Pathogenicity of the fungus, Colletotrichum gloeosporioides (Penz.) Sacc., to Eurasian watermilfoil ( Myriophyllum spicatum L.)

• Published in: Aquatic botany 1989, Vol.33 (1), p.1-12
• Main Authors: Smith, Craig S., Slade, Simon J., Andrews, John H., Harris, Robin F.
• Format: Article
• Language: English
• Subjects: aquatic plants; Biological and medical sciences; biological control; Biological control and other methods; Colletotrichum gloeosporioides; culture media; Freshwater; Fundamental and applied biological sciences. Psychology; fungal diseases; fungi; interspecific relationships; Myriophyllum spicatum; Parasitic plants. Weeds; pathogenicity; pathogens; pathology; Phytopathology. Animal pests. Plant and forest protection; Weeds
• ISSN: 0304-3770; 1879-1522
• DOI: 10.1016/0304-3770(89)90016-8

The pathogenicity to Eurasian watermilfoil ( Myriophyllum spicatum L.) of an isolate of the fungus Colletorichum gloeosporioides (Penz.) Sacc. obtained from diseased milfoil plants was evaluated in laboratory culture experiments. Except in senescent plant tissue, the fungus was confined to the surface of the plant and rarely penetrated beyond the epidermis. Fungal infection prompted a hypersensitive plant response which resulted in the death of a few epidermal cells but evidently halted the internal spread of the fungus. The effect of the fungus was greatest in the commonly used Gerloff's plant culture medium at 25°C. Under these conditions, treated plants did not increase in biomass after inoculation and suffered extensive but superficial damage. At 15 and 20°C inoculation with the fungus did not produce a detectable reduction in yield. In nutrient-amended lakewater and in a carbonate-buffered artificial growth medium, inoculated plants exhibited little visible damage, but the fungus caused a significant reduction in yield. Because these media supported much greater plant growth than Gerloff's medium, the increase in biomass of inoculated plants was 60–70% that of control plants. We concluded that under realistic conditions the effect of this fungal isolate was too small to justify further consideration of it as a possible biological control agent for M. spicatum. Our results illustrate the importance of appropriate culture conditions and media in experiments designed to evaluate microbial pathogens of aquatic plants.