Not available – first paragraph follows: Conventional plant breeding has steadily improved food production efficiency, but in the process, crops have been selected for genetic uniformity and adaptation to relatively optimal environments. Environmental stresses at particularly vulnerable stages during crop development may severely diminish productivity. Adaptation of crops by genetic means to suboptimal temperatures is among the neglected areas of potentially useful research and development. Sensitivity to chilling in many important crop plants limits their climatic distribution for economic production. Even in areas normally suited to these crops, this sensitivity causes losses through injury suffered from sporadic low temperatures.