The tolerance of wheat to high temperatures during reproductive growth. I. Survey procedures and general response patterns

Selected cultivars of wheat from both a wide geographic and genetic background were examined under controlled conditions in the Canberra phytotron, for their response to high temperature at three stages of development: booting (late ear development), anthesis (pollination and fertilization) and grain growth (from 6 days after anthesis to maturity).The overall response to temperature, based on 28 cultivars from Afghanistan, Australia, Europe, India, Mexico, the Middle East and north Africa, demonstrated the sensitivity ofgrain number to high temperature during booting and the sensitivity of weight per grain to high temperature after anthesis. The data indicate a general reduction in yield per ear of 3-4% for each 1�C rise in temperature above a mean of 15�C. The response to temperature varied with the stage of development, and some cultivars sensitive to high temperature at booting were amongst the least sensitive during grain development. Also, the temperature response was found to be dependent on light, with an enhanced sensitivity to high temperature at low irradiance (<10 MJ m-2 day-1). The data did not reveal any clear relationship between the response to temperature, and weight per grain, the number of grains in a head or grains per spikelet of control (18/13�C) plants.