Rhizoctonia Disease on Certain Aquatic Plants

Abstract

1. Great areas of aquatic duck-food plants have been destroyed in Back Bay, Virginia, and Currituck Sound, North Carolina. Directly or indirectly, this has caused a large economic loss to a large population. A fungus disease has been found the factor most responsible for this loss. 2. Pure cultures of a strain of Rhizoctonia have been repeatedly isolated from diseased aquatic duck-food plants collected from the infected waters. A disease, identical with that produced by a strain of R. solani, has been produced in greenhouse aquaria plants by inoculations with this aquatic fungus. Pure cultures of the fungus have again been re-isolated from these greenhouse plants. Moreover, a disease has been produced on potato plants by inoculating the plants with sclerotia from culture of this aquatic fungus. 3. This aquatic strain of Rhizoctonia has been found to attack five species of aquatic duck-food plants: Potamogeton pectinatus, P. perfoliatus, Ruppia maritima, Vallisneria spiralis, and Naias flexilis. Attacks have occurred on plants growing in various types of soils, and in waters containing a wide range of salt content. Muck soils and a salinity of 7-20 per cent normal sea water, however, are most favorable for the growth and activity of the fungus. These suitable conditions of soil and salinity now exist in Back Bay and Currituck Sound. 4. Morphological and cultural characteristics indicate that this fungus is a physiological strain of Rhizoctonia solani, and it is so considered by the writers. 5. To our knowledge, this is the first case ever reported of the occurrence of Rhizoctonia solani on aquatic plants. 6. A strain of Rhizoctonia solani isolated from diseased potatoes has been found to attack aquatic plants growing in various types of soils and salt solutions. This disease was identical with that produced by the aquatic strain of the fungus, but occurred in lower salt concentrations. 7. Under favorable conditions Rhizoctonia solani is an aggressive parasite upon those species of aquatic plants studied in this investigation, and the disease induced by it has caused much damage to these plants growing in the infected waters.