Survey, characterization, host specificity and evaluation of some control methods of Fusarium species associated with wilt disease on cucumber in Jordan

Introduction Cucumber Fusarium wilt is an important soil-borne disease that can substantially limit cucumber production. Despite its importance, the Fusarium populations associated with cucumber wilt in Jordan have not been comprehensively characterized at the species, pathogenic-group, host-range, and management levels. This study aimed to determine the occurrence and identity of Fusarium species associated with symptomatic cucumber plants, characterize pathogenic groups of Fusarium oxysporum associated with cucumber, evaluate their pathogenicity and host specificity, and compare selected disease-management strategies under Jordanian production conditions. Methods A total of 165 symptomatic cucumber plants were collected from major cucumber-producing regions of Jordan during 2024. Fusarium isolates were characterized morphologically, and representative retained isolates were subjected to RPB2-based molecular identification and phylogenetic analysis. F. oxysporum isolates were screened using pathogenic-group-specific PCR markers. Pathogenicity and host specificity were evaluated in three controlled-environment experiments using cucumber and selected cucurbit hosts. Representative symptomatic/dead plants were used for pathogen re-isolation to support the pathogenicity assessment. In addition, an on-farm greenhouse trial compared conventional tillage, deep tillage, grafting, soil fumigation, a grower-style fungicide program, and an untreated control in a randomized complete block design. Results Ninety-six Fusarium cultures were retained from symptomatic cucumber plants, and 50 isolates yielded usable RPB2 sequences. Among the sequenced isolates, F. oxysporum was predominant (46/50), whereas F. falciforme (2/50), F. incarnatum (1/50), and F. solani (1/50) occurred at low frequencies. Pathogenic-group PCR screening identified Groups 1, 3, and 4 among the tested F. oxysporum isolates, with Group 1 being the most frequent and consistently causing the greatest cucumber mortality in the pathogenicity experiments. The tested cucumber-associated isolates showed a restricted host response under the experimental conditions, with disease occurring primarily in cucumber and little or no mortality in the tested non-cucumber cucurbits. In the on-farm trial, treatment significantly affected all end-of-season variables. Soil fumigation with metam potassium and grafting onto Shintoza Prime rootstock produced the lowest cumulative mortality, whereas the untreated control and conventional tillage had the highest cumulative mortality. Conclusion Fusarium oxysporum was the predominant Fusarium species recovered among the sequenced isolates from symptomatic greenhouse cucumber plants in Jordan. The study identified pathogenic Groups 1, 3, and 4 among the tested F. oxysporum isolates and demonstrated differences in aggressiveness, with Group 1 producing the greatest cucumber mortality. The host-response experiments supported a strong association of the tested isolates with cucumber, while pathogen re-isolation from representative symptomatic/dead cucumber plants provided additional support for pathogenicity. Under the conditions of the on-farm trial, soil fumigation and grafting provided the strongest suppression of disease-associated mortality. These findings provide a basis for continued surveillance of cucumber-associated F. oxysporum populations and for developing integrated management programs under Jordanian greenhouse production conditions.