Rhizosphere colonization pattern of Agrobacterium radiobacter strain G12A,an antagonistic rhizobacterium to the potato cyst nematode Globodera pallida

The colonizing behaviour and survival of the rhizosphere bacterium Agrobact erium radiobacter G12A, an effective antagonist of the potato cyst nematode Globodera pallida, was investigated at the soil-root interface. A rifampic in resistant mutant that was used for reisolation after spray application o nto tuber pieces, was quantitatively recovered 7, 14, 21, and 56 days after planting from the rhizosphere, rhizoplane, root tip, stem base, the initia l tuber piece and from root-free soil mix. After 21 days A. radiobacter G12 A constituted 10 to 30% of the total numbers of detectable bacteria on pota to tubers and in the rhizosphere. Feeding groups of rhizoplane-colonizing m icroorganisms increased in density after the introduction of A. radiobacter G12A at 15 and 20 degrees C, but not significantly. All groups of microorg anisms tested (except flourescent Pseudomonads at 25 degrees C) increased i n the potato rhizoplane, some of them significantly, when temperature was i ncreased from 15 degrees C to 25 degrees C.