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- Author or Editor: James L. Brewbaker x
Abstract
‘Hawaiian Super-sweet #9’ is a high-sucrose vegetable corn cultivar bred for the tropics, based on the gene brittle-1. It is harvestable over a longer period than traditional sweet corns (sugary-1) and retains its quality much longer following harvest. It produces high yields on plants of a field corn appearance, with high lodging resistance, low ear position, and large seeds on well-covered ears.
Abstract
‘Hawaiian Super-sweet #6’ is a high-sucrose, high-protein vegetable corn cultivar based on the gene, brittle-2. It is harvestable over a much longer period than sweet (sugary-1) corns, and has exceptional quality retention following harvest. When rehydrated following air- or freeze-drying, ‘Hawaiian Super-sweet #6’ makes a highly acceptable vegetable.
“Waimanalo Supersweet” will be released at the time of the 1992 ASHS meeting in Hawaii. A singlecross supersweet corn based on the brittle gene, “Waimanalo Supersweet” represents over 50 generations of inbreeding and backcrossing in Hawaii. Successive projects involved the development of sugary inbreds and their conversion to Mv. Ht. Rp-d and brittle genes. The inbred parents have very limited temperate germplasm and are relatively daylength sensitive. This single cross hybrid and its related 3X (“Hawaiian Supesweet #10”) and OP variety (“Hawaiian Supersweet #9”) show tolerance to Puccinia sorghi rust and Fusarium Moniliforme kernel rot greatly in excess of commercial sweet corns to which they have been compared, and they have performed capably throughout the tropics. Available data on pest tolerance, growth and quality will be summarized.
Pericarp thickness in maize (Zea mays L.) was analyzed by generation mean analysis for backcross and F2 populations from eight hybrids, derived from two thin-pericarped sweet corn inbreds—AA8 and 677a (55 and 51 μm)—crossed with four field corn inbreds—B37, B68, H55, and Hi26 (range 82-132 μm). Average heterosis was −12.5% and segregating progeny distributions were skewed toward those of thin-pericarped parents. Narrow-sense heritability was high, averaging 55.2%, and the number of effective factors was low, ranging from 1.4 to 5.9 and averaging 3.3. Epistatic effects were as large as additive or dominance effects in many crosses, urging caution in applying models that exclude gene interactions to determine variance components and heritabilities. The mode of action in reducing pericarp thickness appeared to differ among the two thin parents, with AA8 affecting the differential thickening of germinal vs. abgerminal walls, and 677a reducing the number of pericarp cell layers. All genetic parameters suggested that genetic progress in backcross conversions to thin pericarp in sweet corn breeding would be rapid irrespective of the pericarp thickness of exotic parents.
Abstract
Mass selection for improved tenderness was conducted in the corn (Zea mays L.) cultivar ‘Hawaiian Super-sweet No. 9’. Two selection criteria were applied separately—a pericarp thickness measurement of mature kernels, and a bite test of immature ears on the plant. Selection was carried out at 10% intensity among 400 ears each for 3 cycles by pericarp thickness and for 4 cycles by bite test. Selection based on pericarp thickness led to a genetic advance of 9.2% per cycle (from average 73.6 to 53.3 μm), with a concomitant 2.9% increase per cycle in tenderness as evaluated by the bite test. Genetic advance following selection based on the bite test was 3.9% per cycle as evaluated by the bite test and 2.9% per cycle as evaluated by pericarp micrometry, the germinal and abgerminal sides of pericarp differed consistently, with germinal 14.5% thinner than the abgerminal, but correlated so well for all cycles that only one side is advised in a selection program. A significant correlation (r=0.98) was found between average bite-test scores and immature pericarp thickness, but correlations based on individual ears were low (r=0.24). Bite-test scores were subject to high error variability (CV =25%) as opposed to pericarp micrometry (CV=12%). Both techniques deserve recommendation for tenderness-selection programs, possibly as tandem criteria for successive cycles of selection.