Agriculture Reference
In-Depth Information
Chapter 6
S
UPPRESSIVE
M
ECHANISMS OF
U
SED
P
UMICE TO
B
ACTERIAL
W
ILT OF
T
OMATO AND THEIR
A
PPLICATION INTO
B
IOLOGICAL
C
ONTROL IN
H
YDROPONIC
P
UMICE
C
ULTURE
Koki Toyota
Graduate School of Bio-Applications and Systems Engineering,
Tokyo University of Agriculture and Technology, 2-24-16,
Naka, Koganei, Tokyo 184-8588, Japan
A
BSTRACT
Suppressiveness of pumice, which had been used for 13 years for continuous
cropping, was confirmed against bacterial wilt of tomato caused by
Ralstonia
solanacearum
, in comparison with unused pumice. Since there were significant
differences in some of the chemical and biological properties, suppressive mechanisms of
the used pumice were investigated. Contribution of pH, EC and higher amounts of salts,
such as Ca, to the suppression mechanisms appeared to be very low. In contrast,
microbial biomass and respiration were significantly higher in the used pumice than in
the unused pumice and the suppressiveness of the used pumice disappeared after
sterilization by autoclaving and gamma irradiation. These results suggested that
biological factors rather than chemical factors may be involved in the suppression
mechanisms of bacterial wilt in the used pumice. The result of substrate-induced
respiration inhibition method indicated that bacteria, rather than fungi, may be the
predominant microbial community in the used pumice. Only one isolate, designated as
Burkholderia
sp. W3, showed a suppressive effect on bacterial wilt among 50 dominant
bacterial colonies obtained from tomato roots grown in used pumice. When the strain W3
was inoculated into autoclaved used pumice, suppressive effect completely recovered.
The bacterial communities of tomato roots evaluated by PCR-DGGE were different
between the unused and the used pumice, and roots grown in the used pumice showed
more diverse bacterial community. The band corresponding to W3 was not observed in
the unused pumice, but there was the band in the used pumice, suggesting that W3 was an
initially minor bacterium in tomato roots, but became a major colonizer after repeated
cropping. These results may suggest that W3 is involved in one of the major mechanisms
