Susceptibility of Ribes spp. to pine stem rusts in Finland

Abstract

SummarySusceptibility of Ribes spp. to three pine stem rusts, Cronartium ribicola, Cronartium flaccidum and Peridermium pini, was investigated by inoculations both in laboratory and in greenhouse conditions, and by observing sporulation on Ribes spp. leaves under natural and artificial inoculum in 16 experiments. Twenty‐seven Ribes spp. cultivars were inoculated in 2000–2004 using 41 sources of C. ribicola aeciospores from a wide geographic range, and six Pinus spp.; 51 sources of C. flaccidum and 11 sources of P. pini from Pinus sylvestris. The results were very similar both after artificial inoculations and observations under natural inoculum in repeated experiments over the years. Cronartium ribicola uredinia and telia developed frequently or moderately on nine Ribes nigrum cultivars but were not present on two cultivars. Sporulation developed on five Ribes rubrum cultivars but was absent on two cultivars. Three Ribes uva‐crispa cultivars were only weakly susceptible to C. ribicola, while all R. alpinum cultivars were resistant to the rust. The other Ribes spp. tested, Ribes niveum, Ribes aureum, Ribes odoratum, Ribes sp. × nigrolaria, Ribes glandulosum and Ribes × culverwellii Jostaberry, were all susceptible to C. ribicola. Cultivars of R. nigrum were more susceptible than those of any other species. No significant variation in virulence of the aeciospores was observed between and among Ribes hosts over the years. Cronartium flaccidum and Peridermium pini did not form any uredinia or telia on Ribes spp. in any of the experiments.