Apple rubbery wood virus

Transcription

1 New Zealand Journal of Agricultural Research ISSN: (Print) (Online) Journal homepage: Apple rubbery wood virus E.E. Chamberlain, J.D. Atkinson, G.A. Wood & J.A. Hunter To cite this article: E.E. Chamberlain, J.D. Atkinson, G.A. Wood & J.A. Hunter (1971) Apple rubbery wood virus, New Zealand Journal of Agricultural Research, 14:3, , DOI: / To link to this article: Published online: 12 Jan Submit your article to this journal Article views: 394 Citing articles: 7 View citing articles Full Terms & Conditions of access and use can be found at

2 707 APPLE RUBBERY WOOD VIRUS By E. E. CHAMBERLAIN*, J. D. ATKINSON*, G. A. WOOD*, AND J. A. HUNTERt (Received 4 March 1971) ABSTRACT Apple rubbery wood virus (RWV) is widespread in apple and pear varieties in New Zealand, having been found in some trees of all varieties examined. Of 278 apple trees tested, 75 percent were infected; and of 43 pear trees indexed, 70 percent carried the virus. The virus has been found to cause symptoms on two New Zealand produced apple varieties, 'Gala' and 'Splendour'. Symptoms on the former are nearly as severe as those on 'Lord Lambourne'; on the latter they are less pronounced, being comparable with those on 'Golden Delicious'. Rubbery wood symptoms have been observed also on 'Red Delicious' trees known to be infected with RWV. Apple and pear rootstock and scion varieties free from RWV have been secured from overseas or obtained in New Zealand by the heat treatment/tip culture technique. Most rootstock varieties free from RWV have been secured from overseas, and most scion varieties have been obtained by heat treatment locally. RWV-free material available in New Zealand consists of 19 apple and 5 pear scion varieties and 8 apple and 1 pear rootstock varieties. INTRODUCTION As with other viruses carried without symptoms on some hosts, apple rubbery wood virus (RWV) has become widely distributed throughout the world (Cropley 1963). Not only is the virus widespread and frequently of high incidence in apple rootstock and scion varieties (Posnette and Cropley 1952, 1954; Meijneke 1963), but it has been found to occur also in pears (Anon. 1962; Campbell 1966). Although latent in pears and many apples, it produces symptoms on a number of apple varieties (Cropley 1963). In New Zealand RWV was first recognised in 1954 on 'Golden Delicious' (Atkinson et at. 1959), and since then has been found to be of considerable economic importance on this variety (Chamberlain et at. 1969). It has already been reported that the virus is widespread in apples in this country and that incidence is high in some varieties (Anon. 1963). In the present paper incidence of RWV in commercial apple and pear varieties is recorded, expression of symptoms under New Zealand conditions described, economic importance and spread of the disease discussed, and steps being taken for its control outlined. * Plant Diseases Division, DSIR, Auckland, New Zealand. t Retired: Warwick Farm, R.D.l, Morrinsville, New Zealand. N.Z. Journal of Agricultural Research (1971),14:

3 708 Apple rubbery wood virus INCIDENCE OF RWV ON APPLES AND PEARS IN NEW ZEALAND All tests for the presence of RWV were made with the indicator variety 'Lord Lambourne'. Apple seedling stocks were used throughout. The double budding technique was used for indexing, a bud from a healthy 'Lord Lambourne' being inserted immediately above a bud from the tree under test. Diagnosis of RWV infection was made by the hand bending test which, under our conditions, has been found to be more consistently reliable than chemical tests. If definite rubbery wood symptoms had not developed 1 year after budding, trees were retained for 2 or, if necessary, 3 years before a final diagnosis was made. Most buds used for indexing were taken from selected trees used as a source of bud wood for production of commercial nursery trees, but some were taken from standard orchard trees. TABLE I-Incidence of RWV in Apple and Pear Varieties in New Zealand I Variety Number indexed trees INumber infected trees Percentage trees infected I Apples Cox's Orange Pippin Golden Delicious Granny Smith Kidd's Orange Red Red Delicious Red Dougherty Sturmer Pippin 29 other varieties Totals Pears Beurre Bose Louise Bonne Jersey Packham's Triumph P. Barry William's Bon Chretien Winter Cole Winter Nelis Totals

4 E. E. CHAMBERLAIN et al. 709 SCION VARIETIES The varieties listed in Table 1 represent 7 of the 10 most widely grown apple varieties and the 7 most popular pear varieties. In addition to those listed, 29 other apple varieties were indexed for RWV, the number of trees tested in anyone variety ranging from 1 to 7. Results in Table I suggest that the amount of infection is greater in some varieties than others, but not enough trees were indexed for the differences to have any significance. However, it is clear from the results' that RWV is widespread and of high incidence in both apples and pears. ROOTSTOCKS The MaIling series of apple rootstocks were first introduced into New Zealand in 1930 before indexing for RWV began in England. Since the virus is known to have been present in a number of these rootstocks (Posnette and Cropley 1952, 1954), it is probable that some were infected when introduced. Only two of these original introductions, M XII and M XVI, have been indexed for RWV here. Three stools of the former were all infected, but two stools of the latter did not carry the virus. Recent introductions of heat-treated MIX, MXII, and M XVI from England were free from infection. The Merton and MaIling-Merton rootstocks Merton 793, MM 104, MM 106, and MM 115 which have become popular in New Zealand appear to be free from RWV. All stools, 26 in total, of these 4 rootstock varieties that have been indexed here were free from RWV and other viruses. EXPRESSION OF SYMPTOMS OF RWV Among commercial apple varieties symptoms of RWV appear to be most pronounced on 'Lord Lambourne', which has been accepted as the standard indicator variety for this virus (Posnette et al. 1956). However, RWV has been reported to cause symptoms on a number of other varieties including 'Dartmouth Crab', 'James Grieve', 'Miller's Seedling' (Beakbane and Thompson 1945), 'Kingston Black', 'Sturmer Pippin' (Luckwill and Crowdy 1950), 'Golden Delicious' (Van Katwijk 1954), 'Sunset' (Posnette 1954), 'Worcester Pearmain' (Anon. 1962), 'Michaelmas Red' (Cropley 1963), and 'Guldborg' and 'Ingrid Marie' (Kristensen and Thomsen 1966). Of these varieties only three, 'Golden Delicious', 'Sturmer Pippin', and 'Worcester Pearmain', are grown commercially in New Zealand. Under our conditions rubbery wood symptoms have not been observed on either 'Sturmer Pippin', which is very widely grown, or 'Worcester Pearmain', although many trees of the former are known to carry RWV (see Table 1). In New Zealand, symptoms occur on 'Lord Lambourne', 'Golden Delicious', and two locally produced varieties 'Gala' and 'Splendour'. Rubbery wood symptoms have been observed also on a red strain of 'Delicious'.

5 710 Apple rubbery wood virus Fig. l-rwv on l-year-old tree of 'Gala' showing vigorous shoots at base and bending over of central leader, which has ceased growing. [Photo: N. B. Congdon Fig. 2-Grey colour and transverse cracking of bark on rubbery section of branch of 'Golden Delicious' tree infected with RWV. Branch from healthy tree on right. [Photo: J. W. Endt 'Lord Lambourne' SYMPTOM EXPRESSION IN NEW ZEALAND Rubbery wood symptoms described on 'Lord Lambourne' (Atkinson et al. 1959; Chamberlain 1961) are comparable with those in Europe. They range from mild to severe, depending on the strain of RWV present, and are expressed on this variety in all parts of New Zealand. During the growing season symptoms are usually more pronounced than in the dormant period. 'Golden Delicious' Symptoms on 'Golden Delicious', already described by Atkinson et al. (1959) and Chamberlain et al. (1969), are much less pronounced than those on 'Lord Lamboume', and develop on infected trees in some seasons and some localities only. They have been observed only south of the Auckland Province.

6 E. E. CHAMBERLAIN et al. 711 Fig 3-Stunted 7-year-old, RWV-infected 'Red Delicious' tree with rubbery, drooping branches. [Photo: N. B. Congdon 'Gala' Symptoms of RWV on 'Gala' are rubberiness of wood, failure of buds to break on the rubbery sections, marked stunting of trees, and, on young trees, development of vigorous shoots from buds just above the union of scion and rootstock (Fig. 1). Also, on young trees infected with severe strains, the central leader may become so rubbery that it is unable to remain erect and droops sometimes to the ground. The bark on rubbery sections of branches develops the same grey colour and transverse cracking described for 'Golden Delicious' by Chamberlain et al. (1969) and illustrated in Fig. 2. The symptoms are much more prononced than those on 'Golden Delicious', and are nearly as severe as those on 'Lord Lambourne'. They develop on infected trees in all seasons and all localities, including Auckland. 'Splendour' From our limited experience of RWV on this variety it would appear that the degree of symptom expression is about comparable with that on 'Golden Delicious'. Not only does the wood become rubbery, but the bark on affected sections of branches develops the grey colour and transverse cracking observed on 'Golden Delicious' and 'Gala'. Symptoms have been reported only from southern districts. and have not been found on infected trees in Auckland. 'Red Delicious' Symptoms were first observed on this variety in 1968 on one tree, in a block of 7-year-old 'Red Delicious' trees in a Hawke's Bay

7 712 Apple rubbery wood virus orchard. The tree was stunted and had a weeping habit and the branches were rubbery (Fig. 3). Indexing on 'Lord Lamboume' showed that this tree was infected with a severe strain of RWV. Recently further symptoms have been seen in Hawke's Bay in a block of 324 young 'Red Delicious' trees. These had been planted in 1967 as 'Gala' trees, but because an estimated 70 percent developed RWV symptoms during their first year, the grower had budded 'Red Delicious' into the stocks in 1968 and later removed all "Gala' growth. In a survey during December 1970, 255 of the 'Red Delicious' trees showed symptoms that could be attributed to RWV. The branches were more pliable than normal, buds failed to break where the wood was rubbery, and there was a tendency for limbs to droop. The wood of affected trees appeared to be weaker than normal, for there was an unusually high percentage of broken branches. On the same property similar symptoms were seen on 4- and 5-year-old 'Red Delicious' trees on MM 106 rootstocks. During the same survey a stunted 'Red Delicious' tree with rubbery branches was found on another property in the district. TABLE 2-Incidence of RWV Symptoms on 'Gala' Apple Trees in Hawke's Bay Orchards (survey carried out in December 1970) Age of Total Number Orchard Rootstock trees (yrs) number trees trees infected Percentage infected 1 MM MM MM MM Merton Ballarat" Ballarat] MM Frimley Beautyt Merton MM Block a MM Block b MM Block c MM MM ** * 16-year-old Ballarat trees top-worked with graft-wood from 6-year-old RWVfree Gala trees on growers' own property. ** Grower's own estimate made in t 18-year-old Ballarat trees top-worked with graft-wood from the same trees as above. t Frimley Beauty trees top-worked with Gala scions.

8 E. E. CHAMBERLAIN et al. 713 Further investigations are necessary to verify the effect of RWV on 'Red Delicious', but it would appear that under some conditions this variety develops symptoms when infected with the virus. OBSERVATIONS CONCERNING INTRODUCTION OF RWV INTO 'GALA' AND 'SPLENDOUR' 'Gala' This variety, which is a cross between 'Kidd's Orange Red' and 'Golden Delicious', is a high-quality early apple bred by the late Ml' J. H. Kidd of Greytown, New Zealand (McKenzie 1969). It showed such promise while being evaluated that scions were top-worked to a number of apparently healthy mature 'Jonathan' trees which were later shown to carry latent viruses including RWV. When 'Gala' was selected for commercial development in 1964 there was such a demand for trees that bud wood was taken from these top-worked trees. As a result many of the first commercially produced trees were virus infected. Rubbery wood symptoms were first observed on 'Gala' in Hawke's Bay in 1967, and since then have been found on a considerable number of trees in that district. In 1968 one grower estimated that 70 percent of year-old 'Gala' trees showed symptoms. They were so severely affected that he re-budded the stocks with 'Red Delicious'. 'Gala' trees were surveyed for RWV symptoms in December 1970 (Table 2). Symptoms were present on 'Gala' in 8 out of the 9 orchards surveyed, and 33 percent of the 1,498 trees examined were affected. 'Splendour' 'Splendour', a chance seedling from a Hawke's Bay garden, is a late red apple of good quality (McKenzie 1965) that has become established as a commercial variety. Rubbery wood symptoms were first discovered on this variety in 1970 when branches of 'Splendour', top-worked on five 'Dunn's Favourite' and one 'Gravenstein' tree, in a Nelson orchard, were found to be affected. Symptoms were found also on several young trees in a Christchurch orchard. ECONOMIC IMPORTANCE OF RWV ON APPLES Effect on varieties that show symptoms In those apple varieties on which symptoms of RWV are expressed the detrimental effect of the virus is obvious, for affected trees are stunted. The effect is greatest on varieties that show the most pronounced symptoms, total yield of 'Lord Lamboume' being much reduced because of the small size of infected trees (Luckwill and Crowdy 1950). In New Zealand the disease has a marked effect on those 'Golden Delicious' trees that exhibit symptoms. Such trees are stunted and

9 714 Apple rubbery wood virus even if the rubbery branches are cut back to encourage the development of strong rigid shoots from their bases, production is lost through delay in trees reaching fruit bearing size. Even when a young affected tree makes an apparent recovery it fails to make as much growth as a tree that has not shown symptoms (Fig. 4), and, because of its smaller size, yield is reduced. The effects are most serious when symptoms develop on young centre-leader trees, for, when the centre leader becomes rubbery, its growth is retarded and production of a well shaped tree becomes impossible. Although we have only limited knowledge of the disease on 'Splendour', the similarity of symptoms on young trees with those of 'Golden Delicious' suggests that its effects on the two varieties may be also comparable. On 'Gala', however, the severe rubberiness and stunting caused by RWV, and the high incidence of symptoms, which develop under a range of climatic conditions, indicate that the disease is much more serious on this variety than it is on 'Golden Delicious'. Effect on apple varieties that do not show symptoms There is considerable evidence that RWV reduces vigour of apple rootstocks and of tolerant scion varieties grown on them, the extent of reduction depending on the variety of rootstock and of scion (Luckwill 1956; Campbell 1961, 1970; Kristensen and Thomsen 1966; Cropley 1968). Influence on susceptibility of apple rootstocks to fungous diseases Recent work in England (Campbell 1969) has shown that RWV in combination with other latent viruses increases the susceptibility of at least one rootstock variety to the collar rot fungus (Phytophthora cactorum (Lebert & Cohn) Schroeter). SPREAD OF RWV Luckwill and Crowdy (1950) produced evidence from field surveys that suggested that natural field spread of RWV occurred, but Posnette and Cropley (1954), also from results of field surveys, concluded that the virus rarely, if ever, spread in young orchards. The latter authors suggested, however, that tree-to-tree spread might take place in old orchards where root grafting was more likely to occur. Results of seed transmission trials indicate that RWV is not seed carried in apple (Campbell 1964). There is considerable circumstantial evidence that RWV does not spread naturally in the field. Welsh and May (1970) were unable to find this or other viruses in two 35-year-old orchard trees of 'Newtown', a variety that has been in cultivation in North America for well over 200 years. Thatthe Malling-Merton series of rootstocks have remained free from RWV infection both in England (Posnette and Cropley 1954) and in New Zealand is a further indication that natural spread does not occur. Evidence that the virus neither spreads naturally nor is seed carried is provided also by the failure of RWV symptoms to

10 E. E. CHAMBERLAIN et al. 715 Fig. 4-Etfect of RWV on growth of 'Golden Delicious' apple tree. Tree on right has not shown rubbery wood symptoms. Symptoms were first detected in tree on left when it was 5 years old and were still present 13 years later. Trees 18 years old when photographed. Note spreading habit as well as lack of vigour of affected tree. [Photo: E. E. Chamberlain develop on any of the many healthy 'Lord Lambourne' scions worked to apple seedling rootstocks at this Division. Since Luckwill and Crowdy (1950) and Prentice (1950) demonstrated that RWV could be transmitted by budding or grafting, its transmission by this means has been confirmed by many workers. The ease with which the virus can be spread by propagation is illustrated by the manner in which it becomes widespread in new varieties initially free from infection. Luckwill and Crowdy (1950) found that the virus spread into the 'Lord Lambourne' variety mainly through top-working scions into infected though apparently healthy trees of tolerant varieties. Spread of RWV into the varieties 'Gala' and 'Splendour' in New Zealand occurred in the same way. PRODUCTION AND DISTRIBUTION OF TREES FREE FROM RWV Since there is evidence that RWV has a detrimental effect on tolerant varieties as well as those that exhibit symptoms, it would be an advantage if trees of all varieties were free from infection. To produce such trees it is necessary that both rootstocks and scions are free from the virus. RWV-free rootstocks and scion-wood may be obtained either

11 716 Apple rubbery wood virus TABLE 3-RWV-free Apple and Pear Varieties Available in New Zealand Variety Virus status Source of material Year or projected year of release Apple varieties Albany Beauty HT New Zealand 1968 Cleopatra HT New Zealand 1971 Freyberg HT New Zealand 1968 Frimley Beauty HT New Zealand 1971 Golden Delicious HT New Zealand 1968 Granny Smith HT Australia 1971 Lobo HT New Zealand 1971 Oratia Beauty HT New Zealand 1969 Red Statesman HT New Zealand 1971 Splendour Original Seedling Tree 1967 Ballarat LV HT New Zealand 1968 Gala LV HT New Zealand 1969 Kidd's Orange Red LV HT New Zealand 1966 Hawke's Bay Red Delicious LV HT New Zealand 1966 Lord Wolseley LV HT New Zealand 1969 Red Dougherty LV HT New Zealand 1968 Red Jonathan LV HT New Zealand 1969 Spartan LV HT New Zealand 1969 Sturmer LV HT New Zealand 1968 Apple rootstocks MIX M XII M XVI Merton 793 MM 104 MM 106 MM 115 Northern Spy HT England HT England HT England England England England England HT New Zealand * t tt 1970 Pear varieties Beurre Hardy P. Barry William Bon Chretien Winter Cole Winter Nelis HT England HT New Zealand HT New Zealand HT New Zealand HT New Zealand Pear rootstock Quince A HT England 1964 LV HT *t = Free from known viruses Free from RWV but infected with one latent virus Trees heat treated for virus elimination Merton 793 were introduced into New Zealand from England in MM 104 and MM" 106 were introduced from England in 1952 and MM lis in 1954.

12 E. E. CHAMBERLAIN et at. 717 by selection or by heat treatment methods. Posnette et at. (1962) concluded that it would be less time consuming and more rewarding to obtain RWV-free material by heat treatment methods than by indexing large numbers of trees in a selection programme. We came to a similar conclusion in New Zealand, although we have used selection, as a temporary measure, to secure RWV-free trees of 'Golden Delicious' (Chamberlain et at. 1969). ELIMINATION OF RWV BY HEAT TREATMENT Posnette et al. (1962) showed that RWV was inactivated in buds of apple trees grown in a heat chamber at 37 c for 3 weeks. They also found that pear trees free from pear vein yellows and quince bark necrosis could be obtained by removing the shoot-tips of infected pear plants grown at 37 c for 4 weeks and cleft-grafting them to pear seedlings. This heat treatment/tip culture method was shown by Campbell and Best (1964) to be effective in the elimination of RWV from apple. Both methods have been successfully employed for the production of RWV-free apple trees, the former in North America (Welsh and Nyland 1965) and the latter in Europe (Thomsen 1968). PRODUCTION OF RWV-FREE APPLE AND PEAR VARIETIES IN NEW ZEALAND During the season a heat treatment/tip culture programme was initiated in an attempt to secure trees of our main commercial apple and pear varieties free from all known viruses. Fortunately, at that time, we already had a range of Merton and Mailing-Merton rootstocks, imported from England, that were free from viruses; and pear seedlings that are also virus-free were being used as the main rootstock for pears. Therefore, we were able to concentrate our efforts on the elimination of viruses from scion varieties. Although we have not yet succeeded in eliminating all known viruses from all varieties, many have been freed from RWV (Table 3). As well as eliminating viruses locally, we have introduced from overseas several apple rootstocks, one pear rootstock, and one apple scion variety free from known viruses, and these too are listed in Table 3. DISTRIBUTION OF RWV-FREE APPLE AND PEAR VARIETIES As soon as tests have shown that a tree of any variety is free from known viruses it is propagated on seedling or other known virus-free rootstock to form a clone of mother trees. These are maintained by the Division, and material from them is released to the fruit-growing industry through the Department of Agriculture and the New Zealand Fruitgrowers' Federation. Also a number of varieties free from RWV but still infected with a single latent virus have been selected to provide a temporary source of improved propagating material. Mother trees of such varieties will be replaced as soon as trees completely free from known viruses are obtained.

13 718 Apple rubbery wood virus RWY-free apple and pear varieties and rootstocks available in New Zealand are listed in Table 3, with the source from which each variety was obtained and the year or projected year of its release. Acknowledgments Officers of the Horticulture Division, Department of Agriculture, who have kept us informed of the development of R WV symptoms in the field, carried out surveys to determine its incidence, forwarded material for experimental trials, and supplied us with information on any unusual symptoms; Miss Karen Cooper, graduate student, who in December 1970 surveyed the incidence of RWV on 'Gala' trees in Hawke's Bay. REFERENCES ANONYMOUS, 1962: Report of the East Malling Research Station 1961: ~-----_ : Orchardist of N.Z 36: 118. ATKINSON, J. D.; CHAMBERLAIN, E. E.; HUNTER, J. A 1959: Ibid. 32: 2-3. BEAKDANE, A BERYL; THOMPSON, ELEANOR C. 1945: Nature 156: CAMPBELL, A. r. 1%1: Journal of Horticultural Science 36: : Report of the Agricultural and Horticultural Research Station, University of Bristol, 1963: : Ibid. 1965: : Journal of Horticultural Science 44: : Report of the Agricultural and Horticultural Research Station, University of Bristol, 1969: 21. CAMPBELL, A. 1.; BEST, MARGARET W. 1964: Ibid. 1963: CHAMBERLAIN, E. E. 1961: Orchardist of N.Z. 34 Supplement: 8 pp. CHAMBERLAIN, E. E.; ATKINSON, J. D.; HUNTER, 1. A; WOOD, G. A. 1969: Orchardist of NZ. 42: CROPLEY, R. 1963: In "Virus Diseases of Apples and Pears" (Posnette, A. F. Editor). Technical Communications. Imperial Bureau of Horticulture and Plantation Crops, 30: : Scientific Horticulture 20: KRISTENSEN, H. R.; THOMSEN, A. 1966: Tidsskr. PIA vi. 69: CAbs. in Review of Applied Mycology 45: 2161,1966). LUCKWILL, L. C. 1956: Report of the Agricultural and Horticultural Research Station, University of Bristol, 1955: LUCKWILL, L. c., CROWDY, S. H. 1950: Ibid. 1949: McKENZIE, D. W. 1965: N.Z. Gardener 2/: : Orchardist of N.Z. 42: 289. MEIJNEKE, C. A. R. 1963: Phytopath, mediterranea 2: POSNETTE, A. F. 1954: Grower Annual Fruit Review, Autumn 1954: 26-9.

14 E. E. CHAMBERLAIN et al. 719 POSNETTE, A. F.; CROPLEY, R. 1952: Report of the East Mailing Research Station 1951: : Ibid. 1953: POSNETTE, A. F.; CROPLEY, R.; WOLFSWINKEL, L. D. 1962: Ibid. 1961: POSNETTE, A. F.; MEIJNEKE, C. A. R.; MULDER, D. 1956: Tijdschr. PIZiekt. 62: PRENTICE, I. W. 1950: Report of the East Mailing Research Station 1949: THOMSEN, A. 1968: Tidsskr. PIA vi. 72: CAbs. in Review of Applied Mycology 48: 513, 1969). VAN KATWIJK, W. 1954: Meded. Dir. Tuinb. 17: WELSH, M. F.; NYLAND, G. 1965: Canadian Journal of Plant Science 45: WELSH, M. F.; MAY, J. 1970: Fruit Varieties and Horticultural Digest 24: 567.