The tolerance of black currant flowers to induced frosts

Abstract

SUMMARYFlower buds on potted plants of 17 varieties of black currant were frosted to ‐3.3, ‐4.5 and ‐5.2 °C between the grape stage and full flower in 1979 and 1980. In all varieties more flower buds died after the ‐5.2 °C frosts and at full flower, and less after the ‐3.3 °C frosts and at the grape stage. Varieties related to Ben More and Ojebyn tolerated the ‐4.5 °C frosts until after first flower while Baldwin and Magnus became susceptible at the grape stage. Seabrooks Black, Greens Black and Ben Lomond and its relatives were intermediate. In both years flower buds tolerated frosts to similar growth stages but in 1980 the varieties flowered about 2 wk earlier than in 1979 and suffered more frost damage at full flower. The frosted plants had slightly larger fruits than the unfrosted ones in 1979. The immature fruit drop was similar in frosted and unfrosted plants in both years except when it was increased after ‐5.2 °C in 1980. It is pointed out that for reliable cropping, varieties should flower late as well as tolerate spring frosts and that tests of frost tolerance should be done for at least three growth stages.