Pericarp Thickness, Tenderness, and Freeze-drying of Super-sweet Maize

Abstract

Mass selection for tenderness was conducted on the variety 'Hawaiian Super-sweet No. 9' corn which was found to vary widely in tenderness. Selection was carried out on a 10 % selection intensity using criteria of pericarp thickness and bite-test. Selection was carried out for 3 cycles by pericarp thickness measurements and for 4 cycles by bite-testing. All cycles of selection were evaluated by both bite-testing and by pericarp thickness measurements. In the first cycle of selection where pericarp thickness and bite-test measurements were taken on the same ear, a significant product moment correlation coefficient (r = 98%) was found between bite-test scores and pericarp thickness measurements. Pericarp thickness evaluation on the cycles of selection indicated that pericarp thickness decreased by a greater margin when selected for by pericarp thickness than by bite-testing. However, when all cycles of selection were evaluated by bite-testing, the bite-test scores dropped more significantly for selection by bite-testing than by pericarp thickness measurements. There was no significant interaction between the germinal and abgerminal positions measured on the pericarp and the cycles of selection. A generation mean analysis involving crosses between thick and thin pericarped parents was conducted to evaluate the genetics of pericarp thickness. Additive and dominance gene effects were significant in determining pericarp thickness with additive effects being larger. The narrow sense heritability estimate was 51%. The average number of effective factors ranged from 1 through 7. No significant difference in pericarp thickness was: found between su and + kernels segregating on the FI ears. Nine mainland sweet c o m hybrids (Jubilee, Stylepak, Bonanza, NK51036, GCB (N), GCB (T), Midway, and Gold Winner) and a tropical sweet corn hybrid (E68) were evaluated at the locations of Waimanalo and Lalamilo to assess the effect of temperature on pericarp thickness. Generally, all except 3 hybrids Clobelle, GCB (N), and GCB (T)) behaved similarly at both locations. Pericarp thickness was also observed to be lower at sweet corn stage than at maturity. A survey of pericarp thickness on 85 different races of maize was conducted. Some of the races that were duplicately sampled differed only by a second descriptive name for ear characteristics. In some cases, these were similar in pericarp thicknesses while in other cases they were different in pericarp thicknesses. Some of the same races maintained in different seed lots were dissimilar in pericarp thickness. A wide genetic variation in pericarp thickness occurred in the group of races analyzed. Pericarp thickness ranged from 35.8 to 124.4 microns. Two experiments were conducted to evaluate the influence of various endosperm genotypes on the pericarp thickness. In the first experiment, 15 mutants backcrossed to CM104 were evaluated for pericarp thickness. Generally, all mutants highly backcrossed into CM104 were of similar pericarp thicknesses. However, the sh2 mutant seemed to be linked to thick pericarps. Otherwise, there is no evidence of the underlying endosperm affecting pericarp thickness. In the second experiment, 8 inbred lines and their o2 counterparts were analyzed for pericarp thickness. No consistency was found in the data. Half of the comparisons indicated no differences between the + and o2 lines whereas significant differences occurred in the other half. A series of three freeze-drying experiments were conducted on 'Hawaiian Super-sweet No. 9' to improve the methodology and quality of the freeze-dried product. These were: 1) blanched versus unblanched kernels, 2) maturity preferences, and 3) increasing concentrations of brine solution applied to the kernels prior to freeze-drying. The first two experiments were evaluated by sensory panelists on the quality of appearance and flavor. The last experiment was evaluated by flavor only. Blanched and unblanched kernels were of similar flavor, but the blanched kernels were rated higher in appearance. Thus, they were selected over unblanched kernels. A harvest date of 25 days after pollination was selected as the optimum maturity by criteria of appearance and flavor. No treatment of the kernels with brine was found to be most practical in preparing a commercial freeze-dried super-sweet corn product.