Root induction in Pinus ayacahuite by co-culture with Agrobacterium tumefaciens strains.

Transformation of in-vitro-derived shoots of Pinus ayacahuite Ehrenb. was achieved by co-culture with an oncogenic strain (A281 x 200) of Agrobacterium tumefaciens. During co-culture rooting also occurred; however, this rooting was not induced by genetic transformation of host cells, because a "disarmed" strain of A. tumefaciens (EHA101) also induced rooting. Furthermore, direct contact between shoots and bacterial cells was not required. Rooting occurred in agar-solidified medium and in a soilless substrate (9:1 vermiculite:peat mix). We conclude that A. tumefaciens strains induced rooting in P. ayacahuite through a change in the rhizosphere, probably by producing some root-inducing compound(s), and not through transformation of host cells.