Adhesion of conidia of the fungus Dilophospora alopecuri to the cuticle of the nematode Anguina agrostis, the vector in annual ryegrass toxicity

Abstract

The adhesion of conidia of the fungus Dilophospora alopecuri to the surface of the second stage dauer larva (DL 2) of the nematode Anguina agrostis (syn. A. funesta) was examined using both light and electron optics. The process of attachment does not lead to any apparent damage to the epicuticle of the nematode. Photographs of sections cut tangentially through the setulose appendages of the conidia show that a mucilagenous fibrillar material appears to be exuded from the highly convoluted surface of these appendages. This material adheres to the surface of the nematode cuticle and is deposited in the transverse annulations. The adhesion of these spores to DL 2 of A. agrostis was examined in 4822 nematodes from four galls. The mean percentage of DL 2 with spores adhering was 64% and ranged from 43 to 85%. This adhesion was compared with that of Corynebacterium rathayi from bacterial galls and was found to coincide. Thus, bacteria adhere to nematodes with D. alopecuri conidia attached and these conidia adhere to nematodes with C rathayi attached. Furthermore, DL 2 that are free from conidial adhesion appear to be free from bacterial adhesion and, in most instances, DL 2 that remain from from bacterial adhesion remain free from conidial adhesion. These observations draw attention to the potential of D. alopecuri as an agent for the biological control of annual ryegrass toxicity. Conidial adhesion to A. agrostis differs from bacterial adhesion to this nematode in that no visible damage to the cuticle takes place. The concept that adhesion of microorganisms to nematodes occurs in two phases, one involving site recognition and the other, if it occurs, involving physiological interaction and morphological change is discussed.