Growth inhibitory effects of gossypol and related compounds on fungal cotton root pathogens

Authors: Mellon, Jay; Dowd, Michael; Beltz, Shannon; Moore, Geromy

Submitted to: Letters in Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/25/2014
Publication Date: 4/29/2014
Citation: Mellon, J.E., Dowd, M.K., Beltz, S.B., Moore, G.G. 2014. Growth inhibitory effects of gossypol and related compounds on fungal cotton root pathogens. Letters in Applied Microbiology. 59:161-168.

Interpretive Summary: Soil fungal pathogens can induce crop production problems for cotton and maize due to endemic soil populations that are difficult to eliminate. Cotton plants contain high levels of gossypol that provide protection against insect predation and possibly additional defense functions. Gossypolone is an oxidative derivative of gossypol formed in animal systems (e.g. liver detoxification); apogossypolone is another oxidative derivative of gossypol. The root tissues of cotton also contain increased levels of methylated derivatives of gossypol that are naturally formed compounds. In order to investigate the possibility that these methylated gossypol derivatives improve host resistance qualities, growth inhibitory effects were determined against a collection of pathogenic soil fungi. Gossypol, gossypolone, and apogossypolone were effective fungal growth inhibitors at higher concentrations, while gossypol was more potent at lower concentrations. Compared to gossypol, methylated gossypol derivatives yielded reduced growth inhibition activity against this collection of soil fungal pathogens. This research will benefit cotton breeders, producers and pathologists.

Technical Abstract: The aim of this study was to investigate the effects of terpenoids gossypol, gossypolone, apogossypolone, methoxygossypol and dimethoxygossypol on growth of a collection of fungal soil pathogens. The compounds were tested at a concentration of 100 µg ml-1 in a Czapek Dox agar medium at 25°C. Gossypol, gossypolone and apogossypolone demonstrated strong growth inhibitory activity (= 90%) against Pythium irregulare, P. ultimum and Fusarium oxysporum. These same terpenoids provided good growth inhibition against Rhizoctonia solani isolates. Methylated gossypol derivatives yielded reduced growth inhibition against the tested fungi compared to gossypol. Dose response effects of gossypol, gossypolone and apogossypolone were determined for a concentration range of 5 to 100 µg ml-1 against P. irregulare, P. ultimum and R. solani. Gossypol proved to be a more potent growth inhibitor of P. irregulare (ED50 = 7 µg ml-1) and P. ultimum (ED50 = 16 µg ml-1) than the other tested terpenoids. R. solani was more resistant to growth inhibitory effects of all tested terpenoids. Gossypol, gossypolone and apogossypolone were effective growth inhibitors against most isolates of the tested collection of soil fungi at the higher concentration utilized (100 µg ml-1). Methylated gossypol compounds demonstrated reduced growth inhibitory activity against these same fungi. Gossypol is an effective general purpose antimicrobial agent against a wide range of potential fungal pathogens of cotton. Methoxygossypol and dimethoxygossypol, although present in cotton root tissues in elevated levels, apparently do not provide improved resistance for the host plant against the tested fungi.