Armillariella mellea . [Descriptions of Fungi and Bacteria

Abstract

Abstract A description is provided for Armillariella mellea [Armillaria mellea] . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: The fungus has been recorded as a pathogen on an extremely wide range of dicotyledonous and coniferous trees and shrubs (Raabe, 1962; Browne, 1968). It has also been found on potato (1: 357), narcissus (11: 376), strawberry (8: 727), bamboo (40: 436), geranium (12: 5227), sugarcane and banana (25: 355), but attack of monocotyledons and herbaceous plants is rare. DISEASE: Armillaria root rot. Armillaria root disease. Honey fungus. Armillariella mellea has two roles as a plant pathogen. It may act as a lethal pathogen by invading and destroying the cambium of the root and lower stem, following which it may colonize and rot the woody tissues of the host after its death, or it may cause a butt rot without attacking the living tissues of the host. Both types of disease have a patchy distribution in the field, characteristically spreading from inoculum centres in the soil, so that the hosts which have been most recently attacked are found at the edge of the patch. Where lethal attack occurs the host dies rapidly and (in the case of conifers and certain dicotyledonous trees) the bark of the roots and stem base is cracked and covered with gum or resin exudate. Thick, creamy-white, fan-like sheets of mycelium are found under the bark and these are frequently accompanied by flattened, dark brown rhizomorphs ( forma subcorticalis ). These rhizomorphs may also be epiphytic on roots and grow out into the soil, where their form is more cylindrical ( forma subterranea ). Sporophores may be formed on the host in advanced stages of the disease. The butt rot is a typical soft white rot with pronounced black zone lines. It seldom advances more than 1-2 m up the stem. The rotten wood is often luminous. Armillariella mellea also forms balanced mycorrhizal associations with the orchids Galeola septentrionalis and Gastrodia elata . GEOGRAPHICAL DISTRIBUTION: World wide, throughout forests of the temperate and tropic regions (CMI Map 143, ed. 3, 1969). TRANSMISSION: By infection of woody debris and stumps by air-borne basidiospores, by the growth of rhizomorphs through the soil, by root contact with infected soil debris and transport of infected plant material.