Location: Crop Genetics Research2012 Annual Report
1a. Objectives (from AD-416):
Evaluate tetraploid cotton germplasm for host plant resistance to reniform nematode. Begin introgression of genes for host plant resistance to reniform nematode into tetraploid upland cotton from candidate diploid A-genome germplasm. Evaluate the impact of biotic and abiotic crop production factors on reniform nematode populations in Mississippi. Assess the efficacy of cultural and chemical management options to minimize losses to reniform nematode in Mississippi.
1b. Approach (from AD-416):
Stabilize the phenotype of day-neutral Texas race stock lines with moderate levels of resistance to reniform nematode through self pollination, and characterize the heritability and action of genes involved in resistance in these tetraploid lines. Develop a phenotypic screening technique that evaluates root infection by reniform nematode and also allows the evaluated plant to survive to reproductive maturity. Determine if enough variability exists within reniform nematode populations to allow them to adapt to overcome host resistance. Improve efficiency and effectiveness of methods necessary to introgress genes from diploid A-genome Gossypium species into tetraploid G. hirsutum germplasm by choosing the most compatible lines and by developing methods to reduce endogenous contamination of in-vitro ovule cultures without inhibiting their development. Introgress reniform nematode resistance from G. arboreum accession A2-190 into G. hirsutum. Describe the influence of crop production practices such as irrigation, tillage, and planting date on reniform nematode population density. Evaluate the role of weeds as hosts for reniform nematode and determine their importance in maintaining inoculum levels of the nematode. Evaluate adapted cotton lines for tolerance to reniform nematode. Determine effectiveness of new commercial seed treatment nematicides for managing reniform nematode, compared to in-furrow nematicide applications. Determine if a combination of nematicide and rotation to corn will improve reniform nematode suppression over rotation used alone.
3. Progress Report:
A major focus of this project has been to incorporate useful levels of reniform nematode (Rotylenchulus reniformis) resistance into upland cotton (Gossypium G.hirsutum). Replicated trials evaluating the performance of advanced generation materials with reniform nematode resistance from less-adapted G. hirsutum lines (moderately resistant) and G. longicalyx (highly resistant) are underway in anticipation of germplasm releases during the next project (new project 6402-22000-074-00D). Reniform nematode resistance was successfully transferred from diploid species G. aridum and G. arboreum; upland cotton lines with this resistance can now serve as donor parents in traditional breeding programs. Molecular markers for the single resistance gene in G. aridum were identified, published, and used for marker-assisted selection; they also confirmed that the resistance gene from G. aridum is different from and combinable with the gene from G. longicalyx. Experiments describing the number of resistance genes and their inheritance in select G. arboreum accessions are nearly complete. Public release of germplasm line BARBREN-713, with reniform nematode resistance derived from G. barbadense (tetraploid species) is pending; this line was developed in cooperation with other USDA ARS, public university, and Cotton Incorporated scientists. Additional cotton lines are being screened to identify novel sources of resistance for use in cotton breeding. Several new sources of resistance identified from G. arboreum are being transferred into upland cotton and the development of resistant breeding lines is underway. A second goal of the project is to identify production practices with potential to reduce the reniform nematode population. Two field studies examining different combinations of tillage, planting dates, cover crop, and herbicide programs showed that none of these treatments had an effect, either positive or negative, on the reniform nematode population in the field. Additional studies examining planting dates, irrigation, weed management, and crop rotation are nearing completion. Seed treatment nematicides including Aeris, Avicta, and VOTiVO were tested as alternatives to aldicarb in several field trials with inconsistent results. None of the products reduced harvest populations of reniform nematode. Seed cotton yields sometimes benefitted from the use of VOTiVO, but effects were not consistent across environments or cultivars. A bacterium in the genus Pasteuria that infects and kills reniform nematode was identified, though effective season-long nematode suppression and associated yield benefits have not yet been consistently achieved using granular or seed treatment formulations. ARS scientists developed 156 simple sequence repeat (SSR) markers that enable detection of the genetic variability within reniform nematode, and may ultimately help us understand how the pathogen responds to various management practices. Twenty-two of these markers are sensitive enough to detect differences among three populations collected from the same location in MS. This information was published and the DNA sequences were added to the publicly-available database Genebank.
1. Cotton with resistance to reniform nematode released. Reniform nematode resistance in upland cotton is lacking. A germplasm line of upland cotton (Gossypium hirsutum) was developed through a joint effort between USDA ARS in Stoneville, MS, public university, and Cotton Incorporated scientists that has moderate to strong resistance to both reniform nematode and southern root-knot nematode. This germplasm was released as BARBREN-713 and will be available for development and commercialization of new cultivars through the National Germplasm System.