Breeding Multiple Stress Tolerant Corn

Non-Technical Summary: Corn is the most important crop in the U.S. and second only to cotton in gross income in Texas. Drought, heat, aflatoxins, corn earworm and spider mites are major constrains for corn production in Texas and many parts of the world. Frequent drought and heat stress causes significant yield loss and destabilizes crop production. The Texas High Plains has one million acres of irrigated corn and produces the majority of grain and silage corn in Texas. The huge and expanding livestock and dairy industries in this region have already posted a high demand for corn grain and silage production in the state. Declining water level of the Ogallala Aquifer (the sole source for irrigation) and high energy price add significant irrigation cost. Drought stress also contribute to the aflatoxin accumulation in corn. Aflatoxin contamination is a major problem for human and livestock. Drought-tolerant hybrids are critical to sustain corn production in Texas. Breeding corn for drought tolerance and overall adaptation to Texas environment is the first and core objective of this project. Development of a drought-tolerant crop, by utilizing native genetic variation and/or transgenic technology, requires efficient selection tools. Effective selection depends on accurate evaluation of drought tolerance which in turn depends on the timing, intensity, and duration of drought stress. In the past 10 years, our corn breeding program has focused on exploring native genes, established a drought tolerance screening protocol in the field in West Texas, and developed a number of drought tolerant corn lines and hybrids. Many of these lines have been licensed to seed companies. However, little is known of the physiological and genetic basis of drought tolerance. Understanding drought tolerance mechanisms and establishing molecular breeding procedures can help the public and private breeders in using our germplasm and moving the traits/genes quickly into elite germplasm. Discovering the traits contributing to drought tolerance in these lines and hybrids and understanding the physiological and molecular basis of these traits is the second goal of this project. New stress tolerant corn requires new management practices. Irrigation is the largest input factor in feasible corn production within the Texas High Plains. The Texas High Plains ET Network is one of the best available sources for producers to schedule corn irrigations. Assessing the optimum amount of ET and irrigation water during the crop growing season to optimize yield at a particular location is changing given new corn hybrids. Our data indicate that new stress-tolerant hybrids (either commercial or AgriLife experimental) can produce equal (if not higher) grain yields under reduced (75%) ET irrigation, thus reducing groundwater withdrawals. It also appears the current ET network estimations are too high for new stress tolerant hybrids. Finding the optimum ET production range for new corn hybrids is the third goal of this project. <P> Approach: Tropical by temperate breeding crosses from our project and the USDA GEM project will be the primary source for developing inbred lines. The lines and populations will be screened and selected for drought and heat tolerance, pest resistance, yield potential, and or adaptation to Texas environments. Pedigree selection and backcrossing will be the major breeding methods. Double-haploid method will be explored and integrated into our program. Inbred lines and testcrosses of advanced lines with public lines and licensed industry testers will be evaluated for abiotic and biotc stress tolerance, yield (grain or silage), and overall agronomic performance in multiple locations in Texas and other states. Drought and heat tolerance evaluation will be conducted in the field conditions. We have established two fields with subsurface drip irrigation systems in Lubbock and Halfway. These systems can supply uniform amount of water and control the progress of drought stress. We will have three water treatments in the same field and make section based on plant recovery, stay green, anthesis-silking interval, percent barren plants, seed set, grain mold, yield and other ratings. Heat tolerance will be based on leaf firing and tassel blasting in the plants grown in the fields under well-irrigated conditions in West Texas. Selected hybrids will be grown in replicated test in Lubbock and Corpus Christi, TX and in Mississippi and inoculated with a high aflatoxin-producing isolate of A. flavus between rows of each plot when the first hybrids are at mid-milk stage to provide uniform aerial inoculum for infection. Ten inoculated ears per plot will be hand-harvested, rated for grain mold, scored for insect feeding, shelled, and ground for aflatoxin assay. Screening for CEW resistance will be done under natural infestation by following the procedure described previously. Mite resistance evaluation will be conducted in Halfway and Lubbock, TX. The leaves heavily infested with mites will be placed onto the plants two feet above the ground at flowering stage. Mite feeding damages will be rated on a 1 to 10 scale 14 days after infestation. A set of inbred lines will be selected based on the previous field studies and used for greenhouse and field studies. The greenhouse studies will examine for hydraulic lift, water use efficiency, root characters, and other physiological traits. We plan to develop a DH mapping population for mapping QTLs associated with drought stress. A set of 10 commercial and experimental hybrids will be grown corn hybrids under different irrigation treatments at Etter and Halfway in Texas to determine the most profitable combination of hybrids, irrigation level, and plant populations. Detailed records will be made on irrigation, rainfall, plant growth and development, and grain and silage yields. Yield differences will be compared among irrigation treatments, hybrids, and the hybrid by irrigation by population combinations. The PI will continue to conduct the State Silage Corn Performance Tests in the Texas High Plains and provide the public with the timely, unbiased, and valuable data for choosing the best silage hybrids.