Interaction of Fusarium wilt race 4 with root-knot nematode increases disease severity in cotton

Authors: WAGNER, TANYA - Texas A&M University; DAVIE, SHAYLA - Former ARS Employee; MCGILL, CLINT - Texas A&M University; Liu, Jinggao

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/10/2022
Publication Date: 3/14/2022
Citation: Wagner, T.A., Davie, S.S., Mcgill, C., Liu, J. 2022. Interaction of Fusarium wilt race 4 with root-knot nematode increases disease severity in cotton. Plant Disease. https://10.1094/pdis-12-21-2725-sc.
DOI: https://doi.org/10.1094/pdis-12-21-2725-sc

Interpretive Summary: Fusarium wilt, caused by the fungal pathogen Fusarium oxysporum f. sp. vasinfectum (Fov), is a serious threat to U.S. cotton production. Unlike other races or strains of Fov such as race 1 (Fov1), race 4 (Fov4) does not require the presence of parasitic roundworms (nematodes) to cause disease of plants; however, the interaction between nematodes and the potential of Fov4 to cause disease remains unclear. In growth chamber tests, we demonstrated Fov4 is not only capable of causing disease without nematodes, but also can interact with nematodes to significantly increase disease severity. Because the presence of nematodes is not required for Fov4 to cause disease in cotton, efforts to control Fov4 have mainly focused on breeding plants resistant to the pathogen only. Our results suggest that it may be beneficial or necessary to also incorporate resistance mechanisms for nematodes in cotton to control and reduce the spread of Fov4, particularly in fields infested with nematodes.

Technical Abstract: Fusarium wilt, caused by Fusarium oxysporum f. sp. vasinfectum, is a serious disease of cotton (Gossypium spp.). Most of the US strains of the wilt pathogen such as race 1 require the presence of nematodes such as Meloidogyne incognita to cause appreciable disease. A race 4 strain of the wilt pathogen capable of attacking cotton without nematodes was first identified in California in 2001, and recently in Texas and New Mexico since 2017. The effects of interaction of M. incognita with race 1 or race 4 on wilt severity and nematode reproduction on two G. hirsutum cultivars Acala 44 and FM 966 and a G. barbadense cultivar Pima S-4 were elucidated in growth chamber assays. All three cultivars were susceptible to M. incognita. Suppression of nematode reproduction by the wilt pathogen was detected only for race 4 on FM 966. The control, M. incognita alone, and race 1 alone treatments caused no disease. Inoculation with race 1 and M. incognita caused moderate disease severity in Acala 44 and FM 966 and mild wilt in Pima S-4. However, race 4 alone treatment caused severe disease in Pima S-4 and moderate disease severity in Acala 44 and FM 966. The disease severity further increased in the presence of M. incognita. Thus, race 4 is not only capable of attacking cotton without nematodes, but also can interact with nematode to further aggravate disease severity. Though control of wilt caused by race 1 can be achieved mainly through breeding for nematode resistance, it will be imperative to incorporate both nematode and race 4 resistance to effectively control the disease should race 4 expand into the nematode infested fields.