Biological Control of Decay Fungi in Wood by Competition for Non-structural Carbohydrates

Abstract

HYPHAE of fungi that decay wood spread rapidly through their host substrate before any significant loss of weight is detectable¹. Indeed, the rate of advance of Fomes annosus over or through red pine was identical with its growth rate over malt-agar plates² even though fungi that decay wood develop more slowly on cellulose than, on simple sugars³. Glucose stimulates growth over wood⁴, and laboratory cultures provided with a choice of cellulose or a simple carbon source preferentially utilize the latter^5,6, for enzymes that hydrolyse cellulose are generally only produced when growth is restricted⁷. These data suggest, as expected, that fungi initially colonize wood chiefly by utilizing non-structural carbohydrates. Such materials would include simple sugars which have been identified in the sapwood of both hardwoods⁸ and softwoods⁹ and which in the latter account for 0.03 to 0.8 per cent of the dry weight; figures for the inner bark are, of course, considerably higher. Polysaccharides such as starch may also be utilized rapidly: ray cells often provide entrance for invading hyphae and starch reserves of these cells were quickly exhausted, for example, during early decay of sweetgum sapwood by Poria monticola¹⁰. Traces of polysaccharides grouped with holocellulose may also be readily available and thus utilized early in the decay process¹¹.