Chien-Jui Huang

Dimethyl disulfide is an induced systemic resistance elicitor produced by Bacillus cereus C1L.

BACKGROUND Bacillus cereus C1L is a plant growth-promoting rhizobacterium and can elicit induced systemic resistance (ISR) in plants against necrotrophic pathogens. However, little is known about ISR elicitors produced by B. cereus C1L, and no ISR elicitor has been identified and characterised. Therefore, the objective of this study is to identify volatile ISR elicitor(s) produced by B. cereus C1L. RESULTS The volatile metabolites produced by B. cereus C1L were extracted, separated and identified by solid-phase microextraction, gas chromatography and mass spectrometry. Dimethyl disulfide (DMDS) was the only separated metabolite being determined. Afterwards, application of DMDS by means of soil drench significantly protected tobacco and corn plants against Botrytis cinerea and Cochliobolus heterostrophus, respectively, under greenhouse conditions. The results reveal that DMDS could play an important role in ISR by B. cereus C1L. CONCLUSION This is the first report of DMDS as an elicitor produced by an ISR-eliciting B. cereus strain and its ability to suppress plant fungal diseases under greenhouse conditions. It is suggested that DMDS has potential for practical use in controlling plant foliar diseases besides soil fumigation.

Evidence of Induced Systemic Resistance Against Botrytis elliptica in Lily

Lily leaf blight, caused by Botrytis elliptica, is an important fungal disease in Taiwan. In order to identify an effective, nonfungicide method to decrease disease incidence in Lilium formosanum, the efficacy of rhizobacteria eliciting induced systemic resistance (ISR) was examined in this study. Over 300 rhizobacteria were isolated from the rhizosphere of L. formosanum healthy plants and 63 were identified by the analysis of fatty acid profiles. Disease suppressive ability of 13 strains was demonstrated by soil drench application of bacterial suspensions to the rhizosphere of L. formosanum seedlings. Biocontrol experiments were carried out with Bacillus cereus and Pseudomonas putida strains on L. formosanum and Lilium Oriental hybrid cvs. Acapulco and Star Gazer in greenhouse and field studies. Plants treated with B. cereus strain C1L showed that protection against B. elliptica on L. formosanum could last for at least 10 days and was consistent with high populations of B. cereus on lily roots. Analysis of the expression of LfGRP1 and LsGRP1, encoding glycine-rich protein associated with L. formosanum and cv. Star Gazer, respectively, revealed different responses induced by B. cereus or by the pathogen B. elliptica, suggesting that plant defense responses elicited by each follows a different signaling pathway. According to the results of biocontrol assays and LfGRP1/LsGRP1 gene expression analyses with culture filtrates of B. cereus strain C1L, we propose that eliciting factors of ISR are generated by B. cereus and some of them exhibit thermostable and heat-tolerant traits. This is the first report about ISR-eliciting rhizobacteria and factors effective for foliar disease suppression in lily.

Physiological response of Bacillus cereus C1L-induced systemic resistance in lily against Botrytis leaf blight

Bacillus cereus C1L has been demonstrated to induce systemic disease resistance against Botrytis elliptica in lily. The objective of this study was to investigate physiological responses of B. cereus C1L-triggered systemic resistance in lily cv. Star Gazer against B. elliptica. By histological and biochemical analyses, leaves inoculated with B. elliptica displayed cell death, H2O2 accumulation and lignin deposition. As plants were elicited with B. cereus C1L, cell death, H2O2 accumulation and lignin deposition in leaves caused by B. elliptica infection were suppressed, revealing that suppression of oxidative burst might be associated with B. cereus C1L-induced systemic resistance. In reactive oxygen species inhibitors assays, B. elliptica-caused lesion numbers and H2O2 accumulation in lily leaves were significantly reduced as leaves were pretreated with catalase or diphenylene iodonium. Furthermore, the expression of LsGRP1 and LsPsbR in leaves elicited with B. cereus C1L and inoculated with B. elliptica was decreased. The same expression pattern was also observed in leaves pretreated with catalase or diphenylene iodonium and inoculated with B. elliptica. These results suggest that B. cereus C1L-induced systemic resistance may be related to suppression or alleviation of oxidative stress and cell death of lily caused by B. elliptica.