The Effects of Ethephon, Chlormequat Chloride and Mixtures of Ethephon and Chlormequat Chloride Applied at the Beginning of Stem Elongation on Spike‐Bearing Shoots and other Yield Components of Spring Barley (Hordeum vulgare L.)

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Abstract
Effects of chlormequat chloride (CCC), ethephon and mixtures of CCC and ethephon, applied at Zadoks growth stage (ZGS) 30 (the beginning of stem elongation) on the number of spike‐bearing shoots and their contribution to grain yields of four spring barley (Hordeum vulgare L.) cultivars were studied in 1987 and 1988 at McGill University, Quebec, Canada. The results varied between years and among cultivars. The mixtures of CCC and ethephon or ethephon alone, produced significant increases in the number of spikes m−2 in cultivars Joly and Laurier, in both years, and in Leger only in 1988. Ethephon and ethephon containing mixtures reduced the yields of Joly and Leger in 1988. In both years CCC had no effect on spikes m−2 for all cultivars. Increases in spikes m−2 were accompanied by decreases in 1000‐grain weight, and/or grains per spike, which offset or more than offset potential benefits from increased spikes m−2. These results indicate that under continental climatic conditions such as those prevalent in Quebec, Canada, application of PGRs to spring barley at ZGS 30 does not increase grain yield through an increased number of spikes m−2.