Location:2011 Annual Report
1a. Objectives (from AD-416)
Objective 1: Develop non-chemical tactics to reduce Fusarium oxysporum f. sp. vasinfectum (FOV) race 4 inoculum levels, focusing on optimization of solarization methods, impacts of rotational crops, and development of resistant or tolerant germplasm. Subobjective A: Optimize solarization methods focusing on effects of applied moisture levels and duration of coverage on reductions in race 4 FOV inoculum. Subobjective B: Determine the effects of common rotational crops on race 4 FOV inoculum levels. Subobjective C: Develop cotton breeding populations segregating for FOV resistance and evaluate resulting lines for resistance and fiber quality traits. Objective 2: Investigate the population biology of FOV in the U.S. cotton belt. Objective 3: Identify and validate molecular marker associations with fiber quality characteristics and resistance to FOV. Objective 4: Determine collection efficiency and fidelity of population estimates to true population densities for standard lygus sampling methods. Objective 5: Define host-plant relations and cotton cultivar-specific responses to lygus injury. Subobjective A: Define relationships between lygus feeding, feeding preferences, and fruit loss rates. Subobjective B: Develop evaluation criteria and screen a cross-section of available cotton germplasm for lygus tolerance. Objective 6: Evaluate the potential of Beauveria bassiana as a non-cotton season, ecologically-based lygus control tactic. Objective 7: Define key aspects of lygus overwinter ecology and adult diapause.
1b. Approach (from AD-416)
An interdisciplinary team consisting of a plant pathologist, geneticist, and two entomologists will collaborate with Federal, State, and University investigators to solve the major problems facing sustainable production of irrigated crops in the context of environmental stewardship. Efforts to improve insect sampling methods combined with new knowledge of crop responses to insect populations will result in more effective pest management rules and decreased pesticide use. Definition of pest overwintering ecology will provide guidelines for testing and developing ecologically-based management tactics using diseases specific to pest insects. A survey of Fusarium oxysporum vasinfectum (FOV) in the U.S. cottonbelt will indicate potential risks associated with known and undescribed races. Optimization of non-chemical, environmentally benign control tactics will provide safe and effective means of limiting the spread and impact of FOV. Conventional breeding methods in combination with modern molecular techniques will lead to cotton germplasm with improved yield and fiber qualities and increased resistance to insects and diseases.
3. Progress Report
New markers for genes conferring resistance to the causal organism of Fusarium wilt (Fusarium oxysporum f. sp. vasinfectum; FOV) and root-knot nematode were identified from regions of two cotton chromosomes. In cooperation with University of California scientists, more than 2000 plants were evaluated for resistance to FOV races 1 and 4 and the root-knot nematode in field and greenhouse studies. Results indicated activity of resistance genes varied with environmental conditions and parental origin. The collective information is essential to planned research to understand the interactions of genes from resistant and susceptible cottons and for marker-assisted breeding. Studies to better understand the mechanisms by which solarization reduces populations of FOV spores in moist soil indicated heating to 40 degrees C was necessary for rapid death of the spores. These findings contribute to the objective of optimizing solarization for FOV control. Progress was made in characterizing FOV isolates from Alabama and Mississippi based on sequences of two genes. The new isolates were distinct from race 4 of FOV, which is a critically important problem in California cotton. Although most of the new isolates were weak pathogens, two isolates from Alabama were highly damaging to some cotton cultivars. Detection of these new isolates accentuates the need to complete an ongoing FOV survey of the U.S. cottonbelt. Improved methods of evaluating cultivars for resistance to race 4 of FOV, and for quantifying FOV reproduction within the cotton plant were developed. These methods will be useful in identifying cotton cultivars that promote high levels of FOV spore production. Greenhouse studies of plant bug (lygus) feeding injury to cotton validated earlier laboratory feeding assays, and indicated young adults are more injurious than are older adults. Studies to compare injury by adults and nymphs were partially completed. Complementary field experiments indicated older adult lygus are more effectively sampled with the sweep net than are young adults in Pima cotton, but sampling effectiveness was similar between the two age classes in Upland cotton. Studies to define effects of temperature on lygus egg and nymph development, and on reproductive development of adults were completed, as were experiments demonstrating a gradual reduction in reproductive dormancy of adult lygus in response to laboratory rearing. These collective results provide insights into lygus overwintering survival strategies that are necessary to design improved ecologically-based management strategies.
1. Age- and gender-based differences in injury to cotton by adult Lygus hesperus. Lygus species constitute the most important pest complex of U.S. cotton but relationships between lygus population levels and injury to cotton are poorly understood. In greenhouse experiments, ARS researchers at Shafter, California, demonstrated previously observed differences in feeding behaviors among selected classes of Lygus adults correspond to differences in injury to fruiting cotton. Confirmation of this relationship provides key information to reduce or eliminate a major source of variability in studies to quantify lygus-induced crop losses. Techniques developed during this research can be used to design efficient screening protocols to identify lygus tolerance or resistance in commercial cotton cultivars.
2. Identification of a novel source of root-knot nematode resistance in cotton. The southern root-knot nematode is an important pest of cotton in many domestic and foreign production regions. An ARS scientist at Shafter, California, in collaboration with scientists at the University of California, used crosses of nematode-resistant and susceptible Pima and Upland varieties to identify progeny with higher levels of resistance than in either parent plant. Molecular markers associated with the resistance were also identified. The research indicates that susceptible parents can be important contributors to high levels of resistance to the root-knot nematode, and provides markers to speed selection for key resistance elements in breeding programs.
Bennett, R.S., O'Neill, W., Smith, L., Hutmacher, R.B. 2011. Commercial detergents effective against conidia and chlamydospores of Fusarium oxysporum f. sp. vasinfectum. J. Cotton Sci. 15:162-169.