Effects of Stem‐Injected Sucrose on Photosynthesis and Productivity of Water Stressed Corn Plants

Abstract

AbstractWater 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 silking was a major factor in the resulting reproductive failure. A greenhouse experiment was conducted to test the hypothesis that sucrose supplementation of water stressed corn plants can prevent decreased kernel set. Sucrose was injected into corn stems at three concentrations [0 (distilled water), 150 and 300 g L−1] for 30 days starting at silking. Water availability was controlled by either maintaining a water table at 50 cm from the soil surface (well watered) or by withholding water starting one week before silking (water stress) until the fifth day after 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 mL 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 sucrose were injected into corn plants during the 30 day injection period. 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. Injection of 300 g sucrose L−1 increased the weight of the injected internodes by 28%, compared with distilled water injection. The highest grain yield was for the plants injected with 150 g sucrose L−1, but only under 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 under conditions of sufficient soil water supply. These results indicate that plant reproductive development after silking was limited more by water availability than assimilate supply, suggesting that some overall plant response to water stress, perhaps mediated by hormonal signalling, was more important than carbohydrate supply. These results indicated that plant desiccation occurred during floral development or pollination; irreversible loss of florets on unsuccessful pollination could result, thus, grain yield would be limited more by sink size than by availability of photosynthate.