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Pollination Bags Affect Wheat Spike Temperature

Dep. of Crop and Soil Sciences, Washington State Univ., Pullman, WA 99164-6420

^* Corresponding author.

Although breeders use pollination bags routinely in their crossing programs, the effect of pollination bag materials and sizes on wheat (Triticum aestivum L.) spike temperature has not been determined. Some bag materials may trap heat, like a miniature greenhouse, allowing spikes to reach lethal temperatures on hot days. The objectives of this study were to evaluate the effects of pollination bag types on wheat spike temperature, and to compare temperature estimates from an energy budget with measured values. In one field experiment, notable differences were detected in spike temperatures when dialysis tubing or white onion skin typing paper covered the emasculated (simulated) wheat spikes. The measured temperature differences between these pollination bag types were 2 to 3.5 °C at noon on clear days. The dialysis bag consistently produced the highest spike temperatures. Maximum spike temperatures were 6 °C above air temperature for bagged spikes. A second field experiment measured larger differences in spike temperature among five types of pollination bags. Measured spike temperature was highest with a glassine bag and lowest with a bag of white onion skin typing paper wrapped around the spike. Maximum differences at noon on clear days between these pollination bags were 4 to 6 °C, and maximum spike temperatures inside bags were 8 °C above air temperature. Such high temperatures could by physiologically damaging when air temperatures are high. Estimates of spike temperature using an energy budget model were similar to measured values. Both measured and modeled results show that the lowest spike temperatures will occur when a white, small-diameter pollination bag covers the wheat spike.

Received for publication July 29, 1991.