2012 Annual Report 1a.Objectives (from AD-416): To study genetic variation for physiological stress responses in cotton and its relation to productivity and fiber quality under high temperature and water-limited conditions. 1b.Approach (from AD-416): We plan to employ QTL analysis to study the genetic architecture of heat and drought tolerance as well as fiber quality traits in a biparental upland cotton population cultivated under well-watered and water-limited conditions. 3.Progress Report: This Trust Agreement is in support of objective 2 of the parent project- Develop improved germplasm resources for abiotic stress resistance and fiber quality in Gossypium barbadense and G. hirsutum utilizing and integrating classical and biotechnology-based methodologies, Subobjectives 2.a - Develop improved germplasm resources for abiotic stress resistance and fiber quality in G. hirsutum utilizing and integrating classical and biotechnology-based methodologies, and 2.b - Develop improved germplasm resources for abiotic stress resistance and fiber quality in G. barbadense utilizing and integrating classical and biotechnology-based methodologies. The present study was conducted to examine physiological traits that are potentially important for the adaptation of cotton to hot, arid production environments. In collaboration with Cornell University, an ARS scientist at Maricopa, AZ, showed that leaf content of total soluble sugar, chlorophyll content, and abscisic acid was highly variable among individuals of an interspecific cotton recombinant inbred line mapping population subjected to drought stress. Soluble sugars are known to accumulate in various plant tissues during periods of abiotic stress as a form of osmoprotection. Total soluble sugars were higher in drought stressed (DS) plants compared to those growing under well-watered control (WW) control conditions. The leaf content of chlorophyll a, b, and their summation followed a similar trend as total soluble sugars. The increase in leaf thickness of the DS plants relative to the WW plants was probably the cause of their higher chlorophyll content. Leaf ABA content typically increases to induce stomatal closure under drought, which reduces the loss of water from transpiration. However, leaf tissue collected from WW plants had higher ABA levels than DS plants. Although unexpected given that ABA increases in response to drought, these results are consistent with long-term DS studies in other crops. It was likely that the sampled DS cotton leaves from long-term water stressed plants had attenuated ABA levels, while the sampled WW cotton leaves probably experienced an initial burst in ABA that increased to levels higher than DS. In summer 2012, a diurnal sampling strategy will be used to further explore the hypothesis that WW cotton plants undergo a recovery at night and a daily burst of ABA each day in a hot, arid environment. This research provides new insights into the physiological basis of local adaptation, which should be further explored for the genetic improvement of cotton. Progress performance has been monitored through discussion of project plans, reviewing program goals and accomplishments at ARS facilities, teleconference, e-mail, and quarterly reports.