Temperature response of early foliar expansion of potato and wheat

We studied the course of early leaf area expansion and specific leaf area ( S-LA) in potato (Solanum tuberosum L.) and wheat (Triticum aestivum L.) gen otypes and tested whether air temperature explains differences in these cou rses within different environments. Such knowledge can be used to improve c rop growth modelling. The relative rate of leaf area expansion (R-L) of pot ato and wheat decreased with thermal time, but was nearly linear up to a le af area index (L) of 1.0. The R-L (L < 1; mean: 17.9 x 10(-3)degrees C-1 d( -1)) of potato showed an interaction between genotype and environment, and varied with year. The R-L (L < 1; mean: 7.1 x 10(-3)degrees C-1 d(-1)) of w inter wheat was lower than that of spring wheat (mean: 10.9 x 10(-3)degrees C-1 d(-1)), and both varied with year. S-LA of potato increased nearly lin early with thermal time from 5 to 15 m(2) kg(-1) at 50 % emergence, to 20 t o 25 m(2) kg(-1) at 155 degrees Cd, and then decreased slightly. The S-LA o f both winter and spring wheat began at 16 to 23 m(2) kg(-1) and in most ca ses increased slightly with thermal time. In potato, regression parameters of S-LA with thermal time were affected by environment (management conditio ns and year) and genotype; in wheat they were affected by environment (year and site). Treatment effects on R-L of potato were not correlated with tho se on S-LA, and were only partly correlated for wheat. Therefore we conclud e that the early foliar expansion of potato is associated with a strong inc rease in S-LA, and not so for wheat. For both crops the course of early lea f area expansion and of S-LA with air temperature is not robust over enviro nments and genotypes. The consequences of these results for modelling are d iscussed. (C) 2000 Annals of Botany Company.