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Cellular Basis of Growth Rate Differences in Isolates of Rhizoctonia solani: Choice of Isolates, Properties, and Content of DNA, RNA, Protein, and ATP. Fu- Kuen Lin, Research Assistant, Department of Plant Pathology, University of Illinois at Urbana, Illinois, Present address of senior author: Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907; David Gottlieb, Professor, Department of Plant Pathology, University of Illinois at Urbana, Illinois. Phytopathology 64:88-94. Accepted for publication 20 July 1973. DOI: 10.1094/Phyto-64-88.

Investigations were made on the biochemical bases for differences in the growth rate among some isolates of Rhizoctonia solani. Isolates of this fungus were sought whose growth rates relative to each other were different, but which remained in the same order relative to each other under a wide range of nutritional conditions, in response to plant hormones and other growth-promoting metabolites, and under different temp. Three out of the eleven isolates examined possessed these characteristics and were used in these studies. The concns of several important metabolites were determined for these isolates. DNA varied between 0.4 and 0.6%; RNA was constant about 11.5%; and protein ranged between 27.5 and 36.4%. The different isolates contained between 2,870 and 4,900 picomoles of ATP per mg dry weight tissue. The amounts of DNA, RNA, and protein did not correlate with the growth rates of the isolates, nor did the amount of ATP, on a dry weight basis. Indoleacetic acid was deleterious to growth at concns between 1.0 and 40 µg per ml, kinetin increased growth at various concentrations between 10 and 60 µg per ml but there was no clear response to a concentration gradient with either hormone. Gibberellic acid was not stimulatory to any of the three isolates between 50 and 250 µg per ml, but small reductions in growth occurred at all the concentrations that were used. Differences in the growth rates of these isolates could not be attributed to deficiencies in nutrients or other growth-promoting substances or to different temperatures.