|Westphal, Andreas - PURDUE UNIV.|
|Xing, Li Juan - PURDUE UNIV.|
|Egel, Daniel - PURDUE UNIV.|
Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: May 31, 2008
Publication Date: July 26, 2008
Citation: Westphal, A., Xing, L., Goodwin, S.B., Egel, D.S. 2008. Mature watermelon vine decline is associated with Rhizopycnis vagum. Phytopathology. 98: S170 Technical Abstract: For almost 20 years, mature watermelon vine decline (MWVD) has put sustainable watermelon production at risk in southern Indiana. This late-season vine collapse appears to be specific to watermelon; other cucurbits seem unaffected. To test for a biological cause of MWVD, microplot trials were conducted with two problem soils and various fumigants. The greatest increases in plant growth were observed in plots treated with methyl bromide, the second largest in those with methyl iodide. A 1,3-dichloropropene-chloropicrin treatment had plant growth similar to the non-treated controls. Fungal isolations from root pieces collected from infected watermelon plants at harvest resulted frequently in Rhizopycnis vagum, confirmed by sequencing of the internal transcribed spacer (ITS) region of the ribosomal DNA. Specific PCR primers designed from the ITS sequence of R. vagum consistently amplified the R. vagum-specific ITS fragment from infected watermelon roots of plants that had symptoms of MWVD, but not from healthy plants grown in fumigated soil. Pathogenicity tests with R. vagum did not replicate MWVD symptoms. The known pathogenicity on cucurbits and the consistent association of R. vagum with diseased plants suggests that R. vagum plays a role but may not be the sole cause of MWVD. We hypothesize that additional factors are necessary to induce the vine decline.