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1

Pathogenic fungi as a source of insecticides

100%
Bogus M. I.
Biotechnologia
|
2000
|
issue 3
33-46
EN
The potential of fungal pathogens for the control of insect pests has been recognized since the letter part of the 19th century. Lethal infection of insect host involves following steps : (i) attachment of the pathogen to the host surfaces, (ii) penetration of the host cuticle by infection hyphae or germinating conidia, (iii) invasion of host haemocoel and internal organs by fungal hyphae. Host death results from the cumulative effect of mechanical damage and enzymatic digestion of insect tissues, production of mycotoxins and/or nutrient exhaustion by the parasite. Penetration of host cuticles is achieved through a combination of enzymatic and mechanical methods. A number of cuticle degrading enzymes, including proteases, lipases and chitinases, are produced during penetration. Since proteins may account for up to 70% of the cuticle, proteases play a major role in the penetration process. The correlation between pathogenicity and enzyme activity remains unclear. Many entomopathogenic fungi produce toxic metabolites: (1)nonpeptide toxins, (2) linear and cyclic peptide toxins and (3) protein toxins. Some of these compounds have been identified in mycosed insects , but their role in disease development remains unclear. Destruxins, the best known mycotoxins produced by entomopathogenic fungi, inhibit mitochondrial ATPase, secretion of fluid by Malpighian tubules, disturb function of calcium channels what leads to tetanic paralysis as well as suppress host defense. However, the knowledge of the mechanisms of fungal pathogenesis in insects is still fragmentary.
2

Genetic determination of variability of barley doubled haploids inoculated with Fusarium culmorum (W.G.Sm.) Sacc. with regard to mycotoxin accumulation and reduction in yield traits

61%
Surma M., Adamski A. T., Adamski T., Chelkowski C. J., Chelkowski J., Golinski G. P., Golinski P., Kaczmarek K. Z., Kaczmarek Z., Kostecki K. M., Kostecki M., Perkowski P. J., Perkowski J., Wisniewska W. H., Wisniewska H.
Journal of Applied Genetics
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2000
|
vol. 41
|
issue 4
237-246
EN
The genetic determination of variability of barley doubled haploid (DH) lines in regard of their susceptibility to Fusarium head blight caused by Fusarium culmorum was studied. The susceptibility was evaluated in a 3-year field experiment on the basis of reduction in yield traits and mycotoxin accumulation in infected kernels. The following traits were analysed in inoculated and control plants: kernel number and weight per ear, 1000-kernel weight, percentage of plump kernels (>2.5 mm), deoxynivalenol (DON) content and nivalenol (NIV) content of kernels. On the basis of the obtained data, heritability coefficient (ratio of genotypic to phenotypic variance) was assesed, and genetic parameters as well as the number of effective factors were estimated. Heritability coefficients calculated from two-way analysis of variance, i.e. regarding the influence of years and year ? genotype interaction, appeared to be exceptionally low and ranged from 5.2% for the reduction in plump kernels to 38.2% for the reduction in 1000-kernel weight. In the case of mycotoxin accumulation about 60% of the observed variability in NIV concentration and 30% in DON concentration resulted from genetic differences among lines. Additive effects of genes were important for all the analysed traits. Significant effects of dominance and dominance ? dominance were observed for 1000-kernel weight and percentage of plump kernels. Moreover, it was found that the observed variability in yield trait reduction resulted from the segregation of 5-6 effective factors, DON content from 4 factors, while NIV content from 5 factors.
3

Beauvericin cytotoxicity to the invertebrate cell line SF-9

61%
Calo L., Fornelli F., Nenna S., Tursi A., Caiaffa M. F., Macchia L.
Journal of Applied Genetics
|
2003
|
vol. 44
|
issue 4
515-520
EN
The cyclic hexadepsipeptide beauvericin, initially known as a secondary metabolite produced by the entomopathogenic fungus Beauveria bassiana and toxic to Artemia salina larvae, has been more recently recognized as an important mycotoxin synthesized by a number of Fusarium strains, which parasite maize, wheat and rice. Therefore, this mycotoxin may enter the food chain, causing yet unknown effects to the health of both domestic animals and humans. The cytotoxic effects of beauvericin on mammalian cells have been studied. We investigated the cytotoxicity of this compound in an in vitro invertebrate model, viz. the insect cell line SF-9 (immortalized pupal ovarian cells of the lepidopter Spodoptera frugiperda). Cultures of SF-9 cells in the stationary phase were exposed to beauvericin at concentrations ranging from 100 nM to 300 M, for different periods of time (from 30? to 120 h). The effects on cell viability were assessed by the trypan blue exclusion method. After 4 h of incubation no significant decrease in cell viability was recorded in SF-9 cell cultures exposed to low concentrations of beauvericin, i.e. 100 nM and 300 nM. However, a slight decrease in viability (3.9%) was seen already in cells exposed to the mycotoxin at the 1 M concentration. This effect became gradually more evident at higher concentrations ( 28% at 30 M, 50% at 100 M, 68% at 300 M). An even more pronounced reduction in cell viability was observed after a 24 h exposure. Under these conditions, 1 M beauvericin caused an approx. 10% decrease in the number of viable cells, which became more significant at higher concentrations 23% at 3 M, 47% at 10 M, 65% at 30 M, 90% at 100 M, 99% at 300 M). Therefore, the 50% cytotoxic concentrations (CC50) at 4 h and 24 h could be estimated as 85 M and 10 M, respectively. In time-course experiments, no effect of beauvericin (30 M) on cell viability could be seen after exposure for periods of time as long as 30?, 1 h and 2 h, respectively. In contrast, when SF-9 cells were exposed to the mycotoxin for longer periods of time, from 8 h to 120 h, we recorded a strong cytotoxic effect already in the low micromolar concentration range. Thus, the CC50 after both 72 h and 120 h exposure times was assessed as 2.5 M. Higher concentrations caused a virtually 100% cell death. The data collected suggest that beauvericin exerts a substantial dose- and time-dependent cytotoxic effect on invertebrate cells, comparable to the effects described in mammalian cells.
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