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- Author or Editor: David Davis x
- Journal of the American Society for Horticultural Science x
This study was conducted to investigate the effects of mild mass selection for adaptation on the performance, genotypic variance, combining ability, S1 family-testcross correlation, and midparent heterosis of S1 families derived from a sweet corn (su) × tropical maize (Zea mays L.) composite (Composite 1R). Four cycles of random mating followed by 10 cycles of 10% stratified mass selection were conducted for earliness, plant and ear type, and freedom from pests. Selection significantly (P < 0.01) decreased plant height, ear height, percentage barrenness, and ear length, and significantly (P < 0.01) increased stalk breakage, earliness (Celsius heat units to 50% anthesis and silking), and kernel row number of both S1 families and their testcrosses. Juvenile plant height at 45 days after planting increased in testcrosses only. Percentage tip blanking and pericarp thickness did not change. For most traits, the greatest response occurred during the first five of 10 selection cycles. Cycle 10 testcrosses performed at least as well as elite check testcrosses for eight of 10 traits. The tropical parents improved combining ability for increased juvenile plant height and kernel row number, and decreased percentage of stalk breakage. As a result of selection, genotypic variance among S families decreased by >40% for heat units to 50% anthesis and silking, ear height, and percentage of barrenness, although for all traits measured, significant genotypic variation persisted following 10 cycles of mass selection for adaptation. S1-testcross correlations and percentage midparent heterosis tended to be consistent across selection cycles. Five cycles of mild stratified mass selection increased the adaptation of a temperate sweet corn × tropical maize composite to the temperate zone of the United States while maintaining significant genotypic variation.
Concern over insecticide usage for control of European corn borer (Ostrinia nubilalis Hübner) in sweet corn (Zea mays L.) in recent years has increased the need for genetic control. Our objectives were to determine the degree of ear feeding resistance transmitted by resistant breeding lines to testcrosses and to investigate the relationship between resistance and both ear silk channel length, and infestation level. Testcrosses averaged 35% acceptable ears compared to 7%. for two commercial control hybrids and 45% for the lines per se when artificially infested at the ear tip at mid-silk at two locations. Generally, resistance in the testcrosses was closer to the resistance level of the resistant parent, indicating good combining ability for resistance. Heterosis above the resistant parent was found in 8 of 12 testcrosses. Across entries, ears having relatively longer silk channel length tended to have less damage but the relationship was not strong (r 2 = 0.24, P < 0.01). When silk channels were artificially shortened at infestation, resistance levels were lower, but five of seven lines had a higher proportion of acceptable ears than did the control hybrid. Across increasing levels of infestation from 50 to 200 neonate larvae per ear eight of nine lines had higher resistance (P < 0.05) than the control.
Abstract
Pea seed yield (W) and its components—pods per plant (X), seeds per pod (Y), and average seed weight (Z)—and also seeds per plant were found to be controlled by an additive genetic system, on the average. The existence of some departure from additivity was indicated by deviation of the F1 from the midparent, especially for X, W, and seeds per plant. This deviation was more likely due to epistasis or linkage than to dominance. Specific Heterosis (specific combining ability) was important for all components, while Variety Heterosis (general combining) was important only for Y and Z. Estimates of heritability were high, ranging from .38 for seeds per plant to .65 for Z. Yield was found to be closely related to X, Y, and Z in descending order. Pods per plant (X) probably is a good selection index for dry seed yield in the pea.
Abstract
Procedures for forced field infestation of maize with European corn borer egg masses, placed to simulate possible natural ovipositional sites and to emphasize damage to the ear, were compared. A growth chamber procedure using excised ears and a free-choice (preference) infestation procedure were also used. Forced infestation in the field permitted infestation at a uniform relative maturity and uniform development of borers from time of infestation to evaluation. An ear-and-leaf infestation procedure appeared to be the most appropriate for simultaneous evaluation of kernel damage and stalk tunneling. Estimated heritabilities, using this procedure on 2 segregating populations, were 0.71 and 0.84 for kernel damage and 0.39 and 0.79 for stalk tunneling. Phenotypic correlations among 3 ear damage criteria were noted (r = 0.42 to 0.46). Evaluation based on kernel damage alone, excluding cob tunneling and number of surviving larvae, was considered sufficient. There was no evidence that kernel damage was influenced by level of stalk tunneling.
Abstract
Artificial was compared to natural infestation for evaluating kernel damage and stalk tunneling on maize (Zea mays, L.) caused by European corn borer (Ostrinia nubilalis, Hiibner) larvae. Under conditions of natural infestation, differential damage levels among families were more closely correlated with silk date than oviposition frequencies on the host plants. The association between damage and silk date was reduced following artificial infestation. Artificial infestation, which permits infestation at a common stage of maturity (full silk), a uniform and greater insect population on host plants, and a uniform opportunity for larval development on the ear from time of infestation to time of evaluation, is preferred for differentiating maize genotypes for borer resistance.
Abstract
The inheritance of interlocular cavitation (IC), characterized by rupture of the soft, parenchymatous endocarp tissue between the seed locules in developing snap bean pods, was studied using 6 parental cultivars, all 30 possible F1 progenies grown in the greenhouse, and the 30 F2 families grown at various planting dates at 2 field locations.
IC appeared to be a highly heritable character conditioned by a predominantly additive polygenic system with partial dominance for resistance. Reciprocal effects were negligible. Neither epistasis nor transgressive segregation was detected. Order of susceptibility among genotypes was maintained over the wide range of environments. Genotype × environment interaction was significant, but was relatively small compared to total genetic variability. Association between greenhouse-grown F1 and field-grown F2 plants was high for degree of IC, suggesting that F1 performance might be informative in choosing superior crosses. Breeding progress appears to be feasible in a program designed to utilize the large amount of additive genetic variance.
Abstract
Interlocular Cavitation (IC) in snap bean pods was studied in 8 commercial cultivars under several irrigation regimes on a sandy soil. In susceptible cultivars, IC was consistently associated with heavy irrigation during pod growth. Little or no IC was found when no more than 1.27 cm of water was applied per week. Irrigation also influenced pod yield, plant weight, ratio of pod weight to plant weight, pod composition, and seed number. Cultivars susceptible to IC showed rapid increase in pod weight when irrigated after 2-3 weeks of moisture stress conditions. However, this rapid increase in pod weight did not induce IC under the conditions tested. Proportion of pod P and K in relation to Ca and Mg increased as irrigation levels were increased. Seed number was related to irrigation and the severity of IC, depending upon cultivar.