ROOTING PATTERNS IN NEAR-ISOGENIC LINES OF SPRING WHEAT FOR DWARFISM

The effects of Rht alleles on root growth and distribution in isogenic lines of spring wheat (Triticum aestivum L.) are described under diff erent environmental conditions. Above-ground biomass, root length, roo t dry-weight and their distribution along the soil profile were measur ed by destructive sampling for growth of aerial biomass and extraction of soil cores containing roots. Field-experiments were conducted unde r non-limiting water and nutritional conditions during two consecutive years, using an early and a late sowing date each year.Dwarfing genes significantly reduced plant height and above-ground biomass at anthes is. In addition, stem mass ratio also was reduced with increases in th e allelic dosage. Conversely, total root length and root dry-weight pe r unit area at anthesis were increased with decreased plant height, th erefore, root mass ratio tended to be negatively correlated with plant height. Differences in distribution of root length and root dry-weigh t through the soil profile among lines were largely confined to the up per soil layers (i.e. the top 30 cm). Differences in root dry-weight w ere more important than in root length, so that the dwarf line had the highest root mass per unit root length. Furthermore, a significant po sitive correlation between the root mass ratio and stem mass per unit stem length was found. It is suggested that increases in root mass per unit root length associated with Rht alleles are evidencing a surplus of photoassimilates during stem elongation which are used for thicken ing the roots due to the lack of alternative sinks. Agronomic implicat ions of this effect are discussed.