First report of Fusarium wilt of cotton caused by Fusarium oxysporum f. sp. vasinfectum race 4 in Texas, USA

Authors: HALPERN, HANNAH - University Of Georgia; Bell, Alois - Al; Wagner, Tanya; Liu, Jinggao; NICHOLS, ROBERT - Cotton, Inc; OLVEY, JAMES - O&a Enterprises; WOODWARD, JASON - Texas A&M University; SONOGO, SOUM - University Of Georgia; JONES, CHRISTINA - University Of Georgia; CHAN, CYNTHIA - University Of Georgia; BREWER, MARIN - University Of Georgia

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/19/2017
Publication Date: 11/28/2017
Citation: Halpern, H.C., Bell, A.A., Wagner, T.A., Liu, J., Nichols, R.L., Olvey, J., Woodward, J.E., Sonogo, S., Jones, C.A., Chan, C.T., Brewer, M.T. 2018. First report of Fusarium wilt of cotton caused by Fusarium oxysporum f. sp. vasinfectum race 4 in Texas, USA. Plant Disease. 102(2):446.
DOI: https://doi.org/10.1094/PDIS-07-17-1084-PDN

Interpretive Summary: Fusarium wilt of cotton is a widespread and economically important disease. The causal fungal pathogen FOV is genetically diverse with numerous described races and genotypes, most of which cause disease only in the presence of plant-pathogenic nematodes. However, FOV race 4, originally found in India, is extremely virulent and can cause severe, early-season damage in the absence of nematodes. FOV race 4 was first detected in California in 2001, and had not been confirmed elsewhere in the U.S.A. until recently. Recently, severe Fusarium wilt symptoms that were consistent with FOV race 4 were observed on seedlings of Pima cotton in the Upper Rio Grande Valley of Texas. To test for FOV race 4, Fov isolates were recovered from lower stem segments from symptomatic seedlings collected from three fields. DNA sequence analysis indicated that representatives of these isolates all had identical nucleotide sequence with that of FOV race 4 reference isolates. Additionally, a representative isolate from each of the three fields in Texas contained the Tfo1 insertion in the PHO gene that is considered diagnostic for virulent FOV race 4 isolates found in California. The majority of the isolates from the three fields were highly virulent on Pima S-7 and killed the plants in a soil infestation assay while a minority of them caused severe stunting greater than 80%. These results confirm that FOV race 4 is causing wilt in cotton fields in western Texas and is now present in the U.S.A. outside of California.

Technical Abstract: Fusarium wilt of cotton (Gossypium spp.), caused by the soilborne fungus Fusarium oxysporum f. sp. vasinfectum (FOV), is a widespread and economically important disease. FOV is genetically diverse with numerous described races and genotypes, most of which cause disease only in the presence of plant-pathogenic nematodes; however, FOV race 4 is extremely virulent and can cause severe, early-season damage in the absence of nematodes. Race 4 was first described in India and has likely spread to other cotton-producing regions through cotton seed. FOV race 4 was first detected in California in 2001, and had not been confirmed elsewhere in the U.S.A. until recently. In June of 2016 and 2017, severe Fusarium wilt symptoms, including wilting, root rot and stem discoloration, that were consistent with FOV race 4 were observed on seedlings of Pima cotton (Gossypium barbadense) in the Upper Rio Grande Valley of Texas in El Paso and Hudspeth Counties. To test for FOV race 4, lower stem segments from symptomatic seedlings collected from three fields (two in El Paso County and one in Hudspeth County) in June 2017 were surface-disinfected, placed onto acidified quarter-strength potato dextrose agar. Colony morphology of fungal isolates that emerged and grew was characteristic of Fusarium oxysporum. PCR was performed on eight isolates from the three fields (n = 3, 3, 2) using primers for the translation elongation factor (EF-1a) and intergenic spacer (IGS) regions, which together can be used to identify and distinguish described races and genotypes of FOV. All eight isolates from the three fields were identical in nucleotide sequence to FOV race 4 reference isolates ATCC 16613 and NRRL 25434 for EF-1a and IGS. Additionally, a representative isolate from each of the three fields in Texas contained the Tfo1 insertion in the PHO gene that is considered diagnostic for virulent FOV race 4 isolates found in California. Forty-four isolates from the three fields were tested for virulence on G. barbadense ‘Pima S-7’ using a soil infestation assay and found to be highly virulent with 33 of the isolates killing the seedlings and the other 11 causing severe stunting greater than 80%. These results confirm that FOV race 4 is causing wilt in cotton fields in western Texas and is now present in the U.S.A. outside of California.