Naturally produced citral can significantly inhibit normal physiology and induce cytotoxicity on Magnaporthe grisea.

Given the importance of finding alternatives to synthetic fungicides, the antifungal effects of natural product citral on six plant pathogenic fungi (Magnaporthe grisea, Gibberella zeae, Fusarium oxysporum, Valsa mali, Botrytis cinerea, and Rhizoctonia solani) were determined. Mycelial growth rate results showed that citral possessed high antifungal activities on those test fungi with EC50 values ranging from 39.52 to 193.00 µg/mL, which had the highest inhibition rates against M. grisea. Further action mechanism of citral on M. grisea was carried out. Citral treatment was found to alter the morphology of M. grisea hyphae by causing a loss of cytoplasm and distortion of mycelia. Moreover, citral was able to induce an increase in chitinase activity in M. grisea, indicating disruption of the cell wall. These results indicate that citral may act by disrupting cell wall integrity and membrane permeability, thus resulting in physiology changes and causing cytotoxicity. Importantly, the inhibitory effect of citral on M. grisea appears to be associated with its effects on mycelia reducing sugar, soluble protein, chitinase activity, pyruvate content, and malondialdehyde content.

The natural product citral can cause significant damage to the hyphal cell walls of Magnaporthe grisea.

In order to find a natural alternative to the synthetic fungicides currently used against the devastating rice blast fungus, Magnaporthe grisea, this study explored the antifungal potential of citral and its mechanism of action. It was found that citral not only inhibited hyphal growth of M. grisea, but also caused a series of marked hyphal morphological and structural alterations. Specifically, citral was tested for antifungal activity against M. grisea in vitro and was found to significantly inhibit colony development and mycelial growth with IC50 and IC90 values of 40.71 and 203.75 µg/mL, respectively. Furthermore, citral reduced spore germination and germ tube length in a concentration-dependent manner. Following exposure to citral, the hyphal cell surface became wrinkled with folds and cell breakage that were observed under scanning electron microscopy (SEM). There was damage to hyphal cell walls and membrane structures, loss of villous-like material outside of the cell wall, thinning of the cell wall, and discontinuities formed in the cell membrane following treatment based on transmission electron microscopy (TEM). This increase in chitinase activity both supports the morphological changes seen in the hyphae, and also suggests a mechanism of action. In conclusion, citral has strong antifungal properties, and treatment with this compound is capable of causing significant damage to the hyphal cell walls of M. grisea.

Demographic changes in multigeneration Plutella xylostella (Lepidoptera: Plutellidae) after exposure to sublethal concentrations of spinosad.

The sublethal effects of the insecticide spinosad were assessed against Plutella xylostella (L.) (Lepidoptera: Plutellidae) by using a demographic approach. The resulting data were analyzed based on the age-stage and two-sex life table model. Bioassay results showed that the susceptibility of P. xylostella to spinosad decreased in Sub strains selected by LC25 spinosad for 10 generations. Although the egg size was significantly smaller in Sub-1 (selected by LC25 spinosad for one generation) compared with spinosad-susceptible strain SS, egg size recovered to normal levels in Sub-5 (selected by LC25 spinosad for five generations) and were even larger in Sub-10 (selected by LC25 spinosad for 10 generations). The life-history parameters changed in the Sub strains of different generations. Sublethal spinosad had a significant effect on Sub-1; however, the sublethal effect on the Sub strains decreased as selection cycles increased. The intrinsic rate of increase (r(m)), finite rate of increase (lambda) and net reproductive rate (R(o)) in Sub-1 were significantly decreased compared with those in the SS strain. No significant differences were found between the Sub-5 or Sub-10 compared with the SS strain. The greatest difference was observed in the total number of eggs laid by each female, i.e., the fecundity. The fecundity in SS, Sub-1, Sub-5, and Sub-10 were 121.92, 81.26, 114.42, and 159.21, respectively. The life expectancy of an SS, Sub-1, Sub-5, and Sub-10 egg was 10.58, 8.71, 10.21, and 7.45 d, respectively.

[Identification and degradation characteristics of a napropamide-degrading bacterium strain]. / ä¸€æ ªæ•Œè‰èƒºé™è§£èŒçš„åˆ†ç¦»é‰´å®šåŠé™è§£æ€§èƒ½.

In order to investigate the microbial degradation mechanism of amide herbicide napropamide and its degradation bioaugmentation in soil, a bacterial strain LGY06 capable of utilizing napropamide as sole carbon and energy source was isolated from a tobacco-planted soil after successive application of napropamide. LGY06 was identified as Bacillus cereus based on morphological, physiological and biochemical characteristics, and the 16S rDNA homologue sequence analysis. The degradation of napropamide in pure cultures by LGY06 was fitted to the first-order function. The strain LGY06 could degrade more than 75.7% of 50 mg·L-1 napropamide within 7 d. The optimal temperature and pH for napropamide degradation was 35 ℃ and 8.0, respectively. The pathway of napropamide degradation was elucidated based on metabolites identification by GC-MS. The main degradation products of napropamide by LGY06 were α-naphthol and propylacetanilide. The meta-bolism of napropamide by strain LGY06 involved dealkylation and oxidation (or hydrolyzation). Under the laboratory control conditions, the bacterial strain LGY06 could effectively enhance the degradation of napropamide in soil. Compared with the un-inoculated controls, the half-life of napropamide in sterilized soil, non-rhizosphere soil, and rhizosphere soil inoculated with the strain LGY06 was shorted by 79.5%, 36.6% and 41.1%, respectively.