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  • Author or Editor: L.C. Stuart x
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`Fifty-nine cultivars and wild seedlings of pear (Pyrus spp.) from Eastern Europe were evaluated for resistance to feeding by early instar pear psylla [Cacopsylla pyricola (Foerster)] in a 24-hour assay. `Bartlett' (P. communis L.) and NY 10352 (P. communis × P. ussuriensis Maxim. BC1 hybrid) were used as susceptible and resistant controls, respectively. A. high degree of resistance, measured as increased mortality and reduced frequency of feeding, was found in 11 plant introductions: `Erabasma' (PI 483370), `Krupan Burnusus' (PI 483387), `Topka' (PI 484489), `Zelinka' (PI 483393), `Mednik' (PI 483399), `Karamanlika' (PI 502165), `Katman' (PI 502172), `Smokvarka' (PI 502176), `Obican Vodenac' (PI 502177), a clone thought to be `Smiljerka' (PI 502178), and an unnamed seedling (PI 506382).

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Fraser fir [Abies fraseri (Pursh) Poir.] and Norway spruce [Picea abies (L.) Karst.] were grown in seven vegetation management programs ranging from 100% cover of grass-dominated vegetation to bare soil on opposing north and south aspects. Concentrations of 13 nutrients were determined at three growth stages during 2 years: active terminal growth, cessation of terminal expansion, and dormancy. Aspect did not affect nutrient concentrations. Vegetation management programs bad a significant impact on nutrient concentration for both species. Nitrogen, Ca, B, Fe, and Mn concentrations during dormancy were negatively correlated with herbaceous biomass. In contrast, N during active growth and P and Mg concentrations during all stages were positively correlated with herbaceous biomass. Vegetation management only affected the seasonal trend of Mo. Seasonal trends varied by nutrient in both species.

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Rosebay rhododendron (Rhododendron maximum L.) seedlings were grown in controlled-environment chambers for 14 weeks under long (9-hour) days at 18, 22, 26, or 30C in factorial combination with 15-hour nights at 14, 18, 22, or 26C. Total dry-matter production was lowest for 18C days and highest for 26C days. A similar response occurred for top, leaf, root, and stem dry weights. Nights at 22C maximized total plant, top, leaf, and stem dry weights. The optimum day/night cycle for dry-matter production was 26/22C. Leaf area was optimum with 18C nights. Leaf weight ratio (leaf dry weight: total plant dry weight) increased with an increase in night temperature to a maximum at 22C. Root weight ratio (root dry weight: total plant dry weight) decreased with an increase in night temperature to a minimum at 22C. Stem weight ratio (stem dry weight: total plant dry weight) and shoot: root ratio (top dry weight: root dry weight) were not influenced significantly by day or night temperature. A day/night cycle of 26/22C seems to be optimal for producing-salable plants.

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