Leaf development of spring wheat cultivars in an irrigated heat-stressed environment

Abstract

Wheat ( Triticum aestivum L.) is expanding into lower latitudes of the Nile Valley Region, where maximum air temperature can reach 38–40°C during the short growing season. Genotype and environment, particularly temperature, affect the rate of leaf appearance. Field experiments were conducted at the Gezira Research Station, Wad Medani, Sudan in 1992–94. The study aimed to determine the effect of high temperature (by manipulating sowing dates) on leaf and tiller appearance and growth of nine spring wheat cultivars. Linear response was found between rate of leaf appearance and thermal time and it was faster before double-ridge stage than after double ridge. Phyllochron ranged between 99°C d and 122°C d. Differences in phyllochron interval (PI) were pronounced among cultivars and early-maturing cultivars had faster leaf appearance compared with late-maturing ones. Mean final leaf number on the main stem ranged from 8.1 to 12.2 and it was highly correlated with thermal time from sowing to double ridge stage ( r=0.71**). Genetic constitution of cultivars had larger effect on number of leaves per main-stem than temperature. Tillers were initiated at leaf stage 2.9 and cultivars differed in their tillering capacity and only 1.5–2.0 reproductive tillers per plant were produced. About 810°C d were needed to produce tillers 1 and 2 and about 1140°C d for tillers 3 and 4. Leaf senescence started at leaf stage 6.1 for cv. Wadi El Neil and 4.2 for Debeira. Cultivars sown late exhibited delayed senescence of their leaves. High temperature accelerated maturity and the cultivars suited for the irrigated tropical environment were found to be early-sown late-maturing types.