Search Results
You are looking at 1 - 10 of 33 items for :
- Author or Editor: David Davis x
- HortScience x
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.
Attention has been given in recent literature to crop breeding for heat tolerance, but, as with certain other physiological traits, such as photosynthetic efficiency, practical gain has lagged. The question remains as to whether heat tolerance can be improved, and, if so, if it can most efficiently be improved by a holistic approach, as in breeding for yield following timely high temperature levels in the field environment, or whether the breeding for heat (and drought) tolerance components in the laboratory would be feasible. At issue is the identification and repeatability of key plant responses, such as cell membrane damage, heat shock protein formation, increased ethylene output and other responses, and the relevance, effectiveness and cost of screening for such traits. Results from our laboratory, and the work of others, will be reviewed.
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.
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.
Decision cases are designed to enhance students critical thinking by engaging them in authentic problem situations. Students are assigned the role as decision maker with a dilemma to solve. In the assignment, the decision maker has to weigh the issues, identify the options, and develop strategies for solutions either individually or as a group. The authors have been writing and using decision cases in upper level undergraduate production courses in fruits and vegetables to integrate information from classes in plant pathology, entomology, and production horticulture. Decision cases dealing with weed control strategies in small fruit production and vegetable production scheduling will be discussed to illustrate the strengths and weaknesses of the case approach.
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.
Attention has been given in recent literature to crop breeding for heat tolerance, but, as with certain other physiological traits, such as photosynthetic efficiency, practical gain has lagged. The question remains as to whether heat tolerance can be improved, and, if so, if it can most efficiently be improved by a holistic approach, as in breeding for yield following timely high temperature levels in the field environment, or whether the breeding for heat (and drought) tolerance components in the laboratory would be feasible. At issue is the identification and repeatability of key plant responses, such as cell membrane damage, heat shock protein formation, increased ethylene output and other responses, and the relevance, effectiveness and cost of screening for such traits. Results from our laboratory, and the work of others, will be reviewed.
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.
Abstract
AS9 is a sugary-1 breeding population of sweet com (Zea mays L.) having moderate to high resistance to first brood attack (leaf feeding phase) by the European corn borer (Ostrinianubilalis, Hübner). The first sugary-1 source material having such resistance, it has been composited from diverse sources and is being released for its potential value in sweet corn breeding.
Abstract
Fruit of ‘Ruby Red’ grapefruit (Citrus paradisi Macf.) were treated postharvest with sodium-o-phenylphenate (SOPP), benomyl, imazalil, and etaconazole and stored under ambient conditions or were treated with SOPP, imazalil, and etaconazole and stored at 12°C. Imazalil and etaconazole were as effective as benomyl under ambient conditions and were more effective than SOPP under refrigerated conditions; 85% of the stem-end-rot was caused by Phomopsis citri (Fawc).