In vitro testing of rose rootstocks resistance to crown gall disease

Fifteen rose rootstocks which were cultured and propagated in vitro were in oculated with the strain GOU1 of Agrobacterium tumefaciens as a test for re sistance to the crown gall disease. Rosa multiflora and R. multiflora 'K2' were highly susceptible, 95% and 90% of the stems forming large tumors, 6.61 and 3.62 (mm X mm), respectively. Three varieties of R. canina, 'Pfander', 'Superbe', and 'Brogs Stachellose' , and a native one became infected but formed small tumors (0.5 mm X mm). In R. rugosa and R. canina 'Superbe' 40% of the infected shoots formed tumo rs during the first week after inoculation. Thus, these species have a low resistance to tumor formation, whereas R. virginiana formed no tumor during the first week after inoculation; 73% of the shoots produced tumors 3 week s after inoculation. Therefore, R. virginiana is subject to infection but r esistant to tumor formation.