Radiotracer and radiation application for rapid measurement of contribution of stem assimilates towards grain filling and for alleviating terminal heat stress in wheat

Abstract

Contribution of stem photoassimilates towards grain filling may have significance under stress, since it may force the plant to initiate an early leaf senescence, thereby limiting the availability of flag leaf photosynthates for grain filling. Radiotracer feeding of 14C-sucrose to the internode by stem injection method at 20 days stage after anthesis and measurement of 14C activity in grains at 5 days after foliar application of potassium iodide, meant to inhibit current photosynthesis by inducing leaf senescence, showed a gradual decline in flag leaf chlorophyll but an increase in accumulation of 14C particularly in the basal spikelet grains. However, a reduction in grain filling at all the sink positions within the wheat ear was measured with hastened leaf senescence. On the other hand, abiotic stresses such as high temperature stress, is known to cause an abortion of the basal florets in wheat and induce an early flag leaf senescence. We have earlier shown that seed gamma irradiation, at 0.1 kGy causes an increase in grain mass at middle and basal spikelet positions. In this paper we report that the reduction in grain yield in response to terminal heat stress can be compensated by gamma irradiation, owing to better stem reserve mobilization into the basal and middle spikelet under condition of stress induced senescence.