Molecular Identification and Pathogenicity of Novel Tomato Root Rot Fungi, With Insights Into Cultivar Resistance in Saudi Arabia

Tomato (Solanum lycopersicum L.) is a major horticultural crop worldwide but remains highly vulnerable to soil-borne fungal pathogens that threaten greenhouse production. Increasing incidences of root rot and wilt have been observed in tomato nurseries and greenhouses in the Qassim and Riyadh regions of Saudi Arabia. This study aimed to identify the causal fungal agents and assess cultivar resistance under controlled conditions. Symptomatic root samples were collected, and pathogens were isolated, morphologically characterized, and confirmed through internal transcribed spacer (ITS) sequencing. Pathogenicity tests verified Fusarium oxysporum, Fusarium foetens, Ectophoma multirostrata, and Pygmaeomyces thomasii as causal agents of tomato root rot and wilt. Notably, E. multirostrata and P. thomasii were recorded for the first time as tomato root pathogens in Saudi Arabia. Four commercial tomato cultivars (Ace 55 VF, Marmande, Rio Grande, and Red Cherry) were evaluated for resistance. Disease incidence, severity, and growth parameters revealed significant variability among cultivars, with 'Red Cherry' and 'Rio Grande' showing enhanced resistance compared to more susceptible varieties. These results emphasize the novelty of detecting two previously unreported pathogens in Saudi Arabia and demonstrate the practical relevance of identifying resistant cultivars for field application. Overall, the study provides valuable insights supporting sustainable tomato production and offers a foundation for future resistance-breeding strategies.