Journal of the Department of Agriculture, Journal of the Department of Agriculture, Western Australia, Series 4 Western Australia, Series 4
Volume 3
Number 9 1962 Article 2
1-1-1962
Wood-rotting fungi associated with dieback in apple trees : Wood-rotting fungi associated with dieback in apple trees : progress report : orchard surveys and laboratory studies progress report : orchard surveys and laboratory studies
R F. Doepel
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Recommended Citation Recommended Citation
Doepel, R F. (1962) "Wood-rotting fungi associated with dieback in apple trees : progress report : orchard surveys and laboratory studies," Journal of the Department of Agriculture, Western Australia, Series 4: Vol.
3: No. 9, Article 2.
Available at: https://library.dpird.wa.gov.au/journal_agriculture4/vol3/iss9/2
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Wood-rotting fungi associated with dieback in apple trees : progress report : Wood-rotting fungi associated with dieback in apple trees : progress report : orchard surveys and laboratory studies
orchard surveys and laboratory studies
Cover Page Footnote Cover Page Footnote
Grateful acknowledgment is made of the assistance given by Messrs. N. Shorter, S. Hardisty, R. Cahill and J. Rennick of the Horticulture Division in the orchard surveys. The assistance of the Division of Forest Products, C.S.I.R.O., Melbourne, in identifying fungal fruiting brackets collected in the field and also produced by the "sawdust technique" is gratefully acknowledged.
This article is available in Journal of the Department of Agriculture, Western Australia, Series 4:
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WOOD-ROTTING FUNGI ASSOCIATED WITH IN APPLE TREES
PROGRESS REPORT—ORCHARD SURVEYS AND LABORATORY STUDIES
By R. F. DOEPEL, B.Sc. (Agric), Plant Pathologist
D
IEBACK, or decline, of apple trees has been a serious problem for many years in orchards throughout the South-West of Western Australia. Wood-rotting fungi are commonly associated with this condition and often bring about collapse of affected trees.Numerous observations, extending over many years, have been made by Depart- mental officers* on these fungi and the role they play in the dieback complex.
In 1959 a programme of research was started to further investigate the import- ance of the wood-rotting fungi, and to assess methods of control. This was planned in four sections:
(1) Orchard Surveys.
(2) Laboratory examination of die- back-affected apple limbs.
(3) Pathogenicity tests with wood- rotting fungi.
(4) Testing of control measures.
This report covers the first two sections of the programme. Progress on the other two will be reported as results become available.
1.—ORCHARD SURVEYS
In conjunction with district horticul- tural officers, surveys were made of apple orchards in the Donnybrook, Bridgetown
and Manjimup districts during the summer of 1958-59. Information was collected on the onset of dieback and development of wood rots, types of decay and entry points for fungi.
(a) Onset of dieback and development of wood rots.
It was found that trees could be grouped according to age of planting and severity of symptoms as shown in Table 1.
TABLE 1
Onset of Dieback and Wood Rots in Orchards
• T. C. Dunne, W. P. Cass Smith. H. R. Powell. S. E.
Hardlsty and N. H. Shorter. Departmental Records.
—
Group 1
Group 2
Group 3
Appearance of Trees Vigorous
Lacking In vigour.
No leader exten- sion
Dying back. Leaders withering
Age of P l a n t ! RPTr,=rk«
ings (years) Kemarks 5 — V 14
(odd plant- ings 22 & 28)
8 — y 13
13 > 25
No obvious wood rots.
No obvious wood rot*.
Wood-rotting fungi established.
"Papery bark" and
"Ink stain"obvious.
Group 4 Dieback MVan 20 — y 60 j Advanced wood rots Limbs withered Butt rots.
1
668
DIEBACK
Various wood-rotting fungi are associated with dieback of apple trees in Western Australian orchards. "Papery bark" and "ink stain" are the main symptoms of decay on affected trees.
The commonest sites open for fungal invasion are the dead tips of leaders and large wounds on main limbs resulting from removal of stopped leaders.
Other points of entry including pruning cuts on main limbs and laterals, and sunscalded bark.
Laboratory examination of dieback-affected limbs indicates that invasion by wood-rotting fungi is secondary to other factors which initiate the dieback.
Small groups of healthy, vigorous trees were located in a number of orchards where most trees of the same age showed severe dieback and wood-rotting. In some instances these vigorous trees were grow- ing in deep, summer-moist soil but in other cases there was no such association (Fig. 1.)
No variety of apple was found to be resistant to dieback and associated wood rots.
Certain orchards were found to be more prone to wood rots in situations where foggy, damp conditions prevailed during the winter months, for example, along the Blackwood river at Bridgetown. Other orchards located on high ground in the same district showed a much less aggres- sive type of decay on the dieback limbs.
(b) Types of Decay.
Two common types of wood rot are reported on apple trees in New South Wales (Anon., 1957), Tasmania (Ward, 1957) and Victoria (Fisher and Freeman, 1961). These are referred to as "White wood rot," "yellow wood rot" or "paper bark" (associated fungus Coriolus versi- color (Fr.) Quel.) "heart rot" (associated fungus Schizophyllum commune Fr.)
In West Australian orchards the most common wood rot symptoms are known locally as papery bark (Fig. 2) and ink stain (Fig. 3.)
In the course of surveys fungal fruiting brackets were occasionally seen on limbs and butts of trees in advanced stages of decay (Fig. 4) but rarely found on dead leaders in the early stages of dieback.
Fig. 1.—Healthy Granny Smith apple tree, 27 years old, located in an orchard, near Pember- ton, in which the majority of trees of comparable age were severely affected with dieback
669
Fig. 2.—Limb of Granny Smith apple tree showing typical papery bark symptoms collected from a
Manjimup orchard.
Representative specimens were collected and subsequently identified as Coriolus zonatus (Fr.) Quel, (formerly regarded as Polystictus versicolor (Fr.) Cke in this State) and Stereum strigoso-zonatum
(Schw.) G. H. Cunn.
No fruiting brackets of Schizophyllum commune were seen on ink stain limbs.
(c) Stages of Decay.
The manifestation of dieback as stop- page in growth of leaders is followed by a withering of the terminal buds and wood
(Fig. 5.)
As this withering extends down the leader it is preceded by a slimy condition of the bark.
With the subsequent development of papery bark the affected limb shows obvious signs of fungal decay.
The downward extension of papery bark is paralled internally by a brown dis- coloration of the wood tissues. This discoloration occurs as a V-shaped wedge tapering into the normal wood and is found in advance of the external symptoms
for a distance of from a few inches to several feet (Fig. 6.)
Eventually the decay extends down the scaffold limbs, which are easily broken, and may involve the butt of the tree (Fig.
7). Such trees affected with butt rot are readily blown over by wind (Fig. 8.)
Fungal fruiting brackets usually develop in the autumn and winter on limbs and butts of trees in the advanced stage of decline.
In many cases leaders were observed which had partially withered without showing obvious fungal decay. Such leaders remain on the tree in a condition resembling dry or seasoned timber. Suf- ficient fruiting wood is usually produced lower down on the limbs and laterals of these trees to give reasonable crops for a number of years.
Papery bark is very common on Granny Smith and Cleopatra trees, whereas ink stain is rarely seen on these varieties. Ink stain is common on limbs of the coloured varieties Jonathan and Yates.
There is no evidence that ink stain occurs on trees showing a progressive withering unless a limb has been cut dur- ing earlier pruning operations.
Fig. 3.—Typical Ink stain on limb of Yate apple tree, 31 years old, located at Manjimup. The staining Is
associated with a large cut Indicated by arrow
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Fig 4.—Yate apple tree, 24 years old. In an advanced state of decay and showing fungal fruiting bodies of a Coriolus sp. developed on the butt and main limbs.
Location Donnybrook
(d) Entry Points for Fungi.
The presence of wood-rotting fungi in the limbs of apple trees can be traced to several entry points. The commonest avenues open for invasion are the dead tips of leaders showing the early stage of die- back (Fig. 9) and large uncallused wounds on the main limbs. Such wounds have resulted either from removal of stopped leaders to promote growth in a vigorous lateral (Fig. 10) or as a consequence of the long established spur-pruning system.
Other points of entry include cuts on laterals and also sunscalded bark.
In mature trees, which have been re- worked to more popular varieties, fungal invasion has occurred in the stumps left exposed after the grafting operation.
Cracks made in limbs in mid-summer and resulting from weight of ripening fruit were not usually invaded by wood- rotting fungi.
Fig. 5.—Granny Smith apple tree. 13 years old, showing stoppage of growth and withering of leaders. Location
Upper Capel
Fig. 6.—Limbs collected from Granny Smith apple trees in a Manjimup orchard and sectioned to show internal discolouration and V-shaped wedge between normal and
dleback-affected wood
2.—LABORATORY EXAMINATION OF DIEBACK-AFFECTED APPLE LIMBS (a) Identification of Fungi.
In order to establish the presence and identity of wood-rotting fungi in dieback- affected apple trees, representative speci- mens were collected during the surveys and later examined in the laboratory. The specimens included limb portions showing tip dieback, papery bark, ink stain and also butt sections.
The limb portions were sectioned to determine the extent of internal decay and pieces of discoloured wood were trans- ferred onto malt agar (nutrient jelly) in petri dishes. The fungal cultures which developed on these dishes were grouped into types according to cultural characters.
Isolations were made in this way from 57 apple wood specimens representing such varieties as Granny Smith, Cleopatra, Yates, Jonathan, Delicious and Red Delicious.
Of this number only 32, or 56 per cent., yielded wood-rotting fungi. A number of other fungi, not classified as wood-rotting types, were also isolated from discoloured wood but were considered to be of secondary importance.
The identity of many of these wood- rotting fungi was established by means of a "sawdust" technique developed by Tamblyn and DaCosta (1958) at the C.S.I.R.O. Division of Forest Products, Melbourne, Victoria. This involved inocu- lating a jar containing a mixture of saw- dusts of various woods with a fungal
culture. A balsa wood block was then placed on top of the jar and in due course the fungus grew from the sawdust into the block and developed fruiting brackets at the surface (Fig. 11.)
Fig. 7—Yate apple tree, 24 years old, showing dieback of scaffold limbs and butt rot. Location Donnybrook.
Fig. 8—Yate apple tree. 29 years old, affected with butt rot and blown over by wind.
Location Donnybrook.
Pig. 9.—Withered leader of Granny Smith apple tree. 13 years old. A common entry point for woad-rotting
fungi. Location Upper Capel
The wood-rotting fungi obtained from the discoloured limb and butt tissues are listed in Table 2 below:—
TABLE 2
Wood-rotting Fungi Obtained From Dieback-AfTected Apple Trees
Type of Material Dead tips of leaden
Papery bark and Ink stain limbs
Butt
Fungi obtained Coriolta rtbitinvs (Fr.) Qnel.
Slereum $trigoto-znnatum Coriolus vdutinus Corieluf ttmahn
Slereum hwiutum (Willd.) Fr.
Stereum itrigmo-zonatum Coriolui velvtinu*
No fruiting bodies of Schizophyllum commune were formed by any isolate, although this fungus has been reported as being associated with an ink-like stain
on apple trees in New South Wales (Anon 1957.)
Examination of ink-stained bark sug- gests that various dark-coloured fungi
(including Altemaria spp.) are responsible for this discoloration. It is considered that such fungi have developed on the sap exuded from large wounds made higher up on the limbs (as in Fig. 3.)
(b) Dieback Symptoms and Fungal Inva- sion.
In an attempt to determine the relation- ship between dieback symptoms and fungal invasion a number of Granny Smith apple limbs were collected from Manjimup for detailed study in the laboratory.
Pieces of discoloured wood were taken from the limbs and placed on nutrient agar plates. A regular series of such isola- tions was made for each limb, starting at the tip and continuing downwards to the V junction between discoloured and normal
Pig. 10.—Dteback-affected Umb of Granny Smith apple tree, 24 years old, showing large pruning wound result- ing from removal of a "stopped" leader. Note extension of dieback down the Umb. Such wounds are Invaded by
wood-rotting fungi. Location Donnybrook
675
Fig. 11.—Fruiting brackets of a wood-rotting fungus (Coriolus sp.) developed on a balsa wood block by means of the "sawdust" jar technique. The fungus was
obtained from a dieback-affected apple limb
wood (Fig. 12). Details of isolations m a d e and fungi recovered from these dieback- affected limbs a r e shown in Table 3 : —
TABLE 3
Distribution of Wood-Rotting Fungi in Dieback-Affected Apple Limbs
Type of Material
No. of Specimens examined
Wood-rotting fungi obtained Present
above V junction
Present at V junction Dead tips of leaders ....
Papery bark Ink stain
TotaB „_
33 63 15 111
17
i
34 | 10 1 61
1 4 4 9
Of 111 limbs examined, 50 (45 per cent.) yielded no wood-rotting fungi in isolations.
I n the remaining 61 specimens, from w h i c h wood-rotting fungi were recovered, t h e r e were only nine (8 per cent, of t h e t o t a l ) in which fungal invasion h a d progressed down to t h e V j u n c t i o n with t h e n o r m a l wood.
In addition to t h e above isolations a number of limb pieces were sectioned with a sliding microtome a n d stained to detect fungal mycelium using t h e t e c h n i q u e developed by Cartwright (1929). T h e results of these examinations are set out in Table 4:—
TABLE 4
Fungal Mycelium i n Dieback-Affected Apple Limbs
Type of material
Papery bark
No. of specimens examined
20
Fungal mycelium present Above
V Junction 9
At V Junction
2
Extensive gum plugging h a d occurred in all wood specimens examined, irrespective of the presence or absence of fungal mycelium. Where fungal mycelium was detected it was confined mainly to t h e region above the V junction of n o r m a l a n d discoloured wood.
DISCUSSION
A general relationship is a p p a r e n t between t h e onset of dieback in apple orchards a n d the age of t h e plantings.
In some orchards, however, small groups of vigorous trees were found which were
Fig. 12.- -Dieback-affected Granny Smith apple limb sectioned to show internal discolouration of wood,
were made from the sections to determine t he extent of invasion by wood-rotting fungi Isolations
676
of the same age as n e a r b y dieback-affected trees. No consistent explanation c a n be given for the occurrence of such vigour a l t h o u g h in some instances these trees were growing in deep, summer-moist soil.
Wood-rotting of apple trees was found to be m u c h more prevalent a n d aggressive in low-lying situations, such as along t h e Blackwood river a t Bridgetown where foggy d a m p conditions prevail during t h e winter m o n t h s . These observations are in agreement with those of Tufts a n d Harris (1955) who point out t h e risk of wood- decay fungi invading cut apple limbs in districts with foggy climate in California, U.S.A.
Field a n d laboratory investigations h a v e confirmed the associations of such wood- rotting fungi as Coriolus spp. a n d Stereum spp. with dieback-affected apple limbs showing symptoms of papery b a r k a n d ink stain.
No fruiting b r a c k e t s of Schizophyllum commune were seen on ink stain limbs although this fungus h a s been recorded in New South Wales (Anon. 1957) as being associated with s u c h a condition. No isolates of this fungus have been obtained from limbs showing typical ink stain symptoms. Microscopic e x a m i n a t i o n of these limbs suggests t h a t t h e staining is due to dark-coloured fungi, such as Alter- naria spp., which are growing on t h e sap exuded from large p r u n i n g wounds. Von Schrenk and Spaulding (1909) refer to
"slime flux" diseases of apple and o t h e r deciduous trees in which fungi, a n d o t h e r micro-organisms, become established in t h e sap exuded from wounds. T h e f e r m e n - tative processes set u p in such sap kill t h e underlying bark a n d cambium.
Baxter (1957a) h a s reported t h a t Poly- stictus a n d Stereum spp. are t h e two most commonly occurring wood-rotting fungi in Victorian apple a n d pear trees. Both produce papery b a r k symptoms in limbs following on infection by fungal spores through wounds in t h e bark of t h e tree.
Although papery b a r k on limbs of apple trees is commonly associated with infec- tion by wood-rotting fungi this condition may also result from h a r d cutting in t h e absence of fungal invasion. Experiments conducted in England by Montgomery a n d Wormald (1943) showed t h a t such a condi- tion developed on Newton Wonder apples
when cut h a r d back in the spring. How- ever they also found t h a t papery bark was far more pronounced a n d extensive where h a r d cutting back was combined with infection by t h e fungus Stereum pur- pur eum (Persoon) Fries, through t h e cut surface.
T h e results in Tables 3 and 4 indicate t h a t invasion of limbs of declining apple trees by wood-rotting fungi is secondary to other factors which initiate t h e dieback.
This conclusion is supported by t h e fact t h a t wood-rotting fungi were absent from 45 per cent, of the dieback-affected limb specimens examined in t h e laboratory.
F u r t h e r m o r e when fungi were obtained they were confined mainly to t h e dis- coloured wood tissues well above t h e V shaped wedge or junction with t h e normal wood. However, once established in a declining limb t h e fungi proceed to dis- integrate t h e tissues and in time extend their activities down to the b u t t of t h e tree.
T h e discoloration a t the junction of normal and dieback-affected wood is con- sidered to be due to gum formation in t h e tissues. According to Swarbrick (1926) t h e production of gum in t h e wood tissues below pruning wounds on limbs of apple a n d other trees is a normal reaction to such injuries. A dieback of apple shoots h a s been reported by Mix (1916) who described symptoms somewhat similar to those ob- served in local orchards. He considered t h e disorder to be of a non-parasitic n a t u r e and greatly influenced, if not caused, by lack of sufficient moisture. Baker (1931) h a s shown t h a t deposition of gum in t h e conducting tissues of apple wood is related to pruning wounds a n d to drought.
Baxter (1957b) summarised t h e results of a 20 year fertiliser experiment carried out in Victoria a n d reported on t h e favourable effect of a complete m a n u r i n g t r e a t m e n t on yield a n d quality of apples.
He also reported t h a t apple trees receiv- ing no potassium were severely infected with Polystictus a n d Stereum spp., which were almost entirely absent on trees receiving a complete fertiliser.
I n d e p e n d e n t observations by Depart- m e n t a l officers suggest t h e possibility of a n u m b e r of cultural and environmental factors being involved in the initiation of dieback in apple orchards. These include 677
h a r d p r u n i n g , overcropping, s u m m e r drought, restricted root formation due to deep cultivation or a t t a c k by harmful organisms, a n d unsuitable soil types.
Wickens (1938) in a d v o c a t i n g a lighter p r u n i n g system, suggested t h a t h a r d p r u n - ing was one of t h e causes of dieback.
Other forms of dieback in local apple orchards h a v e been shown by D u n n e (1938, 1951) to be due to copper deficiency a n d i n a d e q u a t e d r a i n a g e a n d by D u n n e a n d Gulvin (1946) to m a n g a n e s e deficiency.
ACKNOWLEDGMENTS
Grateful acknowledgment is m a d e of t h e assistance given by Messrs. N. Shorter, S. Hardisty, R. Cahill a n d J . Rennick of t h e Horticulture Division in t h e orchard surveys.
T h e assistance of t h e Division of Forest Products, C.S.I.R.O., Melbourne, in i d e n t i - fying fungal fruiting b r a c k e t s collected in t h e field a n d also produced by t h e "saw- dust t e c h n i q u e " is gratefully acknowledged.
REFERENCES
Anon. (1957).—Agric. Gaz. N.S.W. 68 : 314.
Baker, C. E. (1931).—"Water conductivity in t h e apple t r e e a s affected by p r u n - ing a n d d r o u g h t " (Thesis, Univ. of Illinois, U.S.A.).
Baxter, P . (1957a).—J. Dept. Agric. Vic.
55 : 357.
Baxter, P. (1957b).—J. Dept. Agric. Vic.
55 : 497.
Cartwright, K. St. G. (1929).—Ann Bot., Lond. 43 : 412.
Dunne, T. C. (1938).—J. Dept. Agric. West.
Aust. (2nd. Ser.) 15 : 120.
Dunne, T. C. (1951).—Departmental records.
Dunne, T. C. a n d A. T. Gulvin (1946).—
J. Dept. Agric. West. Aust. (2nd. Ser.) 23 : 127.
Fisher, E. E. a n d H. F r e e m a n (1961).—
J. Dept. Agric. Vic. 59 : 115.
Mix, A. J. (1916).—N.Y. Agric. Exp. S t a t . Geneva Bull. 426.
Montgomery, H. B. S. a n d H. Wormald (1943).—Ann. Rep. E. Mailing Res.
Stat. 1943 p . 51.
Swarbrick, T. (1926).—J. Pom. a n d Hort.
Sci. 5 : 98.
Tamblyn, N. a n d E. W. B. DaCosta (1958).
—Nature, Lond. 181 : 578.
Tufts, W. P. a n d R. W. H a r r i s (1955).—
Circ. Calif. Agric. Ex. S t a t . 444 p. 15.
Von Schrenk, H. and P. Spaulding (1909).
—U.S.D.A. Bureau of P l a n t I n d . Bull.
149.
Ward, J. R. (1957).—Tasm. J. Agric. 28 : 127.
Wickens, G. W. (1939).—J. Dept. Agric.
West Aust. (2nd. Ser.) 16 : 319.
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