Search Results

You are looking at 1 - 10 of 33 items for

  • Author or Editor: David W. Davis x
Clear All Modify Search
Author:

Abstract

From June 6 to July 21, 1979, I visited Cuba as a member of a team of 4 agricultural science faculty from the University of Minnesota. Our general goal was to assist in determining the advisability of further development of a preliminary agricultural and veterinary faculty and student exchange program between Cuba and the University of Minnesota. The more specific objectives were to observe and interpret the current status of agricultural production and research, with special attention to organizational structure, educational programs, and research priorities and progress in relation to national production goals. Included were one faculty member each from plant pathology, animal science, veterinary medicine, and horticultural science.3 Our visit represented the first on-site analysis of training, research and production in Cuba by U.S. agricultural scientists since the culmination of the revolution in 1959.

Open Access

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.

Free access

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.

Open Access

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.

Free access

European corn borer, Ostrinia nubilalis Hübner, is an economic pest of sweet corn. Consumer demand for high-quality, insect-free produce with minimal pesticide residue necessitates exploitation of various control options. Ear feeding resistance could reduce insecticide inputs. The inheritance of ear feeding resistance and silk channel length in the F1 derived from a diallel cross (Griffing's model I, method 2) of eight breeding stocks describing a wide range of feeding resistance was investigated in field experiments. Feeding damage, based on a 1 (no damage) to 9 (>10% ear damage) visual rating scale, and silk channel length of ears that had been manually infested at the ear tip with O. nubilalis were recorded. A significant (P ≤ 0.05) year by location interaction was found for ear feeding damage and silk channel length. Genotype ear feeding damage and silk channel length differences were significant (P ≤ 0.01) beyond genotype by environment (year and location) interactions. Mean feeding damage ranged from 2.5 (parents 1 × 7) to 8.8 (parent 2) and mean silk channel length ranged from 1.9 cm (parents 2 × 7) to 9.0 cm (parent 3). Ten of the 28 possible crosses (reciprocals combined) and 1 parent were classed as resistant (damage rating < 3.0). Eleven crosses, including all 7 involving parent 2, and 2 parents were susceptible (damage rating > 4.0). Pearson's correlation analysis indicated lower damage levels were weakly to moderately associated with increased silk channel length for both parents (r = –0.18) and progeny (r = –0.44). The general combining ability (GCA) component was significant (P ≤ 0.01) for ear feeding damage, suggesting additive effects control ear feeding damage. GCA and specific combining ability (SCA) effects did not account for silk channel length variability, suggesting strong environmental influences. Improved ear feeding resistance should be possible via recurrent selection with recombination.

Free access

Some scales combine quantitative and qualitative components that inadvertently may skew damage estimates and eliminate potentially useful germplasm. Two visual evaluation scales to estimate European corn borer feeding damage were compared for their effectiveness in classifying sweet corn germplasm. Both the traditional 1 to 9 scale, combining ear feeding damage and damage location, and the alternative 1 to 5 scale, based solely on ear feeding damage, consistently separated sweet corn genotypes into resistant, marginally resistant, and susceptible classes. Inbred MN 3002, Hybrid MN 3004, `Apache', and `More' were classified as having marginally acceptable resistance levels. Inbred Mn 3003, Inbred W182E, and `Jubilee' were susceptible to European corn borer. Individual genotype rankings varied by scale, but genotype classifications were consistent with regard to the degree of commercial acceptability. The combination of quantitative and qualitative components did not compromise genotypic characterization, as the previously untested hybrid, MN 3004, was placed in the marginally acceptable class by both scales. Plant breeders should carefully evaluate the efficacy of individual visual scales before incorporating them into a selection program.

Free access

The germplasm evaluation techniques in resistance breeding programs may improperly characterize insect damage. For example, the relationship between economic damage levels and biological damage levels may not be linear as some techniques assume. Most commercial sweet corn hybrids are highly susceptible to European corn borer (ECB), Ostrinia nubilalis Hübner, ear feeding. Genotype variation for ECB damage in our breeding program traditionally has been identified by using a 1 (no damage) to 9 visual rating scale that combines damage levels, damage site on the ear, and the economic consequences of ECB feeding for the processing industry. An alternative 1 to 5 scale based solely on a visual percentage assessment of ear feeding damage was developed and compared to the traditional scale. Seven entries, including moderately resistant and susceptible hybrids and inbred lines of the ECB ear resistance breeding program, were evaluated with both scales in 1994 and 1995 at two locations. Inbred MN3002, Hybrid MN3004, `Apache', and `More' had lower mean damage ratings (3.4, 3.4, 3.6, 3.8, traditional vs. 2.4, 2.2, 2.2, 2.3, alternative, respectively) than `Jubilee', Inbred W182E, and Inbred MN3003 (5.3, 5.6, 7.3, traditional vs. 3.3, 3.0, 4.2, alternative, respectively). Thus, four entries were classified as moderately resistant (3.0 to 4.0 traditional vs. 2.0 to 3.0 alternative) and three entries were classified as susceptible (>4.0 traditional vs. >3.0 alternative). Individual entry ranks varied by scale, but this did not alter resistance classifications. Although the nine traditional ratings were based on economic consequences and the five alternative ratings were based strictly on feeding levels excluding damage location, both scales effectively identified genotypes historically classified as moderately resistant and susceptible. The value of scales is often questionable for many situations and should be considered prior to evaluation.

Free access

Abstract

The large number of horticultural crops represents a great genetic diversity. This diversity is important in numerous ways such as in pollination control, product use, and environmental requirements for the production and handling of seeds, propagules, and the commercial product, to name only a few. The diversity is reflected further in the business structure of horticulture and, most relevant to our discussion, to relationships at the interface between the public and the private sectors in crop improvement.

Open Access