Abstract
#1. A survey of the relevant literature on canker diseases and
factors associated with the ultimate infection was made. This
review also included literature dealing with spore discharge,
dispersal and methods of recording.
#2. The working area has a coastal climate. Over the experimental
period it was found that the area received 2 peak wet periods
annually, first in April and May and then again from September to
November collectively. October was consistently wet in both years.
The soil type is mainly brown forest soil, with decomposed andesite
as parent material.
#3. An investigation was made into the symptoms and manifestation
of the disease. Infection studies, anatomical investigations, spore
collection and germination studies, as well as cultural studies were
made. Field investigations were carried out at Pitmedden Forest,
Fife.
#4. The progress of cankering on the stems and branches has been
arbitrarily divided into 7 stages, depending upon the size of the
canker lesion. It is clear that. stems and branches infected by
cankers with a progress intensity of Stage IV or worse would
eventually die. Vigorous and suppressed trees showed quite
different reactions to the infection.
#5. All areas with Corsican pine in Pitmedden Forest, Fife, showed
the presence of C. sororia cankers. Trees on north and north-east
facing slopes were the most severely affected.
#6. Infection occurred both directly on the stems at the inter -
nodes and through the branches. Infection through the branches
occurred 3 times more frequently than directly on the stems.
Infected branches were generally killed once the infection has
reached stage III.
#7. Branch tissues aged 3-4 years were found to be most susceptible.
However, canker initiation on the stem was most frequent when the
stern tissues were aged 9 years.
#8. Younger stands showed less infection than older stands but as
a result of the small amount of data available this conclusion
must be taken with caution.
#9. The rate of canker development was up to 3 times faster
longitudinally than the tangential spread.
#10. Among the physical and climatic factors influencing disease
outbreak aspect played the dominant role. Canker lesions were
most frequently found on the north- eastern side of the trees and
also on trees growing on areas with north and north -eastern facing
slopes. On the north -eastern side of the trees the air temperature
was much lower than on the other sides. The rate of rise of
temperature on this side in the growing, season was lower than on
the other side. That aspect played an important role in disease
outbreak was also attributed to the effect of wind. Pitmedden
Forest is subjected to north-easterly winds in the spring and
during the to and fro sways cracks and failures occurred in the bark.
These wounds were readily colonised by C. sororia.
#11. The fruit bodies of the fungus were found to be produced from
June to September though maximum production occurred in July and
August (1968). These fruit bodies could be found on trees or
branches that were either living or moribund. 1\o fruit bodies of
the fungus could be collected on dead tissues.
#12. The bulk of the ascospores were collected in July (1968).
Periodicity of discharge was seen in this fungus; ascospores were
mostly discharged at 10.00 a.m. (in July and zugust, 1968). This
coincided with a situation when the relative humidity prior to the
discharge was always high ( > 75%) and where the air temperature
was high and rising.
#13. Successful infection on seedlin =s in the greenhouse and on the
branches in trees in the field occurred only when the tissues had
been wounded prior to inoculation. Inoculation of specially made
needle scars on the seedlin:s also resulted in successful infection.
Inoculation with ascospores failed to promote infection.
Results of inoculation on the branches of trees in the field
showed that branch tissues aged 3-4 years were most frequently
affected. Isolates from Pitmedden and Ringwood were more virulent
than the Netherland isolates.
The fungus could be re-isolated from 95% of infections that
had reached Scale 4.
#14. Anatomical investigation showed that the most frequently
infected tissues were the xylem and rays. The pith was rarely
infected. However the pith was occasionally infected as a
result of invasion from ray infection or from a branch stub.
Infected wood was flinty, resin- soaked and discoloured. This
discolouration was dark and blch, principally due to the deposition
of a dark granular substance in the lumens of the tracheids, initially
deposition was at the periphery of the lumens.
Infection resulted in a proliferation of tracheid cells, though
the size of the individual cells was not significantly affected.
The.tracheids produced after infection were very much shorter than
normal tracheids. The rays were increased in number as a result
of infection and the average ray height was more than those in tissues
not infected. The number of cells in the rays were not significantly
affected by the infection.
As a result of infection there was an increase in the production
of resin ducts but the size of the ducts was not affected.
Resin ducts were very often colonised by the fungus; the
epithelial cells and eventually the resin dues would become
completely filled with the fungal hyphae.
#15. The ascocarps showed greenish hymenium and black excipulum
with irregular margins. At the edges, hair-like protuberances
could be found.
#16. Laboratory observations of the spores confirmed the field
investigations. Spores were discharged when the temperature was
high (10-20°C) and then only when the relative humidity was 75% or
higher. Generally the ascospores were discharged in groups.
#17. Discharged ascospores remained viable up to 72 hours at 0.5°C.
#18. In water ascospores germinated best between 17.5 and 27.5°C.
#19. No germination occurred in ascospores kept at 100; relative
humidity, even after an incubation of 10 days. However, germination
occurred quite readily when the ascospores came into contact with
liquid water soon after discharged. Generally the percentage
germination of the ascospores was not greatly affected if these
ascospores came in contact with liquid water within 36 hours of
discharge.
#20. The ascospores germinated well in water containing sucrose and
extracts of Corsican pine bark, Corsican pine wood and Lodgepole
pine bark.
#21. Ascospores germinated best at pH 5.5 and very poor germination
occurred in solutions with pH values on either side of this value.
#22. In cultures, the fungal hyphae were thin-galled when young but
became progressively thicker with age. Black exudation droplets
were produced by fungus in culture.
#23. All isolates grew best at 22.5°C but differently at other
temperatures. At 4.5°C isolates from Pitmedden and the Netherlands
grew very much more poorly than isolates from Ringwood, Bramshill
and Hallyburton.
#24. Light suppressed growth of all isolates except the Pitmedden
isolate. This apparent effect of light in this case may have
been aggravated by the occasional high temperature reached under
the light source.
#25. All isolates showed tolerance to a wide range of moisture
content and pH values. The isolates from Pitmedden grew best
in media containing 1.50% agar; Ringwood, Hallyburton and the
Netherlands at 2.005; and Bramshill at 0.75% agar.
#26. The pH's for optimum growth of the different isolates range
from 4.0 to 6.0. The Pitmedden isolate grew best at pH 5.0;
Ringwood, Hallyburton and the Netherlands at pH 6.0, and Bramshill
isolate at pH 4.0.
#27. All isolates grew best on 2.5% malt agar and very poorly on
Czapek Dox and Nutrient Broth.
#28. Of the amino -acids tested, asparagine, glutamic acid and
aspartic acid were the best sources of organic nitrogen. Tryptophan
suppressed the growth of all isolates. With the addition of glucose
as an energy source both ammonium and nitrate nitrogen supported
good growth.
#29. Maltose supported poor growth of all isolates. In contrast
sucrose resulted in the best growth. Growth of all isolates showed
a linear relationship with the concentration of sucrose added, within
the range 1-10%.
#30. Biotin was essential for the growth of all isolates but growth
was not affected. by the absence of thiamine. Within the range of
0.005 and 2.500 ug/l, growth of all isolates tested showed a linear
relationship with the Biotin added.
#31. In Scotland the fungus C. sororia was found to occur mainly on
Corsican and Lodgepole pines and was concentrated mainly in the
north-east and south of Scotland.
#32. Proposals for control included the use of disease- resistant
varieties of Corsican pine, careful selection of sites (not to plant
poor and north facing areas) and eventually chemical control.
