1a. Objectives (from AD-416):
1) Identify virulence/pathogenicity genes in Pantoea agglomerans, a causal agent of South Carolina seed rot that affects cotton, and apply this knowledge to disease management strategies. Subobjective 1A: Sequence the complete genome of the opportunistic P. agglomerans strain that is vectored by the southern green stink bug (Nezara viridula L.) into bolls causing seed and boll rot. Subobjective 1B: Conduct a bioinformatics analysis (BA) of the generated sequence data to putatively identify virulence and pathogenicity genes. Subobjective 1C: Generate mutants of the sequenced strain that contain a disruption in a gene presumptively involved in the infection process and test for pathogenicity in developing green cotton bolls. 2) Determine if a fusaric acid transporter gene can be used to increase resistance to Fusarium oxysporum f. sp. vasinfectum (F.o.v.) in cotton and apply this knowledge to disease management. Subobjective 2A: Identify and clone transporter genes located near the fusaric acid biosynthetic gene cluster to identify the putative gene(s) responsible for the pathogen's resistance to fusaric acid. Subobjective 2B: Generate knock-out mutants of the cloned genes to confirm their role in resistance to fusaric acid toxicity. Subobjective 2C: Determine if the targeted gene for knock-out is involved in self-protection against fusaric acid and test the mutant for pathogenicity. Subobjective 2D: Identify and clone a microbial gene for an enzyme that converts fusaric acid in a single step to a non-toxic product. 3) Develop and deploy new sources of cotton resistance to both the reniform nematode and root rotting fungal pathogens. Subobjective 3A: Develop germplasm lines with high levels of resistance to the reniform nematode and desirable agronomic properties derived from G. barbadense (GB713) using DNA marker assisted selections (MAS). Subobjective 3B: Determine the role of fungal root pathogens in the stunting of LONREN germplasm lines in reniform-infested fields. Subobjective 3C: Develop LONREN germplasm lines that have high levels of resistance to reniform nematodes and to stunting associated with the Ren1 **lon gene under field conditions.
1b. Approach (from AD-416):
To develop technology to identify piercing-sucking pests that harbor pathogenetic bacteria that cause cotton boll rot, the complete genome of an opportunistic bacterium will be sequenced. Statistics and computer programs will be used to map and analyze potential pathogenicity genes from the genome sequence. Mutants of the sequenced strain that contain a disruption in the gene putatively involved in the infection process will be generated, and these mutants will be tested for pathogenicity. To combat new virulent strains of the fungal pathogen Fusarium oxysporum f. sp. vasinfectum, genes that protect the pathogen from its own phytotoxic metabolites will be identified and cloned. Gene knock out mutants will be generated and the mutants will be tested for resistance to the metabolites. New cotton germplasm exhibiting resistance to the reniform nematode will be developed from Gossypium barbadense accession GB713 using marker assisted selection. In addition, the role of fungal root pathogens in causing stunting of cotton plants expressing the Renlon gene from G. longicalyx will be determined using greenhouse assays. Based on these studies, plants resistant to the reniform nematode will be identified and released as germplasm.
3. Progress Report:
The Fusarium fungus produces many chemicals that help it survive in the environment and to act as a pathogen. In the case of the plant pathogen Fusarium oxysporum f. sp. vasinfectum (FOV) race 4 that threatens cotton production in the U.S., this pathogen produces high levels of a plant toxin called fusaric acid that causes severe necrosis on cotton foliage. Project work identified a soil-dwelling microorganism that degrades fusaric acid into a compound that is not toxic to plants, thus establishing that some soil microbes can degrade fusaric acid, which may be useful in developing control strategies for FOV race 4. Nematodes cause 4% yield loss to cotton production in the U.S.; project work in FY 2014 developed new cotton germplasm with superior agronomic traits that show strong resistance to nematodes that attack cotton. The annotated genomic sequence of a Pantoea sp. strain that causes cotton boll rot was established by project work in FY 2014; this is the first genome sequence of a bona fide Pantoea insect-vectored cotton pathogen.
1. Nematode resistant cotton germplasm. The root-knot and reniform nematodes destroy over 4% of the U.S. cotton crop annually. ARS researchers at College Station, Texas, working with cooperators at Texas A&M AgriLife Research, and Cotton Incorporated, developed eight new lines of cotton that have resistance to these nematodes. These lines also demonstrate superior agronomic performance and have been released to the public for use in commercial and institutional breeding programs. They are expected to increase cotton yields and quality by reducing damage caused by nematodes and by reducing diseases associated with nematodes.
Crutcher, F.K., Liu, J., Puckhaber, L.S., Stipanovic, R.D., Duke, S.E., Bell, A.A., Williams, H., Nichols, R. 2014. Conversion of fusaric acid to fusarinol by Aspergillus niger: A detoxification reaction. Journal of Chemical Ecology. 40:84-89.
Bell, A.A., Robinson, A.F., Quintana, J., Dighe, N.D., Menz, M.A., Stelly, D.M., Zheng, X., Jones, J.E., Overstreet, C., Burris, E., Cantrell, R.G., Nichols, R.L. 2014. Registration of LONREN-1 and LONREN-2 germplasm lines of Upland cotton resistant to reniform nematode. Journal of Plant Registrations. 8(2):187-190.
Akhunov, A., Golubenko, Z., Mustakimova, E., Abdurashidova, N., Pshenichnov, E., Vshivkov, S., Stipanovic, R.D. 2013. The effect of phytohormones on the dynamics of protein biosynthesis and enzyme activity in linted and naked cotton seed. Asian and Australasian Journal of Plant Science and Biotechnology. 7(Special Issue 2):48-52.
Cai, Y., Sun, Q., Li, S., Chen, M., He, Z., Jiang, H., Yuan, Y., Shi, Y., Liu, J. 2013. Identification of the genes and pathways associated with pigment gland morphogenesis in cotton by transcriptome profiling of near-isogenic lines. Biologia. 68(2):249-257.
Kumar, V., Joshi, S.G., Bell, A.A., Rathore, K.S. 2013. Enhanced resistance against Thielaviopsis basicola in transgenic cotton plants expressing Arabidopsis NPR1 gene. Transgenic Research. 22(2):359-368.