Geographical variation in heading date was investigated for wild emmer wheat, Triticum dicoccoides, collected in Israel. A wide variation ranging from 6th April to 8th May was observed among 404 accessions, and inter- and intra-population variations were also detected. Correlation analysis with eco-geographical variables clearly showed that early heading types are adapted to warmer and drier conditions, while late heading types are adapted to cooler and more humid conditions. Especially for the inland populations, about 2/3 of the inter-population variation could be explained by five eco-geographical variables, that is, altitude. temperature, rainfall. humidity, and evaporation. Intra-population variation was also largely affected by temperature and water conditions. In contrast to the relatively uniform populations in the western area, the variation was larger in the southeastern area where wild emmer wheat grows under severe aridity stress. Considering that vernalization response and narrow-sense earliness were related to heading dale in wild emmer wheat, the variation of these traits was essential for the adaptation to macro- and microgeographical heterogeneities or instability of growing conditions. It was concluded that eco-geographical heterogeneity is an important indicator to measure the genetic variability of adaptive traits.
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