Phyllochron responds to acclimation to temperature and irradiance in maize

Crop models need accurate simulation of leaf canopy development. Thermal in terval for leaf tip appearance (phyllochron) is critical for predicting dur ation of vegetative development. Phyllochron in maize is shorter in tempera te than in tropical and subtropical environments. As existing data has been evaluated in a narrow range of environments, underlying mechanisms that af fect phyllochron have not been adequately examined. The objectives of this study were to quantify the response of phyllochron to environmental variabl es and determine its stability across maize cultivars, to aid modelers in d eveloping tools which accurately predict phenology. Maize was grown in fiel d experiments at Wageningen, The Netherlands, Temple, Texas, USA, and three sites in Mexico, and in controlled environments at Wageningen. The experim ent at Temple included grain sorghum and shading treatments to alter irradi ance of the crop. Detailed data on leaf production and environmental condit ions were collected. These data were combined with published data from held studies. Maize phyllochron acclimated to temperature and increased as mean daily temperature before tassel initiation increased from 12.5 to 25.5 deg rees C, and increased in maize and sorghum in response to low irradiance. T emperature was the dominant influence, with phyllochron increasing by 1.7 d egrees Cd per degrees C increase in daily mean temperature, as daily mean t emperature before tassel initiation increased from 12.5 to 25.5 degrees C, and declined or remained constant when mean daily temperature before tassel initiation exceeded 25.5 degrees C. Only small differences in phyllochron occurred among cultivars. Phyllochron increased by 2-4 degrees Cd MJ(-1) ph otosynthetically active radiation (PAR) as irradiance decreased from 9.6 to 1.1 MJ PARm(-2) day(-1). (C) 1998 Elsevier Science B.V. All rights reserve d.