GENETIC VARIATION FOR TEMPERATURE RESPONSE IN ALFALFA (MEDICAGO SATIVA L.)

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Abstract
Physiological studies had indicated that low mid-summer yields of alfalfa (Medicago sativa L.) can be attributed to high temperature. A program was initiated to study genetic variation for response to high temperatures. Two thousand genotypes were grown from seed in the growth room at 20/15 °C, harvested twice, then grown at 30/25 °C for two more harvests. A great deal of variation among genotypes was found to exist for response to temperature. Genotypes that were found to yield well at higher temperatures tended to be early-maturing with few stems per plant. Genotypes that yielded well at low temperatures tended to be later in maturity and to have a large number of stems. Based upon dry matter yields, 300 genotypes were selected to represent differences in responses, namely: 100 had high yields at high temperature only; 100, high at low temperature only; and 100, high at both temperatures. These selections were transplanted to the field for subsequent field trials to substantiate growth room findings. Little or no relationship was found between growth room performance and field performance. This lack of association was due in part to winter injury experienced the first year. In addition, temperatures experienced in the field were much lower than those used indoors.

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