Heat Stress during Late Vegetative Growth of Maize: Effects on Phenology and Assessment of Optimum Temperature

摘要

Prediction of phenology is based on thermal time (TT) computation, which requires the correct definition of base (TB) and optimum (TO) temperatures. Most information on these traits came from controlled environments using a wide range of mean air temperatures (TX), including TX TO and TX TB These conditions are rarely found in field environments. We assessed the effect on development of day-time temperatures above TO during late-vegetative growth of maize (Zea mays L), and established a model based on TT computation on a per hour (TTh, in ?°C h) rather than per day basis (TTd) for TO estimation. Field experiments included two temperature regimes (TC: control; TH: heated) between V11 and tasseling of TC We registered temperature at ear level, and dates of anthesis and silking. We computed developmental rates (DR), TTh above 8?°C during treatment period (TTh1) and between V11 and silking (TTh2), a stress index based on the quotient of differences in TTh (?”TTh) between TH and TC (SI = ?”TTh2/?”TTh1), and TO Heat stress caused a delay in flowering events, and a decline in DRs. Estimated TB was higher (12.7?°C) than normally used in computations. Estimated TO was within the expected range (36?°C TO 30?°C), independently of TB Stressful temperatures promoted a delayed in silking, identified as an increase of at least 2.14?°C h in TTh for each degree above TO Estimated TO differed between growing seasons (P = 0.04), suggesting possible variation due to climatic effects.