Effect of growth stage, cultivar, and root wounding on disease development in cotton caused by Fusarium wilt race 4 (Fusarium oxysporum f. sp. vasinfectum)

Authors: ZHU, YI - New Mexico State University; ELKINS-ARCE, HEATHER - Texas A&M University; WHEELER, TERRY - Texas A&M University; DEVER, JANE - Texas A&M University; Whitelock, Derek; HAKE, KATER - Cotton, Inc; WADEGAERTNER, TOM - Cotton, Inc; ZHANG, JINFA - New Mexico State University

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/17/2022
Publication Date: 1/20/2023
Citation: Zhu, Y., Elkins-Arce, H., Wheeler, T., Dever, J., Whitelock, D.P., Hake, K., Wadegaertner, T., Zhang, J. 2023. Effect of growth stage, cultivar, and root wounding on disease development in cotton caused by Fusarium wilt race 4 (Fusarium oxysporum f. sp. vasinfectum). Crop Science. 63:101-114. https://doi.org/10.1002/csc2.20839.
DOI: https://doi.org/10.1002/csc2.20839

Interpretive Summary: Fusarium wilt caused by the soil-borne fungus FOV4 is an early season disease, causing seedling wilt and death immediately after emergence under field conditions. It has been shown during testing that the highest seedling mortality occurs during early growth stages when seedlings were inoculated with FOV4 in temperature-controlled growth chambers. However, it was unknown whether cotton plants artificially infected with FOV4 at different growth stages differed in their responses to the infections. In this study, under temperature-controlled conditions, cotton plants inoculated with FOV4 at different growth stages showed progressive reduction in disease and mortality. The results indicated that the cotyledon stage when leaves first appear from the seed is the most sensitive to FOV4 infections and infection resistance increased with the plant age. Also, the study showed that, regardless of resistance levels of the cotton cultivars, root wounding followed by artificial infection at the cotyledon stage made all tested cotton cultivars highly susceptible to infection. This suggests that current Upland and Pima cotton cultivars do not have resistance provided other than that by the root and that root wounding should be avoided for research on cotton resistance to FOV4, unless resistance mechanisms that do not rely on root protection are sought. Further, results suggested that the use of only pre-infested soil with high FOV4 spore counts is adequate for testing and supplementing with FOV4 inoculation may overwhelm resistance of cultivars to FOV4 and contribute to conflicting results. These results will help direct future studies of the FOV4 disease that aim to reduce its impact on the cotton industry in the Western U.S.

Technical Abstract: Fusarium wilt caused by soil-borne fungus Fusarium oxysporum f. sp. Vasinfectum race 4 (FOV4) is an early season disease causing root rot, and seedling wilt and death. However, it was unknown if cotton (Gossypium spp.) growth stages and root wounding affected genotypic responses to FOV4. The objectives of this study were to investigate the effects of cotton growth stage, cultivar, and root wounding on FOV4-associated disease development at 7-, 14-, 21-, and 28-d post inoculation through five replicated tests in controlled environmental conditions with temperatures at 21 to 23 °C. Seedlings inoculated at the cotyledon stage incurred the highest disease incidence (DI), disease severity rating (DSR), and mortality (MR), followed by seedlings inoculated at the 1-, 3-, and 5-true leaf stages in descending order. Root wounding at the cotyledon stage followed by immediate inoculation with FOV4 inoculum made all the tested cultivars and lines highly sceptible. Among the six cultivars tested, FM 2334GLT and Pima DP 359 RF were the most resistant, Pima S-7 was highly susceptible, and Acala 1517-08, Acala 1517–18 GLS, and Pima PHY 881 RF were susceptible. The importance of artificial inoculation at a true leaf stage with or without rootwounding to identify resistance that may be undetected under field conditions was discussed.