Antibacterial Activity and Mechanisms of Ethanol Extracts from Scutellaria baicalensis Georgi and Magnolia officinalis against Phytophthora nicotianae

Phytophthora nicotianae causes substantial economic losses in most countries where tobacco is produced.At present,the control of P.nicotianae mainly depends on chemical methods,with considerable environmental and health issues.We investigated the effects of ethanol extracts from Scutellaria baicalensis Georgi(SBG)and Magnolia officinalis(MO).On mycelial growth,sporangium formation,and zoospore release of P.nicotianae.Both extracts inhibited the growth of P.nicotianae,with mycelial growth inhibition rates of 88.92%and 93.92%,respectively,at 40 mg/mL,and EC50 values of 5.39 and 5.74 mg/mL,respectively.The underlying mechanisms were the inhibition of sporangium formation,the reduction of zoospore number,and the destruction of the mycelium structure.At an SBG extract concentration of 16.17 mg/mL,the inhibition rates for sporangia and zoospores were 98.66%and 99.39%,respectively.At an MO extract concentration of 2.87 mg/mL,the production of sporangia and zoospores was completely inhibited.The hyphae treated with the two plant extracts showed different degrees of deformation and damage.Hyphae treated with SBG extract showed adhesion and local swelling,whereas treatment with MO extract resulted in broken hyphae.Mixture of the extracts resulted in a good synergistic effect.

Screening of an Antagonistic Strain of Phytophthora nicotianae and Its Application Potential

Soil samples were taken from healthy tobacco plant rhizosphere in Phytophthora nicotianae severely infected tobacco field in Hunan Province to screen out antagonistic strains against Phytophthora nicotianae by the plate confrontation method.Subsequently,we had obtained a strain LZW-118 which had an obvious inhibitory effect on Phytophthora nicotianae with the plate inhibition rate of 71.14%.The strain LZW-118 was identified as Burkholderia vietnamiensis based on morphological,physiological and biochemical characteristics analysis and 16 S rDNA sequence.The growth-promoting potential test results showed that the strain not only had a significant inhibitory effect on Phytophthora nicotianae but also had the functions of nitrogen fixation,phosphorus dissolution and growth promotion for tobacco plant height,leaf length,leaf width and the number of leaves,showing a good application potential in biological control.

INTERFERENCE BY NON-HOST PLANT ROOTS AND ROOT EXUDATES IN THE INFECTION PROCESSES OF PHYTOPHTHORA NICOTIANAE

Crop rotations are widely used because they can significantly reduce the incidence of pests and diseases.The interactions between non-host roots and pathogens may be key in the inhibition of soilborne pathogens in crop rotations.Interactions between fennel(Foeniculum vulgare)roots/root exudates and Phytophthora nicotianae were investigated because of the known allelopathy between fennel and tobacco(Nicotiana tabacum).The effects of the key compounds in the fennel rhizosphere on the mycelial growth and zoospore behavior of P.nicotianae were assessed.The roots of fennel attracted P.nicotianae zoospores and inhibited their motility and the germination of cystospores,with some cystospores rupturing.4-ethylacetophenone,vanillin and N-formylpiperidine were consistently identified in the fennel rhizosphere and were found to interfere with the infection of P.nicotianae,especially vanillin.Hyphae treated with these compounds produced more abnormal branches and accumulated reactive oxygen species.These interspecific interactions between non-host roots and pathogens were found to be an important factor in the inhibition by fennel of infection by P.nicotianae.

Stem Blight Control of Schizonepeta tenuifolia Caused by Phytophthora nicotianae Using Trichoderma spp.

Objective To control stem blight disease of Schizonepeta tenuifolia caused by Phytophthora nicotianae. Methods The antagonist effect of 13 Trichoderma strains (including T. viride and T. harzianum) was evaluated upon mycelia growth of P. nicotianae. Trichoderma strains with high antagonistic activities against the pathogen were used to control stem blight of S. tenuifolia in the field. Results Of 13 Trichoderma strains tested, T. viride strain M3 showed maximum mycelia growth inhibition (83.2%) to the pathogen, followed by T. viride strain Tv04-2 (78.2%) and then T. harzianum strain ThB (65.0%), in vitro. Fungal cell wall degrading enzymes, protease, and β-1,3-glucanase were analyzed qualitatively and quantitatively in further study. T. viride strains M3, Tv04-2, and T. harzianum strain ThB efficiently against P. nicotianae were used to control stem blight of S. tenuifolia in the field, and T. viride strain M3 showed the best biocontrol potential. Conclusion Trichoderma spp. can be used as alternatives of pesticides to control stem blight, one of the serious soilborne diseases of S. tenuifolia caused by P. nicotianae. However, though T. viride strains Tv04-2 and T. harzianum strain ThB are also highly against P. nicotianae in vitro, the controlling efficacy of them on stem blight disease is not as excellent as T. viride strains M3 in the field.

Combined Toxicity Test of Complex Agents of Metalaxyl and Other Fungicides against Phytophthora parasitica var. nicotianae

[ Objective] To overcome the resistance of Phytophthora parasitica var. nicotianae against metalaxyl and effectively control its damage, new efficient complex agent of metalaxyl was studied and developed. [ Method] The toxieities of nine fungicides against P. parasitica were measured using growth rate method. On this basis, the fungicides with good effects were selected to compound with metalaxyl, and the optimum complex ratio was confirmed. [Result] The toxicity of metalaxyl was the strongest with EC50 of 2. 130 5μg/ml; followed by carbendazim, mancezeb and dimethomorph with EC50 of 2.357 9, 2.639 8 and 2. 778 8 μg/ml. The effect of cyazofamid was the poorest with EC50 of 6. 278 8 μg/ml. The optimum complex ratios of dimethomorph, carbendazim and mancezeb with metalaxyl were 40： 60, 30：70 and 20： 80, and their co-toxicity coefficients were 138.80,124.25 and 115.00, respectively. [ Conclusion] The complex agents had application and promotion value, which could be used to carry out further field trials.

A Preliminary Study on the Resistance to Different Fungicides in Phytophthora parasitica var. nicotianae

[Objective] This study aimed to investigate the resistance to different fungicides in Phytophthora parasitica var. nicotianae. [Method] Under indoor incubation conditions, the resistance to dimethomorph, metalaxyl-mancozeb, propamocarb and ovraclostrobin.dimethomorph in P. parasitica strain isolated from Zhenyuan County in Qiandongnan State was analyzed with colony growth measurement method. [Result] P. parasitica exhibited different levels of sensitivity to four fungicides. To be specific, P. parasitica exhibited the highest resistance to dimethomorph, and ECho reached 1.19 μg/ml. [Conclusion] In Zhenyuan tobacco-growing area, long-term single use of dimethomorph possesses certain resistance risk in prevention and control of black shank disease.

Identification of stably expressed QTL for resistance to black shank disease in tobacco(Nicotiana tabacum L.) line Beinhart 1000-1

Cigar line Beinhart 1000-1 has effective durable resistance to black shank(BS) and is considered one of the most resistant sources in tobacco(Nicotiana tabacum L.). To investigate the inheritance and identification of stable quantitative trait loci(QTL) for BS response, F2,BC1 F2 individuals and BC1 F2:3 lines were produced from a cross between Beinhart 1000-1 and Xiaohuangjin 1025. Two major quantitative trait loci(M-QTL) named qBS7 and qBS17 were repeatedly detected under different conditions. QTL qBS7 was mapped to the region between PT30174 and PT60621 and explained 17.40%–25.60% of the phenotypic variance under different conditions. The other QTL qBS17 in interval PT61564–PT61538 of linkage group 17 was detected in a BC1 F2 population in the field and in BC1 F2:3 in both the field and at the seedling stage, explaining 6.90% to 11.60% of the phenotypic variance. The results improve our understanding of the inheritance of resistance to BS and provide information that can be used in marker-assisted breeding.