A RELATIONSHIP BETWEEN OXYGEN TRANSPORT AND THE FORMATION OF THE ECTOTROPHIC MYCORRHIZAL SHEATH IN CONIFER SEEDLINGS

Abstract

SummaryThe response of the mycorrhizal fungus, Boletus variegatus, to living coniferous roots and to hollow silicone rubber ‘roots’ in anaerobic media was investigated. Mycelial macerates were cultured in nutrient and non‐nutrient agar media in tubes. The roots of whole seedlings or silicone ‘roots’ were placed in the media to a depth of several centimeters below the air‐agar interface. The silicone ‘roots’ were either provided with access to the atmosphere by means of a capillary tube exposed above the agar surface, or were sealed.In young seedlings with unsuberized roots a diffuse fungal growth occurred over the whole root surface. In older, suberized, root systems, colonization was restricted to areas of the main axis through which short laterals were appearing. It was demonstrated polarographically that the area stimulating fungal growth were the only areas of significant oxygen evolution along the root. Fungal growth occurred around the silicone ‘roots’ only when access to air was provided by the capillary. It took the form of a diffuse mycelial ball in non‐nutrient medium but, in mitrient agar, of a tight sheath with a distinct tendency for pseudoparenchyma formation. The possible role of oxygen evolution from roots is discussed both in terms of the initial stimulus to the symbiont and of the continued physiological activity of the mycorrhiza.