Survival, Colonization and Dispersal of Genetically Modified Pseudomonas fluorescens SBW25 in the Phytosphere of Field Grown Sugar Beet

Abstract

A genetically modified microorganism (GMM), Pseudomonas fluorescens SBW25 (lacZY and kanr-xylE), derived from a strain taken from the leaves of mature sugar beet (Beta vulgaris var. Amethyst), was released as a seed inoculum (ca 1×107 cfu/seed) to field-grown sugar beet in 1993 and 1994. The inoculum successfully colonized the roots and leaves of developing plants and survived in the phytosphere throughout the growing season, (270 days post release). Variation in the population dynamics of the GMM colonizing the immature leaf habitat was observed over two consecutive seasons. In 1993, the GMM represented a minor component of the pseudomonad community in emerging seedlings (<6%), (4×104 cfu g−1, coefficient of variation, CV=7%) whereas, in 1994, plants of similar size were colonized by significantly greater numbers of the GMM (1.1 × 106 cfu g−1, CV=10%) (81% of the total pseudomon-ads) reaching maximum densities 102 days after release. Limited dispersal of the GMM from sugar beet to other plants species was recorded. Although GMMs could not be detected in soil (<1 cfu g−1) or on overwintering plant tissue (<20 cfu g−1) GMMs persisted and colonised plants grown the following season. No transfer of the marker genes to other indigenous microorganisms was recorded.