EFFECTS OF PHOTOPERIOD ON REPRODUCTIVE DEVELOPMENT OF PEANUT (ARACHIS-HYPOGAEA L) IN A COOL SUBTROPICAL ENVIRONMENT .2. TEMPERATURE INTERACTIONS

The effects of temperature on the response to photoperiod by peanut (Arachis hypogaea L.) cultivars were examined under glasshouse and phytotron conditions at two locations (Kingaroy and Canberra). Two Virginia cultivars (Early Bunch and Robut 33-1), two Spanish cultivars (White Spanish and TMV-2) and a single Valencia (NC17090) cultivar were grown in the experiments. White Spanish was common to both studies. Strong photoperiod x temperature interactions were shown for all cultivars in both experiments, with the sensitivity of peg number to photoperiod increasing at higher temperatures. Photoperiod responses were all indicative of short-day (SD) response types, and were always expressed in post-flowering reproductive development. No effects of photoperiod on time to first flower were evident, but numbers of pegs and pods and total pod weight per plant were reduced in long (16 or 17 h) photoperiods. Data from field experiments at Kingaroy were pooled with those from the glasshouse and controlled environment studies to estimate the critical temperatures above which photoperiod sensitivity became significant. Hourly temperature readings were used to calculate a daily heat sum (degrees-C h) above a base temperature of 10-degrees-C for each experiment. This index of the temperature condition proved satisfactory as a possible discriminatory method to describe environments based on likely photoperiod response. Environments where daily heat unit accumulations greater than 340-350-degrees-C h were recorded during the treatment period showed significant photoperiod responses. The possibility of minimum temperature being the predominant component of the temperature x photoperiod interaction is also discussed. This proved less effective in discriminating between environments for photoperiod response, but data were insufficient to discount this possibility and further studies are needed. Results question the relevance of photoperiod as a factor limiting reproductive development of peanuts in cooler, subtropical environments.