1a.Objectives (from AD-416)
The objective of this cooperative research project is to identify interspecific cotton progenies that have been converted from sterile triploids into fertile hexaploids, and to determine which chemical compounds and concentrations are most effective at producing such conversions. In addition, interspecific tetraploid breeding populations will be developed.
1b.Approach (from AD-416)
Triploid progenies of Gossypium hirsutum/G. arboreum will be treated with amiprofosmethyl, colchicine, oryzalin, or trifluralin at four concentrations each. Cuttings of each triploid cross will be made and axillary buds treated with the dissolved compounds mixed in a lanolin paste. Controls will include no paste and water-lanolin. The number of self-fertile cuttings per treatment will be recorded. Chromosome counts will be conducted to confirm the ploidy of fertile plants. When tetraploid progeny of the interspecific hybrids are produced, random mated breeding populations will be developed to break up linkage blocks.
The agreement was established in support of Objective 2 of the in-house project, the goal being to transfer resistance to reniform nematode into upland cotton from wild relatives of cotton. Transferring resistance is difficult, because upland cotton has four sets of chromosomes and the wild relatives of cotton that are resistant to reniform nematode only have two sets of chromosomes. Thus, plants resulting from crosses between the species have three sets of chromosomes and are sterile (unable to produce viable seeds). For the plants to be of use in breeding efforts, fertility must be restored by doubling the number of chromosomes the plants contain. Several chemical treatments have been used to double the number of chromosomes in plants, but the best methods for use with our plant materials are still in the early stages of development.
Plants resulting from crosses between upland cotton and its wild relatives were treated with a variety of chemicals at several concentrations to double the number of chromosomes. After treatment, plants that were able to set bolls with viable seeds were identified. Cuttings from these plants were sent from ARS to Texas A&M, where chromosome counts will confirm whether or not the chromosome numbers were in fact successfully doubled. Collection and preparation of the plant material for the chromosome counts has begun, and work on this aspect of the project is expected to continue into the fall. Research activities during this reporting period were monitored by the ADODR primarily through email communications with the cooperator.