TEMPERATURE AND PHOTOPERIOD SENSITIVITY OF DEVELOPMENT IN 5 CULTIVARSOF MAIZE (ZEA-MAYS L.) FROM EMERGENCE TO TASSEL INITIATION

Prediction of phenological development is crucial to the successful us e of crop simulation in crop adaptation studies. Previous studies have shown existing predictive algorithms to be inadequate when applied to a broad range of cultivars and environments. The primary objective of the study was to quantify the temperature and photoperiod responses o f the rates of development during emergence to tassel initiation (ETI) for a diverse set of maize cultivars. Five cultivars of maize, differ ing in maturity and adaptation, were sown on seven dates from 1 Octobe r 1993 to 29 March 1994 and grown under natural and extended (16.5 h) photoperiods at Gatton, Southeast Queensland, under non-limiting condi tions of water and plant nutrient supplies. Timing of emergence and ta ssel initiation were observed for all treatments. The base, optimum, a nd maximum temperatures, and photoperiod sensitivity of each cultivar were determined using an iterative optimisation procedure. The critica l photoperiod (12.5 h) was adopted from Literature sources, as there w as inadequate range in the short photoperiods in the present study to determine it with confidence. Photoperiod extension increased the dura tion of ETI and increased the number of leaves on all cultivars, the l argest increases occurring in a tropically adapted cultivar (Barker), in five of the seven sowings. No response to photoperiod extension occ urred in the crops sown on 24th February and 29th March 1994. The temp erature response was the same in all cultivars, and was best described by a three-stage broken-stick linear function. Photoperiod sensitivit y was linear at photoperiods in excess of 12.5 h. The optimised base, optimum and maximum temperatures were 8, 34 and 40 degrees C respectiv ely. Photoperiod sensitivity, expressed as the increase in number of l eaves produced per hour of photoperiod in excess of 12.5 h, ranged fro m 0.3 to 1.5 leaves h(-1). When expressed as the increase in thermal d uration of the photoperiod-sensitive interval prior to tassel initiati on, it was 5.0 to 27.3 degrees C d h(-1), (using the optimised base, o ptimum and maximum temperatures). The fitted values for the chronologi cal duration of ETI were in close agreement (RMSD = 1.9 days) with the 57 observed values at Gatton, which spanned a range of 13-34 days. Th e optimised values for temperature and photoperiod responses should im prove the prediction of tassel initiation in maize crop simulation mod els. (C) 1998 Elsevier Science B.V.