Different bacteria can enhance the micropropagation response of Cotoneaster lacteus (Rosaceae)

Cotoneaster species are widely used ornamental shrubs, and research is unde r way to select genotypes which are more resistant to fire blight by somacl onal variation. During the establishment of micropropagation, one genotype, Cotoneaster lacteus, showed the development of endogenous bacterial contam inants. Two strains were isolated from in vitro explants: Bacillus pumilus and Alcaligenes faecalis. These two strains, and some Pseudomonas fluoresce ns and Ps. putida, promoted in vitro multiplication and rooting of explants . In Pseudomonas strains, rooting enhancing capacity appeared to be related to indole-3-acetic acid (IAA) production, as only strains which produced I AA promoted rooting. Moreover, all deleterious strains included in the stud y for in vitro culture produce cyanide, unlike the above mentioned strains. As to endogenous contaminants, micropropagation enhancing capacity may be attributed to a direct or indirect action on endogenous auxin concentration .