Response of Wild Cucumis Species to Inoculation with Fusarium oxysporum f. sp. melonis Race 1,2y

Abstract

Fusarium wilt of melon (Cucumis melo L.), caused by Fusarium oxysporum f. sp. melonis, is regarded as a severe disease worldwide. Many resources that are resistant to races 0, 1, and 2 have been reported; nevertheless, no resource of high resistance to either race 1,2w or 1,2y has been reported, although partial resistance has been found. Wild Cucumis species have been reported as genetic resources which have resistance to some diseases and pests of melon. This study identified novel sources of high resistance to race 1,2y in wild Cucumis species. In all, we tested 76 accessions belonging to 11 wild species of the genus Cucumis. After artificial inoculation, the disease severity in each plant was evaluated using a 0–3 disease severity scale (0 = no symptoms, 1 = beginning of yellowing symptom on leaves, 2 = leaves strongly affected, 3 = plant death). The disease index (DI) was calculated as DI = summation of (disease severity × number of plants in that disease severity) × 100/(3 × total number of plants). Accessions showing high resistance (DI = 0) were 34 among six species: C. africanus, C. anguria, C. metuliferus, C. prophetarum, C. subsericeus, and C. zeyheri. By contrast, most accessions in C. dipsaceus, C. meeusei, C. pustulatus, and C. sagittatus exhibited high susceptibility (DI = 80–100). Among these four species, no accession showed high resistance. This is the first report of genetic resources having high resistance to race 1,2y. To introduce this high resistance of race 1,2y to melon, we should investigate methods to overcome reproductive barriers to interspecific crosses between melon and wild Cucumis species.