Wa. Dunstan et al., EFFECTS OF BACTERIA ON MYCORRHIZAL DEVELOPMENT AND GROWTH OF CONTAINER-GROWN EUCALYPTUS-DIVERSICOLOR F MUELL. SEEDLINGS, Plant and soil, 201(2), 1998, pp. 241-249
The development of ectomycorrhizas on inoculated eucalypt seedlings in
commercial nurseries is often slow so that only a small percentage of
roots are mycorrhizal at the time of outplanting. If mycorrhizal form
ation could be enhanced by co-inoculation with bacteria which promote
rapid root colonisation by specific ectomycorrhizal fungi, as demonstr
ated by certain bacteria in the Douglas fir-laccaria bicolor associati
on, this would be of advantage to the eucalypt forest industry. Two ba
cterial isolates with a demonstrated Mycorrhization Helper Bacteria (M
HB) effect on ectomycorrhiza formation between Pseudotsuga menziesii a
nd Laccaria bicolor (S238), and seven Western Australian bacterial iso
lates from Laccaria fraterna sporocarps or ectomycorrhizas were tested
in isolation for their effect on ectomycorrhizal development by three
Laccaria spp. with Eucalyptus diversicolor seedlings. Mycorrhizal for
mation by L. fraterna (E710) as measured by percentage infected root t
ips, increased significantly (p < 0.05) by up to 296% in treatments co
inoculated with MHB isolates from France (Pseudomonas fluorescens Bbc6
or Bacillus subtilis MB3), or indigenous isolates (Bacillus sp. Elf28
or a pseudomonad Elf29). In treatments coinoculated with L. laccata (
E766) and the MHB isolate I! fluorescens (Bbc6) mycorrhizal developmen
t was significantly inhibited (p < 0.05). A significant Plant Growth P
romoting Rhizobacteria (PGPR) effect was observed where the mean shoot
d.w. of seedlings inoculated only with an unidentified bacterium (Elf
21), was 49% greater than the mean of uninoculated controls (-fungus,
-bacterium). Mean shoot d.w. of seedlings coinoculated with L. bicolor
(S-238), which did not form ectomycorrhizas with E. diversicolor; and
an unidentified bacterium (Slf14) or Bacillus sp. (Elf28) were signif
icantly higher than uninoculated seedlings or seedlings inoculated wit
h L. bicolor (S-238) alone. This is the first time that an MHB effect
has been demonstrated in a eucalypt-ectomycorrhizal fungus association
. These organisms have the potential to improve ectomycorrhizal develo
pment on eucalypts under nursery conditions and this is particularly i
mportant for fast growing eucalypt species where the retention time of
seedlings in the nursery is of short duration (2-3 months).