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expression of plant resistance to nematode parasitism ( Pedrosa et al., 2000 ). These nematodes have a high reproduction rate, reaching large populations in the soils after successive crops of plants considered as good hosts ( Campos et al., 2001 ). Dry

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In controlled tests, 110 cultivars (77.5%) of common bean (Phaseolus vulgaris L.) responded to broad bean wilt virus (BBWV) with a localized infection (resistant), while 32 cultivars (22.5%) reacted with local and systemic infection (susceptible). The majority of susceptible cultivars were of the yellow-podded (wax bean) and red kidney types. In F1, F2, and backcross populations of the BBWV-resistant cultivar Sanilac with the BBWV-susceptible ‘California Light Red Kidney’ (‘CLRK’) resistance to systemic infection was conferred by a single dominant gene, to which the symbol Bbw is assigned. BBWV was not transmitted in 471 ‘CLRK’ seeds derived from severely infected plants.

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Fourteen Prunus rootstocks were evaluated against mixtures of several isolates of the root-lesion nematode Pratylenchus vulnus Allen and Jensen in three greenhouse experiments. Most of the tested rootstocks are new releases or materials in advanced stages of selection that also have incorporated root-knot nematode resistance. The plums Torinel (Prunusdomestica L.) and Redglow (P. salicina Lindl. P. munsoniana Wight and Hedrick cv. Jewel) showed a moderately resistant response; their final nematode population levels were lower or slightly higher than inoculation levels. Low nematode reproduction also was found in the peach–almond hybrid G N No 22 [P. persica (L.) Batsch P. dulcis (Mill.) D.A. Webb] and the plum Bruce (P. salicina P. angustifolia Marsh.), and although these rootstocks did not perform as well as Torinel and Redglow, they also appear to be poor hosts for P. vulnus.

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A single plant selection of the cucumber (Cucumis sativus L.) cultivar Taichung Mou Gua (TMG-1) from China was the source of resistance to zucchini yellow mosaic virus (ZYMV) in crosses with the domestic cultivars Marketer and Marketmore 76. In F1, F2, and reciprocal backcross populations, resistance to ZYMV-CT (Connecticut strain) was demonstrated to be conferred by a single recessive gene to which the symbol zym was assigned.

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Western flower thrips (Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae)] collected from greenhouse, laboratory, and native populations were evaluated for resistance to the insecticide spinosad. Individual cut stems of transvaal daisy (Gerbera jamesonii H. Bolus ex Hook. f.) were inoculated with 25 adults from 1 of 9 thrips populations and maintained in isolation chambers. Treatments of no spray, water spray, spinosad at one-half label rate (0.41 mL·L-1) and spinosad at the recommended label rate (0.81 mL·L-1) were applied to the flowers. Three days after treatment, the number of live and dead thrips was recorded. Significantly more thrips were recovered from the control treatments than the spinosad treatments. Thrips survival varied by treatment and insect population. Based on an odds ratio analysis, the likelihood of recovering live thrips was greater in the IL-GH1 (Illinois greenhouse) population than in the NV-N1 (Nevada native) reference population for both spinosad treatments, suggesting resistance to spinosad in the IL-GH1 population. The IL-GH1 population was collected from a greenhouse regularly sprayed with spinosad whereas the NV-N1 population was collected in Incline Village, Nev., on wildflowers with no history of exposure to spinosad. This is the first documented indication of spinosad resistance in a thrips population. In comparison to the NV-N1 reference population, none of the populations collected from laboratory or native nonagricultural environments exhibited evidence of resistance to spinosad. Resistance to an insecticide with a novel mode of action, such as spinosad, indicates the necessity of rotating insecticides and implementing alternative methods of managing western flower thrips. Chemical names used: spinosad including spinosyn A and spinosyn D (Conserve SC).

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Resistance to wilt caused by Verticillium dahliae Kreb. was evaluated for 41 strawberry genotypes from the Univ. of California breeding program and 1000 offspring from crosses among 23 of these genotypes. Runner plants from these genotypes and seedlings were inoculated with a conidial suspension containing a mixture of five isolates of V. dahliae from strawberry. Symptoms were scored as the number of dead or seriously stunted plants per plot, or based on a subjective phenotypic resistance score assigned to each plot on five dates during the spring after planting. Most of the California germplasm is highly susceptible to V. dahliae, with an average resistance score of 2.1 (±0.10) and 84.1% (±2.1) plants stunted or dead compared with a score of 3.2 (±0.24) and 57.4% (±4.9) of plants stunted or dead for a control set of six non-California genotypes identified previously as resistant. However, a broad range of intermediate resistance was detected, and 4 of the 41 California genotypes evaluated had resistance scores superior to the mean score for the non-California resistant checks. Plot-mean heritabilities for resistance and stunting scores estimated using genotypic, full-sib family, and offspring-parent analyses ranged from 0.44 to 0.88. Comparison of different estimates of variance components suggests that half or more of the genotypic variance for resistance traits detected is due to the additive effects of genes. There appears to be sufficient variation within the California population to proceed with an effective selection program, despite the absence of directional selection for resistance during the past 3 decades. However, developing cultivars with adequate resistance will ultimately depend on the recovery of transgressive segregants from superior parents, as even the most resistant genotypes from all sources showed some disease symptoms.

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Resistance to white lupin mosaic virus (WLMV), a recently characterized member of the potyvirus group, was found in pea (Pisum sativum L.) plant introductions from Ethiopia (PI 193835) and India (PI 347485). In cross and backcross populations between plants of resistant PI 193835 with those of susceptible `Bonneville' and PP-492-5, this resistance was demonstrated to be governed by a single recessive gene. This gene was distinct from other genes previously found in PI 193835 and PP-492-5 (from PI 347492, India) conferring resistance to clover yellow vein virus (CYVV) and three strains of pea seedborne mosaic virus (PSbMV). Indirect evidence suggests that this newly recognized viral resistance gene, wlv, is a member of a cluster of closely linked genes located on chromosome 6. This gene cluster includes sbm-1, sbm-3, and sbm-4, which govern resistance to three PSbMV pathotypes, and cyv-2, which governs resistance to CYVV.

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An Australian strain of passionfruit woodiness potyvirus (PWV-K) infected peas and caused a light to moderate mosaic consisting of chlorotic spots, veinal chlorosis, and some plant stunting. Resistance to PWV-K was found in pea cultivars and plant introductions (PI) known to be resistant to bean yellow mosaic virus (BYMV). In cross and backcross populations involving the resistant cultivar Bonneville (United States) and PI 140295 (Iran) with the susceptible cultivar Ranger, a single recessive gene was responsible for the high level of resistance to PWV-K. From crosses involving PI 391630 (China), which is resistant to BYMV but susceptible to PWV-K, and the cultivar Bonneville (resistant to both viruses), it was evident that different genetic factors conferred resistance to these two potyviruses. The symbol pwv is tentatively assigned to this newly recognized pea resistance gene. Three other Australian strains of PWV did not infect peas.

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Field resistance to white pine blister rust (WPBR) (Cronartium ribicola J. C. Fischer) was investigated on 53 black currant (Ribes nigrum L.) genotypes (cultivars and breeding selections) in 1998 and 1999. Uredia did not form on the black currant `Titania' and 17 advanced selections during field evaluations made at the Experimental Orchard at Dabrowice, near Skierniewice, Poland.

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Passionfruit woodiness virus (PWV) can infect bean (Phaseolus vulgaris L.), causing a light and dark green foliar mosaic, veinbanding, downward curling, and plant stunting. The intensity of these symptoms can vary with the strain of the virus and cultivar, but they resemble those caused by bean common mosaic virus. In genetic populations derived from crosses and backcrosses involving cultivars that are resistant (`Black Turtle 1', `Clipper', and `RedKote') or susceptible (`Black Turtle 2', `California Light Red Kidney', and `Pioneer'), a single dominant gene conferred resistance to an Australian strain PWV-K. To this gene, the symbol Pwv (Passionfruit woodiness virus) is tentatively assigned. In plants derived from rooted cuttings of backcross populations, the same factor also conditioned resistance to three other Australian strains, PWV-Mild, PWV-51, and PWV-Tip Blight.

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