Genetic diversity and pathogenicity of Verticillium dahliae isolates and their co-occurrence with Fusarium oxysporum f. sp. vasinfectum causing cotton wilt in Xinjiang, China

Authors: WAGNER, TANYA A - Texas A&M University; GU, AIXING - Xinjiang Agricultural University; Duke, Sara; Bell, Alois - Al; MAGILL, CLINT - Texas A&M University; Liu, Jinggao

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/13/2020
Publication Date: 3/12/2021
Citation: Wagner, T., Gu, A., Duke, S.E., Bell, A.A., Magill, C., Liu, J. 2021. Genetic diversity and pathogenicity of Verticillium dahliae isolates and their co-occurrence with Fusarium oxysporum f. sp. vasinfectum causing cotton wilt in Xinjiang, China. Plant Disease. 105:978-985. https://doi.org/10.1094/PDIS-09-20-2038-RE.
DOI: https://doi.org/10.1094/PDIS-09-20-2038-RE

Interpretive Summary: A wilt disease caused by the fungus, Verticillium dahliae, is a serious disease of cotton in cooler producing areas of the world. This fungal pathogen has been categorized into several groups and subgroups based on the severity of disease and associated symptoms they cause in cotton. Thus, effective management of this disease requires accurate identification of the groups and subgroups on a field by field basis. We used a variety of molecular tools to differentiate these groups/subgroups based on their genetic makeup. These tools were then used to determine the composition of pathogen groups/subgroups of wilted cotton plants collected from eight counties in Xinjiang, China, the largest cotton producing area in China. Two main groups of the pathogen were identified - one that causes severe defoliation and the other that causes no appreciable defoliation. Overall, 42% of the plants obtained from Xinjiang were infected with the defoliating type, but the percentages varied widely among counties and some plants were attacked by both types. Additionally, 22% of the plants were infected with a Fusarium pathogen that also causes wilting of plants, suggesting both Verticillium and Fusarium wilt pathogens should be considered when developing wilt resistant/tolerant plants for use in areas where both pathogens are prevalent.

Technical Abstract: Cotton production in Xinjiang, the largest cotton producing area in China, has an increasingly serious disease threat from Verticillium dahliae. Eighty-five V. dahliae isolates were obtained from wilted cotton plants collected from 8 counties in Xinjiang. The isolates were assessed for genotypic diversity by DNA sequence analysis and PCR molecular genotyping with specific markers for race 1, race 2, defoliating (D) pathotype, non-defoliating (ND) pathotype, and mating type idiomorph Mat1-2. Isolates belonged to lineages 1A or 2B with 3 sub-genotypes found in each lineage. All isolates tested positive for race 2 and Mat1-2 markers. All isolates in lineage 2B tested positive for the ND pathotype marker, but only isolates in the major sub-genotype in lineage 1A tested positive for the D pathotype marker. Pathogenicity assays on Gossypium hirsutum ‘Acala 44’ demonstrated no significant difference among sub-genotypes within each lineage. Isolates in lineage 1A caused greater shoot weight reductions, % leaf drop, and % diseased leaves than isolates in lineage 2B. One isolate in each lineage for 1A and 2B was avirulent. Isolates in lineage 1A caused greater than 50% leaf drop and a 17 gram shoot weight reduction compared to a 9% leaf drop and a 6 gram shoot weight reduction by isolates in lineage 2B. Overall, 42% of the V. dahliae isolates from Xinjiang were D pathotype, but the percentage varied widely among locations. Two plants had both pathotypes. Nineteen isolates of Fusarium oxysporum f. sp. vasinfectum VCG0114 also were recovered from wilted plants in Xinjiang. Two plants had both Verticillium and Fusarium wilt pathogens. Both pathogens should be considered when using or developing wilt resistant/tolerant materials for Xinjiang.