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Inhibition of the germination and growth of Phymatotrichopsis omnivora (cotton root rot) by oilseed meals and isothiocyanates

Hu, P., Wang, A.S., Engledow, A.S., Hollister, E.B., Rothlisberger, K.L., Matocha, J.E., Zuberer, D.A., Provin, T.L., Hons, F.M., Gentry, T.J.
Applied soil ecology 2011 v.49 pp. 68-75
cotton, crop production, germination, clay soils, isothiocyanates, seeds, Phymatotrichopsis omnivora, Jatropha, mustard meal, plant pathogens, soil microorganisms, oilseed crops, coproducts, root rot, application rate, flax, fungi
The meals (co-products remaining after oil extraction) from many oilseed crops contain biocidal chemicals that are known to inhibit the growth and activity of some soil microorganisms including several plant pathogens. The fungus Phymatotrichopsis omnivora (Duggar) Hennebert is the causal agent of cotton root rot that has greatly hindered the production of cotton and alfalfa in Texas and the southwestern USA. We investigated the effect of oilseed meals from both brassicaceous plants including mustard and camelina as well as non-brassicaceous plants including jatropha, flax, and Chinese tallow on P. omnivora sclerotial germination and hyphal growth in Branyon clay soil, as well as the effects of 4 types of individual isothiocyanates (ITCs) including allyl, butyl, phenyl, and benzyl ITC on P. omnivora growth on potato dextrose agar (PDA). The oilseed meals were added to the soil at rates of 0%, 1%, and 5% (w/w). The results showed that all tested brassicaceous and jatropha seed meals were able to inhibit P. omnivora sclerotial germination and hyphal growth at 5% and 1% application rates respectively, with mustard seed meal being the most effective. Neither flax nor Chinese tallow showed any inhibitory effects on sclerotial germination. All tested ITCs inhibited P. omnivora OKAlf8 hyphal growth, although the level of inhibition varied with concentration. The IC₅₀ values were 0.62±0.19, 4.47±0.08, 5.67±0.10, and 20.48±0.30μgcm⁻³ for allyl, butyl, phenyl, and benzyl ITC respectively. These results indicate that press meals of several brassicaceous species as well as jatropha may have potential for reducing cotton root rot.