Silencing of Agrobacterium tumefaciens oncogenes ipt and iaaM induces resistance to crown gall disease in plum but not in apricot

BACKGROUND In this study, two vectors with short‐length chimeric transgenes were used to produce Prunus rootstocks resistant to crown gall disease through RNA‐interference‐mediated gene silencing of the Agrobacterium tumefaciens oncogenes ipt and iaaM. RESULTS Transgenic plum and apricot lines were produced with efficiencies of up to 7.7 and 1.1% respectively. An in vitro evaluation method allowed identification of susceptible lines and reduction in the number of lines to be evaluated in the greenhouse. Five transgenic plum lines, expressing transgene‐derived small interfering RNA (siRNA) and low levels of transgene hairpin RNA (hpRNA), showed a significant reduction in the development of the disease after infection with Agrobacterium strains C58 and A281 under greenhouse conditions. However, unexpectedly, all transgenic apricot lines were gall susceptible. The infection of apricot plants with a binary vector containing only the 6b oncogene demonstrated that the expression of this gene is involved in the induction of tumours in the apricot species. CONCLUSION RNAi‐mediated gene silencing can be used for inducing crown gall resistance in plum rootstocks. These could be used to graft non‐genetically modified commercial fruit cultivars reducing, or eliminating, the disease symptoms. © 2017 Society of Chemical Industry