plant surface microbiology.pdf

cells by hyphae. No penetration structures are observed except for swollen
hyphae at the penetration site.Five days after planting,at which the first disease
symptoms can be observed, a tight network of hyphae has grown around the
root surface and epidermal cells are intercellularly colonised by hyphae. After
complete destruction of the root system, the fungus forms macroconidia and
starts colonising the cotyledons.
After introduction of biocontrol bacteria to the test system, observations
show that in the F.o.r.l. -tomato biocontrol system Pseudomonas bacteria not
only colonise the tomato root surface, but also fungal hyphae (Bolwerk and
Lagopodi, unpublished). These are indications that biocontrol bacteria not
only protect the roots against fungi by niche exclusion and production of
antibiotics, but that they actively attack the pathogen. Still, there is much to be
discovered from these rhizosphere studies. The use of autofluorescent proteins
has shown to be a promising way of visualising and understanding the
interactions taking place in the rhizosphere between Pseudomonas and Bacillus
biocontrol strains and fungal pathogens.
6 Conclusions
The whole procedure of isolation, screening for antifungal activity, and determining
disease suppression in bioassays allows fast isolation of potential biocontrol
strains. The gnotobiotic test system has proven to be a valuable test
system to study interactions between biocontrol bacteria, phytopathogen, and
host plant. Combined with the use of autofluorescent proteins, it provides us
with an extraordinary opportunity to study the intricate cellular and molecular
interactions that the key players use to mediate their actions in the rhizosphere.
References and Selected Reading
23 Visualisation of Rhizosphere Interactions 443
Alabouvette C (1986) Fusarium wilt suppressive soils from the Chateaurenard region:
reviews of a 10 year study. Agronomie 6:273–284
Alexeyev MF, Shokolenko IN, Croughan TP (1995) New mini-Tn5 derivatives for insertion
mutagenesis and genetic engineering in gram-negative bacteria. Can J Microbiol
41:1053–1055
Andersen JB, Sternberg C, Poulsen LK, Bjorn SP, Givskov M, Molin S (1998) New unstable
variants of green fluorescent protein for studies of transient gene expression in
bacteria. Appl Environ Microbiol 64:2240–2246
Anderson M, Pollitt CE, Roberts IS, Eastgate JA (1998) Identification and characterization
of the Erwinia amylovora rpoS gene: RpoS is not involved in induction of fireblight
disease symptoms. J Bacteriol 180:6789–6792
Baird GS, Zacharias DA, Tsien RY (2000) Biochemistry, mutagenesis, and oligomerization
of DsRed, a red fluorescent protein from coral. Proc Natl Acad Sci USA
97:11984–11989