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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