Environmental and endogenous controls of developmental pathways: variation and its significance in the forest pathogen, Heterobasidion annosum.

Cultural studies of the forest root pathogen Heterobasidion annosion (Fr.) Bref. have shown that the mycelium of the fungus possesses a high degree of developmental versatility, being able to grow in a variety of distinctive functional modes. Consequently the fungus can alternate between conidiogenous and meiotic reproductive pathways, rapid, sparsely branched and slow, densely branched mycelial extension, nutritive and non-nutritive modes, and 'juvenile' and senescent' phases. This ability is probably of considerable' importance in natural infection cycles and provides an interesting model for examining interrelationships between developmental regulation and host-pathogen interactions generally. It also raises important questions about the interface between environmental and endogenous controls of developmental pathways. [ABSTRACT FROM AUTHOR]