| Summary: | 碩士 === 國立中興大學 === 植物病理學系 === 86 === Weed hosts of Ralstonia solanacearum are reported in many
countries. The weed hosts are considered as sources of
inoculum for bacterial wilt ofsusceptible crops, or may
serve as alternative hosts for long-term survival ofthe pathogen
in fields whenever nonhost plants are cultivated. The
informationon weed hosts for R. solanacearum in Taiwan is
poorly known. This study istherefore to identify the
potential weed hosts of the bacterium in Taiwan.Toual of 1844
weed plants were randomly collected from 73 fields in Taiwan. R.
solanacearum was isolated from the roots of 9 weed species:
Caryophllaceae(Drymaria cordato), Compositae (Ageratum
hosustonianum, Ageratum conyzoides,Bidens bipinnata, Erechtites
valerianafolia), Cyperaceae (Cyperus rotundus,Kyllinga
brevifolia), Oenotheraceae (Ludwigia octovalis), and
Eeuphorbiaceae(Ephorbia hirta). All these plants showed
neither wilt symptoms nor vascularbrowning. All 21 strains of R.
solanacearum from weeds were classified as race1 and biovar 3.
Their physiological and biochemical characteristics
weresimilar to those of strains isolated from the crops, except
that some strainsfrom weeds possessed flagella. The 14 species
of weeds that were frequentlyobserved in the fields were
inoculated at stem with 10 weed strains. Theseweed strains
were moderately to highly virulent to Drymaria cordato,
Ageratumhosustonianum, Erechtites valerianafolia, Cyperus
rotundus, Kyllingabrevifolia, Portulaca oleracea and Solanum
nigrum, and were very low or notvirulent to Verononia cinerea,
Ludwigia octovalis, Phyllanthus urinaria andEphhorbia hirta.
For Physalis angulata, four of the strains were
highlyvirulent, but others were very low virulent or
nonvirulent. Using the soilpouring method for inoculating
the uninjured roots of weed with two weedstrains, R.
solanacearum was not detected in roots and stems of
symptomlessplants of Ludwigia octovalis (excepted one
strain) and Ephhorbia hirta,whereas all other symptomless
plants of weed species were found to be infectedby the pathogen.
Inoculation of crops belonging Leguminosae and
Cucurbitaceaeshowed that pea, watermelon, pumpkin and bottle
gourd were susceptible to R.solanacearum. R. solanacearum
detected in the roots and stems most symptomlessplants of
Cucurbitacous crops. The populations of weed strains in
infestedsoil, during the 8 weeks detection, mostly maintained
at about 106 cfu/g drysoil. During the detection period, some
strains (Pw8 & Pw21) produced varianttype of colonies recovered
from the infested soil. The weed strains multipliedin the roots
and stems of A. hosustonianum, K. brevifolia, and P.
oleracea,especially the population in P. oleracea was the
highest. The fluctuation ofpopulations of weed strains in
rhizosphere soils was large, and thepopulations were in
the range of 106-108 cfu/g dry soil five weeks
afterplanting.
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