Sugar Accumulation in Shrunken-2 Sweet Corn Kernels

Sweet corn (Zea mays L.) quality is judged in part by the sugar concentration of its kernels at fresh harvest. Genotypes promoting high kernel sugar throughout the fresh harvest period may improve sweet corn quality and consumer acceptance. This study was undertaken to determine the influence of environment, harvest date, and inbred parent on kernel sugars of shrunken-2 (SuSu sh2sh2) sweet corn hybrids. Ten hybrids from a diallel cross of five shrunken-2 sweet corn inbreds were assayed for reducing sugar, sucrose, and total sugar as proportion of kernel dry weight. Kernels were sampled at three fresh harvest dates in 3 yrs. Warmer seasons resulted in lower reducing sugar and higher sucrose at Harvests 1 and 2 (200 and 245 thermal units after pollination, base 10 °C), while cooler seasons were associated with higher reducing sugar and lower sucrose. At Harvest 3 (290 thermal units after pollination), reducing sugar was near 45 g kg⁻¹, and sucrose was near 325 g kg⁻¹ in all years. Compensation by these two carbohydrates at Harvests 1 and 2 led to uniformity in total sugar among years. Total sugar was near 430 g kg⁻¹ at Harvest 1, 415 g kg⁻¹ at Harvest 2, and decreased to near 370 g kg⁻¹ at Harvest 3. Hybrid differences were detected for sucrose and total sugar, but not for reducing sugar. The predominance of specific combining ability (SCA) and SCA ✕ harvest effects on sucrose indicate that the concentration and pattern of sucrose accumulation in each hybrid depended upon the combination of inbreds involved in the cross. In addition to SCA and SCA ✕ harvest effects, total sugar was also influenced by general combining ability (GCA) effects; hybrids sharing a common inbred had similar levels of total sugar accumulation. Kernel sugar was high in these shrunken-2 sweet corn hybrids relative to standard sugary (susu Sh2Sh2) sweet corn hybrids. Sugar concentration at any one harvest was not as useful for selection among these hybrids as stability of sugar concentration throughout the fresh harvest period. Two hybrids were found not to change significantly in total sugar during the harvest period. One inbred generally promoted stability in kernel sugar across harvests in its crosses.