| Pythium oligandrum Drechsler is one kind of saprophyte living in soil. It has been shown to colonize the rhizosphere of a wide range of agriculturally important crops. It is antagonistic to and parasitic on more than twenty important pathogenic fungi or other oomycetes. It is Non-pathogenic, harmless to plant and environment. Its antagonistic mechanisms include mycoparasitism, antibiosis and induce resistance. Oligandrin, the elicitin-like protein produced by P. oligandrum, induces systemic resistance in tomato plants, but cause no hypersensitive response (HR). In this study, we applied oligandin to roots to study the effects and mechanism of anti-stress by oligandrin to induce resistance of tomato seedling against B. cinerea in greenhouse. We also researched the mechanisms of the interactions between oligandrin and pathogens or host plant.The main results were obtained as followings:1. Inhibitory of the secretion of Pythium oligandrum strain RCU1 on plant pathogenic fungi and the control effect against tomato gray mould in greenhouse.The inhibition effect of the molecular weight less than 8 kD secretion of P. oligandrum on total 16 isolates of plant pathogenic fungi belonging to 9 species was tested on Petri dishes with cellophane paper and growth rate methods. The secretion of P. oligandrum distinctly depressed the mycelial growth of P. sylvaticum, Botrytis cinerea, and Fusarium culmorum with inhibition rates of 88.9%,86.7% and 84.6%, respectively. The inhibition rates of four Pythium species and four formae speciales of F. oxysporum were significantly differet (P=0.05), respectively. The morphology of B. cinerea treated with the secretion of P. oligandrum was abnormal under scanning electron microscope with mycelia shriveled, small spores appeared in the cell wall and reduced spore output significantly. In the greenhouse trial, the filtrate of P. oligandrum had significantly protective and curative effect against tomato gray mould, and the protective effect of the filtrate was equivalent strong with that of the trearment by using carbendazim.2. Defense responses in tomato leaves against Botrytis cinerea induced by application of oligandrin to rootsIn the greenhouse trial, the root treatment with oligandrin (10μg/mL) had significantly protective and curative effect against tomato gray mould in tomato leaves with efficiency of 61.3% and 51.8%, respectively. Furthermore, the expression of the pathogenesis-related proteins (PRs) genes,β-1,3-glucanase and chitinase were upregulated in the leaves of treated tomato plant 4.7 fold and 3.1 fold, respectively.The oligandrin treatment increased contents of lignin with 18.5% and 34.4% on cultivar Hezuo-903,22.3% and 27.6% on cultivar Kaite-2 than that in control at the peak stage, respectively, 3d and 5d after inoculation. The results from bio-assay indicated that the oligandrin treatment stimulated the activity of the defense related enzymes, peroxidase (POD), polyphenol oxidase (PPO) and phenylalanine ammonia-lyase (PAL). Their activity in the oligandrin-treated plant was about 20.0%,32.6%,57.1% (Hezuo-903),43.9%,32.6%,41.5%(Kaite-2) higher than that in control at the peak stage after inoculation, respectively. We conclude that antioxidant enzyme activities and pathogenesis-related proteins (PRs) genes upregulated were two crucial targets of oligandrin in tomato leaves during the establishment of defense responses.3. Signal pathway induced by oligandrin against Botrytis cinerea in tomato plantOligandrin (10μg/mL) treatment of tomato root induced the expression of ethylene (ET) -related transcription factor (ERF2) genes and the jasmonic acid (JA)-responsive gene for the basic PR-6 proein up-regulated 6.6 fold and 3.6 fold in tomato plants, respectively. These results indicated that the JA/ET signaling pathway is required for oligandrin induced resistance against B. cinerea in tomato. Furthermore, the expression of the pathogenesis-related proteins (PRs) genes, β-1,3-glucanase and chitinase are upregulated in the leaves of treated tomato plant 4.7 fold and 3.1 fold, respectively. Defense responses in tomato leaves against B. cinerea induced by oligandrin have the features both ISR and SAR. Oligandrin perhaps induced SA and JA/ET Signal pathway together.4. Defense responses in tomato fruit induced by oligandrin against Botrytis cinereaOligandrin (10μg/mL) treated tomoto fruit tampuk (20μl) significantly reduced incidence and severity of gray mould (Botrytis cinerea). After artificial inoculation the severity of body rots was decreased by 49.5%. Vc contants was increased 36.1%. The results from bio-assay indicated that the treatment stimulated the activity of the defense related enzymes, phenylalanine ammonia-lyase (PAL), polyphenol oxidase (PPO), peroxidase (POD) activity in the oligandrin-treated fruit was about 18.8%,20.0%,22.7% higher than that in control on the 3rd day after the inoculation, respectively. Furthermore, increased expression of genes encoding pathogenesis -related proteins (PRs), such as PR-2a (extracellularβ-1,3 -glucanase) and PR-3a (extracellular chitinase) at mRNA level in tomato fruit was about 2.7-fold and 3.6-fold above that in the control plant at the peak stage. These results suggest that the defense responses of tomato fruit induced by oligandrin against gray mould might be attributed to systemic acquired resistance (SAR). Antioxidant enzyme activities and pathogenesis-related proteins (PRs) genes upregulated are two crucial targets of oligandrin in tomato leaves during the establishment of defense responses.5. Cytology of the interactions between oligandrin and host plantThe analysis of hyphae of P. oligandrum, tomato roots and leaves by electron microscopy immunogold labeling with polyclonal antibodies against oligandrin confirmed that oligandrin was distributed on the cell wall of the mycelia and secreted outside. During the infection and colonization process P. oligandrum secreted oligandrin, the antigen sites were found in the tomato plant cell wall and the cell nucleus which maybe contacted the induced resistance. Tomato is a good host for P. oligandrum. Spraying oligandrin to tomato leaves, the antigen sites were found in the plant cell wall, chloroplast, and the cell nucleus. Oligandrin can translocated throughout the plant. Even though the exact mechanisms by which oligandrin operates to trigger resistance in tomato are not fully elucidated, the present results demonstrate that oligandrin maybe a signal for triggering synthesis and accumulation of defense gene products, thus increased the disease resistance in tomato.
|
PDF Full Text Request