Agriculture Reference
In-Depth Information
in the suppression of bacterial wilt in the used pumice. Unused pumice inoculated with
W3 showed higher resistance to bacterial wilt, compared with that without inoculation,
and this resistance was further enhanced by the addition of xlyose and glucose. It was
further confirmed in small pot and greenhouse experiments that the application of
biocontrol agent with substrates, such as lysine, available for the antagonist and not for
the pathogen enabled more stable disease suppression in unused pumice. Possible
methods to make unused pumice suppressive to bacterial wilt are presented.
I
NTRODUCTION
In modern greenhouses, soilless culture methods are employed. In Japan, while total
cultivation area decreases year by year, cultivation area for hydroponics is increasing at a rate
of 5 to 10% per year and has now exceeded 1000 ha (Japan Greenhouse Horticulture
Association). Advantages of hydroponics are 1) higher productivity, 2) reduced intensity/cost
of cultivation management, 3) elimination of soil-borne plant pathogens (Zinnen, 1988). But,
in these systems there is sometimes a high risk for the establishment of plant pathogens,
especially
Oomycetes
, which are well adapted to aquatic life (Folman
et al
. 2004). Once
introduced in the nutrient solution of hydroponics, which is weak in buffering capacity to
microbial attacks, pathogenic organisms may spread rapidly through the system and infect the
roots more vigorously than in the soil culture. Therefore, different control methods for
diseases, especially for the pathogens attacking from the root, are required for safe
production, such as disinfection of pathogens in nutrient solutions using heat, filtration,
radiation, chemicals or biological control (Komada 1994; Zhang and Tu, 2000; Ehret
et al
.
2001; Karras
et al
. 2007).
Tomato (
Lycopersicon esculentum
Mill.) is the major crop occupying ca. 50% of total
hydroponics (Japan Greenhouse Horticulture Association). In tomato cultivation, the
following diseases are considered to be serious: bacterial wilt caused by
Ralstonia
solanacearum
, Fusarium wilt by
F. oxysporum
f. sp.
lycopercisi
, Fusarium crown and root rot
by
F. oxysporum
f. sp.
radicis-lycopersici
and Pyhtophthora blight caused by
P. capsici
(Takeuchi 1995). To control these diseases, a variety of methods are already developed and
applied, but techniques with low cost and that are environmentally friendly are still required.
As we found that used pumice was suppressive to bacterial wilt, Fusarium wilt and damping-
off of tomato, we report the phenomenon, suppression mechanisms and possible application
into hydroponics under near-commercial conditions.
M
ATERIALS AND
M
ETHODS
Pumice and Pathogens Used
Two types of pumice were used: 1) unused (new) pumice (Ecoporous
R
, Ebara Corp.,
Tokyo, Japan; particle size distribution: > 2mm 78% , 1 to 2 mm 21%, < 1mm 1%), 2) used
pumice in which Boston lettuce was cultivated for 13 years (particle size distribution: > 2mm
40% , 1 to 2 mm 51%, < 1mm 9%). Pumice is a medium used in hydroponics, instead of
rockwool, sand or palm husk, etc. (Savvas et al. 2003; Van Der Gaag and Wever 2005).