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

Recent studies have shown genotypic variation in sensitivity of leaflet CO2 exchange rate (CER) to cool night temperatures. However, no information is currently available on the relative importance of this trait 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 assess the importance of genotypic differences in sensitivity to low night temperatures in that adaptation. Eight genotypes were grown in the field at Delhi, Ontario in 1991, and six of these eight were grown in 1992. Phenological development was monitored, dry matter (DM) accumulation was determined from destructive samples, and radiation use efficiency (RUE) was calculated from measurements of fractional interception of incident photosynthetically active radiation (PAR). Accumulated degree-days in 1991 (1245 degrees C d from sowing to frost) greatly exceeded those in 1992 (885 degrees C d), despite similar calendar-day duration. Only five genotypes matured in 1991 and two in 1992. The degree-days required to reach key reproductive stages including maturity varied considerably among genotypes and between seasons. Seasonal variation was probably due to effects of low temperatures on continuity of reproductive development and the proportion of total kernels that were mature at harvest. Total DM was reduced by 30 to 50% in 1992, compared with 1991, whereas pod and kernel yields were reduced by 40 to 75 and 38 to 83%, respectively. The lower DM in 1992, and genotypic differences in both seasons, were due primarily to the amount of incident PAR intercepted 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 1991, with relative genotype RUE generally consistent with CER sensitivity 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.