Putative fungal effectors for the identification of aggressive isolates of Fusarium oxysporum from soybean.

Fungi within the Fusarium oxysporum species complex (FOSC), including F. commune can cause root rot, seedling blight, and wilt of soybean. Isolates recovered from soybean vary in aggressiveness and also the type of symptoms they produce. The first objective of this study was to screen isolates of F. oxysporum from soybean with previously described fungal effectors. The second objective was to determine each isolates ability to produce wilt symptoms on soybean. The goal of these objectives was to identify a genetic marker that might be useful in the detection of aggressive wilt isolates towards soybean. The fungal effectors Fmk1, Fow1, Pda1, PelA, PelD, Pep1, Prt1, Rho1, Sge1, Six1, Six6, and Snf1 were used to screen 80 isolates within the FOSC collected from soybean roots. Additionally, 27 isolates were screened with the fungal effector Six6 collected from other host, primarily from common bean. All PCR amplicons were sequenced, and phylogenies were inferred for each gene using a Bayesian analysis. The 107 isolates used in this study were tested in the greenhouse for their ability to produce wilt symptoms using susceptible cultivars Jack and/or MN1805. Fungal effectors Fmk1, Fow1, PelA, Rho1, Sge1, Six1, Six6, and Snf1 were present in all isolates screened and corresponded to isolate clade based on previous designation using the translation elongation factor (tef1α) and mitochodrial small subunit (mtSSU) genes. The fungal effector Pda1, PelD, Pep1, Prt1, Six1, and Six6 were dispersed among isolates. Vascular discoloration was observed in roots and/or stems of 42 isolates collected from soybean, common bean, or tomato. Nine of these isolates caused high levels of vascular wilt. Of the six fungal effectors dispersed among isolates, all isolates with the Six6 gene produced low to high levels vascular wilt in soybean. The results from this study suggest that the Six6 gene may be involved in some isolates ability to cause wilt in soybean.