Impacts of increasing soil salinity on genetic resistance (I-3 gene)-based management of Fusarium wilt (F. oxysporum f. sp. lycopercisi race 3) in California processing tomatoes

California is the primary processing tomato ( Solanum lycopersicum) producer in the United States. Fusarium oxysporum f. sp. lycopercisi race 3 (Fol3), the cause of Fusarium wilt, is a major driver of yield losses. Fol3 has recently been observed causing disease in resistant cultivars ( I-3 R-gene), often reported in association with high soil salinity. This study was undertaken to better understand the role of salinity in compromising resistance-based management of Fol3. Surveys established opportunity for salinity–Fol3–tomato interactions in 44% of commercial fields examined, with harmful soil salt levels up to 3.6 dS/m ( P < 0.001), high sodium ( P < 0.001), and high sodicity (sodium adsorption ratio > 13; P < 0.001). In controlled field studies of Fol3 in NaCl/CaCl 2 -treated soil, Fol3-resistant cultivars either only developed wilt under salt or only developed wilt above the industry non-hybrid threshold (2%) under salt across two trial years. The absence of yield differences indicates low to no economic impact of disease enhancement ( P > 0.05). NaCl, CaCl 2 , and Na 2 SO 4 had no effect on Fol3 propagule production in liquid agar versus water agar controls ( P > 0.05), although CaCl 2 increased propagule loads sevenfold versus ionic controls (polyethylene glycol) ( P = 0.036). NaCl/CaCl 2 (2:1) reduced propagule loads up to 65% versus no salt ( P = 0.029) in soil with pathogen-infested tomato tissue. These results together establish the opportunity for salinity–Fol3–tomato interactions and potential for salt to influence the efficacy of resistant cultivar-based management—this does not appear to be primarily due to salt enhancement of pathogen populations, pointing to a yet-unexplored direct influence of salt on host resistance.