Crown gall on stone fruit trees

Out of 80 monitored nurseries of stone fruit trees, crown gall symptoms were found in 39 nurseries located in different regions of Poland. The disease was observed on nine different rootstocks. Out of 400 isolates obtained from galls, majority ( 371) were identified as R. rhizogenes, while other isolates were classified as members of Agrobacterium tumefaciens complex, A. nepotum, A. skierniewicense, A. arsenijevicii and 15 could not be classified. Generally, the results of PCRs with primers complementary to Ti plasmid were congruent with the results of pathogenicity tests with the exception of two strains, which were positive in PCRs but negative for the pathogenicity test. In in vitro tests, 59% of tested strains, independent of their pathogenicity, were not sensitive to agrocin 84. The bacteria causing tumours were heterogeneous and even in the single tumour strains classified to different taxa were found.