Examination of latent infection in raspberry canes with Phytophthora rubi and P. idaei and transmission in micropropagation

Buds of raspberry canes from naturally and artificially infected root stocks were tested by nested PCR for the latent presence of Phytophthora rubi and P. idaei to establish the risk of introducing these pathogens into micropropagation. Fifteen out of 201 buds tested positive for P. rubi and only 1 out of 176 for P. idaei. These infections were not restricted to buds in the lower part of the cane and mostly do not appear to spread systemically up from the rootstock but seem to be caused by secondary infections of the canes. Buds from symptomless canes from infected root stocks were used for micropropagation and P. rubi could be detected in 5.8% of the obtained microplants after ten generations in one of the two trials. This indicates that micropropagation procedures are not absolutely infallible in eliminating infection and underlines the necessity of a zero tolerance towards diseases in the starting material.