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Black currant (Ribes nigrum L.) plants of eight varieties were grown either through black plastic mulch or in bare soil and with the area between the rows cultivated or sodded with red fescue (Festuca rubra L.). Over 6 years, black plastic mulch increased yields by 26% over no mulch and cultivation between the rows increased yield by 32% compared to sod. The effect of both treatments was additive, cultivation and black plastic increased yield by 68% over grass and no black plastic. Growers are recommended to plant black currants through black plastic and avoid using sod between the rows.

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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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Powdery mildew (Sphaerotheca mors-uvae) severely infects young shoots and leaves of black currants (Ribes nigrum) and red currants (R. rubrum) in the Pacific northwestern U.S. Environmentally sound control measures are being sought as alternatives to sulfur or demethylation-inhibiting fungicides. This study examined the effect of mineral oil spray on powdery mildew infection in susceptible black and red currants. Mineral oil at 8 mL·L-1(8000 ppm) was applied to plants until runoff at 0-, 2-, and 4-week intervals from April through June in 1999 and 2000 on eight currant cultivars growing in Corvallis, Ore. Shoot and leaf surfaces were rated for powdery mildew incidence in early July both years. Oil applications significantly reduced mildew severity in vegetative growth as compared with that of the unsprayed control. The disease control from 2-week interval and 4-week interval oil applications was not significantly different.

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The low-temperature tolerance of flowers from three blackcurrant (Ribes nigrum L.) cultivars, `Brödtorp', `Ben Tirran', and `Baldwin', was determined at two stages of floral development. The three cultivars together represent a large part of the available genetic base for this subgenus of Ribes. Plants were maintained either at 4 °C in a growth cabinet under a 16-hour photoperiod or outdoors in Scotland during Spring 1997. Observed genotypic differences in survival were not associated with differences in LT50 of the flowers, and observations of freezing damage to flowers on intact plants suggest that the flowers can often survive by supercooling. This hypothesis is partly confirmed by the finding that detached flowers from all three cultivars have the capacity to supercool to at least –9 °C. Ice nucleation in stem tissue, however, was found to occur at or above –2 °C. That flowers on intact plants can apparently survive by supercooling, together with the finding that ice nucleation in stem tissue occurs at temperatures well above the LT50 of flowers, indicate the presence of barriers to propagation of ice from stem tissue to raceme. Such barriers within individual racemes are also indicated by patterns of freezing damage to flowers on intact plants cooled to –5 °C.

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Artificially inoculated single-leaf cuttings and small plants consistently differentiated european black currant (Ribes nigrum L.) cultivars susceptible to white pine blister rust (WPBR; Cronartium ribicola J.C. Fisch.) from immune cultivars carrying the Cr resistance gene. Black currant cultivars Consort, Crusader, and Titania showed no signs of infection with any of 21 strains of WPBR, suggesting that strains able to overcome immunity conferred by the Cr resistance gene, if they exist, are uncommon in North America. However, in red currant (Ribes rubrum L.), two sources of material presumed to represent the immune cultivar Viking showed no resistance to infection. All rust strains infected and sporulated as if the cultivar were fully susceptible, casting doubt on the true identity of available sources of `Viking'.

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In North America for many years the commonly held solution to white pine blister rust (Cronartium ribicola J.C. Fischer) (WPBR) was to eradicate all currants and gooseberries (Ribes L.). That approach was tried to no avail. Can currants and gooseberries be successfully grown in North America? You bet they can! Vast areas of the United States and Canada are ideal for Ribes production. Black currants (Ribes nigrum L.) are a processed fruit and production may compare to that of grain. Many of the areas that presently grow other berries could easily grow Ribes. The main barriers for production in North America are state restrictions and the availability of up-to-date information and data for growers, processors, legislators and the consuming public. I suggest that this conference and the people herein form that task group and initiate the cooperative dialogue and set forth a process to approach the WPBR problem in a holistic manner.

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Black currant (Ribes nigrum L.) cultivars with heavy, light, and no gooseberry mite (Cecidophyopsis grossulariae Collinge) infestation levels (MIL) were tested for cold hardiness by visually determining the bud injury rating (BIR) after laboratory freezing in Jan. 1998. Lightly mite-infested cvs. Blackdown and Risager, usually thought of as less cold hardy than Nordic cultivars, survived -35 °C, while mite-infested buds of the Finnish cv. Brödtorp were injured at -35 °C. Heavily mite-infested buds of the Swedish R. nigrum L. cv. StorKlas from Corvallis, Ore., were injured at -20 °C while lightly infested buds were injured to -25 °C. Noninfested `StorKlas' buds from Pennsylvania and British Columbia survived laboratory freezing to -35 °C. Heavy mite infestation lowered the bud cold hardiness of `Brödtorp' and `StorKlas' by 10 °C, as estimated by a modified Spearman-Karber T50, relative to the hardiness of lightly mite-infested buds of these cultivars. Heavily mite-infested buds contained unusual tissues forming what appeared to be spherical blisters or eruptions, ≈100 μ in diameter. Other tissues in the region of heavy mite infestation appeared to be more turgid than their noninfested counterparts. Abiotic and biotic stresses can have a combined impact on field-grown black currants.

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A seasonal study was conducted to assess the freezing injury of `Boskoop Giant' black currant (Ribes nigrum L.) samples from Oct. 1991 through Mar. 1992. Buds were subjected to either differential thermal analysis (DTA) or one of a series of temperatures (0 to -36C). Freeze injury was then assessed either visually or with TTC. Results indicated that black currant floral buds have multiple low-temperature exotherms (LTE). Freeze injury in intact buds could not be visually quantified because of the lack of visible browning, nor assayed with TTC reduction. Excised floral primordia incubated in TTC, however, developed colored formazan following exposure to nonfreezing and sublethal freezing temperatures, but remained colorless when exposed to lethal temperatures. The percentage of floral primordia that were colored and colorless were tabulated and a modified Spearman-Karber equation was used to calculate the temperature at which 50% of floral primordia were killed (T50 The T50 temperature was correlated with the temperature at which the lowest LTE was detected (R2 = 0.62). TTC reduction assay using excised floral bud primordia was a good indicator of viability in frozen blackcurrant buds. Chemical name used: 2,3,5-triphenyltetrazolium chloride (TTC).

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method was tested for: Rubus idaeus ‘Willamette’, Lyc ium barbarum , Amelanchier canadensis ‘Rainbow Pillar’, Ribes nigrum ‘Tisel’, cherry rootstock ‘Gisela 5’ ( Prunus cerasus × P. canescens ), Drosera capillaris , Drosera rotundifolia , and

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leaf area and decreasing leaf thickness. As the level of shading increased, plant yield decreased, and the authors concluded that shade levels should be no more than 60% for blueberries to remain economically viable. Black currants ( Ribes nigrum ) have

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