ECOLOGY AND HOST-PARASITE RELATIONSHIPS
Kretzschmaria species, as
exemplified by K.
deusta, cause white rots whereby both cellulose and lignin are utilized.
A good description of the decay caused by K. deusta (as Ustulina
vulgaris) is given by Cartwright and Findlay (1950). Nilsson et al. (1989)
subjected birch wood to decay by K. deusta (as Hypoxylon
deustum) and categorized it as causing Type 2 decay featuring cell wall
erosion from the cell lumen outward. Schwarze et al. (1995) showed that K. deusta
(as Ustulina deusta) causes a soft-rot featuring cavity
formation in the S2 layer of secondary cell walls. Hyphae appeared to move laterally
between contiguous cells entirely by way of pits; typical bore holes apparently were
absent. Sound transmission appeared to be little reduced in wood decayed by K.
deusta and the authors concluded that the stress-wave timer cannot detect
decay caused by this fungus (Schwarze et al., 1995). Decayed wood usually contains
blackish sheets or sacs of hyphae that appear as black lines, so-called zone lines, in
cuts (Cartwright and Findlay, 1950).
Kretzschmaria species are found throughout the temperate and tropical regions of the world. One species, K. deusta, is most commonly encountered in the North Temperate Zone. Unfortunately, it is widely reported from the subtropics and tropics owing to its confusion with K. pavimentosa, K. sandvicensis, K. zonata, and other predominantly tropical taxa (see later herein for new combinations and authorities). Kretzschmaria deusta is reported as especially common on Fagus in the British Isles (Cannon et al., 1985). Wilkins (1935, 1939b) has given a detailed account of its activities in England and a comprehensive review of the early literature (Wilkins, 1933). Campbell and Davidson (1940) discuss this fungus as causing butt rot of Acer negundo L., A. saccharum Marsh., Betula papyrifera Marsh., Fagus grandifolia Ehrh., and Ilex opaca Ait. Other host genera listed from the United States include Aleurites, Alnus, Citrus, Liriodendron, Nyssa, Poncirus, Quercus, Tilia, and Ulmus (Farr et al, 1989; Hepting, 1971). It is apparent that K. deusta has a very wide host range among woody angiosperms. It has been reported as causing root disease of Hevea and other tropical trees, but in Ceylon (now Sri Lanka) the common causal fungus is K. zonata (Petch, 1923, 1924). Weir (1927) recognized that K. deusta and K. zonata are different taxa; Petch was equivocal on these taxa (see NOTES on K. zonata). Roger (1953) discussed diseases of rubber tree, tea bush, oil palm, cacao, and others caused by Ustulina vulgaris (U. deusta). He followed Van Overeem (1924), as did Petch (1928), in considering U. zonata to be a form of U. vulgaris. Indeed, his broad concept of U. vulgaris included Kretzschmaria micropus (Fr.: Fr.) Sacc. He recognized Ustulina diseases as serious problems on a variety of woody crop plants throughout the African, American, and Asian tropics.
Kretzschmaria clavus was reported by Ko et al. (1977) to cause root rot of Macadamia integrifolia Maiden & Betche, the most serious disease of this tree in Hawaii. In Hawaii the fungus apparently moves from stumps and debris of forest trees into macadamia trees in plantations established on former forest land (Ko et al., 1986). Petch (1923) described a similar situation in relation to K. zonata among several hosts in Ceylon. In any case, Kretzschmaria clavus, K. deusta, K. zonata, and probably other taxa of the genus are undoubtedly pathogens, entering roots and/or butts through dead sprouts, wounds, etc. (Campbell and Davidson, 1940; Ko et al., 1977, 1986; Petch, 1923; Weir, 1927). Because of their capacity to survive on dead material and because they seem to be parasites of opportunity rather than necessity they are considered by us to be facultative parasites. Many more papers dealing with the pathology of Kretzschmaria (as Ustulina) are briefly summarized and a host index presented by Wilkins (1933).