SCREENING TECHNIQUES AND SOURCES OF TOLERANCE TO EXTREMES OF MOISTUREAND AIR-TEMPERATURE IN COOL-SEASON FOOD LEGUMES

Breeding for resistance to extremes of temperature and moisture in coo l season food legumes is limited by the lack of adequate screening tec hniques. The success of each technique depends upon the representative ness and reproducibility of the type of stress created. Descriptions o f successful techniques are presented for frost and terminal drought. Development of new screening tests designed to select for specific ada ptive traits require a better knowledge of the mechanisms of resistanc e in these crops, especially to drought. Rooting depth, early vigor, r educed branching, and osmotic adjustment are discussed. Other mechanis ms of resistance to drought, heat, freezing, or chilling have been pro posed but need to be studied jointly by crop physiologists and plant b reeders.