| Summary: | 碩士 === 國立中興大學 === 植物病理學系 === 86 === The main objective of this investigation were to explore
the potentialapplication of methyl jasmonate (MJ) ,
sodium salicylate (SA) , andbenzothiadiazole (BTH) in
the control of bacterial spots of tomato(Lycopersicon
esculentum cv. Known-You 301) caused by Xanthomonas
campestrispv. vesicatoria (XCV), and to elucidated the
mechanisms possibly involved. Apreliminary screening test
indicated that spray application of each of thethree tested
chemical individually at certain range of concentration
waseffective in reducing the infection of XCV on tomato
leaves. The effectiveconcentration appeared to be 2.23 mM
for MJ, 2.5 mM for SA and 0.28 mM forBTH. The observed disease
control efficacy was very likely due to the functionof enhanced
resistance of plant host since the test chemicals at
appliedconcentration were not bacterocidal against XCV in an in
vitro system. Afterthe chemical application, the
effectiveness was detected 2 days aftertreatment for both
MJ and BTH, and 6 days for SA. In tomato
plantsartificially inoculated with XCV, the propagation of
test bacteria in foliartissue was reduced by an order when a
pretreatment of these test chemicalenhancement of disease
resistance, changes of various redox enzymes andcertain
defensive chemicals were detected from test plant. The
application ofBTH greatly enhanced the activity of superoxide
dismutase (SOD), catalase(CAT), peroxidase (PO), and
polyphenol oxidase (PPO) in foliar tissue. Theeffectiveness
of BTH application seemed to be more prominent among
youngerfoliar tissue; and except that of PPO, the
effectiveness of enzyme activityenhancement appeared to be
strengthened or even dependent on the challengeinoculation of
XCV. Among MJ treated plants, the activation of SOD and PPO
wasalso detected, However, unlike that of BTH treatment, a
substantial reductionof catalase activity and an
accumulation of H2O2 and phenolic contentsappeared to remain
unchanged. Whereas in SA treated plants, most of mentionedredox
enzymes and defensive chemicals within the foliar tissue
remained at thesame level as that of water treated control,
although a transient increase ofPPO was detected when these
plants were challenge inoculated with XCV. Theprovided
evidence indicated that the disease resistance enhancement
providedby MJ or BTH application was due greatly in part to the
increased activity ofSOD, CAT, PO, and PPO and the accumulation
of defensive chemicals like H2O2 orphenolic compounds. The
reason how SA contributed to the observed resistanceenhancement
remained to be elucidated. The efficacy of disease control
ofthree tested chemicals appeared to be consistent, required
only low doses. Theenvironmental safety characteristic further
warrants their potential to becomeideal plant protectants for
the future.
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