HOST RANGE AND IMPLICATIONS OF PLANT INFECTION BY AGROBACTERIUM-RHIZOGENES

Agrobacterium rhizogenes is the bacterial agent of "hairy root" disease of many higher plants. This bacterium has been used for insertion of selectable markers into host plants, the culture of immortal root lines for secondary metabolite production, and studies of root physiology and plant-fungal and plant-nematode interactions. This review reports the results of infection trials, including 36 in the author's laboratory, of 183 varieties, 463 species, 109 families, 49 orders, 5 classes, and 2 divisions. Contrary to earlier reports, A. rhizogenes is infectious on a high percentage (57%) of those plants tried, and neither primitive nor advanced plants are, as a rule, resistant. Four families have been identified which should be considered resistant from the number of unsuccessful trials on several species inoculated with multiple bacterial strains. These are the Cactaceae, Gesneriaceae, Lamiaceae, and Liliaceae. However, the latter two families may be revised on further work. The Solanaceae, Rosaceae, Fabaceae, Crassulaceae, Caesalpinaceae, Brassicaceae, Polygonaceae, and Asteraceae are all highly susceptible to infection. No chemical basis could be found to explain susceptibility or resistance. The strain specificity of the bacterium was also reviewed with an examination of the infection percentages of each of the tested strains. Successful infection descended in the order K47 = K599 = HRI > TR105 > ATCC 15834 > A4 > NCPPB 1855 > NCPPB 2655 > TR101 > NCPPB 8196 > 232 > ATCC 11325 > ATCC 43057 > TR7 > TR107 = ATCC 13332 = ATCC 13333 for the naturally occurring strains and A4/ARCx > C58C1 (pRiA4) > C58C1 (pRi15834) > C58C1 (pRiTR105) > BL3- >> C58C1 (pRi8196) for genetically engineered strains. In general, naturally occurring strains were superior to engineered strains in effecting plant transformation.