Document Type

Thesis - Open Access

Award Date


Degree Name

Doctor of Philosophy (PhD)

Department / School


First Advisor

Martin L. Carson


Physiological and pathogenic variability among isolates belonging to anastomosis groups (AG) one and four of Rhizoctonia solani Kuhn pathogenic on flax were investigated. Isolates were obtained from a soil survey of flax (Linum usitatissimum L.) fields in South Dakota, from cooperators in Minnesota, and Japan, and by the production of single basidiospore cultures. Isolates showed physiological variability (both inter and intra-AG variability) in linear growth at different temperatures, linear growth at different matric potentials of cornmeal agar (CMA) ammended with NaCI, and linear growth at different pH of CMA adjusted with HCI or NaOH. Inter and intra-AG variability among the isolates in aggressiveness on flax cultivars were observed in two separate greenhouse experiments conducted at different temperature· regimes. However, the variability in aggressiveness were not the same at the two temperature regimes. In a host range study, variability in aggressiveness between and within AG of the isolates on pinto bean (Phaseolus vulgaris T. L.), rapeseed (Brassica napa L.), and pigweed (Amaranthus retroflexus L.) were found, whereas, on alfalfa (Medicago sativa L.) the isolates showed little variability in aggressiveness. These isolates failed to cause disease on soybean (Glycine max L.), sunflower (Helianthus annuus L.), wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), and oats (Avena sativa L.) within the four week duration of the experiment. There were low but significant positive correlations between the linear growth of R. solani isolates at ·20, 25, 30, and 35 C (:t:2 C) and aggressiveness of the isolates on flax cultivars at greenhouse day temperature regimes of 24 C (±4 C) and 30 C (±4 C) respectively. There was no correlation between the ability of the isolates to grow on CMA at different matric potentials, and the aggressiveness of the isolates on flax at different soil moisture regimes. Also there was no correlation between growth response of selected isolates to media pH and their aggressiveness on flax at varied soil pH levels.

Library of Congress Subject Headings

Rhizoctonia solani

Flax -- Diseases and pests

South Dakota State University Theses



Number of Pages



South Dakota State University