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ARS Home » Plains Area » College Station, Texas » Southern Plains Agricultural Research Center » Insect Control and Cotton Disease Research » Research » Research Project #436189

Research Project: Fusarium Wilt of Cotton: Pathogen Population Characterization, Virulence/ Resistance Mechanism Determination & Marker Assisted Resistance Breeding

Location: Insect Control and Cotton Disease Research

Project Number: 3091-22000-035-59-R
Project Type: Reimbursable Cooperative Agreement

Start Date: Jan 1, 2019
End Date: Dec 31, 2019

Objective:
1.Characterize genetic variation, virulence, and nematode interactions of F. oxysporum isolates. 2. Advance and evaluate tolerance to FOV4 from ‘Pima S-2’, ‘Pima S-4’, ‘Pima S-6’, ‘Sakel’, ‘Seabrook Sea Island 12B-2’, and Gossypium arboreum accession #190 into BAR 32 lines that are homozygous for Ren2,3 and Mi1,2 and are highly resistant to both root-knot and reniform nematodes. Identify markers associated with resistance. 3. Identify FOV4 virulence genes affected by transposon ‘Tfo1’ and other mutator-like elements, and confirm the virulence role of the identified gene by gene knock-outs subsequent pathogenicity assays with knock-outs. 4. Determine the importance of fusaric acid in virulence and competition with antagonists using pathogenicity assays of various knock-out mutants in root rot pathotype isolates of Fov race 4 and Australian biotype.

Approach:
1) Characterize the genetic variation, virulence, and nematode interactions of FOV isolates from the Mid-South (AL, AR, LA, MS). 2) Characterize the genetic variation, virulence, and nematode interactions of FOV isolates belonging to the root rot pathotype (VCG 0113, 0114, and 01111). 3) Pima S-2, Pima S-4, Pima S-6, Sakel, Seabrok Sea island 12B2, Gossypium arboreum Acc. No. 190 will be backcrossed twice into BAR 32 lines to introgress resistance genes. The progenies will be selfed and selected for homozygous resistant and susceptible S1 plants. BAR 32 lines are homozygous for Ren2,3 and Mi1,2 and are highly resistant to both root-knot and reniform nematodes. Lines resistant to both the root rot and vascular competent FOV pathotypes as well as the nematodes will be identified, developed and released. 4) Genetic markers associated with resistance will be identified and mapped using DNA from susceptible and resistant backcross lines. Emphasis will be placed on SSR markers already reported to be associated with resistance to race 3 (VCG 0113) or race 4 (VCG 0114) in the literature. 5) Transposon Tfo1 and mutator like elements are highly active in the genome of FOV4 and may be responsible for virulence variation among isolates. The genes affected by these elements will be identified by virulence profiles of the isolates, and the virulence role of the identified genes will be confirmed by gene knock-out approaches and pathogenicity assays. 6) Use various knock-out mutants to determine the importance of fusaric acid in virulence and competition with potential antagonists. Four knock-out mutations that stop fusaric acid synthesis have been obtained in root rot pathotype isolates Fov 1089 (VCG 01111) or CA-9 (VCG 0114). These mutants will be compared with their parent for ability to cause Fusarium wilt of ‘Pima S-7’ cotton in pasteurized soil and in soils infested with the biocontrol organisms Trichoderma virens, Bacillus subtilis or Bacillus pumilis, which are sensitive to fusaric acid and not effective against the root rot pathotype. The results should clarify whether genetic modification of cotton or biocontrol organisms to increase fusaric acid tolerance has potential for controlling F. oxysporum isolates in the root rot pathotype.