The tolerance of wheat to high temperatures during reproductive growth. III. Booting to anthesis

Abstract

A range of Australian and overseas wheat cultivars was grown in the naturally lighted glasshouses of the Canberra phytotron, with a standard day/night temperature regime of 18/1 3�C. Grain number per main culm ear under these standard conditions was compared with the response obtained when sets of plants were transferred to high temperature (24/19�C, or 30/25�C) over the period from flag leaf ligule to ear emergence (booting), or from ear emergence to the end of anthesis (pollination and fertilization).Some Australian lines such as Isis and Hybrid Titan were tolerant of high temperature at booting, while others such as Pinnacle and Olympic showed a marked sensitivity to high temperature at this stage. Cultivars from the Middle East and tropical areas were generally more tolerant of high temperature at booting than cultivars from regions such as North America and Europe, while the Australian lines were intermediate in their response. With the cultivar Pinnacle, it was shown that at least part of the low fertility associated with high temperature at booting was related to poor pollen development. Commencing the high temperature treatment earlier in the development of the ear and continuing this until ear emergence resulted in adaptation in the cultivar H757 from Afghanistan, which showed an increase in grain set above that of the short high temperature booting treatment. However, this contrasted with the response of the cultivar Banks when the extended high temperature treatment resulted in a further reduction, not an increase in grain set. It was shown that the presence of the rye translocation for rust resistance (1B/1R) in near isogenic lines of Condor resulted in reduced sensitivity to high temperature. This would suggest that species such as rye should be examined more closely for their sensitivity to environmental stress.Exposure to high temperature only during anthesis generally had a small effect oil grain set. Some cultivars showed an increase in grain set, whereas others showed a decrease. Part of this variation may be related to the finding that under high temperature conditions, high humidity (v.p.d. 6.7 mb) could reduce grain set. However, given the normal relation between temperature and humidity in Australia, this effect is likely to be limited to glasshouse conditions.