EFFECTS OF HIGH TEMPERATURE ON YIELD AND YIELD COMPONENTS OF NINE WHEAT CULTIVARS AND A TRITICALE

Anthesis and grain filling period of wheat in many arid and semi-arid areas of the world is shortened by high temperature. An experiment was carried out to determine the effects of high temperature on yield and yield components of nine wheat (Triticum aestivum L.) cultivars(ʹBesostayaʹ,CrossRowshan 11ʹ, Falat, ʹGhodsʹ, ʹMaroonʹ, ʹHirmandʹ, ʹMoroccoʹ, ʹNavidʹ, and ʹRowshanʹ) and a triticale (x Triticosecale Wittmack) cultivar ʹJuvanillo-92ʹ. High temperature treatments consisted of a control (no heat stress) and three levels of heat stress during different growth stages (a temperature of 28/23° C from the beginning of booting stage, anthesis, and grain filling to grain maturity). High temperature during any developmental stages significantly reduced wheat grain yield. The reduction was significantly less when high temperature was imposed for only a part of the reproductive stage than when it was imposed continuously from the booting stage to kernel maturity. The relative grain yield in the high temperature treatment from booting, anthesis and grain filling was only 5.6, 16.6 and 29.1 % of control plants which were grown at 17/15°C day/night, respectively. Triticale and ʹHirmandʹ prouced the highest yield after heat-stress during booting, and ʹBesostayaʹ, ʹRowshan", and ʹNavidʹ yielded most after heat stress during anthesis. The highest yielding cultivars, when high temperature was imposed during grain filling period were ʹGhodsʹ and triticale. Kernels per spikelet was the main yield component which reduced grain yield in the presence of heat stress. In conclusion, cultivars ʹGhodsʹ and ʹNavidʹ showed better performance than the other cultivars and "Maroonʹ and Falat performed the poorest in the presence of heat stress. Therefore, these cultivars could be used as the relatively heat-tolerant and heat-susceptible genotypes, respectively.