Morphological and anatomical modifications in winter barley culm after late plant growth regulator treatment

One of the major factors limiting yield production in barley (Hordeum vulga re L.) has been its poor straw strength. Consequently, a greater stiffness of the upper part of the culm was desirable. So, a late application of plan t growth regulator could be interesting for weak-strawed barley cultivars. The objective of these experiments was to investigate the effect of a late application of a combination of chlormequat chloride (2-chloroethyl-trimeth yl-ammonium chloride), ethephon (2-chloroethyl phosphonic acid) and imazaqu in (2-[4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl] nicotinic acid) on the morphological and anatomical characteristics of barley main stems. In a fi eld trial and a greenhouse experiment, a foliar treatment was applied to a two-row winter barley (Labea) at growth stage 7 (Feekes, 1941). Measurement s of plant height, internode lengths, dry weights and microscopic examinati on of cross-sections of the top three internodes were made at anthesis. The plant growth regulator (PGR) decreased significantly plant height by reduc ing the length of the upper internodes. The PGR did not modify the total we ight of the upper internodes, but induced an increase of the dry weight per unit length of the main stem. The shortening of the internodes combined wi th the higher density of the tissues contributes to the stiffness of the st em. This was confirmed by anatomical studies which showed the modifications of the supporting tissues. The application of the plant growth regulator d id not affect grain yield. (C) 1999 Elsevier Science B.V. All rights reserv ed.