Fusarium Stem Rot and Decline Caused by Fusarium noneumartii and F . martii : A Widespread Outbreak-Associated Disease in California Processing Tomatoes, Distinguishable from F . falciforme -Driven Foot Rot

A recent stem rot and canopy decline outbreak associated with the Fusarium solani species complex (FSSC) is causing major losses in California processing tomatoes. In a 6-year survey, FSSC isolates were associated with outbreak-related symptoms in 187 fields across 14 counties. F. noneumartii was the most prevalent species (63% of fields), followed by F. martii (38%) and F. falciforme (16%). As F. martii lacked precedence as a tomato pathogen, greenhouse studies confirmed stem rot abilities (32 to 53 mm lesions, P < 0.001 vs. mock control). In comparative studies, F. noneumartii and F. martii isolates produced stem lesions (6 to 162 mm) in 92 to 100% of plants and canopy decline in 8 to 94% of plants (P < 0.05 vs. mock for 1 to 3 isolates per species); F. noneumartii was more virulent (P < 0.05 vs. F. martii) and uniquely caused plant death. F. falciforme did not cause vine decline; 1 of 6 isolates caused small stem lesions (6 mm) in more plants than the mock (50% of plants; P < 0.05). Full-season field studies corroborated abilities for F. noneumartii to cause outbreak-related canopy collapse (up to 45% of plants) and stem lesions (93 to 96% of plants; max 300 mm), resulting in damage of 7.5 to 26% of fruit across two cultivars. We propose that the name Fusarium foot rot be used for the minor F. falciforme-driven disease and the new name Fusarium stem rot and decline be used for the disease caused by F. noneumartii and F. martii, driving outbreak-level losses in the California tomato industry.