ICOM1 Abstract
session 4
ANDRADE, GALDINO, LINDERMAN, ROBERT G. & BETHLENFALVAY, GABOR J. USDA-
ARS, Horticultural Crops Research Laboratory, 3420 NW Orchard Ave,
Corvallis OR 97330, USA. The microbial populations in the
mycorrhizosphere of sorghum inoculated with species of Glomus.
Bacterial surround arbuscular mycorrhizal (AM) hyphae on water agar
using of hyphal exudates. We studied bacteria on sorghum mycorrhizae in
pasteurized-soil pot cultures. Plants were inoculated with 2 different
isolates of three AM fungal species, or were left uninoculated (7
treatments). Bacterial populations in the rhizosphere soil or soil
colonized by AM fungal hyphae were counted on TSA medium (total
bacteria) or P1 medium (fluorescent pseudomonads). Twenty-four isolates
were selected for taxonomic study. Bacterial proliferation was greater
in rhizosphere than in hyphosphere soil. Bacillus (5) and Arthrobacter
(3) species dominated the latter, vs. 1 species of each in the
rhizosphere. The rhizosphere had more species of Pseudomonas (3) than
the hyphosphere (1). The bacterial community (TSA medium) was more
diverse in the hyphosphere (16 species) than in the rhizosphere (11),
but these numbers varied greatly within AM treatments. The hyphosphere
of an isolate of Glomus intraradices was associated with 1 bacterium
(Burkholderia cepacia), while an isolate of Glomus mosseae was
associated with 5 bacterial species. One bacterium (B. cepacia) occurred
in the soils of all 6 fungi, but not in the nonAM control) while others,
like Variovax paradoxus, colonized only an isolate of G. mosseae.
Burkholderia pickettii was found only in nonAM soil. AM fungi
selectively stimulated specific bacterial strains in hyphosphere soil.
Thus, different fungus-bacterial associations may affect plant growth
and health differently.