Developing effective rotation strategies for Fusarium wilt management in California tomato based on systemic hosts,...

Fusarium wilt, caused by Fusarium oxysporum f. sp. lycopersici race 3 (Fol3), is an economically important disease of tomato in California. Rotation strategies can be effectively used for managing Fol3 if disease risk in rotational crops is known. In greenhouse studies, several common rotation crops were evaluated for stem colonization by Fol3, and soil propagule loads were assessed following burial of Fol3-infested crop residue in soil. Cryptic, systemic hosts for Fol3 included sunflower and wheat (similar to tomato; P > 0.050); others, including onion and corn, were not systemic hosts (P < 0.050). Burial of infested bean and cotton consistently resulted in non-detectable soil propagule levels, but most crops generated propagule levels similar to or lower than tomato. Soil propagule loads were 69 to 375% higher after burial of likely systemic hosts versus ambiguous or non-systemic hosts, with a negative linear relationship between soil CFUs and decomposition. In a microplot field study, Fol3 propagules had a half-life of 6.5 ± 0.5 months, with the greatest (97%) reduction from 6 to 9 months and non-detectable levels at 36 months. Similarly, in two-year field studies, tomato disease development was 2-fold higher after a 6-month fallow versus a 12-month fallow (P = 0.011). Whereas cotton, lima bean, and onion rotation resulted in low disease levels, broccoli, hairy vetch, lettuce, pepper, and sunflower rotation increased disease incidence by 37-177% versus fallow. This work was used to develop the first science-based rotation guidelines for Fusarium wilt management in tomato.