RETENTION AND SPREAD OF A GENETICALLY-ENGINEERED PSEUDOMONAD IN SEEDSAND PLANTS OF ZEA-MAYS L - A PRELIMINARY-STUDY

The survival of a genetically engineered strain of Pseudomonas fluores cens introduced to the seeds, stems and leaves of maize plants was mon itored using viable cell counts on selective agars. The bacterium was introduced to the seeds under vacuum and stored at either room tempera ture or 5-degrees-C. The bacterium was detected after 1 d, but not aft er 8 d, in seeds stored at room temperature, whereas at the lower temp erature it was still detected after 43 d. Other inoculated seeds were grown either in a nutrient solution or in potting compost. Studies of survival within both seed remnants and roots, and on the aerial parts of the plants, demonstrated that the majority of bacteria remained in the seeds with some movement into the roots. Seeds retained a greater colonization frequency than roots in plants grown in both soil and nut rient solution. Those plants grown in nutrient solution maintained hig her bacterial populations in seed remnants and roots than those grown in soil. Viable counts of P. fluorescens within seed remnants and root s decreased in soil-grown plants over a 43 d monitoring period. No int roduced organisms were detected in either stem core sections or other aerial parts of any of the inoculated plants, yet the cores were shown to contain an indigenous population of up to 4.8 x 10(4) cells g-1 ti ssue. When mature plants were injected with the bacterium viable count s of the pseudomonad below and above the injection points demonstrated the ability of the bacterium to translocate in the stem after the wou nding process. P. fluorescens applied to the leaf surfaces remained vi able for at least 20 d but showed great variations in numbers with val ues ranging from 0 to 1.4 x 10(6) g-1 tissue. The practical applicatio ns of introducing genetically engineered microorganisms into plants as control measures against pathogens and insect pests are briefly discu ssed.