Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2001
Publication Date: N/A
Interpretive Summary: The results of this research show that seedling disease of cotton begins when chemicals released by the germinating seeds stimulate disease-causing fungi to germinate and attack the plant. Disease can be prevented by treating the seed with another fungus that breaks down the chemical stimulants before they turn on the disease-causing fungi. The results also show that resistance to disease that is shown by different cotton varieties is related to their ability to prevent the release of chemicals during germination that stimulate disease-causing fungi to attack. This work should help cotton producers choose the best varieties to grow for disease prevention and the most effective seed treatments for varieties that are susceptible to disease.
Technical Abstract: Planting the cotton cultivar SureGrow 747 in cotton seedling disease plots during the 2001 growing season resulted in high levels of pre-emergence damping-off among the seedlings. Four cotton pathogens, Pythium aphanidermatum, Pythium ultimum, an unidentified Pythium sp., and Rhizopus oryzae were isolated from diseased seeds and seedlings. Disease incited by the Pythium spp. could be controlled by seed treatment with Metalaxyl, but disease incited by R. oryzae could not. Since seed treatment with Metalaxyl in naturally infested field soil was only partially effective, symptoms in 47% of the seedlings could be attributed to R. oryzae. Susceptibility to disease appeared to be related to release in the spermosphere, by the germinating seeds, of compounds that stimulate pathogen propagule germination, because exudates from seed of the suspect Sure-Grow 747 and extracts from wheat bran induced pathogen germination and growth, while exudates from the resistant cultivar Stoneville 213 did not. However, even Stoneville 213 became susceptible when infested soil was amended with wheat bran. Seed treatment with preparations of Trichoderma virens parent, mutant, and hybrid strains gave effective biocontrol of pre-emergence damping-off. Disease control was attributable to metabolism by the biocontrol agent of pathogen germination stimulants released by the seed, because amendment of pathogen infested soil with the propagule germination stimulant in wheat bran negated the protective effect of seed treatment.