CONSEQUENCES OF BREEDING ON BIOMASS, RADIATION INTERCEPTION AND RADIATION-USE EFFICIENCY IN WHEAT

Field experiments were conducted during 1991 and 1992 to identify the effect of wheat breeding on crop biomass production and its physiologi cal determinants, i.e. radiation interception and radiation-use effici ency. To address this objective, biomass accumulation and its physiolo gical attributes of seven cultivars (including a commercial hybrid) re leased between 1920 and 1990 were compared in fertilised and irrigated plots. Weeds, pests, diseases and lodging were controlled or prevente d. Crop radiation interception was calculated from measurements of inc ident and transmitted radiation at different times after sowing. Above -ground dry matter was determined at particular stages of development of the cultivars. Radiation-use efficiencies and crop growth rates wer e calculated for each cultivar for pre-anthesis (in both years) and po st-anthesis (in 1992) periods. Biomass at anthesis tended to be less i n most recently released cultivars than in older materials. Accumulate d intercepted radiation at similar developmental stages also differed between cultivars. These differences, as well as the trend of biomass at anthesis, were caused by differences in the length of developmental phases between cultivars rather than by changes in the architecture o f the canopies. The most recently released cultivars had shorter seedl ing emergence-anthesis periods than older cultivars. Moreover, all cul tivars had similar canopy Light extinction coefficients (k), pre-anthe sis radiation-use efficiencies, and crop growth rates. After anthesis, the two oldest cultivars accumulated the least biomass and their radi ation-use efficiencies and crop growth rates were smaller than those o f modem cultivars. Remarkably, modern cultivars maintained during post -anthesis almost the same levels of crop growth rates and radiation us e efficiencies reached during the pre-anthesis period.