Improvements in the growth and yield of olive trees by transformation with the Ri plasmid of Agrobacterium rhizogenes

Results of experiments to determine the beneficial effects of Agrobacterium rhizogenes inoculation on olive seedlings are reported herein. Young, bare root stock, olive trees treated with Agrobacterium rhizogenes 232 possessed a larger ratio of new root to older root mass, a larger total root mass, and a greater total top dry weight after 60 days than those treated with autoclaved A. rhizogenes 232 or a strain of the bacterium lacking the Ri plasmid. Over a course of 3 years, transformed trees grew more quickly and produced significantly more flowers, fruits, and oil than control trees, in the field. New secondary roots initiated by A. rhizogenes were well integrated into the existing vascular system of the older roots. The treatment of olive seedlings with A. rhizogenes should be seriously considered as an agronomic practice deserving further testing.