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United States Department of Agriculture

Agricultural Research Service

Title: Carbon-T0-Nitrogen Ratio, Carbon Concentration, and Amino Acid Composition of Growth Media Influence Conidiation of Helminthosporium Solani

Authors
item Elson, Marshall - VIRGINIA
item Schisler, David
item Jackson, Mark

Submitted to: Mycologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 4, 1997
Publication Date: N/A

Interpretive Summary: Silver scurf disease cost the potato industry 8.5 million dollars in Idaho alone during the 1992-93 tuber storage season. Researchers working on ways to control the fungus that causes this disease are limited by difficulties in growing the fungus on laboratory media. Discovery of a laboratory medium that increases sporulation of the fungus would greatly aid researchers in finding a way to reduce this devastating disease. The present work was conducted to determine how various media ingredients affect growth and sporulation of the fungus. We discovered that different strains of the fungus respond differently to media ingredients. We developed a medium that improved growth and spore production by several strains of the fungus that causes silver scurf on potato tubers. This medium, and further improvements based on it, should permit more rapid progress in controlling silver scurf disease as researchers can now more easily produce the fungus for experimental use.

Technical Abstract: Silver scurf, caused by Helminthosporium solani, is an important storage disease of potatoes. Experiments designed to evaluate control alternatives are limited by difficulty in producing conidial inoculum. In an effort to better understand how this difficulty could be overcome, this study evaluated the influence of various carbon-to-nitrogen (C:N) ratios, carbon concentrations, and amino acids on conidial germination, colony diameter, and conidiation of Helminthosporium solani grown on solid-phase basal salts media. Under the conditions tested, the highest concentrations of conidia were produced with 1.25 to 2.5 g of carbon per liter at a C:N ratio of 10:1. Higher C:N ratios or higher carbon concentrations reduced conidiation. Total conidia production was improved by use of tyrosine or arginine as the sole nitrogen source. Use of leucine, lysine, methionine, phenylalanine, or threonine severely inhibited H. solani conidia production. When assays were conducted on a range of H. solani strains, the influence of media components on growth and sporulation were not always consistent. Use of a nitrogen source containing a mixture of amino acids resulted in a defined medium that permitted conidiation and growth of H. solani that was similar to or better than that obtained with standard V8 juice medium.

Last Modified: 4/19/2014