SHORT-TERM COMMUNITY DYNAMICS IN THE PHYLLOSPHERE MICROBIOLOGY OF FIELD-GROWN SUGAR-BEET

Short-term fluctuations in the number of culturable microorganisms and the composition of the bacterial community colonising the phyllospher e of field grown sugar beet were determined at 6 h intervals over a 42 h period. The number of culturable bacteria and Erwinia were found to fluctuate diurnally, increasing in size overnight and declining durin g daylight hours. In contrast, the number of Arthrobacter and yeasts w ere constant throughout the study, even after rainfall. Over most of t he study the number of filamentous fungi and pseudomonads decreased. T he short-term fluctuations in bacterial numbers were similar in magnit ude to those detected over most of the previous season. No significant variation was observed in microbial numbers between samples taken fro m three locations within the field. Fatty acid analysis of isolated ba cteria revealed the community to be similar in composition to that det ected during the same period the previous year and indicated no signif icant short-term temporal or spatial variation. To limit the effects o f diurnal fluctuations on the number of culturable bacteria detected, it is recommended that in long-term studies, samples be collected at t he same time of day on each occasion.