Effects of osmotic and matric potential on radial growth and accumulation of endogenous reserves in three isolates of Pochonia chlamydosporia

Abstract

For the first time, the effects of varying osmotic and matric potential on fungal radial growth and accumulation of polyols were studied in three isolates of Pochonia chlamydosporia. Fungal radial growth was measured on potato dextrose agar modified osmotically using potassium chloride or glycerol. PEG 8000 was used to modify matric potential. When plotted, the radii of the colonies were found to grow linearly with time, and regression was applied to estimate the radial growth rate (mm day⁻¹). Samples of fresh mycelia from 25-day-old cultures were collected and the quantity (mg g⁻¹ fresh biomass) of four polyols (glycerol, erythritol, arabitol and mannitol) and one sugar (glucose) was determined using HPLC. Results revealed that fungal radial growth rates decreased with increased osmotic or matric stress. Statistically significant differences in radial growth were found between isolates in response to matric stress (P<0.006) but not in response to osmotic stress (P=0.759). Similarly, differences in the total amounts of polyols accumulated by the fungus were found between isolates in response to matric stress (P<0.001), but not in response to osmotic stress (P=0.952). Under water stress, the fungus accumulated a combination of different polyols important in osmoregulation, which depended on the solute used to generate the stress. Arabitol and glycerol were the main polyols accumulated in osmotically modified media, whereas erythritol was the main polyol that was accumulated in media amended with PEG. The results found that Pochonia chlamydosporia may use different osmoregulation mechanisms to overcome osmotic and matric stresses.

Keywords:

• biological control
• water stress
• Pochonia chlamydosporia
• root-knot nematodes
• cyst nematodes
• endogenous reserves

Acknowledgements

The authors are grateful for the financial support received from the EU for the project, ICA4-CT-2002-10044, MiCoSPA – Microbial Pest Control for Sustainable Peri-urban/urban Agriculture in Latin America (Cuba and Mexico). We also thank Rothamsted International, who sponsored Belkis Peteira. Rothamsted Research receives grant aided support from the Biotechnology and Biological Sciences Research Council of the UK.