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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 #432550

Research Project: Molecular and Genetic Approaches to Manage Cotton Diseases

Location: Insect Control and Cotton Disease Research

Project Number: 3091-22000-035-00-D
Project Type: In-House Appropriated

Start Date: Apr 9, 2017
End Date: Apr 8, 2022

Objective:
1) Utilize both genetic and biological approaches to identify genes involved in vector-borne microbial cotton boll infections. Sub-objective 1.A: Confirm the ability of the verde plant bug to transmit cotton seed and boll rot pathogens. Sub-objective 1.B: Sequence the complete genome of a representative opportunistic bacterial strain that is vectored by the verde plant bug into bolls causing seed and boll rot. Sub-objective 1.C: Conduct bioinformatics analyses of the generated sequence data to putatively identify virulence and pathogenicity genes. 2) Determine the transport efficiency of each of the Fov4 fusaric acid transporter isoforms and their stoichiometric combinations, as well as their membrane localization or co-localization, to identify an optimal transport system that can be used to increase resistance to Fov4 in cotton. Sub-objective 2.A: Tag one fusaric acid transporter isoform with GFP and the other with RFP and overexpress them in Fov individually or in combination, determine their membrane localizations, and test their role in fusaric acid resistance. Sub-objective 2.B: Overexpress the two forms of fusaric acid transporter individually or in combination in a biocontrol agent, Trichoderma virens, to test whether fusaric acid resistance can be transferred to another organism. Sub-objective 2.C: Test the transporter isoform(s) overexpressing in Fov for pathogenicity on cotton. Sub-objective 2.D: Test the transporter isoform(s) overexpressing in T. virens for enhanced biocontrol activity against root rotting Fov. 3) Identify genetic sources and molecular DNA markers for resistance to Fov4 in cotton by screening germplasm. Sub-objective 3.A: Determine the population structure of F. oxysporum isolates from cotton and identify those isolates best suited to a resistance breeding program directed at all F. oxysporum populations. Sub-objective 3.B: Develop reliable inoculation protocols and identify different sources of resistance to Fusarium wilt with and without root-knot nematode. Sub-objective 3.C: Determine the inheritance of resistance and association with specific DNA markers.

Approach:
Two emerging diseases, internal boll rots and Fusarium wilt caused by race 4, confront U.S. cotton producers. To address boll rots, we will identify genes for pathogenicity that are common to boll rotting pathogens with the long-term goal to develop a test kit to be used in the field that can determine if field insects harbor pathogens. To this end, we previously identified and sequenced the genome of bacterial pathogens transmitted by stink bugs and fleahoppers. In this study, we will confirm that the verde plant bug is a vector of boll rot pathogens, and identify and sequence the genome of a representative pathogen transmitted by this insect. In addition, a new strain of Fusarium oxysporum f. sp. vasinfectum (CA-Fov4) has been found for the first time in the western hemisphere in California fields from which cottonseed for planting originates. Spread of race 4 in the U.S. could be catastrophic. Race 4 is unique in that it produces prodigious quantities of fusaric acid, a plant toxin to which cotton is particularly sensitive. To address this problem, localization and efficiencies of transporter isoforms involved in secretion and detoxification of fusaric acid will be elucidated and their role in pathogenicity will be determined. The isoforms will be incorporated into a biocontrol agent to improve its biocontrol activity against Fov, because fusaric acid may enhance Fov’s ability to compete with other microbes in the soil. Sources of resistance to race 4 in cotton germplasm will be identified and incorporated into nematode-resistant germplasm; DNA markers will be identified to facilitate use of this germplasm.