Shrunken2 Sweet Corn Yield and the Chemical Components of Quality

Extensive variability was found among 24 currently available commercial sh2 hybrids of sweet corn (Zea mays L.) for yield and yield components, and for the chemical components of eating quality. The primary source of variation was explained by genotypic differences, with the environmental effects due to planting locations having a minor influence. Kernel sugar concentrations, however, had a highly significant level of genotype by environment interaction. The extensive genotypic variability among the sh2 hybrids indicated that allelic variation at other loci is profoundly influencing sucrose and total sugar levels in freshly harvested sweet corn. In each case, the kernel chemical components of quality decreased from 20 to 29 days after pollination (DAP). Mean performance of sh2 hybrids for yield, yield components, and kernel quality parameters was in all cases equal or better than the hybrids homozygous for the su1 endosperm mutation. In addition, there were no strong negative relationships between yield and some of the important chemical components of kernel quality, suggesting that it may be feasible to develop superior sh2 hybrids with acceptable yield potential and improved eating quality targeted for the different sweet corn markets. The primary components of sweet corn eating quality associ- ated with consumer preference are kernel flavor, texture, and aroma (Flora and Wiley, 1974). Sweetness in sweet corn consti- tutes most of what the average consumer perceives as flavor (Culpepper and Magoon, 1927), and it is closely related to kernel sucrose content (Reyes et al., 1982), the primary sugar in develop- ing kernels (Cobb and Hannah, 1981). Textural eating quality of sweet corn consists of several factors, including pericarp tender- ness (Bailey and Bailey, 1938), level of water soluble polysaccha- rides or phytoglycogen (Culpepper and Magoon, 1927), and mois- ture content (Wann et al., 1971). Aroma, which has not been as easily defined as either sweetness or texture, is most often associ- ated with dimethyl sulfide (DMS), a volatile compound described by taste panelists as lending a pleasing and "corn-like" character (Wiley, 1985). Several studies have reported significant differ- ences in DMS levels among sweet corn genotypes and harvest maturities, with DMS content decreasing with increasing kernel age (Dignan and Wiley, 1976; Williams and Nelson, 1973). Traditional sweet corn hybrids homozygous for the sugary1 (su1) mutation are characterized by rapid moisture loss and the conver- sion of endosperm sugars to starch. This decline in quality places a time constraint on the shipment of fresh sweet corn to major urban markets and also creates a very narrow harvest window for the sweet corn processing industry (Marshall, 1987). Conse- quently, there has been a dramatic shift away from the traditional su1 hybrids to hybrids with the shrunken2 (sh2) mutation. Com- pared to su1, the sh2 phenotype is characterized by kernels that have two to three times more sucrose at harvest maturity (Creech, 1965), can retain higher sugar and moisture content for longer postharvest periods (Garwood et al., 1976), and is preferred by consumers in taste tests (Evensen and Boyer, 1986; Showalter and Miller, 1962). While the long-distance shipping market of fresh sweet corn has largely converted to the use of sh2 hybrids, acceptance and use in the processing sector of the industry has lagged behind because there has been a perception that these hybrids display poor stand establishment and yield potential. Some of the first sh2 hybrids released in the 1960s and 1970s suffered from these problems, but numerous extension publications suggest that more recent hybrids have improved yield and enhanced quality. Comparison of sh2 hybrids with widely used su1 hybrids for yield, yield components, and kernel quality is needed to determine any improvements. The following experiments were designed to provide information on the phenotypic variability among commercial sh2 hybrids for yield and yield components, and for the chemical composition of eating quality. Additional objectives were to determine the effect of harvest maturity on the chemical composition of eating quality, examine the relationships between yield, yield components, and quality attributes, and provide sweet corn breeders with the infor- mation needed to develop superior sh2 hybrids.