in tomato

Authors: JELINSKI, NICOLAS - University Of Minnesota; Broz, Karen; JONKERS, WILFRIED - University Of California; MA, LI-JUN - University Of Massachusetts; Kistler, Harold

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/13/2017
Publication Date: 7/1/2017
Citation: Jelinski, N.A., Broz, K.L., Jonkers, W., Ma, L., Kistler, H.C. 2017. Effector gene suites in some soil isolates of Fusarium oxysporum are not sufficient predictors of vascular wilt in tomato. Phytopathology. 107:842-851.

Interpretive Summary: Fusarium oxysporum is a fungus responsible for billions of dollars in economic losses to agricultural plants. We have conducted research aimed at understanding how genes in this alternately parasitic and free-living fungus are maintained and transmitted especially if they influence the ability of the fungus to cause disease. Using a genomics approach, we identified genes in the tomato wilt fungus that allow for disease causing ability and tracked these genes among free-living strains in the soil. Surprisingly, although the soil strains could maintain several pathogenicity genes, these alone were not enough to assure pathogenicity to tomato Factors which alter disease causing ability away from the plant potentially could be exploited for disease control measures. These disease management strategies may involve disruption of vital fungal developmental pathways. The primary users of the research in this publication will be other scientists engaged in research to improve disease management on crop plants.

Technical Abstract: This is the first study examining the distribution of fungal effector genes among soil populations of Fusarium oxysporum in a tomato field undergoing a wilt disease epidemic. 74 F. oxysporum soil isolates were assayed for known effector genes present in a Race 3 tomato wilt strain (FOL MN-25) obtained from the same field in Manatee County, Florida. Based on the presence or absence of these genes, four haplotypes were defined, two of which represented 95% of the surveyed isolates. These two most common effector haplotypes contained either all or none of the assayed Race 3 effector genes. We hypothesized that isolates with all effector genes, like FOL MN-25, would be pathogenic toward tomato whereas isolates lacking all effectors would be non-pathogenic. However, inoculation experiments using a subset of these isolates revealed that presence of the effector genes alone was not sufficient to ensure pathogenicity on tomato. Interestingly, a non-pathogenic isolate containing the full suite of effector genes (FOS4-4) appears to have undergone a chromosomal rearrangement yet remains vegetatively compatible with FOL MN-25 and contains no DNA sequence differences in the effector genes. The presence of effector genes toward tomato is therefore not an accurate predictor of pathogenicity among soil isolates of F. oxysporum.