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Modification of Tiller Productivity in Spring Barley by Application of Chlormequat or Ethephon

Dep. of Plant Science, P.O. Box 4000, Macdonald Campus of McGill Univ., 21,111 Lakeshore Rd., Ste. Anne de Bellevue, PQ, Canada H9X 1C0

^* Corresponding author.

Application of plant growth regulators (PGR) to control lodging in cereal crops often increases the number of tillers and/or spikes. It is not clear whether the increment in spike numbers is due to enhanced tiller production or to an increased percentage of tiller spikes. The objective of this study was to evaluate the timing of chlormequat (2- chloroethyl-N,N,N-trimethylammonium chloride) (CCC) or ethephon (2-chloroethyl phosphonic acid) application on tiller production and subsequent tiller growth and development in spring barley (Hordeum vulgare L.). A 3-yr field study with two widely grown cultivars, Leger and Cadette, was conducted on Bearbrook clay soil (fine, mixed, nonacid Mesic Humaquept) at the Emile A. Lods Agronomy Research Center, McGill University, Canada, from 1988 to 1990. Treatments consisted of CCC (1.2 kg a.i. ha^–1) or ethephon (0.48 kg a.i. ha^–1) applied at Zadoks growth stages (ZGS) 13,30, or 39. Tiller production was monitored at ZGS 12,32,51, and 90. Plants treated with an early application of CCC (ZGS 13 or ZGS 30) or ethephon (ZGS 30) produced greater numbers of shoots, appearing later in time, than control plants. Early PGR treatment increased the number of spike-bearing shoots, primarily by enhancement of tiller number (tiller-derived spikes) rather than the spike production rate (tiller survival). Late application of CCC or ethephon at ZGS 39, when most of the tillers had emerged, resulted in a higher number of spike-bearing shoots, mostly through the increased percentage of tiller spikes.

Received for publication April 22, 1991.