Page Banner

United States Department of Agriculture

Agricultural Research Service

Research Project: ECOLOGICALLY-SOUND PEST, WATER AND SOIL MANAGEMENT STRATEGIES FOR NORTHERN GREAT PLAINS CROPPING SYSTEMS

Location: Agricultural Systems Research Unit

Title: Structural analysis of the inhibition of Pyrenophora teres by Laetisaria arvalis

Authors
item Ghoshroy, Kajal -
item Cisneros, Dawn -
item LARTEY, ROBERT
item Ghoshroy, Soumitra -

Submitted to: Microscopy and Microanalysis
Publication Type: Proceedings
Publication Acceptance Date: March 21, 2012
Publication Date: July 1, 2012
Citation: Ghoshroy, K., Cisneros, D., Lartey, R.T., Ghoshroy, S. 2012. Structural analysis of the inhibition of Pyrenophora teres by Laetisaria arvalis. Proceedings of Microscopy & Microanalysis 2012 Meeting, Phoenix, Arizona. July 29 - August 2, 2012. Microscopy and Microanalysis. 18(S2): 168-169.

Interpretive Summary: The basidiomycete fungus, Laetisaria arvalis has been reported to have biological control activity over some plant pathogens [1]. This soil-inhabiting Basidiomycete strain was isolated in a Nebraska sugar beet field [3] . Net blotch, a foliar disease of barley, is caused by the ascomycete fungus Pyrenophora teres, and can result in high yield losses [5]. The objective of this research was to utilize light and electron microscopic techniques to examine the interaction between L. arvalis and P. teres, as a basis for the biological control at structural levels. P. teres and L. arvalis were first grown on agar plates. The specimens for SEM study were fixed in glutaraldehyde, post fixed in OsO4, dehydrated, dried, gold coated, and viewed under a Zeiss Ultraplus FESEM. The hyphal specimens for TEM study were fixed in glutaraldehyde, post fixed in OsO4, dehydrated, embedded in EMBed 812 epoxy resin, and cured. Ultrathin sections were stained with uranyl acetate and lead citrate, and viewed under a Hitachi H-8000 TEM operated at 200kV. The blocks were thick sectioned, stained with toluidine blue, and viewed under a Zeiss light microscope. Visual observation of fungal dual cultures growing on agar (Fig.a), showed growth inhibition of P. teres mycelium soon after contact with L. arvalis. Light microscopic examination of interacting colonies showed loss of structural integrity in P. teres hyphae at the interactive zone (Fig b). Ultrastructural changes in both fungi were observed. L. arvalis hyphae grew round, vesiclular structures but had no apparent structural damage (Fig. d, e). P. teres, formed indentations on the hyphal wall, large wall perforations, underwent shrinkage, lost subcellular structural integrity and content (Fig. h, i, j). The structural damage of P. teres hyphae, in presence of L. arvalis, indicates possible degradation of P. teres and growth inhibition. Fungal interaction and lack of inhibition zone suggest absence of diffusible substances, produced in advance of the antagonism. Cell surface interactions between the hyphae seemed to be crucial for growth inhibition. Formation of vesicular structures in L. arvalis, in presence of P. teres, may indicate production of metabolites or toxins responsible for damage. Laetisaric acid, isolated from L. arvalis, has been demonstrated to have a biocontrol activity against some soil pathogens [1]. In many fungi, laetisaric acid stimulates sexual spore development [4, 2]. However, our data indicate damage and destruction to the pathogen instead. Future experiments will be performed to analyze laetisaric acid involvement. Immunocytochemistry experiments will be used to characterize any potential toxins or enzymes produced by L. arvalis, at molecular level. The goal will be to develop a biological control system of P. teres in order to manage Net Blotch Disease.

Technical Abstract: The basidiomycete fungus, Laetisaria arvalis has been reported to have biological control activity over some plant pathogens [1]. This soil-inhabiting Basidiomycete strain was isolated in a Nebraska sugar beet field [3] . Net blotch, a foliar disease of barley, is caused by the ascomycete fungus Pyrenophora teres, and can result in high yield losses [5]. The objective of this research was to utilize light and electron microscopic techniques to examine the interaction between L. arvalis and P. teres, as a basis for the biological control at structural levels. P. teres and L. arvalis were first grown on agar plates. The specimens for SEM study were fixed in glutaraldehyde, post fixed in OsO4, dehydrated, dried, gold coated, and viewed under a Zeiss Ultraplus FESEM. The hyphal specimens for TEM study were fixed in glutaraldehyde, post fixed in OsO4, dehydrated, embedded in EMBed 812 epoxy resin, and cured. Ultrathin sections were stained with uranyl acetate and lead citrate, and viewed under a Hitachi H-8000 TEM operated at 200kV. The blocks were thick sectioned, stained with toluidine blue, and viewed under a Zeiss light microscope. Visual observation of fungal dual cultures growing on agar (Fig.a), showed growth inhibition of P. teres mycelium soon after contact with L. arvalis. Light microscopic examination of interacting colonies showed loss of structural integrity in P. teres hyphae at the interactive zone (Fig b). Ultrastructural changes in both fungi were observed. L. arvalis hyphae grew round, vesiclular structures but had no apparent structural damage (Fig. d, e). P. teres, formed indentations on the hyphal wall, large wall perforations, underwent shrinkage, lost subcellular structural integrity and content (Fig. h, i, j). The structural damage of P. teres hyphae, in presence of L. arvalis, indicates possible degradation of P. teres and growth inhibition. Fungal interaction and lack of inhibition zone suggest absence of diffusible substances, produced in advance of the antagonism. Cell surface interactions between the hyphae seemed to be crucial for growth inhibition. Formation of vesicular structures in L. arvalis, in presence of P. teres, may indicate production of metabolites or toxins responsible for damage. Laetisaric acid, isolated from L. arvalis, has been demonstrated to have a biocontrol activity against some soil pathogens [1]. In many fungi, laetisaric acid stimulates sexual spore development [4, 2]. However, our data indicate damage and destruction to the pathogen instead. Future experiments will be performed to analyze laetisaric acid involvement. Immunocytochemistry experiments will be used to characterize any potential toxins or enzymes produced by L. arvalis, at molecular level. The goal will be to develop a biological control system of P. teres in order to manage Net Blotch Disease.

Last Modified: 8/19/2014
Footer Content Back to Top of Page