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Green islands
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Volume 8, Part 4, November 1994
CORRESPONDENCE Green islands I read with interest Harry Hudson's note on fungal pathogens on stamps in the Mycologist 8, p. 85. With reference to Tom Preece's suggestion, it is worth noting that the 'green islands' on hazel leaves caused by Phyllactinia guttata may have been the very first ones to be described - see the following excerpt from my Presidential Address:* 'To redress the sacrilege that Berkeley's work on Phytophthora was not mycological, I must therefore draw attention to another of his mycological 'firsts'. It occurs in his classic paper on Phytophthora (Berkeley, 1845) and appears to have gone unnoticed for nearly 150 years. The accumulations of host carbohydrates that are characteristic of many biotrophic infections of leaves by true fungi frequently occur in regions around pustules where chlorophyll is retained as other parts of the leaf senescence, the so-called 'green islands'. Reviews which mention these (e.g., Brian, 1967) have, to date,
Spalted Beech wood I refer to recent correspondence (Mycologist 8 of May 1994) and an earlier letter concerning spalted beechwood. As a PhD student at the University of Wales (1984-1987), I worked with fungi at various stages during the decay of beech wood. Some of the most remarkable fungi in this study were those responsible for the 'spalted' appearance of the wood. These are principally ascomycetes ofthe genus Hypoxylon (especially H. fragiforme in beech, but other species appear to occur in a similar 'ecological niche' on other trees) which establish themselves in the healthy, living wood well before it is cut. In the living tree, however, these fungi do not grow out, but are triggered to develop once the wood starts to dry. They are able to respond to relatively small drops in the water content of the wood, such as can be expected following an attack by insects to the tree canopy, and I believe they help the tree by producing just enough decay to make the wood brittle, allowing for the 'self-pruning' of ineffective branches, as well as by rapidly taking over recently exposed wood, preventing the entrance of more aggressive fungi. Since these fungi establish in a similar way as plant pathogens on the healthy tree, it is not surprising that attempts at 'infecting' cut, dried wood consistently fail. There is, in fact, no need at all to inoculate the fungus artificially: all that is needed to obtain spalted beechwood is some polythene bags, rubber bands
cited Cornu (1881) as the first person to describe them. However, in a footnote to his paper on the potato murrain, Berkeley records 'A curious instance has, within a few days, fallen under my notice. The hazel leaves, a week or two back, were very generally spotted with dark patches of green. On examination, it was found that the reverse of such patches was covered with Erysiphe guttata, which had been living at the expense of the paler portions ofthe leaf, while in the subjacent part the chlorophyll had become a deeper green.' The only place I have seen this observation of Berkeley repeated is in a religious tract by Edwin Sidney entitled Blights of the Wheat and published in 1846. * Mycological Research 95:
897-904 (1991).
D.H. Lewis Department of Animal and Plant Sciences University of Sheffield and some patience. Freshly cut lengths of beech are covered on their ends with polythene film (plastic bag) secured and sealed with tightly wound rubber bands. I have worked with branches up to 15 em in diameter and this method has worked for various lengths. Under British conditions, a 20-cm length will develop spalting after some 8 weeks incubation. The typical appearance of spalting is preceded by a generalized cinnamon-staining of the wood occurring approximately between 6 and 8 weeks after cutting, when the fungi are leaving their quiescent state and beginning active growth. The spalting produced by such 'latent colonizers' or 'endophytic' fungi is finely-structured, forming small (about 0.5-1 cm wide) pockets of light-coloured wood surrounded by darker-coloured lines. These lines mark the zones where different fungal individuals (even if they are of the same species) meet, recognize each other and lay down barriers to delimit their territory. Spalting developed under controlled conditions from freshly cut wood tends to be more homogenous than the spalted wood found in nature, where the effect of various factors plays a role in creating a diverse (and surely more interesting) pattern. I.H. Chapela US Department of Agriculture Beltsville Agriculture Research Center Beltsville, MD, USA
Volume 8, Part 4, November 1994
CORRESPONDENCE Green islands I read with interest Harry Hudson's note on fungal pathogens on stamps in the Mycologist 8, p. 85. With reference to Tom Preece's suggestion, it is worth noting that the 'green islands' on hazel leaves caused by Phyllactinia guttata may have been the very first ones to be described - see the following excerpt from my Presidential Address:* 'To redress the sacrilege that Berkeley's work on Phytophthora was not mycological, I must therefore draw attention to another of his mycological 'firsts'. It occurs in his classic paper on Phytophthora (Berkeley, 1845) and appears to have gone unnoticed for nearly 150 years. The accumulations of host carbohydrates that are characteristic of many biotrophic infections of leaves by true fungi frequently occur in regions around pustules where chlorophyll is retained as other parts of the leaf senescence, the so-called 'green islands'. Reviews which mention these (e.g., Brian, 1967) have, to date,
Spalted Beech wood I refer to recent correspondence (Mycologist 8 of May 1994) and an earlier letter concerning spalted beechwood. As a PhD student at the University of Wales (1984-1987), I worked with fungi at various stages during the decay of beech wood. Some of the most remarkable fungi in this study were those responsible for the 'spalted' appearance of the wood. These are principally ascomycetes ofthe genus Hypoxylon (especially H. fragiforme in beech, but other species appear to occur in a similar 'ecological niche' on other trees) which establish themselves in the healthy, living wood well before it is cut. In the living tree, however, these fungi do not grow out, but are triggered to develop once the wood starts to dry. They are able to respond to relatively small drops in the water content of the wood, such as can be expected following an attack by insects to the tree canopy, and I believe they help the tree by producing just enough decay to make the wood brittle, allowing for the 'self-pruning' of ineffective branches, as well as by rapidly taking over recently exposed wood, preventing the entrance of more aggressive fungi. Since these fungi establish in a similar way as plant pathogens on the healthy tree, it is not surprising that attempts at 'infecting' cut, dried wood consistently fail. There is, in fact, no need at all to inoculate the fungus artificially: all that is needed to obtain spalted beechwood is some polythene bags, rubber bands
cited Cornu (1881) as the first person to describe them. However, in a footnote to his paper on the potato murrain, Berkeley records 'A curious instance has, within a few days, fallen under my notice. The hazel leaves, a week or two back, were very generally spotted with dark patches of green. On examination, it was found that the reverse of such patches was covered with Erysiphe guttata, which had been living at the expense of the paler portions ofthe leaf, while in the subjacent part the chlorophyll had become a deeper green.' The only place I have seen this observation of Berkeley repeated is in a religious tract by Edwin Sidney entitled Blights of the Wheat and published in 1846. * Mycological Research 95:
897-904 (1991).
D.H. Lewis Department of Animal and Plant Sciences University of Sheffield and some patience. Freshly cut lengths of beech are covered on their ends with polythene film (plastic bag) secured and sealed with tightly wound rubber bands. I have worked with branches up to 15 em in diameter and this method has worked for various lengths. Under British conditions, a 20-cm length will develop spalting after some 8 weeks incubation. The typical appearance of spalting is preceded by a generalized cinnamon-staining of the wood occurring approximately between 6 and 8 weeks after cutting, when the fungi are leaving their quiescent state and beginning active growth. The spalting produced by such 'latent colonizers' or 'endophytic' fungi is finely-structured, forming small (about 0.5-1 cm wide) pockets of light-coloured wood surrounded by darker-coloured lines. These lines mark the zones where different fungal individuals (even if they are of the same species) meet, recognize each other and lay down barriers to delimit their territory. Spalting developed under controlled conditions from freshly cut wood tends to be more homogenous than the spalted wood found in nature, where the effect of various factors plays a role in creating a diverse (and surely more interesting) pattern. I.H. Chapela US Department of Agriculture Beltsville Agriculture Research Center Beltsville, MD, USA