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  • Author or Editor: R.L. Bell x
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Eight 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. All were compared to a susceptible control, `Bartlett' (P. communis L.), and to a moderately resistant control, NY10352 (P. communis × P. ussuriensis Maxim. BC hybrid). Three P. communis cultivars, Bartjarka (PI 483391), Lucele (PI 483402), and Kajzerka (PI 506387), and a wild seedling (PI 506381) of undetermined species, exhibited a high degree of host resistance, measured as reduced frequency of feeding and increased either mortality or movement off of the plants.

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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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Narrow-sense heritability estimates were computed for five fruit quality characteristics and their weighted total index. Grit content and skin russeting were moderately heritable traits, while flesh texture, flavor, appearance, and the weighted total score were of relatively low heritability. Within sub-populations of crosses, defined by the species ancestry of the parents, the relative magnitudes of heritabilities for each trait varied, but were in general agreement with those for the entire population. The general combining ability variances were 4.5 to 12.0 times those for specific combining ability, although both were statistically significant for all traits and the weighted quality index. The species ancestry of a parent had no effect on its general combining ability rank. While selection of individual seedlings on the basis of their own phenotype will result in genetic improvement for grit and russet, selection based on a combination of full-sib family means and individual phenotypes is recommended for flavor, texture, appearance, and overall fruit quality.

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Twenty-eight greenhouse screening materials, with predetermined airflow resistance values, were evaluated for exclusion of silverleaf whitefly (Bemisia argentifolii Perring & Bellows) and thrips from a mixed-species population. Screens differed in exclusion efficacy, as a percentage of the fiberglass window screen control and at an approach velocity of at 92 m/min, from –35 to 94% for silverleaf whitefly and from –13 to 95% for thrips. Seventeen screens excluded more silverleaf whitefly, whereas seven excluded more thrips than the window screen control. One material differentially excluded whitefly over thrips; many more differentially excluded thrips over whitefly. Airflow resistance, indicative of mesh hole size, did not necessarily correspond with degree of exclusion. Though two high-resistance screens, No-Thrips and Econet S, excluded both pests, not all materials characterized as highly resistant to airflow provided significant exclusion. Exclusion of both pests was also attained with three moderate resistance screens, BugBed 123, BugBed 85, Pak 44×44, and one low-resistance screen, BugBed 110UV.

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During 1976-1980, three plant exploration trips were made throughout eastern Europe in search of native Pyrus germplasm. A total of 384 accessions (231 from Yugoslavia, 86 from Romania, 43 from Poland, and 12 each from Hungary and Czechoslovakia) were collected as budwood and propagated at the National Plant Germplasm Quarantine Center in Glenn Dale, Md. Following 8 years of exposure to the fire blight bacterium [Erwinia amylovora (Burr.) Winsl. et al.], 17.49” of the accessions remained uninfected, 11.2% rated resistant, 6.8% moderately resistant, and 64.6% blighted severely (26% to 100% of tree blighted). Some of the superior accessions have been released for use in the pear breeding program.

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`Blake's Pride' has been released jointly by USDA and The Ohio State Univ. as a new fire blight-resistant cultivar. The original seedling tree was selected in 1977 at the Ohio Agricultural Research and Development Center in Wooster by R.C. Blake and T. van der Zwet from a cross of US 446 × US 505, performed in 1965 by H.J. Brooks, and was tested under the original seedling number, OHUS 66131-021. The fruit of `Blake's Pride' is pyriform to round-pyriform in shape, and is moderate in size, averaging ≈2.75″ to 3″ in diameter, and 3.25″ in height. The stem is short, medium in thickness, and upright. Skin undercolor is yellow, the finish is glossy, and 20% to 30% of the fruit surface is covered with a smooth, light tan russet. Harvest maturity occurs about 3 weeks after `Bartlett', and the fruit will store in air storage for at least 3 months without core breakdown or superficial scald. The flesh texture is moderately fine, juicy, and buttery. Grit cells are moderately small and occur primarily around the core and in a thin layer under the skin, similar to `Bartlett'. The flavor is subacid and aromatic. The tree is moderate in vigor on `Bartlett' seedling rootstock, and upright-spreading in habit. Yield has been moderate to moderately high. Fire blight infections are rare, and extend no further than 1-year-old growth. Artificial blossom inoculations indicate a moderate degree of resistance of blossoms to fire blight infection. Resistance of `Blake's Pride' to both shoot and blossom infection is much greater than that of `Bartlett'.

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Potential phytotoxicity and plant growth-regulating activity of insecticidal dips for poinsettias was investigated by dipping, then growing unpinched, rooted cuttings of `Red Sails', `Freedom', and `V-14 Glory' in the following insecticidal emulsions for five durations: 2% insecticidal soap (Safer's), 2% horticultural oil (Sunspray Ultrafine), fluvalinate (Mavrik Aquaflow), oxythioquinox (Joust), kinoprene (EnstarII), azadirachtin (Margosan-O), fenoxycarb (Precision), and an oil-carrier formulation of Beauveria bassiana (Naturalis-L). Dips in soap, oxythioquinox, Naturalis-L, and oil were phytotoxic to all three cultivars. Also, kinoprene and fenoxycarb were phytotoxic to `Red Sails'. At dip durations of 10 s and greater, soap, Naturalis-L, and oil were phytotoxic. Oxythioquinox was phytotoxic at durations of 1 min, 15 min, and 1 h. Only fluvalinate was not phytotoxic as a 4-h dip. After 2 weeks, plants dipped in oxythioquinox, Naturalis-L, and oil were stunted. By week 4, differential cultivar effects were seen: six dips (all but fluvalinate and azadirachtin) stunted growth of `Red Sails', whereas only Naturalis-L and oil retarded growth of `V-14 Glory'. Six weeks after treatment, growth of all cultivars was stunted by oxythioquinox, Naturalis-L, and oil, but was not retarded by fluvalinate or azadirachtin. Dip duration significantly affected growth by weeks 4 and 6, when all durations of Naturalis-L and oil reduced growth. Additionally, 4-h dips of oxythioquinox and kinoprene stunted plants after 4 weeks, and 1- and 4-h dips of oxythioquinox, kinoprene, and fenoxycarb adversely affected growth after 6 weeks.

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Since whiteflies preferentially oviposit on the newest leaves, it is the early life stages that are most likely to be present on poinsettia cuttings from infested stock or infested during rooting. This study evaluated efficacy of insecticidal dips against eggs and first nymphal instars of the silverleaf whitefly, Bemisia argentifolii. Dip efficacy was investigated by dipping rooted cuttings of whitefly-infested `Freedom' in the following insecticide emulsions: 2% insecticidal soap (M-Pede), 1% horticultural oil (Ultrafine), fluvalinate (Mavrik), oxythioquinox (Joust), kinoprene (EnstarII), azadirachtin (Margosan-O), fenoxycarb (Precision) and imidacloprid (Merit). Two dip durations, 10 seconds and 1 hour, were tested for each insecticide. Water dips for the two durations were used as control treatments. Fenoxycarb and azadirachtin dips for durations of 10 seconds and 1 hour and oxythioquinox dips for 1 hour resulted in greater egg mortality than the other treatments. No insecticide/dip duration treatment gave 100% mortality of eggs. Dips found to be efficacious killed proportionately fewer eggs than first instar nymphs.

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Abstract

Sample sizes for detection of differences of flower bud survival in peach and nectarine [Prunus persica (L.) Batsch] were chosen on the basis of theoretical confidence intervals (Cl) and least detectable differences (LDD) for the binomial distribution. Theoretical Cl and LDD for 1000-bud samples were comparable to Cl and Duncan's multiple range test separation computed from an analysis of variance for 1000 buds, based upon 10 replicates of 100 buds. Variability in survival was a function of eultivar, height of bud in canopy, and bud type. Variability may be minimized by sampling a given bud type (single, double, distal) at >1.5 m above ground level.

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