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 Rht dwarfing alleles alter radiation interception. A field study (involving two sowing dates in two growing seasons) with lines containing different allelic dosage of Rht1 and Rht2 (i.e. dwarf, DD; semi-dwarf, SD and tall SH), was conducted without water and nutritional deficiencies. Dwarfing genes did not modify the timing of occurrence of phenological events. Above-ground biomass at anthesis was reduced by 22% in the DD line in relation of the rest of the lines. However, at maturity accumulated biomass of the DD and SH lines were not significant different. Dwarfing genes increased the light attenuation coefficient (k, with values of 0.48, 0.62 and 0.78 for the SH, SD and the DD line respectively). A similar trend was followed to the leaf thickness (estimated by the specific leaf weight, SLW). Despite the differences observed among the lines, both in k and SLW values, they did not differ significantly 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 significantly 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 reductions in leaf sheath and internode lengths and/or (ii) reduced canopy CO2 exchange rate. Post-anthesis RUE was lower than that recorded pre-anthesis in all lines. But the magnitude of the reduction was inversely related to the doses of the Rht alleles. Post-anthesis RUE appeared to be closely and positively associated with the number of grains set per unit biomass at anthesis. This relationship suggests a regulatory effect of the sink size on the efficiency of the crop to convert radiation into biomass during this period.