Observations on the Biology of Fomes annosus, with Particular Reference to East Anglian Pine Plantations: II. Spore Production, Stump Infection, and Saprophytic Activity in Stumps

F. annosus produces conidia abundantly in culture but rarelyunder natural conditions. Sporophorea are formed on stumps anddying trees throughout the year provided that the humidity issufficiently high. Spore discharge in the plantations may occurat any time of year, but slowa down or ceases during very dryweather. It takes place at low temperatures, ceasing only whensporophores freeze. In the laboratory, F. annosus basidiospores germinate in relativehumidity exceeding 92 per cent. on freshly cut, unsterilizedpine wood. Viability is lost rapidly in light at temperaturesabove 15°C. Under humid conditions F. annosus spores will infect freshlycut pine stumps. There is evidence that spores of F. annosus washed down intosoil remain viable for at least a short period and that stumpscovered with soil are infected from this source. F. annosusspores can infect stumps for only a few weeks after felling,colonization after a longer interval probably beingprevdntedby competing fungi. In stumps inoculated with a mixed suspensionof F. annosus and Peniophora gigantea spores, Fomes at firstcolonized the wood but was soon replaced by P. gigantea. Otheraspects of competition are discussed. The incidence of natural infection in stumps and the factorsaffecting it are discussed Growth rates of F. annosus on malt agar and in lengths of pineroot are given. The fungus grows in stump roots at about 1 m.per year, and so closely approaches adjacent trees within ayear of thinning the plantation: In large stumps, F. annosusmay survive 15 or even 30 years after felling. Data are givenwhich suggest that the infective capacity of stumps containingF. annosus is greater in alkaline than in acid mils, while replacementby other fungi is slower. Competition of F. annosus with other fungi during colonizationof stumps is discussed. The parasite can grow along roots alreadyoccupied by certain fungi but not along roots containing others.The probable course of succession in stumps rotted by F. annousis described.