TITLE: Developing Sustainable Field Cropping Systems in Semi-arid Eastern Oregon
DURATION: Five years (July 1, 2002 to June 30, 2007)
Drought and Heat Stress Studies
Wheat in eastern Oregon matures under drought and heat stresses that accelerate leaf senescence. Work to improve pre- and post-flowering drought and heat tolerance should be initiated. At present no OSU program is specifically targeting drought and heat stress tolerance in wheat. Furthermore there is no new variety that has consistently out-yielded Stephens, a soft white wheat that was released 24 years ago. Introducing new varieties that have higher levels of pre- and post-flowering drought and heat tolerance will not only increase yields but will stabilize yields from year to year while ensuring plump grains with good quality. In the short-term, a steady production of good quality grain is one way to secure world markets and high wheat prices. In the long-term, steady markets and high wheat prices improve the viability and sustainability of rural societies and associated agro-businesses. The greatest impact the proposed work will have is in the reduction of crop failures, which are common in years when rainfall is less than normal. With reduced crop failures, farmers have steady grain production and secure markets.
PREVIOUS WORK AND PRESENT OUTLOOK
Drought and High Temperature Studies
Wheat grown in eastern Oregon matures under decreasing water supply and increasing temperatures. Under these conditions leaves, which carry out photosynthesis, senesce more rapidly (Rosenow and Clark, 1981; Turner and Begg, 1981). The rate of leaf death depends on the amount of available soil moisture and intensity of heat, being faster when soil water is limited. In most cereals including wheat, current photosynthesis accounts for about 90% of the carbohydrates that are translocated into the grain (Thomas and Smart, 1993). The premature death of the leaves, therefore, reduces the amount of carbohydrates going into the grain resulting in shriveled grain of poor quality. Grain quality is increasingly becoming important in securing world markets. Over production of wheat in other regions of the world has kept wheat prices low and demands for better grain quality has tightened competition for world markets. The Australians, in particular, are now competing fiercely against US wheat and have successfully out-competed US wheat where certain grain qualities are desirable. To compete with other countries for world markets, we need to produce good quality grain consistently. I hypothesize that increasing the lifespan of wheat leaves during the post-flowering period, through increased drought and heat tolerance, will increase grain-filling duration, improve grain quality, and reduce crop failures.
Plants that delay leaf senescence have a stay-green character (Rosenow and Clark, 1981; Thomas and Howarth, 2000). In sorghum, the stay-green character is largely due to perennial tendencies and it is positively associated with grain yield under drought conditions (Rosenow and Clark, 1981). In crops with annual tendencies, the stay-green character may be brought about by many physiological processes that include the production of cytokinins, the endogenous hormones that delay leaf senescence. It is envisaged that different wheat varieties show different levels of the stay-green character but the basis of genetic variation of this trait is not known. I also hypothesize that the onset and rate of leaf senescence differ among different wheat varieties. Therefore, it should be possible to screen wheat varieties for this trait.
Work will also be conducted to determine mechanisms of drought and heat tolerance and to determine the interactions between drought and heat tolerance and disease tolerance. Plants that are water-stressed are more susceptible to diseases particularly Fusarium root rot. Experiments should determine if susceptibility of the plants to this disease is related to drought tolerance and come up with tillage and fertilizer treatments that conserve soil water to reduce drought stress during the final phases of plant growth.
The ultimate objective of this project is to develop acceptable and sustainable cropping systems for north-central Oregon and south-central Washington. The desired cropping systems should increase residue cover, increase soil OM, increase soil available moisture, reduce wind and water erosion, reduce soil water evaporation, sustain soil productivity, and increase farm profits. Work to accomplish this objective, however, will be conducted in separate experiments whose specific objectives are listed below.
