Stress tolerance and virulence of insect-pathogenic fungi are determined by environmental conditions during conidial formation

• Published in: Current genetics Vol. 61; no. 3; pp. 383 - 404
• Main Authors: Rangel, Drauzio E. N., Braga, Gilberto U. L., Fernandes, Éverton K. K., Keyser, Chad A., Hallsworth, John E., Roberts, Donald W.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01-08-2015; Springer Nature B.V
• Subjects: Adaptation, Biological; Animals; Biochemistry; Biological control; Biomedical and Life Sciences; Cell Biology; Coleoptera; Environment; Environmental conditions; Fungi - pathogenicity; Fungi - physiology; Fungi - radiation effects; Heat tolerance; Host-Pathogen Interactions; Hot Temperature; Hypoxia; Insecta - microbiology; Insects; Lepidoptera; Life Sciences; Metarhizium; Microbial Genetics and Genomics; Microbiology; Phenotype; Plant Sciences; Proteomics; Research Article; Sodium chloride; Spores, Fungal; Stress, Physiological; Ultraviolet radiation; Ultraviolet Rays; Virulence; Phenotypic plasticity; Trehalose; Virulence to insect host; Stress tolerance; Mannitol; Erythritol
• ISSN: 0172-8083; 1432-0983
• DOI: 10.1007/s00294-015-0477-y

The virulence to insects and tolerance to heat and UV-B radiation of conidia of entomopathogenic fungi are greatly influenced by physical, chemical, and nutritional conditions during mycelial growth. This is evidenced, for example, by the stress phenotypes of Metarhizium robertsii produced on various substrates. Conidia from minimal medium (Czapek’s medium without sucrose), complex medium, and insect (Lepidoptera and Coleoptera) cadavers had high, moderate, and poor tolerance to UV-B radiation, respectively. Furthermore, conidia from minimal medium germinated faster and had increased heat tolerance and were more virulent to insects than those from complex medium. Low water-activity or alkaline culture conditions also resulted in production of conidia with high tolerance to heat or UV-B radiation. Conidia produced on complex media exhibited lower stress tolerance, whereas those from complex media supplemented with NaCl or KCl (to reduce water activity) were more tolerant to heat and UV-B than those from the unmodified complex medium. Osmotic and nutritive stresses resulted in production of conidia with a robust stress phenotype, but also were associated with low conidial yield. Physical conditions such as growth under illumination, hypoxic conditions, and heat shock before conidial production also induced both higher UV-B and heat tolerance; but conidial production was not decreased. In conclusion, physical and chemical parameters, as well as nutrition source, can induce great variability in conidial tolerance to stress for entomopathogenic fungi. Implications are discussed in relation to the ecology of entomopathogenic fungi in the field, and to their use for biological control. This review will cover recent technologies on improving stress tolerance of entomopathogenic fungi for biological control of insects.