The Effect of Irrigation and Genotype on Carbon and Nitrogen Isotope Composition in Peanut (Arachis hypogaea L.) Leaf Tissue

Water scarcity is a significant problem faced by producers worldwide and is becoming an increasing problem to growers in the U.S. peanut (Arachis hypogaea L.) producing areas due to years of drought and increasing urban demands on water resources. Because of this, high water-use efficiency (WUE) has now become a priority in many peanut breeding programs. To support this effort, the variation in WUE, as measured by carbon isotope composition (δ13C), of three commonly grown peanut cultivars was evaluated under differing irrigation environments during 2001 and 2002 at a research farm in Shellman, GA, U.S.A. The specific experimental objectives were: 1) to determine if genetic variability existed in δ13C, δ15N SLA, and SPAD among three commonly grown U.S. peanut genotypes; 2) to determine if differing irrigation levels affected the pattern of variability; and 3) to quantify the relationship between δ13C and the measured leaf phenotypic characteristics. During both 2001 and 2002, cv. Georgia Green had significantly higher yields and lower δ13C and SPAD chlorophyll content than the other two genotypes, and lower %N than the cultivar C99R. Specific leaf area and %C for Georgia Green were significantly greater than for the cultivar AT201. In addition, irrigation treatment significantly affected yield such that the NI (nonirrigated) treatment yields were significantly lower than any of the irrigated treatments (33%, 66%, or 100%). However, the irrigation effects on leaf phenotypic characteristics were less apparent with differences existing only for δ15N, SPAD chlorophyll, and SLA. The correlation of δ13C and yield was significant for C99R in 2001 and AT201 in 2002, while correlations with δ13C and the other leaf phenotypic characteristics were scarce. This makes the utility of the traits as easily measured surrogates for WUE very limited.