Pathogenicity of seedborne Fusarium oxysporum of watermelon and effect of its crude toxin on seed germination.

The pathogenicity of Fusarium oxysporum isolated from the seed coat of watermelon seeds(cv.Jingxin No.1) was studied using radicle-dipping and root-dipping inoculation method.Morphological observation and molecular detection of isolates from diseased watermelon seedlings and the corresponding Fusarium used for inoculatation were carried out.The results showed that morphological characters including colony morphology and growth rate between the isolates and the corresponding Fusarium were approximately identical.Nucleotide sequences of PCR products of rDNA of the isolates and the corresponding Fusarium amplified by the same primers were exactly same.This showed that the isolates from diseased seedlings and the Fusarium used for inoculatation were the same.Thus,the Fusarium oxysporum isolated from the seed coat of watermelon seeds(cv.Jingxin No.1) is pathogenic.This is the first report that the seedborne Fusarium oxysporum can be pathogenic to watermelon.The effects of culture filtrate and crude toxin of this fungus on watermelon seed germination were also conducted.The germination energy,percentage germination and germination index of watermelon seeds decreased significantly after treatment with culture filtrate and crude toxin of the seedborne Fusarium oxysporum.The germination energy,percentage germination and germination index reduced by 16.7%-29.0%,14.4%-22.3%,19.1%-37.1%,respectively.The results indicated that culture filtrate and crude toxin of this fungus could affect the seed germination.