RADIATION INTERCEPTION AND RADIATION USE EFFICIENCY OF NEAR-ISOGENIC WHEAT LINES WITH DIFFERENT HEIGHT

Three near isogenic lines of spring wheat grown to determine whether R ht dwarfing alleles alter radiation interception. A field study (invol ving two sowing dates in two growing seasons) with lines containing di fferent allelic dosage of Rht1 and Rht2 (i.e. dwarf, DD; semi-dwarf, S D and tall SH), was conducted without water and nutritional deficienci es. Dwarfing genes did not modify the timing of occurrence of phenolog ical events. Above-ground biomass at anthesis was reduced by 22% in th e DD line in relation of the rest of the lines. However, at maturity a ccumulated biomass of the DD and SH lines were not significant differe nt. Dwarfing genes increased the light attenuation coefficient (k, wit h values of 0.48, 0.62 and 0.78 for the SH, SD and the DD line respect ively). A similar trend was followed to the leaf thickness (estimated by the specific leaf weight, SLW). Despite the differences observed am ong the lines, both in k and SLW values, they did not differ significa ntly in the proportion of incoming radiation intercepted by the canopy , nor in the cumulative intercepted radiation during the pre and post- anthesis periods. Radiation use efficiency (RUE) differed significantl y among the lines. While RUE during pre-anthesis was the lowest in the DD line, from anthesis to maturity the lines with Rht alleles showed higher RUE values than the SH line. The low pre-anthesis RUE in the DD lines could be associated with (i) poor canopy architecture due to re ductions in leaf sheath and internode lengths and/or (ii) reduced cano py CO2 exchange rate. Post-anthesis RUE was lower than that recorded p re-anthesis in all lines. But the magnitude of the reduction was inver sely related to the doses of the Rht alleles. Post-anthesis RUE appear ed to be closely and positively associated with the number of grains s et per unit biomass at anthesis. This relationship suggests a regulato ry effect of the sink size on the efficiency of the crop to convert ra diation into biomass during this period.