Physiological and Metabolic Responses to Water-deficit and Heat Stress of Virginia-type Peanut Cultivars and Breeding Lines

Abstract

The Virginia-Carolina (VC) region including Virginia, North Carolina, and South Carolina, is the most important peanut production region for the large seeded, virginia-type peanut in the United States. In recent years, an increased frequency of heat and drought episodes with significant effects on peanut yield was observed in the VC region. Because limited information is available on the mechanisms virginia-type peanut develops in response to heat and water stress, the present study evaluated several physiological and metabolic characteristics and their relationship with yield for eight cultivars and breeding lines. Experiments were conducted under rainfed and irrigated field trials in 2011 and 2012, and in a growth chamber under optimum (30/25 "C) and high temperature (40/35 "C) conditions. The long term goal of this study is to help development of more tolerant peanut cultivars to heat and drought in the VC region. Visible symptoms of water-deficit stress were observed in peanut during the field experiments in both years. Significant (p d 0.05) variations for yield, membrane injury, chlorophyll fluorescence (Fv/Fm ratio), specific leaf area, SPAD chlorophyll content, and relative levels of polar and non-polar metabolites were observed in response to water regime, growth stage, and genotype in both years during the field studies. Similarly each year, the Fv/Fm ratio, organic acids, and saturated fatty acids decreased in rainfed vs. irrigated plants, while the sugar and sugar alcohol relative levels increased. Regardless the water regime, lower levels of saturated fatty acids and sugars, and higher levels of unsaturated fatty acids and sugar alcohols were associated (p < 0.05) with higher pod yield in field conditions. Genotypes Phillips, SPT06-07, and N05006 showed potential tolerance and N04074FCT, CHAMPS, and Bailey susceptibility to water deficit in field studies. Significant physiological and metabolic changes were also observed in response to heat stress under controlled conditions in peanut seedlings. A general decrease in organic acid and saturated fatty acid levels and an increase in membrane injury, sugar, and unsaturated fatty acid levels were observed under both water deficit and heat stress conditions. Overall, results from both experiments were suggestive of natural stress responses rather than adaptive mechanisms to water deficit and heat stress of the virginia-type genotypes used in this study. Among all genotypes, SPT 06-07 showed improved tolerance to both stresses. Our results suggest that monitoring chlorophyll fluorescence and changes in the levels of selected metabolites can be used to screen new peanut lines for drought and heat stress tolerance.