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An unusual occurrence of spore horns
Volume 8, Part 3, August 1994
AN UNUSUAL OCCURRENCE OF SPORE HORNS G.A. FENWICK Department of Microbiology, The Royal Victoria Infirmary, Queen Victoria Road, Newcastle-upon-Tyne NEl 4LP During a storm in November 1992, a mature common beech tree (Fagus sylvatica L.) 23.5 m (c. 77 ft) tall was blown down in Gosforth Park Nature Reserve, Newcastle upon Tyne (NZ 257702). The tree had not been uprooted by the wind, instead the trunk had been snapped off at approximately 1 m above its base where a butt rot was well established, so that a hollow, jagged stump remained in the soil and the main body of the tree lay level on the ground. The tree was thought to have been between between 180 y and 190 y old. During the second week of September 1993, after a period of prolonged rain followed by dry but muggy weather, the main trunk (but not the stump or the thinner upper branches of the tree) began to manifest a spectacular orange outgrowth, unmistakedly fungal in character, which covered its surface to such an extent that the colour imparted to the lower third of the tree was evident to the naked eye from many metres away. On inspection, it was found that the eye-catching colour suffusing the bole of the fallen tree was the result of innumerable, macroscopic, orange spore horns which had emerged en masse from the bark. (Fig 1). The newly-emerged spore horns were soft, glistening and pliable and many had coiled round to form helices or spirals as they issued from the bark. Others remained straight, or became undulated, but all, after several hours exposure to the atmosphere, began to harden and eventually they set rigid, so that their consistency became more like that of candle wax. Three or four days after emerging, they became so brittle that it was possible to snap the whole spore horn in one piece from the bark, using a pair of fine forceps, and a large number of such specimens was obtained in this manner. Most of the spore horns were cylindrical and tendril-like with a diameter of about 0.5 mm but some were broader and formed ribbon-like bands, with what appeared to be longitudinal striations. The majority of the spore
horns were approximately 1.5 cm long but the largest had attained a length of slightly over 2.5 cm. Others were so small that they barely surfaced above the bark. Although, from a distance, the bole appeared to be completely and uniformly covered with the spore horns, this was not in fact the case, and at close quarters it was estimated that only c. 60% ofthe total surface area affected was covered with irregular patches of the fungus, with bare areas of bark in between. However, over the next few days similar outgrowths appeared in many of the bare areas indicating that spore production was taking place over an extended period. In the densest patches, between 5 and 9 spore horns were found on each square centimetre of the bark, which was approximately 8 mm thick and still firmly attached to the wood. About ten days after first noticing this phenomenon the production of fresh spore horns seemed to cease, and during the whole of this time and since, there was absolutely no evidence to the naked eye, either on the surface or underneath the bark, of the mycelium which has produced this enormous number of spores. Samples of the spore horns were returned to the laboratory for investigation, and on revisiting the
Fig 1 Spore horns xi
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Volume 8, Part 3, August 1994 park several days later, it was found that following two very wet days, all of them, save those on the sheltered underside of the bole, had vanished without trace, so-it seems probable that the spores are adapted to be dispersed in droplets of rain. To date, no further spore horns have emerged from any part of the tree. In the laboratory, it was found that the spore horns consisted entirely of hyaline, sickle-shaped conidia measuring between 15 /lm and 18 /lm long but only 1.5 /lm in breadth at the thickest point mid-way between the two ends of the spore (Fig 2 top, right). They all appeared to be thin-walled and stained well with conventional microbiological stains which showed them to contain numerous metachromatic granules. The spores were found to be arranged within the horn in a series of parallel chains, thousands of spores long, which were aggregated into fasicles some 25 spores thick, such that the convex side of one spore was lying alongside the concave side of its adjacent neighbour. (Fig 2 centre.)
Fig 2 Conidia xlOOO.
When placed in a small amount of water, the spore horns rapidly disintegrated and the individual spores dispersed in a uniform manner so, by diluting a suspension and using a counting chamber, it was possible to obtain some estimate ofthe numbers involved. It was found that a spore horn 1.5 cm long consisted of some 5 x 105 spores and the largest one encountered contained in the region of 8 x 105 . After drying at 25°C for three weeks, 1 g of the spore horns was accurately weighed out and the numbers of spores counted as before. This proved to comprise some 1.7 x 108
conidia, from which it is possible to calculate the weight of a single spore as being in the region of 5.9 x 10- 9 g. It was unfortunately not possible to obtain an accurate assessment ofthe total number of conidia produced, as the distribution of the spore horns was too irregular. However, the bole was measured and the total surface area was conservatively estimated to be 3.4 x 105 cm3 . All the spore horns from five thickly covered areas of bark measuring 5 cm x 5 cm were then collected using a small wire brush, so that the number of conidia in each collection could be determined as before. It was found that the number of spores present on each of the five patches varied from 3 x 106 to 6 X 106 per cm 2 of bark. If the lower figure is taken, and the area of bark so covered is assumed to be only 60% of the total possible, there still must have been, at the very least, some 6 x 1011 conidia on the bole of the tree, weighing something over 3.6 kg! These conidia resisted all attempts at germination on agar or in liquid media. However when they were incubated in ,distilled water for up to 3 weeks at 25°C many of them began to straighten out (Fig 2 top, centre) and about 50% developed small projections either on the concave side (Fig 2 top, left) or convex side (Fig 2 bottom, left) of the spore. Rarely, two such projections were seen on a single spore (Fig 2 bottom, right). However, no further growth was ever observed and the role of these conidia in the life cycle of the fungus remains unknown. Although spore horns on wood are met with fairly frequently in the field, they are normally quite inconspicuous and seldom occur in such profusion. Spores of this nature, which are considered to be asexual stages of members of the Diatrypaceae, are produced by acervular coelomycetes and referred to the genus Libertella Desm. The number of species within this genus is not known with any certainty as the spore horns found on widely differing hosts are usually very similar microscopically. Likewise, the perfect stage of these conidial forms is difficult to determine - only members of the genus Diatrypella, (Ces. & de Not.) de Not. have been successfully cultured to produce spore horns (Croxall, 1950) and the two forms are often linked only by the fact that they are found growing together in close proximity on the same substrate. In this case, the area of bark which had borne the spore horns was
Volume 8, Part 3, August 1994 covered by a mass of confluent Quaternaria quaternata (Pers.) Fr. stromata, which imparted a characteristic pimply grey appearance to its surface. The perithecia of this. species are commonly seen in dense swarms on the bark of freshly-felled beech trees, and this fungus was assumed to be the source of the spore horns in this instance. Q. quaternata was not found on either the stump or the upper branches, and it is interesting to note that members of the Diatrypaceae are frequently restricted to certain areas of their preferred hosts with, for instance, Eutypa spinosa (Pers.) Tul. & C. Tul. typically being found at the base, and Diatrype disciformis, (Hoffm.) Fr. being confined to the smaller branches of beech trees.
Quatenaria quaternata ascospores from perithecia collected from the Gosforth Park beech tree were obtained and these germinated readily on malt agar. Bipolar germ-tubes emerged and these gave rise to a non-sporulating mycelium which failed to produce spore horns on any of the laboratory media tested. Similarly, the mycelium failed to interact in any way with the conidia when growing in contact with them, on the same agar plate. That these structures have a role as spermatia, however, cannot be ruled out at this stage. Reference Croxall, H.E. (1950) Studies on British pyrenomycetes III. The British species of the genus Diatrypella Cesati & De Notaris. Trans. Br. mycol Soc. 33: 45-72.
The next issue of the Mycologist will appear in November 1994. The contents will include articles on: • Aseroe rubra - the first outdoor record of this fungus in Europe.
• The uses of 'Gasteromycetes' - a sequel to the article in this issue. • Luminous fungi - 'Glowing Wood' and similar phenomena. • Xylaria polymorpha in culture. • Henningsia brasiliensis.
• A Malaysian Fungus Foray - with phosphorescent Pleurotus .
..
AN UNUSUAL OCCURRENCE OF SPORE HORNS G.A. FENWICK Department of Microbiology, The Royal Victoria Infirmary, Queen Victoria Road, Newcastle-upon-Tyne NEl 4LP During a storm in November 1992, a mature common beech tree (Fagus sylvatica L.) 23.5 m (c. 77 ft) tall was blown down in Gosforth Park Nature Reserve, Newcastle upon Tyne (NZ 257702). The tree had not been uprooted by the wind, instead the trunk had been snapped off at approximately 1 m above its base where a butt rot was well established, so that a hollow, jagged stump remained in the soil and the main body of the tree lay level on the ground. The tree was thought to have been between between 180 y and 190 y old. During the second week of September 1993, after a period of prolonged rain followed by dry but muggy weather, the main trunk (but not the stump or the thinner upper branches of the tree) began to manifest a spectacular orange outgrowth, unmistakedly fungal in character, which covered its surface to such an extent that the colour imparted to the lower third of the tree was evident to the naked eye from many metres away. On inspection, it was found that the eye-catching colour suffusing the bole of the fallen tree was the result of innumerable, macroscopic, orange spore horns which had emerged en masse from the bark. (Fig 1). The newly-emerged spore horns were soft, glistening and pliable and many had coiled round to form helices or spirals as they issued from the bark. Others remained straight, or became undulated, but all, after several hours exposure to the atmosphere, began to harden and eventually they set rigid, so that their consistency became more like that of candle wax. Three or four days after emerging, they became so brittle that it was possible to snap the whole spore horn in one piece from the bark, using a pair of fine forceps, and a large number of such specimens was obtained in this manner. Most of the spore horns were cylindrical and tendril-like with a diameter of about 0.5 mm but some were broader and formed ribbon-like bands, with what appeared to be longitudinal striations. The majority of the spore
horns were approximately 1.5 cm long but the largest had attained a length of slightly over 2.5 cm. Others were so small that they barely surfaced above the bark. Although, from a distance, the bole appeared to be completely and uniformly covered with the spore horns, this was not in fact the case, and at close quarters it was estimated that only c. 60% ofthe total surface area affected was covered with irregular patches of the fungus, with bare areas of bark in between. However, over the next few days similar outgrowths appeared in many of the bare areas indicating that spore production was taking place over an extended period. In the densest patches, between 5 and 9 spore horns were found on each square centimetre of the bark, which was approximately 8 mm thick and still firmly attached to the wood. About ten days after first noticing this phenomenon the production of fresh spore horns seemed to cease, and during the whole of this time and since, there was absolutely no evidence to the naked eye, either on the surface or underneath the bark, of the mycelium which has produced this enormous number of spores. Samples of the spore horns were returned to the laboratory for investigation, and on revisiting the
Fig 1 Spore horns xi
•
..
Volume 8, Part 3, August 1994 park several days later, it was found that following two very wet days, all of them, save those on the sheltered underside of the bole, had vanished without trace, so-it seems probable that the spores are adapted to be dispersed in droplets of rain. To date, no further spore horns have emerged from any part of the tree. In the laboratory, it was found that the spore horns consisted entirely of hyaline, sickle-shaped conidia measuring between 15 /lm and 18 /lm long but only 1.5 /lm in breadth at the thickest point mid-way between the two ends of the spore (Fig 2 top, right). They all appeared to be thin-walled and stained well with conventional microbiological stains which showed them to contain numerous metachromatic granules. The spores were found to be arranged within the horn in a series of parallel chains, thousands of spores long, which were aggregated into fasicles some 25 spores thick, such that the convex side of one spore was lying alongside the concave side of its adjacent neighbour. (Fig 2 centre.)
Fig 2 Conidia xlOOO.
When placed in a small amount of water, the spore horns rapidly disintegrated and the individual spores dispersed in a uniform manner so, by diluting a suspension and using a counting chamber, it was possible to obtain some estimate ofthe numbers involved. It was found that a spore horn 1.5 cm long consisted of some 5 x 105 spores and the largest one encountered contained in the region of 8 x 105 . After drying at 25°C for three weeks, 1 g of the spore horns was accurately weighed out and the numbers of spores counted as before. This proved to comprise some 1.7 x 108
conidia, from which it is possible to calculate the weight of a single spore as being in the region of 5.9 x 10- 9 g. It was unfortunately not possible to obtain an accurate assessment ofthe total number of conidia produced, as the distribution of the spore horns was too irregular. However, the bole was measured and the total surface area was conservatively estimated to be 3.4 x 105 cm3 . All the spore horns from five thickly covered areas of bark measuring 5 cm x 5 cm were then collected using a small wire brush, so that the number of conidia in each collection could be determined as before. It was found that the number of spores present on each of the five patches varied from 3 x 106 to 6 X 106 per cm 2 of bark. If the lower figure is taken, and the area of bark so covered is assumed to be only 60% of the total possible, there still must have been, at the very least, some 6 x 1011 conidia on the bole of the tree, weighing something over 3.6 kg! These conidia resisted all attempts at germination on agar or in liquid media. However when they were incubated in ,distilled water for up to 3 weeks at 25°C many of them began to straighten out (Fig 2 top, centre) and about 50% developed small projections either on the concave side (Fig 2 top, left) or convex side (Fig 2 bottom, left) of the spore. Rarely, two such projections were seen on a single spore (Fig 2 bottom, right). However, no further growth was ever observed and the role of these conidia in the life cycle of the fungus remains unknown. Although spore horns on wood are met with fairly frequently in the field, they are normally quite inconspicuous and seldom occur in such profusion. Spores of this nature, which are considered to be asexual stages of members of the Diatrypaceae, are produced by acervular coelomycetes and referred to the genus Libertella Desm. The number of species within this genus is not known with any certainty as the spore horns found on widely differing hosts are usually very similar microscopically. Likewise, the perfect stage of these conidial forms is difficult to determine - only members of the genus Diatrypella, (Ces. & de Not.) de Not. have been successfully cultured to produce spore horns (Croxall, 1950) and the two forms are often linked only by the fact that they are found growing together in close proximity on the same substrate. In this case, the area of bark which had borne the spore horns was
Volume 8, Part 3, August 1994 covered by a mass of confluent Quaternaria quaternata (Pers.) Fr. stromata, which imparted a characteristic pimply grey appearance to its surface. The perithecia of this. species are commonly seen in dense swarms on the bark of freshly-felled beech trees, and this fungus was assumed to be the source of the spore horns in this instance. Q. quaternata was not found on either the stump or the upper branches, and it is interesting to note that members of the Diatrypaceae are frequently restricted to certain areas of their preferred hosts with, for instance, Eutypa spinosa (Pers.) Tul. & C. Tul. typically being found at the base, and Diatrype disciformis, (Hoffm.) Fr. being confined to the smaller branches of beech trees.
Quatenaria quaternata ascospores from perithecia collected from the Gosforth Park beech tree were obtained and these germinated readily on malt agar. Bipolar germ-tubes emerged and these gave rise to a non-sporulating mycelium which failed to produce spore horns on any of the laboratory media tested. Similarly, the mycelium failed to interact in any way with the conidia when growing in contact with them, on the same agar plate. That these structures have a role as spermatia, however, cannot be ruled out at this stage. Reference Croxall, H.E. (1950) Studies on British pyrenomycetes III. The British species of the genus Diatrypella Cesati & De Notaris. Trans. Br. mycol Soc. 33: 45-72.
The next issue of the Mycologist will appear in November 1994. The contents will include articles on: • Aseroe rubra - the first outdoor record of this fungus in Europe.
• The uses of 'Gasteromycetes' - a sequel to the article in this issue. • Luminous fungi - 'Glowing Wood' and similar phenomena. • Xylaria polymorpha in culture. • Henningsia brasiliensis.
• A Malaysian Fungus Foray - with phosphorescent Pleurotus .
..