Studies of seasonal changes in the microbial populations on the phyllosphere of spring wheat as a prelude to the release of a genetically modified microorganism

Populations of bacteria, yeasts and filamentous fungi colonising leaf 3, the flag leaf and the ears of spring wheat were analysed over two complete growing seasons in both the glasshouse and field in 1990 and the field only in 1991. Bacterial isolates were identified by analysis of their fatty acid methyl-ester (FAME) profiles and a total of 37 genera and 88 species was identified. Of the 15 bacteria most frequently recovered and identified, Curtobacterium flaccumfaciens, Microbacterium lacticum, Pantoea agglomerans, Pseudomonas aureofaciens, Pseudomonas fluorescens, Pseudomonas putida and Serratia plymuthica occurred in both years in the glasshouse and field but only Pseudomonas aureofaciens occurred at a similar frequency in all three experimental series. Several plant pathogenic species were identified. By dilution plating, 12 genera of fungi were identified with Aureobasidium, Cladosporium, pink and white yeats being the most common, occurring at 80% or more of the sampling times and sites. Populations of the major groups of microbes (pink and white yeasts, filamentous fungi and bacteria) generally increased in size with time on all tissues sampled in both glasshouse and field, despite plants growing faster in the glasshouse than the field. However, microbial populations were generally significantly larger on field grown plants than on glasshouse grown ones. The value of using FAME profiles to quantity bacterial populations in environmental samples is considered. The significance of the results in relation to monitoring the impact of a future introduction of a genetically modified microorganism (GMM) into the phyllosphere of wheat is discussed.