Studies on Rhizoctonia solani damping-off of flax
Hawn, Elmer Joseph
Rhizoctonia solani Kühn is one or the most widely distributed of all pathogenic soil fungi. Its ability to live as a saprophyte in the soil has been shown by Blair (3), and by Roth and Riker (25), and the extremely wide host range of this fungus testifies to its ability to carry on a parasitic mode of existence. Peltier (23), in 1916, reported that 165 species of plants, arising from all the important families of the dicotyledons, a number of monocotyledons, several gymnosperms, and Eguisetum were more or less subject to attack by this fungus. His list also included most of the floricultural plants, vegetable and field crops, herbaceous plants and many weeds. Undoubtedly this list of host plants has had many additions made to it during the intervening years. Pathogenically R. solani plays a triple role. First, it is the causal organism of root and stem diseases of potatoes, beets and other root crops; second, it is one of the main causes of damping-off among seedlings of many species of plants; and third, it causes a foliage blight of sugar beets (12). The damping-off action of R. solani on flax seedlings causes a thinning out of the stand. This, in itself, need not reduce the final yield appreciably since the survivors would have more available moisture and light resulting in larger and more vigorous plants with increased yield of seed. However, flax is unable to compete successfully with weeds and a thinned out stand gives them a much better opportunity of becoming established and crowding out the surviving flax plants. The result is a loss of seed and a reduction in yield that may discourage further planting of this valuable crop to say nothing of soil contamination by weed seeds. … Work has been done by Sanford (29, 31), Le Clerg (15, 16) and others on R. solani damage to potatoes and sugar beets but there has been little work of an experimental nature devoted to a study of R. solani as a flax seedling parasite. This scarcity of information together with the frequent reports of damage to flax suggested that research in the nature of studies on R. solani damping-off of flax be carried out in an attempt to gather data which might indicate some means of controlling the disease. Numbers in brackets refer to bibliography.