Development of an indigenous pathogen for management of the submersed freshwater macrophyte Hydrilla verticillata

• Published in: Phytopathology 2005-06, Vol.95 (6)
• Main Author: Shearer, J F
• Format: Article
• Language: English
• Subjects: Hydrilla verticillata; Mycoleptodiscus terrestris
• ISSN: 0031-949X

Hydrilla verticillata (L.f.) Royle (hydrilla) is considered one of the three most important aquatic weeds in the world. Plant infestations can impede navigation, clog drainage or irrigation canals, affect water intake systems, interfere with recreational activities, and disrupt wildlife habitats. The plant is an excellent competitor in aquatic habitats because it can photosynthesize at low light levels, has wide environmental tolerances, and produces several types of extended survival propagules. The indigenous fungal pathogen, Mycoleptodiscus terrestris (Gerd.) Ostazeski, (Mt) has shown significant potential for use as a bioherbicide for management of hydrilla. Liquid fermentation methods have been developed and patented that yield stable, effective bioherbicidal propagules of Mt. Under appropriate nutritional conditions, aerated Mt cultures produce high concentrations of vegetative biomass that differentiates to form compact hyphal aggregates or microsclerotia (ms). The microsclerotia germinate both vegetatively and sporogenically thus improving their potential to infect and kill hydrilla. Applied as a liquid inoculum to hydrilla the microsclerotial matrix was capable of significantly reducing hydrilla shoot biomass as high as 99%. Air-dried microsclerotia were capable of hyphal germination in 24 hours and sporogenic germination in 72 hours. Hyphal germination of the microsclerotia that impinge on hydrilla plant surfaces can provide initial infection sites followed several days later by secondary infection resulting from the development and release of spores from the surface of the microsclerotia. Dry inoculum applied at 40 mg/L has been shown to reduce hydrilla shoot biomass greater than 93% and up to 100% by 4 weeks post inoculation compared to untreated control plants.