Gas Exchange, Yield and Seed Quality of Peanut in Response to Decreasing Soil Moisture.

Peanut (Arachis hypogaea L.) production worldwide and in the U.S.A. is mostly rainfed therefore lack of precipitation may have significant impact on yield and quality. Although the Virginia-Carolina (VC) region is classified as sub-humid, recurrent droughts during June, July, and August have been often reported. VC is the major production region for the big seeded Virginia market-type peanut that may require ample water and carbon for seed filling. Leaf carbon assimilation and transpiration decrease during drought episodes. How this affects yield and quality of peanut is essential for the development of drought tolerant cultivars for the VC region and worldwide. The objective of this study was to evaluate gas exchange characteristics, i.e., carbon assimilation, stomatal conductance, and transpiration, and their relationship with yield, grading characteristics, and oil profile of twelve peanut cultivars and breeding lines grown in the field with soil moisture conditions controlled by three rainout shelters each designated as well-watered, intermediate stress, and severe drought stress. Soil water regimes were maintained by irrigation. Gas exchange measurements were taken repeatedly throughout the growing season. Pod yield, grading characteristics, and kernel oil profile were determined at physiological maturity. Significant differences due to water regime and genotype were observed for all physiological and agronomic characteristics each year.  Carbon assimilation decreased significantly with decreasing the volumetric soil water content, but genotypes GP-NC WS 17 (tested as experimental line SPT 06-07) and N05006 maintained higher carbon assimilation, yield, and oleic fatty acid content than other genotypes. This work provided clarification of the drought effect on peanut gas exchange characteristics, yield and quality by using controlled water regimes at the field scale, and identified two breeding lines with improved drought tolerance, GP-NC WS 17 and N05006.