Effects of seed treatment with a plant growth regulator on growth and tillering in spring barley (Hordeum distichum) cv. Triumph

Doses of the growth retardant, Terpal, were applied to seeds of spring barley. Germination was delayed as the concentration and duration of exposure to Terpal increased. Tiller bud outgrowth was promoted in treated seedlings and at maturity the total tiller production and number of ear-bearing tillers per plant was increased by the Terpal treatment. The yield of the main shoot was similar in both control and treated plants but the mean ear weight of the tillers was reduced in the latter, and thus there was no overall effect of the treatment on yield. Observations on vegetative plants showed that Terpal also reduced the growth of successive main shoot leaves and the elongation and dry weight of the seminal root system. The results are discussed in terms of an early modification in the distribution of resources during establishment that favour the outgrowth of tiller buds at the expense of the initial development of the main shoot and root system. It is proposed that seed treatment is a viable alternative to foliar spraying particularly in arid regions.