Studies On The Field Control Of Watermelon Fusarium Wilt Disease And Pathogenicity Of Fusarium Oxysporum F. Sp. Niveum

Watermelon Fusarium wilt disease as one of the most serious hazards is a threat to the further development of the watermelon industry. The disease is caused by Fusarium oxysporum f.sp. niveum, which has four recognized physiological species, namely physiological race0,1,2and3. The control of watermelon wilt disease mainly rely on the use of resistant varieties, grafting and chemical control. However, variety with high level of resistance to F. oxysporum f.sp. niveum is not avavilable in practice. Grafted watermelon has been shown to be an efficient mean to control of watermelon wilt disease, but it will affect the quality. Chemical control is still the most important way to control watermelon wilt disease. In this study, we performed field trails to exanmine the effect of two inducers A101and A102on control of watermelon and melon wilt diseases, yield and fruit quality, by using50%carbendazim flutter and50%iprodione as control agents and water treatment as CK. Field test results show that the inducers A101and A102not only more efficient to control watermelon and melon Fusarium Wilt diseases than the control agents, but also significantly improve the yield and fruit quality of watermelon and melon.Through Agrobacterium-mediated transformation, we have gained2800T-DNA insertion mutants of F. oxysporum f.sp. niveum race1. Pathogenicity test of transformants eventually found three transformants whose pathogenicity on watermelon decline significantly. TAIL-PCR amplified the flanking sequence in the T-DNA mutants and identified that the genes that were disrupted in the T-DNA insertionmutants were medl2, btf3a and ChsV. Medl2is one member of the Mediator complex family, which is composed by25-30subunits. To explore the functions of these genes in pathogenicity of F. oxysporum f.sp. nievum, we genertated knockout and complementary mutants for each candidate gene and assayed theiro pathogenicity on watermelon Experimental results showed that:(1) knockout of FoCdk8, Fomedl9and Fomed10gene resulted in lost of pathogenicity of F. oxysporum f.sp. nievum, whereas knockout of FoCycc gene led to reduced virulence on watermelon;(2) the Fomedl9, Fomed10, FoCycc nockout mutants affected vegetable growth, and FoCycc or FoCdk8knockout mutants produced a black pigment when cultured in PDA;(3) The sporulation and spore germination rate of FoCdk8, Fomedl9, FomedlO or FoCycc knockout mutants significantly decreased;(4) scanning electron microscopy observation found that Fomed19and FoCycc knockout mutants had the same invasion capacity with wild-type strain;(5) gene expression analysis showed that FoCycc and FoCdk8may have functions in regulating expression of other pathogenicity genes; and (6) The sporulation, germination and mycelial growth of FoCdk8, Fomedl9, FomedlO and FoCycc complementary mutants recovered all phenotype including pathogenicity, mycelial growth, sporulationa dn spore germination to wild-type. These results indicate that FoCdk8, Fomedl9, Fomed10and FoCycc have important functions in regulating spore formation, gemination, mycelial growth and pathogenicity of F. oxysporum f.sp. nievum.