Location: Crop Genetics Research2013 Annual Report
1a. Objectives (from AD-416):
Objective 1. Identify new sources of reniform nematode resistance in Gossypium (G.) arboreum and G. herbaceum accessions and characterize the genetics of host resistance. Subobjective 1a. Discover new sources of resistance in Gossypium arboreum and G. herbaceum. Subobjective 1b. Characterize new sources of reniform nematode resistance in G. arboreum and G. herbaceum. Objective 2. Develop and release adapted Gossypium hirsutum breeding lines or varieties with resistance to reniform nematode. Subobjective 2a. Introgress reniform nematode resistance from G. arboreum and G. herbaceum into G. hirsutum. Subobjective 2b. Develop Gossypium hirsutum germplasm with reniform nematode resistance from related Gossypium species. Objective 3. Develop sustainable crop production systems which include the use of host plant resistance to effectively manage the reniform nematode in cotton. Subobjective 3a. Determine the influence of cotton variety and cropping system on management of reniform nematode. Subobjective 3b. Evaluate efficacy of seed treatment nematicides to control reniform nematode on susceptible or resistant cotton. Subobjective 3c. Evaluate efficacy of seed treatment nematicides on cotton which is resistant or susceptible to the reniform nematode.
1b. Approach (from AD-416):
Screen accessions in the national germplasm collection to identify as many sources of reniform nematode resistance from Gossypium (G.) arboreum and G. herbaceum as possible that can be used for germplasm improvement. Once resistance sources are identified, determine the inheritance of reniform nematode resistance from those accessions and identify molecular markers linked to the resistance genes. Concurrently, transfer the reniform nematode resistance from these species to G. hirsutum. Generate and release G. hirsutum breeding lines with useful levels of resistance to reniform nematode. Determine if reniform nematode resistant cotton combined with crop rotation will be more effective at lowering subsequent reniform nematode populations than current production methods with commercial varieties. Determine if commercially available seed treatment nematicides reduce relative infection of reniform nematode on cotton and result in increased yield regardless of host resistance status.
3. Progress Report:
Development of upland cotton (Gossypium [G.] hirsutum) with resistance to reniform nematode (Rotylenchulus reniformis) from related diploid species is underway. Germplasm lines with resistance from the diploid species G. aridum and/or G. arboreum accession A2-190 were developed in the previous project (6402-22000-005-00D) and seven lines have been advanced to the F6 generation based on a combination of phenotypic screening and marker assisted selection. Although many lines in this population have had a problem maintaining their resistance over several generations of self pollination, a breeding line from this set of materials should be released within the next two years. Based on preliminary screening and previous reports, it is likely that additional resistance sources exist within the G. arboreum and G. herbaceum collections. Ninety G. herbaceum accessions and 1,506 G. arboreum accessions were planted in the field in 2011 and 2012 to assess uniformity in agronomic characteristics. Because many rows were not uniform for traits like flower color, petal spot, and plant height, single plant selections were harvested for use in future germplasm development. Growth chamber screening for reniform nematode resistance using these single plant selections was initiated and will take several years to complete. To date, 70 G. arboreum accessions with resistance to reniform nematode have been identified. Nondestructive screening techniques that allow recovery of resistant plants for advancement to the next generation are being optimized. Embryo rescue techniques were used to recover plants from five crosses made in the summer of 2012 between upland cotton and either one G. herbaceum accession or four different G. arboreum accessions with resistance to reniform nematode. Sterile plants were successfully recovered, and cuttings from them are being treated to restore fertility so that they can be screened to confirm the resistant phenotype and used in future germplasm improvement efforts. Work to develop sustainable crop production systems incorporating cotton resistant to reniform nematode was initiated. The first year of a study examining the use of resistant cotton in combination with crop rotation to corn or soybean was successfully completed; the second year is in progress. Commercially available seed treatment nematicides were tested on cotton genotypes susceptible or resistant to reniform nematode to determine if their use provided additional benefit beyond that conferred by the resistance. Results from trials in fields with low and high populations of reniform nematode, respectively, indicated that no combination of nematicide and host plant resistance reduced the soil nematode population at harvest compared to the untreated susceptible control. Under high nematode pressure, cotton lint yield was unaffected by the treatment combinations; however, differences in yield among treatments occurred under low nematode pressure. In general, lines with the G. longicalyx source of resistance yielded less than the others. Details on the crop production systems aspect of the research can be found in the report for subordinate project 6402-22000-074-01S.