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  • Author or Editor: B.J. Smith x
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Abstract

Successful in vitro propagation of white rubber rabbitbrush [Chrysothamnus nauseosus (Pallas) Britt, ssp. albicaulis] was achieved using both stem segments and axillary shoot explants. Medium stem segments (2–3 mm diameter) were more successfully cultured than either small (0.8–1 mm diameter) or large (4–5 mm diameter) explants. Axillary shoot explants (10–15 mm long) began to form roots within 1 week after placement in media containing 5–10 μM (1–2 mg/liter) indolebutyric acid (IBA) or 5.3–10.6 μM (1–2 mg/liter) naphthalene-acetic acid (NAA). Root growth was accelerated in the presence of IBA. In the presence of 8.9 μM (2 mg/liter) benzyladenine (BA) and 0.53μM (0.1 mg/liter) NAA, both medium stem segments and axillary shoots rapidly produced numerous side shoots that were rooted easily on media containing IBA. In vitro culture appears to be a feasible means for the mass multiplication of this potentially important rubber-producing shrub.

Open Access

Research was conducted to evaluate the performance of a hydraulically driven turfgrass sod strength machine equipped with a force transducer to measure various strength parameters. The most commonly reported strength parameter, peak force (PF), continued to provide the quickest and easiest measurements of sod strength. Calculations of work involving the continuous measurement of sod strength over the duration of the stretch did not consistently improve the information provided by the PF measurement. Changes in sod bed pull speeds altered the calculations of work, whereas pull speed changes generally had little effect on force measurements, an important consideration for sod strength measurement devices that have limited control of sod bed pull speed. The unit was marginally successful in distinguishing sod strength differences between St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze.] treated with various levels of pyridine herbicides. The device also provided strength parameters that distinguished the relative strengths of four warm-season turfgrass sods.

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A rapid and reliable assay for screening European hazelnut (Corylus avellana L.) genotypes for quantitative resistance to eastern filbert blight [Anisogramma anomala (Peck) E. Müller] was tested by comparing two methods using the same clones. In the first assay, disease spread was followed for five consecutive years (1992-96) in a field plot planted in 1990. Measured responses included disease incidence (the presence or absence of cankers) and total canker length, quantified as the length of perennially expanding cankers. The second assay consisted of annually exposing replicated sets of 2-year-old, potted trees to artificially high doses of pathogen inoculum and measuring incidence and canker lengths at the end of the next growing season. The potted trees were exposed to inoculum in 1990, 1992, 1993, and 1994. Compared to the field plot, disease incidence and total canker length were higher in all the potted-tree experiments. Nonetheless, disease responses of individual clones in the two screening methods were significantly correlated in some contrasts (rs = 0.97 between 1996 field and 1995 potted trees). However, for a few clones (`Camponica', `Tombul Ghiaghli', and `Tonda di Giffoni'), disease developed slowly in the field plot, but disease incidence on these clones averaged > 30% in most of the potted-tree studies. Disease responses also were significantly correlated among some of the potted-tree experiments (rs = 0.72 for the comparison of 1994 to 1995). Highly susceptible and highly resistant hazelnut clones were identified by both methods. However, the field plot method was superior to the potted-tree method for distinguishing among moderately resistant clones. `Bulgaria XI-8', `Gem', `Camponica', `Tombul Ghiaghli', and `Tonda di Giffoni' were identified as promising sources of quantitative resistance to eastern filbert blight.

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Anthracnose crown rot of cultivated strawberry (Fragaria ×ananassa Duchesne ex Rozier) has been a major disease problem in the strawberry producing regions of the southeastern United States since the early 1970s. Chemical controls are often inadequate, but use of resistant cultivars is seen as a credible option for managing this disease. Only a small portion of Fragaria L. germplasm has been screened for resistance to anthracnose crown rot. A core subset of the Fragaria collection maintained at the U.S. Department of Agriculture National Clonal Repository in Corvallis, OR, has been constructed to contain an elite group of native F. virginiana Mill. and F. chiloensis (L.) Mill. This collection, referred to as the “core collection,” has been characterized for many horticultural traits, including reactions to several common foliar diseases, resistance to black root rot (causal organisms unknown), and resistance to northern root-knot nematode (Meloidogyne hapla Chitwood) and root-lesion nematode [Pratylenchus penetrans (Cobb) Filipjev & Shuurmans Stekhoven]. Our objective was to evaluate the core collection for resistance to a selection of isolates of three Colletotrichum Corda species known to cause strawberry anthracnose, Colletotrichum fragariae A.N. Brooks, Colletotrichum gloeosporioides (Penz.) Penz. & Sacc. in Penz. [teleomorph Glomerella cingulata (Stoneman) Spauld. & H. Schrenk], and Colletotrichum acutatum J.H. Simmonds (teleomorph Glomerella acutata J.C. Guerber & J.C. Correll). No Fragaria subspecies or geomorph was more resistant than any other; rather, individual genotypes within these groups were identified as sources from which resistance can be obtained. Collecting germplasm in areas of intense disease pressure may not be as beneficial as one might assume, at least where anthracnose crown rot disease is concerned.

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In the mid-1980s, a statewide educational program was initiated to help improve productivity in replanted apple orchards. This effort began with a study of the background of the problem in Washington and an assessment of the problems growers faced when replanting orchards. An array of potential limiting factors were identified-most important, specific apple replant disease (SARD)-but also low soil pH, poor irrigation practices, arsenic (As) spray residues in the soil, soil compaction, nematodes, nutrient deficiencies, and selection of the appropriate orchard system. The educational program was delivered using a variety of methods to reach audience members with different learning styles and to provide various levels of technical information, focusing on ways to correct all limiting factors in replant situations. Results have been: Acceptance of soil fumigation as a management tool: increased recognition of soil physical, chemical, and moisture problems; reduced reliance on seedling rootstock, and an increase in the use of dwarfing, precocious understocks; and better apple tree growth and production in old apple orchard soils.

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