Plant growth regulator effects on spring cereal root and shoot growth

Plant growth regulators (PGR) shorten the straw of cereals, but their effects on other traits of plant stand structure have been inconsistent. To arrive at an assessment of whole-plant response, experiments were conducted in the greenhouse to study the effect of PGR applications on root and shoot growth of spring cereals. Ethephon, chlormequat chloride (CCC), and trinexapac-ethyl were applied during early growth stages to barley (Hordeum vulgare L.), oat (A vena sativa L,), and wheat (Triticum aestivum L,) cultivars grown either in sand mixture or in clay illitic topsoil. The effects on root and shoot growth (mg plant(-1)), root/shoot ratio, tiller number, and weight per main shoot were studied in all cereal species. The response of CO2 exchange rate (CER) (mu mol CO2 m(-2) s(-1)) and formation of yield potential to PGR treatment were studied more closely in "Mahti" wheat. The effect of CCC application on root area (cm(2)), length (cm), specific root length (SRL cm/mg), and width (mum) at soil depths of 0 to 20, 20 to 40, and 40 to 60 cm was studied in Mahti wheat. Plant growth regulator applications reduced main shoot growth in barley and wheat up to 20%, Tiller production was enhanced by ethephon and TE treatment in all species, but not adequately to compensate for PGR-induced reduction in main shoot growth. Carbon dioxide exchange rate was reduced temporarily by ethephon and TE treatments in Mahti wheat, Plant growth regulator applications have modest potential for modifying traits of spring cereal plant stand structure other than straw length.