High population of Sphingomonas species on plant surface

A unique microbial community exists on upper leaf surfaces because strong irradiation by the sun restricts and selects growing micro‐organisms. The micro‐organisms on plant aerial parts are possibly able to control plant pathogens and to promote plant growth as do some of the micro‐organisms on plant roots. Sphingomonas species on plant tissues (seed, leaf and flower) were detected and enumerated by the amplification of a specific part of the small subunit rRNA gene. Sphingomonads were found on 26 plant species belonging to 11 families. The maximum population number of Sphingomonas was 108 g−1 (wet weight) plant tissue. The maximum population ratio of Sphingomonas to the total aerobic bacteria was 58% when it was counted on glucose‐nutrient agar plates. Consistent differences in population number and population ratio were not found among seeds, leaves and flowers. The role of sphingomonads on plant aerial parts is discussed.