- Email: [email protected]
Studies in the genus Ustulina with special reference to parasitism
[ 169 ]
STUDIES IN THE GENUS USTULINA WITH SPECIAL REFERENCE TO PARASITISM VI. A BRIEF ACCOUNT OF HEART ROT OF BEECH (FAGUS SYLVATICA L.) CAUSED BY USTULINA
By W. H. WILKINS, M)'cology Laboratory, University Department of Botany, Oxford (With Plate XII)
When starting the investigation into the pathogenicity of Ustulina in 1933, the intention was to show that beech is subject to a serious heart rot caused by this fungus. This work was delayed by inability to secure adequate evidence because material for detailed examination was not available. In the meantime, however, it has been shown that Ustulina causes a heart rot of lime (Wilkins, 1936) and of elm (Wilkins, 1939). In both trees no fungus other than Ustulina could be isolated from the diseased timber, so this was obviously the pathogen. Several beech trees have been examined during the past six years, and though no old tree has been found in which Ustulina was the only fungus present, it seems probable that it is often the primary and major cause of decay, for in younger trees, where decay is less advanced, no other causal organism has been isolated. Recently, a beech tree which showed typical Ustulina heart rot was felled in the Botanic Gardens, Oxford. Though, owing to the author's preoccupation with medical research, this tree was not investigated in detail, it seems desirable briefly to put this and other cases of Ustulina heart rot of beech on record. . . The tree was a fine specimen, about 170 years old with no external symptoms of disease. When cut across about 2 ft. 6 in. above ground level, the greater part of the centre of the trunk was seen to be decayed in the manner characteristic of Ustulina (PI. XII, fig. 3). Isolations from the decayed timber showed that though certain other (unidentified) fungi were present, the greater part of the wood was diseased by Ustulina as most of the isolations gave pure cultures of that fungus. This tree was situated about twenty yards from the site of the lime tree previously recorded by me (1936) as being diseased by Ustulina. This might imply infection via lateral roots, but though the roots of the lime were to some extent decayed, this decay did not extend to the extremities, and, moreover; the lateral roots of the beech were quite sound. The centre of the root was completely rotten, and it seems probable that the heart-rot infection was due to dieback and consequent decay of the tap-root system as described by Day (1934)' Ustulina may be a wound parasite, but in all the cases of heart rot of beech examined by me, and in most other heart rots caused by this fungus, infection was invariably via the decayed tap root. The decay extended up the trunk to a height of re ft., rendering the timber economically useless. The symptoms of decay in this tree are almost identical with those found in beech trees examined at Blenheim Park, Woodstock (PI. XII,
170
Transactions British Mycological Society
fig. I), Arundel Park, Sussex (PI. XII, fig. 2) and elsewhere, all of which were decayed by Ustulina. Macroscopic examination of a transverse section across a diseased trunk indicates the major symptoms of decay as follows: (I) The centre of the trunk is more or less occupied by a patchily discoloured area with a very irregular outline which bears no relation to the distribution of annual rings (PI. XII, figs. 1-3). (2) This area may be bounded by a definite black line as shown on the left side of the section illustrated in PI. XII, fig. 2. If this line is not present when the tree is freshly cut, it may develop as the timber dries out. (3) If a transverse slice of the trunk be put in the dark and kept moist, the surface will probably become covered with the dark, felty, white-edged mycelium of Ustulina (Wilkins, 1936, PI. XII, fig. 3). (4) Certain isolated patches of the timber in the discoloured area are distinguished as being darker, softer and distinctly more wet than the rest. These patches usually indicate the presence of another species of fungus. Such patches are well shown in PI. XII, figs. I, 3. (5) Whether a peripheral black line is evident or not, the most characteristic feature of the disease is the presence of black lines irregularly distributed throughout the decayed wood (PI. XII, figs. 1,4). These have a general tendency to run radially but with numerous interconnexions and irregularities. They may occasionally be double. Black lines may be produced by certain other fungi but those of Ustulina are very characteristic and slight experience enables them to be used as a diagnostic feature. An example of the general arrangement of the black lines in a dried-out block of timber is shown in PI. XII, fig. 4. A photograph of a trunk of beech showing typical symptoms of Ustulina heart rot, with peripheral black line well emphasised in certain parts, is shown by Cartwright and Findlay (1942) PI. V, fig. c. It is hoped that microscopic examination of the fungus timber relationship may be done later. REFERENCES CARTWRIGHT, K. ST G. & FINDLAY, W. P. K. (1942). Principal decays of British hardwoods. Ann. appl. Biol, XXIX, 219-53. DAY, W. R. (1934)' Development of disease in living trees. Woodpresero, Assoc. J. IV, 25-44· . WILKINS, W. H. (1936). Studies in the genus Ustulina with special reference to parasitism. II. A disease of the common lime (Tilia vulgaris Hayne) caused by Ustulina. Trans. Brit. A{Yc. Soc. XX, 133-57. WILKINS, W. H. (1939). Studies in the genus Ustulina with special reference to parasitism. V. A disease of elm (Ulmus campestris Srn.) caused by Ustulina. Trans. Brit. A{)'c. Soc. XXIII, 171-85.
Fig. Fig. Fig. Fig.
, EXPLANATION OF PLATE XII Transverse sections across beech trunks decayed by Ustulina heart rot. I. An advanced stage of decay in tree from Blenheim Park, Woodstock. 2. A young beech from Arundel Park, Sussex, with actively growing Ustulina, 3. Tree from Botanic Gardens, Oxford, with a stage of decay intermediate between the above two. . 4. Transverse section of dried-out timber' from fig. I enlarged to show black line.
iAcceptedfor publication 18 April 1943)
Trans. Brit. Myc . Soc.
Vol. XXVI. PI. XII
STUDIES IN THE GENUS USTULINA WITH SPECIAL REFERENCE TO PARASITISM VI. A BRIEF ACCOUNT OF HEART ROT OF BEECH (FAGUS SYLVATICA L.) CAUSED BY USTULINA
By W. H. WILKINS, M)'cology Laboratory, University Department of Botany, Oxford (With Plate XII)
When starting the investigation into the pathogenicity of Ustulina in 1933, the intention was to show that beech is subject to a serious heart rot caused by this fungus. This work was delayed by inability to secure adequate evidence because material for detailed examination was not available. In the meantime, however, it has been shown that Ustulina causes a heart rot of lime (Wilkins, 1936) and of elm (Wilkins, 1939). In both trees no fungus other than Ustulina could be isolated from the diseased timber, so this was obviously the pathogen. Several beech trees have been examined during the past six years, and though no old tree has been found in which Ustulina was the only fungus present, it seems probable that it is often the primary and major cause of decay, for in younger trees, where decay is less advanced, no other causal organism has been isolated. Recently, a beech tree which showed typical Ustulina heart rot was felled in the Botanic Gardens, Oxford. Though, owing to the author's preoccupation with medical research, this tree was not investigated in detail, it seems desirable briefly to put this and other cases of Ustulina heart rot of beech on record. . . The tree was a fine specimen, about 170 years old with no external symptoms of disease. When cut across about 2 ft. 6 in. above ground level, the greater part of the centre of the trunk was seen to be decayed in the manner characteristic of Ustulina (PI. XII, fig. 3). Isolations from the decayed timber showed that though certain other (unidentified) fungi were present, the greater part of the wood was diseased by Ustulina as most of the isolations gave pure cultures of that fungus. This tree was situated about twenty yards from the site of the lime tree previously recorded by me (1936) as being diseased by Ustulina. This might imply infection via lateral roots, but though the roots of the lime were to some extent decayed, this decay did not extend to the extremities, and, moreover; the lateral roots of the beech were quite sound. The centre of the root was completely rotten, and it seems probable that the heart-rot infection was due to dieback and consequent decay of the tap-root system as described by Day (1934)' Ustulina may be a wound parasite, but in all the cases of heart rot of beech examined by me, and in most other heart rots caused by this fungus, infection was invariably via the decayed tap root. The decay extended up the trunk to a height of re ft., rendering the timber economically useless. The symptoms of decay in this tree are almost identical with those found in beech trees examined at Blenheim Park, Woodstock (PI. XII,
170
Transactions British Mycological Society
fig. I), Arundel Park, Sussex (PI. XII, fig. 2) and elsewhere, all of which were decayed by Ustulina. Macroscopic examination of a transverse section across a diseased trunk indicates the major symptoms of decay as follows: (I) The centre of the trunk is more or less occupied by a patchily discoloured area with a very irregular outline which bears no relation to the distribution of annual rings (PI. XII, figs. 1-3). (2) This area may be bounded by a definite black line as shown on the left side of the section illustrated in PI. XII, fig. 2. If this line is not present when the tree is freshly cut, it may develop as the timber dries out. (3) If a transverse slice of the trunk be put in the dark and kept moist, the surface will probably become covered with the dark, felty, white-edged mycelium of Ustulina (Wilkins, 1936, PI. XII, fig. 3). (4) Certain isolated patches of the timber in the discoloured area are distinguished as being darker, softer and distinctly more wet than the rest. These patches usually indicate the presence of another species of fungus. Such patches are well shown in PI. XII, figs. I, 3. (5) Whether a peripheral black line is evident or not, the most characteristic feature of the disease is the presence of black lines irregularly distributed throughout the decayed wood (PI. XII, figs. 1,4). These have a general tendency to run radially but with numerous interconnexions and irregularities. They may occasionally be double. Black lines may be produced by certain other fungi but those of Ustulina are very characteristic and slight experience enables them to be used as a diagnostic feature. An example of the general arrangement of the black lines in a dried-out block of timber is shown in PI. XII, fig. 4. A photograph of a trunk of beech showing typical symptoms of Ustulina heart rot, with peripheral black line well emphasised in certain parts, is shown by Cartwright and Findlay (1942) PI. V, fig. c. It is hoped that microscopic examination of the fungus timber relationship may be done later. REFERENCES CARTWRIGHT, K. ST G. & FINDLAY, W. P. K. (1942). Principal decays of British hardwoods. Ann. appl. Biol, XXIX, 219-53. DAY, W. R. (1934)' Development of disease in living trees. Woodpresero, Assoc. J. IV, 25-44· . WILKINS, W. H. (1936). Studies in the genus Ustulina with special reference to parasitism. II. A disease of the common lime (Tilia vulgaris Hayne) caused by Ustulina. Trans. Brit. A{Yc. Soc. XX, 133-57. WILKINS, W. H. (1939). Studies in the genus Ustulina with special reference to parasitism. V. A disease of elm (Ulmus campestris Srn.) caused by Ustulina. Trans. Brit. A{)'c. Soc. XXIII, 171-85.
Fig. Fig. Fig. Fig.
, EXPLANATION OF PLATE XII Transverse sections across beech trunks decayed by Ustulina heart rot. I. An advanced stage of decay in tree from Blenheim Park, Woodstock. 2. A young beech from Arundel Park, Sussex, with actively growing Ustulina, 3. Tree from Botanic Gardens, Oxford, with a stage of decay intermediate between the above two. . 4. Transverse section of dried-out timber' from fig. I enlarged to show black line.
iAcceptedfor publication 18 April 1943)
Trans. Brit. Myc . Soc.
Vol. XXVI. PI. XII