| Summary: | 碩士 === 國立中興大學 === 植物病理學系 === 84 === A total of 227 bacterial strains antagonistic to Pseudomonas
solanacearum on media were isolated from interior tissues of
stems of healthy tomato plants ( 208 strains ) and other sources
(welsh onion rhizospheres , tobacco plants ). They were tested
for the ability to control tomato bacteria wilt after
introducing into plants by the Kijima,s hypocotyl-cuttings
method in a screenhouse. Only nine strains can reduce the
disease severity significantly. Among the nine strains, strains
K8-1、EA2-4、KA4-1 and A10-5 were more consistent in their
control efficacy during repeated testing. These four strains
were all isolated internaly from the stem of healthy tomato
plants, and were termed endophytic antagonistic bacteria in this
study. Strain KA8-1 was identified as Bacillus sp., strains
KA4-1 and A10-5 as Pseudomonas spp. , but strain EA2-4 could not
be identified based on the Biolog identification system. Factors
affecting the biocontrol efficacy of the four strains of
endophytic antagonistic bacteria by the hypocotyl-cutting method
were studied in the greenhouse. The influence of each factor on
the control efficacy varied among tested antagonistic bacteria.
The antagonistic bacteria were more effective when using 10 and
13-day old seedlings for hypocotyl-cutting treatment than
seedlings at the other ages. When soaking period during the
hypocotyl-cuttings treatment was too long or short, it was not
suitable for all or some strains of the antagonistic bacteria ;
the best soaking period was 12 hr. Except strain EA2-4,
allstrains showed biocontrol efficacy on susceptible and
resistant varieties ( lines ) of tomato. The best concentration
of the antagonistic bacteria used for dipping was 108 cfu/ml .
Control efficacy of the antagonistic bacteria varied when the
disease was caused by different strains of P. solanacearum. The
control efficacy of antagonistic bacteria was more easily
demonstrable in the soil infested with P. solanacearum at the
density of 107 or 106 cfu/g dry soil. Biocontrol efficacy of the
antagonistic bacteriawas affected by temperature ; Except strain
EA2-4, the best control efficacy was obtained at 30℃. Among
different treatment methods of antagonistic bacteria , the
hypocotyl-cutting and seed bacterization methods resulted the
best control efficacy by all or most strains of the antagonistic
bacteria. The antagonistic bacteria existed in stems and roots
after introducing into tomato plants by the hypocotyl-cutting
method. The populations of antagonistic bacteria declined more
slowly in roots than in stems with the time during the growth of
tomato. Fourty-two days after introduced into plants,
populations of all antagonistic strains in roots and stems
remained as 104-106 cfu/g fresh root and 103-105 cfu/g fresh
stem, respectively. The population of K8-1 was the highest
detected in the plant, which were 1.17×106 cfu/g fresh root and
2.90×105 cfu/g fresh stem, respectively; the population of
EA2-4 was the lowest, which were 1.80×104 cfu/g fresh root and
1.35×103 cfu/g fresh stem, respectively.When the antagonistic
bacteria and P. solanacearum were present together in the tomato
plants, the population dynamics of the antagonistic bacteria in
roots and stems were similar to those described above, whereas
the populations of P. solanacearum increased with the time. Even
though the population of P. solanacearum did not seem to be
declined, the disease severities of the plants treated with all
antagonistic bacteria were significantly lower than control
plants.
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