Source and sink development during kernel filling of two spring wheats as affected by root size and cytokinin applications

The effects of partial root removal and cytokinin applications at different times during kernel filling were examined at two contrasting wheat genotypes grown in controlled environmental conditions. Treatments affected the development of leaves, and grain setting, but hardly grain growth; the influence strongly depended on time, but not on genotype. Cutting off roots „early” after heading caused immediate damage, especially in the lower leaves. Later on, chlorophyll decomposition and loss of green area was accelerated. „Early” cytokinin applications were not able to prevent these effects. If root size was reduced at a „medium late” or „late” stage no spontaneous effects were observed, but leaf senescence was more drastic, the later the treatments were carried out. Enhancement of senescence due to root removal, could generally be inhibited by (medium) „late” cytokinin applications. As to grain setting, „early” cytokinin applications could not counteract the reduction induced by „early” root removal. In most of the trials there was no evidence that root removal or cytokinin applications affected grain growth. Some secondary effects of the treatments on root growth are discussed with regard to the importance of root system as a site of cytokinin synthesis during grain filling.