Plant growth regulator effects on spring cereal root and shoot growth

Plant growth regulators (PGR) shorten the straw of cereals, but their effec ts on other traits of plant stand structure have been inconsistent. To arri ve at an assessment of whole-plant response, experiments were conducted in the greenhouse to study the effect of PGR applications on root and shoot gr owth of spring cereals. Ethephon, chlormequat chloride (CCC), and trinexapa c-ethyl were applied during early growth stages to barley (Hordeum vulgare L.), oat (A vena sativa L,), and wheat (Triticum aestivum L,) cultivars gro wn either in sand mixture or in clay illitic topsoil. The effects on root a nd 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 exc hange 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 (SR L 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 enh anced by ethephon and TE treatment in all species, but not adequately to co mpensate for PGR-induced reduction in main shoot growth. Carbon dioxide exc hange rate was reduced temporarily by ethephon and TE treatments in Mahti w heat, Plant growth regulator applications have modest potential for modifyi ng traits of spring cereal plant stand structure other than straw length.