IMPORTANCE OF VARIATION IN CHILLING TOLERANCE FOR PEANUT GENOTYPIC ADAPTATION TO COOL, SHORT-SEASON ENVIRONMENTS

Recent studies have shown genotypic variation in sensitivity of leafle t CO2 exchange rate (CER) to cool night temperatures. However, no info rmation is currently available on the relative importance of this trai t for successful peanut production in a cool, short-season environment . The objectives of this study were to examine the physiological basis of genotype adaptation to a cool, short-season environment and to ass ess the importance of genotypic differences in sensitivity to low nigh t temperatures in that adaptation. Eight genotypes were grown in the f ield at Delhi, Ontario in 1991, and six of these eight were grown in 1 992. Phenological development was monitored, dry matter (DM) accumulat ion was determined from destructive samples, and radiation use efficie ncy (RUE) was calculated from measurements of fractional interception of incident photosynthetically active radiation (PAR). Accumulated deg ree-days in 1991 (1245 degrees C d from sowing to frost) greatly excee ded those in 1992 (885 degrees C d), despite similar calendar-day dura tion. Only five genotypes matured in 1991 and two in 1992. The degree- days required to reach key reproductive stages including maturity vari ed considerably among genotypes and between seasons. Seasonal variatio n was probably due to effects of low temperatures on continuity of rep roductive development and the proportion of total kernels that were ma ture at harvest. Total DM was reduced by 30 to 50% in 1992, compared w ith 1991, whereas pod and kernel yields were reduced by 40 to 75 and 3 8 to 83%, respectively. The lower DM in 1992, and genotypic difference s in both seasons, were due primarily to the amount of incident PAR in tercepted by canopies (i.e., 520-790 MJ m(-2) in 1991 and 360-480 MJ m (-2) in 1992). The RUE was 13 to 24% lower during 1992, compared with 1998, with relative genotype RUE generally consistent with CER sensiti vity to low night temperature. Early maturity combined with an ability to rapidly expand a canopy to intercept incident PAR were the factors most important for peanut production in this environment.