Fusarium stem rot and decline caused by <i>Fusarium noneumartii</i> and <i>F. martii</i> : A widespread outbreak-associated disease in California processing tomatoes, distinguishable from <i>F. falciforme</i> -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 six-year survey, FSSC isolates were associated with outbreak-related symptoms in 187 fields across fourteen counties. Fusarium 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 (32-53 mm lesions, P < 0.001 vs. mock control). In comparative studies, F. noneumartii and F. martii isolates produced stem lesions (6-162 mm) in 92-100% of plants and canopy decline in 8-94% of plants (P < 0.05 vs. mock for 1-3 isolates/species); F. noneumartii was more virulent (P < 0.05 vs. F. martii) and uniquely caused plant death. F. falciforme did not cause vine decline; 1/6 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 (93-96% of plants; max 300 mm), resulting in damage of 7.5-26% 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 (FRD) be used for the disease caused by F. noneumartii and F. martii, driving outbreak-level losses in the California tomato industry.