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  • Author or Editor: H. Philips x
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Three transgenic yellow crookneck squash (Cucurbita pepo var. melopepo) and five transgenic cantaloupe (Cucumis melo, Reticulatus group) lines were field-tested in 1993 and 1994, respectively, for resistance to Zucchini Yellow Mosaic Virus and Watermelon Mosaic Virus II. During both years, non-transgenic plants were inoculated with virus before transplanting to provide a high virus threat to the transgenic plants. Before and after transplanting, serological (ELISA) testing was used to obtain baseline information on transformed plants and to confirm field virus infection. In both years, plant disease development was rated weekly; yield was assessed during 1993. Disease progression, yield, and end-of-season ELISA indicated a significant reduction in frequency of disease incidence in the transgenic lines. Total squash yields did not differ between the transformed and unchanged lines, but the transgenic lines yielded more marketable fruit than the non-transgenic line.

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Impact of natural infection of common corn smut (Ustilago maydis) on processing characteristics of three F1 hybrid sweet corn (Zea mays L.) cultivars was evaluated in a two-year study with early and late spring-planting dates. At harvest maturity, size and location of galls were recorded and quality characteristics measured. Galls on the lower stalk, upper stalk and tassel reduced fresh weight and diameter of husked ears while galls on the base of the plant reduced fresh weight only. Ear length was reduced by galls on the upper stalk. As gall size increased from 0 to >10.2 cm. diameter, ear fresh weight and diameter decreased. The presence of galls >10.2 cm diameter reduced ear length. Kernel depth was not affected by size or location of gall. Additional ears of the same three cultivars were sampled from commercial fields planted in mid-season near Walla Walla and Patterson, Wash. Galls located on the upper and lower stalk reduced fresh weight, length, diameter and kernel depth, while galls on the tassel or base had reduced or no effect on these parameters. As gall size increased, fresh weight, length, diameter, and kernel depth decreased.

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The impact of natural infection of Ustilago maydis (causal agent of common smut) on processing characteristics of three F1 hybrid sweet corn (Zea mays L.) cultivars was evaluated in a 2-year study with early and late spring planting dates. At harvest maturity, size and location of galls were recorded and quality characteristics measured. Galls on the lower stalk, upper stalk, and tassel reduced fresh weight and diameter of husked ears, whereas galls on the base of the stalk reduced fresh weight only. Ear length was reduced by galls on the upper stalk. As gall size increased from 0 to greater than 10.2 cm in diameter, ear fresh weight and diameter decreased. The presence of galls greater than 10.2 cm in diameter reduced ear length. Kernel depth was unaffected by size or location of gall. Additional ears of the same three cultivars were sampled from commercial fields planted in midseason near Walla Walla and Patterson, WA. Galls located on the upper and lower stalk reduced fresh weight, length, and diameter, whereas galls on the base of the stalk reduced fresh weight only. As gall size increased, fresh weight, length, diameter, and kernel depth decreased.

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Fragaria ×ananassa, the cultivated octoploid strawberry, is an intensively cultivated fruit crop in which relatively small variations in disease susceptibility and flowering habit can have significant economic impacts. In order to facilitate future studies of the molecular mechansisms governing these characters, we have initiated studies to identify and sequence the strawberry homologs of a number of important genes known to be critical to pathogenesis response and photoperiodism in model systems such as arabidopsis, rice, and tomato. Using the primary Florida cultivar Strawberry Festival, we have employed a variety of techniques to identify such genes, including EST sequencing of a salicylate-induced cDNA library, PCR with degenerate primers, and colony hybridization. Possible homologs of the targeted genes and their relationships to similar genes in other species are presented. These results will form the basis of future studies of gene expression and evolutionary relationships among the Rosaceae and other species.

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In growth chamber experiments with five concentrations of NH4NO3 and inoculation of lettuce (Lactuca sativa L.) cv. Salinas with Rhizomonas suberifaciens, the causal agent of corky root (CR), symptoms of noninfectious corky root induced by high rates of N were distinct from those of infectious corky root (ICR). Nitrogen toxicity was observed at 350 kg·ha-1 and above, and was not affected by inoculation with R. suberifaciens. There was a curvilinear relationship between concentration of NH4NO3 applied and ICR severity with a maximum at 525 kg·ha-1. In a similar growth chamber experiment with NH4NO3 plus urea, ICR severity decreased and N toxicity increased at increasing N levels (N at 160 to 650 kg·ha-1). In microplots at Davis, Calif., sidedressing with NH4NO3 (N at 170 kg·ha-1) increased ICR severity on `Salinas' lettuce over the nonfertilized control. There was a significant interaction between N fertilization and soil-infestation with R. suberifaciens with respect to head fresh weight: sidedressing with NH4NO3 increased head weight in noninfested plots, but decreased head weight in infested plots. In four field experiments at Salinas, Calif., sidedressing with N at 78 to 213 kg·ha-1, with N as (NH4)1SO4, NH4NO3, urea, or Ca(NO3)2, increased ICR over the control, but there were no significant differences between the forms of N. Head fresh and dry weights were either increased or unaffected by sidedressing with N fertilizers, depending on the residual concentrations of N in the soil. The increase in ICR was likely related to concentrations of soil NO3 rather than NH4.

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Unlike cold-hardy apple germplasm, dormant vegetative buds from cold-tender accessions require stabilization of meristematic tissue to protect against injury during desiccation and cryopreservation. Dormant buds of six apple cultivars [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf. `Cox's Orange Pippin', `Einshemer', `Golden Delicious', `Jonagold', `K-14', and `Mutsu'] collected at specific intervals in 1993, 1994, and 1995 at Geneva, N.Y., were stabilized by encapsulation in 5% alginate, treated with step-wise imbibition of 0.5 to 1.0 m sucrose and 0.2 m raffinose solution, and desiccated with forced air at 0 °C. Sugar-alginate stabilization reduced injury during desiccation, increased cold-hardiness of the six cold-tender cultivars frozen to -30 °C, and improved recovery following cryopreservation of buds collected before optimal cold acclimation was attained. Sucrose tissue levels did not increase following stabilization treatment, but levels of glucose and fructose, and of an unknown disaccharide increased. This procedure used nontoxic cryoprotectants, and has potential to expand the scope of dormant bud cryopreservation to include cold-tender apple germplasm.

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Abstract

A computer simulation of asparagus growth is developed and used to evaluate the effects of various harvest strategies on short and long term commercial yield of asparagus (Asparagus officinalis L.). At present asparagus is harvested until the canners stop buying, usually in the 3rd or 4th week of June in southern Michigan, purchase generally being terminated by the reduction of spear diameter (whips), increase in fiber content of the spears or opening of the bracts. The simulation shows that this stragety is economically optimal for any single year; however, if the grower terminates the harvest every year on June 1, then the average yearly yields are significantly greater than those derived from the previous strategy. Skipping strategies, in which the grower skips a harvest every nth year (2nd, 3rd, or 4th), produced significantly lower 15 year average yields than either of the other 2 strageties, but produced significantly greater yields per plant.

Open Access

Hard cider is an important and growing part of the U.S. beverage market. Previous research suggests there is an opportunity for growers interested in selling locally grown cider-specific apple (Malus domestica) varieties. However, cider apple growers face production, distribution, and marketing challenges. This article fills a gap in the literature using survey data from four states. We find that growers are interested in expanding cider apple production to supply local craft cider makers, but may be constrained by gaps in current production information, such as how to grow cider varieties. Uncertainty about the regional suitability of different varieties, disease management, and the willingness of cider makers to pay a premium for cider apple production constitute significant concerns. Survey respondents most commonly requested information on horticultural qualities of varieties and disease management. Top marketing needs include the ability to garner premium prices. A regional “terroir” approach to cider marketing holds promise.

Open Access

The purpose of this study was to evaluate the U.S.-Canadian Greenhouse Certification Program (USGCP) that was initiated in 1998. A survey consisting of 34 questions was designed and 43 out of ≈48 nurseries in Florida participating in the USGCP were visited. Based on the answers to the questionnaire, most of the nurseries were in compliance with the majority of USGCP requirements, growers were satisfied with the program, and there was an economic benefit to participating in the program. The main problems identified were the ambiguous wording of some of the requirements and the impracticality of keeping imported and domestic plants completely segregated. Moreover, many of the respondents did not have a written description of a pest management plan. Chi square statistical analysis showed that there was almost no difference between nursery groups in their responses to the majority of the survey questions, indicating that the USGCP is a successful program for both large and small nurseries. This quantitative assessment of the USGCP is the first assessment conducted for this program and discussed in a peer-reviewed publication.

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To be useful for indicating plant water needs, any measure of plant stress should be closely related to some of the known short- and medium-term plant stress responses, such as stomatal closure and reduced rates of expansive growth. Midday stem water potential has proven to be a useful index of stress in a number of fruit tree species. Day-to-day fluctuations in stem water potential under well-irrigated conditions are well correlated with midday vapor-pressure deficit, and, hence, a nonstressed baseline can be predicted. Measuring stem water potential helped explain the results of a 3-year deficit irrigation study in mature prunes, which showed that deficit irrigation could have either positive or negative impacts on tree productivity, depending on soil conditions. Mild to moderate water stress was economically beneficial. In almond, stem water potential was closely related to overall tree growth as measured by increases in trunk cross-sectional area. In cherry, stem water potential was correlated with leaf stomatal conductance and rates of shoot growth, with shoot growth essentially stopping once stem water potential dropped to between −1.5 to −1.7 MPa. In pear, fruit size and other fruit quality attributes (soluble solids, color) were all closely associated with stem water potential. In many of these field studies, systematic tree-to-tree differences in water status were large enough to obscure irrigation treatment effects. Hence, in the absence of a plant-based measure of water stress, it may be difficult to determine whether the lack of an irrigation treatment effect indicates the lack of a physiological response to plant water status, or rather is due to treatment ineffectiveness in influencing plant water status. These data indicate that stem water potential can be used to quantify stress reliably and guide irrigation decisions on a site-specific basis.

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