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Abstract

Root culture was adapted for screening a diverse collection of tomato (Lycopersicon esculentum Mill.) strains for tolerance to low supplies of P. Fifty-one tomato strains were screened in 10 consecutive experiments for root fresh weight (RFW) production with high non-growth-limiting (25 μm) and low growth-limiting (7 μm) concentrations of P in a sterile, liquid medium. Twenty strains showing the most and least restricted root growth at low P in the initial 10 experiments were grown simultaneously in three final screening experiments. Restrictions in RFW at low P averaged 51% for four strains, consequently classed as low-P “intolerant”, and averaged 27% for three strains, consequently considered low-P “tolerant”. At high P, RFW of tolerant strains averaged 17% less than RFW of intolerant strains. At low P, RFW of tolerant strains averaged 23% greater than RFW of intolerant strains. The greater RFW production of intolerant strains at high P was due to higher internal P use ratios (IPUR = mg root dry weight (RDW) per mg P adsorbed). Differences in growth at low P were due primarily to differences in P uptake. However, the relative contributions of P use and P uptake efficiencies to low-P tolerance were different among strains. Root hairs of tolerant strains at low P were longer and covered a greater proportion of the root length than root hairs of intolerant strains. The pH of the culture medium of one tolerant strain was significantly lower than the medium pHs of the other strains.

Open Access

Abstract

‘Caruso’ tomatoes (Lycopersicon esculentum Mill.) were grown in peat-perlite-vermiculite in a greenhouse with five nitrate-nitrogen (NO3-N) fertilization concentrations in irrigation waters managed to maintain 200, 400, 600, 900, or 1200 µg NO3-N/ml in petiole sap as determined by weekly NO3-N quick tests. Nitrate-N fertilization concentrations immediately were increased 50% when petiole sap NO3-N levels first fell below these target levels; thereafter, NO3-N fertilization concentrations were increased only after petiole sap levels fell below target levels for 2 consecutive weeks. The critical target level of sap NO3-N was defined as the lowest petiole sap NO3-N target level producing maximum marketable fruit yields. Total fruit yields increased with increasing petiole sap NO3-N target levels through 1200 µg·ml–1. Marketable fruit yields were maximized at 3.2 kg/plant, with an estimated critical sap NO3-N target level of 1105 µg·ml–1. Application of the sap NO3-N management rules used in this experiment resulted in five adjustments in N fertilization concentrations over the 27-week crop cycle, with an average of 4.5 weeks between adjustments. This approach to the management of N fertilization based on the sap NO3-N level of the crop has potential to provide significant benefits in improved N use and crop productivity at a modest cost.

Open Access

Nursery management, a course covering practices involved in production of woody landscape plants, was developed for delivery to place-bound students at distant sites around the state. Course subject matter was divided into 41 modules and involved aspects of site selection, cost accounting, plant propagation, nursery trade associations, licensing, as well as container and field production practices. Each module began and ended with a 1- to 2-min introduction and summary to the subject matter, and these segments were taped on location at nurseries in the Pacific Northwest. The lecture portion of each module was taped in a multimedia classroom, and presentation software was used to present text, slides, drawings and animation. Videotape footage of some cultural practices was also inserted into lectures as a “field trip.” Students in the course also received a lecture note guide for all modules in the course. In Idaho, the videotapes were distributed to education centers around the state. The first time the course was offered, 11 students at distant sites and three time-constrained students on campus enrolled. Students contacted the instructor by phone or e-mail. Homework assignments were sent via FAX or e-mail attachments, and tests were sent to the education centers where proctors gave three exams and a final exam. All tests and homework assignments were graded by the instructor located on campus. A videotaped course in nursery management can adequately convey principles involved in landscape plant production, but logistics of mailing videotapes and grading assignments and tests should be carefully evaluated when deciding if a course should be offered at a distance.

Free access

Abstract

Viruses consist of nucleic acid packaged in a protective shell composed of protein or, in some cases, protein plus lipid. This shell protects the nucleic acid from enzymatic degradation while it is outside the host cell in a potentially hostile environment. Recent advances in virus detection and diagnosis are based on increased sensitivity of methods for the detection of proteins and nucleic acids.

Open Access

Abstract

Tomato plants were grown in two greenhouse experiments to determine sampling guidelines for using semiquantitative quick tests of petiole sap nitrate to monitor crop N status. In Expt. 1, a 40-µg NO3-N/ml liquid feed rate produced maximum marketable yields of ‘Celebrity’ tomatoes (Lycopersicon esculentum Mill.) (3.4 kg/plant) with estimated petiole sap concentrations of 2138, 1091, and 636 µg NO3-N/ml at early bloom, small fruit, and full-ripe fruit stages, respectively. In Expt. 2, a stable minimum level of petiole sap NO3-N of about 800 µg·ml−1 was found during fruit production in maximally yielding (3.1 kg/plant) ‘Tropic’ tomato plants. These plants received 60 µg NO3 N/ml in liquid feed solutions during fruit production. Liquid NO3-N feed rates producing maximum yields in these experiments were about five times lower than those typically used for growing tomatoes. Sap nitrate content did not fluctuate greatly between 0803 hr and 1430 hr. Sap nitrate levels rose sharply in response to increased N feed concentrations and as a result of lower leaf pruning. Because of high day-to-day and plant-to-plant variation in petiole sap nitrate readings, strategies for obtaining results with sufficient diagnostic value would appear to involve at least weekly samplings of five to 15 plants, and restricting diagnoses of deficient crop N to instances where readings < 800 µg NO3-N/ml for two or more consecutive samplings have been obtained.

Open Access

Limited budgets and downsizing have threatened the delivery of technological and educational information by the cooperative extension service. As such trends continue, volunteers become more important. Background factors, influence of specific individuals, attitudes toward the value of the program, and personal benefits received influence a person's decision to become a Master Gardener volunteer. In this study, individuals who were older than 50 and had children and parents who were former volunteers in an extension program were more likely to become Master Gardener volunteers, as were individuals who felt that the Master Gardener program benefited the community and themselves. Specific individuals, such as garden club members, other Master Gardeners, a neighbor, or persons holding leadership positions in the community, might also influence an individual's decision to volunteer.

Full access

Abstract

Potted seedlings of white birch (Betula papyrifera Marsh.) and pin oak (Quercus palustris Muenchh.) were grown in the field for 3 months in relatively high- and low-ambient sulfur dioxide air. Biweekly throughout the growing season, plants from each site were harvested, and height and leaf, stem, and root dry weight were measured. The overall growth of white birch, an SO2-sensitive species, was found to be greater in the higher, but sub-phytotoxic SO2 environment. Conversely, the growth of pin oak, an SO2-tolerant species, was greater at the low SO2 site.

Open Access

Abstract

Intraclonal variation in Ulmus americana, American elm and U. pumila, Siberian elm was compared with seedling variation in the same species for the following characteristics: height growth; shoot, root, and total fresh weight; stem, leaf, root and total dry weight; root-shoot ratio, and leaf area. Intraclonal variation was as great as seedling variation for all characteristics in 3-month-old American and 12-month-old Siberian elms and for height growth in 13-month-old American elms. It was significantly less for all other characteristics in the 13-month-old American elm clone.

Open Access

Abstract

Responses of bell peppers (Capsicum annuum L.) to inoculation with the vesicular–arbuscular mycorrhizal fungus (VAMF) Glomus aggregatum (Schenck and Smith emend Koske) were examined under greenhouse and field conditions. Inoculation did not affect tissue P concentrations, growth, or yields in “high”-P soil (0.30 mg P/liter of soil solution) in either the greenhouse or field. In “low”-P soil (0.03 mg P/Iiter), inoculation increased tissue P concentrations, plant weights, and fruit yields relative to noninoculated plants. Tissue P concentrations increased more rapidly after transplanting when seedlings were inoculated at seeding than when inoculation was delayed until transplanting. In the field, total fruit yields and final shoot fresh weights also were higher when transplants were inoculated before transplanting. Water stress reduced fruit yields of plants growing in P-deficient soil less if they were inoculated than if they were not inoculated.

Open Access

Abstract

Growth, shoot P concentrations, and vesicular-arbuscular mycorrhizal infection by Glomus aggregatum (Schenck and Smith emend. Koske) were studied on transplants of bell pepper (Capsicum annuum L. ‘Emerald Giant’) and leek (Allium ampeloprasum L. ‘Catalina’) grown in a 1 peat : 1 vermiculite medium (v/v). Various amounts of Osmocote (19N–2.6P–10K) were added to the transplant medium, resulting in solution P concentrations of 0.6 to 17.5 mg·liter–1. The transplants received 0 to 12,500 spores of G. aggregatum per plant. Increased solution P concentrations increased growth and shoot P concentrations in both leeks and peppers, but decreased the degree of mycorrhizal infection of the root systems. At low solution P concentrations, inoculation increased the shoot P concentrations and growth of the peppers, but decreased the shoot P concentrations of the leeks. Increasing the number of spores per plant did not influence growth or tissue P concentrations of transplants, but did increase mycorrhizal infection at low and intermediate solution P concentrations.

Open Access