RESPONSE OF PEANUT (ARACHIS-HYPOGAEA) TO TEMPERATURE, PHOTOPERIOD AND IRRADIANCE .1. EFFECT ON FLOWERING

For peanut (Arachis hypogaea L.), the time to first flower appearance is shown to be little affected by photoperiod, but flower production is enhanced significantly in short-day photoperiods. Over 14 days, twice as many flowers opened in a 10-h than in a 16-h photoperiod. Therefore peanut can be classified as a short-day plant (SDP). Although time to first flower was little affected by photoperiod, temperature had a major and positive effect. A linear thermal-time model adequately described first flower appearance if we excluded mean temperatures above 30-degrees-C. The Spanish varieties manifested a higher base temperature (approximately 13.6-degrees-C) than either Valencia (12.5-degrees-C) or Virginia types (11.4-degrees-C). However, over a wider temperature range, quadratic curves were shown to be more accurate representations of time to first flower. The extrapolated base temperatures from curves were 2-3-degrees-C higher than those from straight line fits. Photon flux density (Q) close to saturating for photosynthesis gave earliest first flowering, and photoperiod effects could be seen only at very low Q. A major role for temperature in flowering of peanut is indicated by these data, with some modulation by photoperiod and irradiance.