Temperature adaptation of tropical highland maize ( Zea mays L.) during early growth and in controlled conditions

Abstract

For economic and ecological reasons, the chilling tolerance of maize must be further improved. This seems to be possible by the introgression of tropical highland germplasm if chilling and heat tolerance can be combined to obtain a high yield consistency. Two adapted and two semi-exotic highland varieties were grown at 16, 25 and 30°C until the third and sixth leaf stage. Thereafter, some plants were transplanted and grown at 24°C in the glasshouse until anthesis. Exotic germplasm improved the leaf appearance and shoot growth during the early heterotrophic phase at all temperatures, with a marked advantage at low temperature. This superiority was almost completely lost during the succeeding autotrophic growth phase with some residual effects at low temperature and a marked relative retardation in leaf appearance and growth at high temperature. Relative growth rates (RGR) of exotic germplasm were not superior at low temperature or inferior at high temperature. At low temperature, their comparatively reduced leaf area ratio (LAR) was still compensated by a high net assimilation rate (NAR). Their expression of the latter trait was comparatively decreased at a high temperature, which explained the low RGR. Early growth at low and medium temperatures had similar effects on final leaf number for all varieties; a high temperature increased the final leaf number up to 20%, especially in exotic germplasm. In conclusion, the good early vigor of Mexican highland germplasm seems to be mainly restricted to the heterotrophic phase; a relation to adaptative mechanisms, such as a low LAR, must be overcome for an efficient utilization in conventional breeding programs.