EFFECTS OF STEM-INJECTED SUCROSE ON PHOTOSYNTHESIS AND PRODUCTIVITY OF WATER-STRESSED CORN PLANTS

Water stress during silking or early kernel development decreases the number of kernels set by corn (Zea mays L.) plants. Previous work has suggested that lack of assimilate supply due to water stress at silkin g was a major factor in the resulting reproductive failure. A greenhou se experiment was conducted to test the hypothesis that sucrose supple mentation of water stressed corn plants can prevent decreased kernel s et. Sucrose was injected into corn stems at three concentrations [0 (d istilled water), 150 and 300 g L-1] for 30 days starting at silking. W ater availability was controlled by either maintaining a water table a t 50 cm from the soil surface (well watered) or by withholding water s tarting one week before silking (water stress) until the fifth day aft er silking. The photosynthesis rate of water stressed plants was 25 % that of well-water plants on the first day of silking. On average, the daily injection rate for distilled water was 1 mt higher than that of the sucrose treatments over a 30 day injection period. No difference in daily uptake rate was observed between the 150 and 300 g sucrose L- 1 treatments. Over water availability treatments approximately 17 g su crose were injected into corn plants during the 30 day injection perio d. Corn plants receiving sufficient water supply produced bigger ears, with more seeds and greater 100-seed weight values, leading to higher total plant dry matter accumulation than water stressed plants. Injec tion of 300 g sucrose L-1 increased the weight of the injected interno des by 28 %, compared with distilled water injection. The highest grai n yield was for the plants injected with 150 g sucrose L-1, but only u nder sufficient water supply. The plants injected with 300 g sucrose L -1 produced the least grain regardless of moisture availability. Thus, the exogenous sucrose supplementation influenced kernel set only unde r conditions of sufficient soil water supply. These results indicate t hat plant reproductive development after silking was limited more by w ater availability than assimilate supply, suggesting that some overall plant response to water stress, perhaps mediated by hormonal signalli ng, was more important than carbohydrate supply. These results indicat ed that plant desiccation occurred during floral development or pollin ation; irreversible loss of florets on unsuccessful pollination could result, thus, grain yield would. be limited more by sink size than by availability of photosynthate.