Breeding Short-to-Full Season Multiple Stress Tolerant Corn
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Corn is the most important summer crop in the U.S. and second only to cotton in gross income in Texas. Drought, heat, aflatoxins, corn earworm and spider mite are major constraints 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 livestock and dairy industries in this region post a high demand for corn grain and silage production in the state. Irrigation is the largest input factor in feasible and sustained corn production within the Texas High Plains. Drought stress is prone in the rain-fed regions of the state. Currently, predominant corn hybrids grown in the Texas have a relative maturity of 115 days. Although these hybrids can yield 300 bu/ac, the declining Ogallala Aquifer water level and increasing pumping restrictions by the ground-water districts for crop production cannot sustain the current yield level. Thus, drought-tolerant hybrids are critical to sustain corn production in Texas, and shorter-season corn is one genetic approach to meet the forecasted reduction of irrigation. Breeding corn for drought tolerance and overall adaptation to Texas environments is the core objective of this project.Aflatoxin contamination of corn, caused by A. flavus, is a chronic problem in the southern states where a hot and dry environment favors aflatoxin production (Payne, 1992). A recent association study has confirmed previously reported QTLs and identified new makers associated to aflatoxin (Warburton et al., 2013, 2014). Insects can exacerbate aflatoxin levels in corn. The natural population of corn earworm (CEW) is high and very active in Texas and southern states due to widespread host plants (cotton, corn, sorghum, and spring weeds), mild winters, and 5-6 generations per year. The insect causes a significant loss in yield and grain quality and a great increase in aflatoxin contamination. In collaboration with Drs. Ni and Brewer, we infested corn plants with larvae of CEW and fall army worm and confirmed insect resistance in our inbred lines (Farias et al., 2014; Ni et al. 2012, 2014a, and 2014b). W In addition, spider mites can cause serious damage to corn plants in the High Plains. Periods of hot dry weather favor rapid mite population increase in conjunction with accumulation of aflatoxins in corn grains. Therefore, we believe that to effectively reduce aflatoxin risk in corn, we should improve drought and heat tolerance, and insect resistance in addition to incorporating direct kernel resistance into Texas corn germplasm.Development of a multiple stress-tolerant crop via selection of native genes, incorporation of transgenes, or both, requires efficient selection tools. Effective selection depends on accurate evaluation of the traits. Drought tolerance in crop plants is a complex trait. Its evaluation depends on the timing, intensity, and duration of drought stress. 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. Drought resistant corn genotypes show short anthesis-silking interval (Byrne et al., 1995), and maintain higher leaf water and leaf turgor potential due to deeper root systems. We determined that root characters and hydraulic lift (a process of water movement from relatively moist to dry soil layers using plant root systems as a conduit) play an important role in hybrid drought tolerance (Wan et al; 2000). Understanding genetic and physiological mechanisms of drought tolerance and establishing molecular breeding procedures for target traits (drought and heat tolerance, aflatoxin and others) can help the public and private breeders using our germplasm to move the traits/genes quickly into elite germplasm.