Genetic divergence of heat production within and between the wild progenitors of wheat and barley: evolutionary and agronomical implications.

We compared and contrasted calorimetrically heat production in seedlings incubated at 5°C and 24°C using genotypes from cold and warm Israeli populations of the wild progenitors of barley (Hordeum spontaneum) and wheat (Triticum dicoccoides). The wild barley sample comprised 14 accessions, 7 from cold localities and 7 from warm localities. The wild emmer wheat sample consisted of 12 accessions, 6 from a cold locality, and 6 from a warm locality. Our results indicated that (1) heat production was significantly higher in the two wild cereals at 5 °C than at 24 °C; (2) interspecifically, wild barley generates significantly more heat than wild wheat at both 5 °C and 24 °C; (3) intraspecifically, wild barley from warm environments generates significantly more heat than wild barley from cold ones, at 24 °C. We hypothesize that both the inter- and intraspecific differences in heat production evolved adaptively by natural selection in accordance with the niche-width genetic variation hypothesis. These differences presumably enhance biochemical processes, hence growth, thereby leading to the shorter annual cycle of barley compared to that of wheat, and may explain the wider range of the wild and cultivated gene pools of barley, as compared with those of wheat. We propose that a shortening of the growth period through utilizing heat production gene(s) is feasible by classical methods of breeding and/or modern biotechnology.