Virus and Other Graft-Transmissible Diseases and Disorders of Apples
Virus diseases cause economic losses through lower yields and reduced quality of apples and apple products. In general, virus diseases in perennial crop plants, such as apples, are more potentially damaging than in annual crops. Viruses can remain latent, spreading through an orchard and inflicting damage, often without the growers’ knowledge. Latent virus infection can produce small to moderate losses in fruit production. Often growers can maintain the productivity of diseased orchards at a profitable level by removing infected plant parts and replacing dead trees to limit the spread of the virus. Sometimes, however, losses are severe, and an acute viral infection can require tree removal.
How Virus Diseases Are Spread
Apple virus diseases are mainly spread thorough vegetative propagation. Because of this, in apple production, two methods are used to control virus diseases: adoption of virus-free propagation materials and eradication of contaminated trees. In addition, in areas where tomato ringspot virus is endemic, practices may be employed to minimize alternative virus hosts (i.e., deciduous weeds) and reduce nematode vector populations.
Some virus infections cause incompatibility between apple rootstock and scion cultivars, affecting yields and profitability of apple nurseries. A low success rate of successful grafting in nurseries may be attributed to virus infection. Reductions in bud survival have been reported to range from 20% to 67%. The degree of impact depends on the pathogen or its strain in combination with fruit type, cultivar, rootstock, nutrient supply, and tree age.
Virus Testing
Virus testing of imported propagation materials into the United States has been the most important measure used to prevent the introduction and spread of unwanted viruses.
The testing and use of virus-free materials have different benefits for each of the three sectors involved: nurseries, growers, and consumers.
Growers and nurseries benefit from virus testing in three ways:
- reduced yield losses from viruses.
- no need to invest in other virus control measures.
- reduced risk of virus spread.
Consumers benefit from lower prices and more abundant fruit.
National Virus-Testing Facility
There are two facilities that tests for viruses in fruit trees in the United States. One is the National Research Support Project 5 (NRSP-5). The NRSP-5, located at the Washington State University Irrigated Research and Extension Center in Prosser, Washington, implements the nation’s virus protection program for all deciduous fruit trees. NRSP-5 is responsible for providing sources of deciduous fruit tree propagation materials free of virus and virus-like diseases. NRSP-5 also develops, evaluates, and implements new technologies for virus detection and the elimination of viruses and virus-like agents from commercially important cultivars. Prior to the establishment of NRSP-5, viruses abounded in every fruit-growing region in the United States. The success of this project has resulted in a dramatic reduction in the incidence of viral diseases. The other, according to Renee DeVries, is the Plant Germplasm Quarantine Office (PGQO), Beltsville Agricultural Research Center, Beltsville, Maryland. For more information on Plant Quarantine Programs Managed by APHIS-PPQ, click here.
List of Potential Viruses
A short list and description of potential viruses are provided in Table 1. The list is not exhaustive, as many other viruses and strains of known viruses are not listed here. In addition, many unconfirmed graft-transmissible causal agents may ultimately be shown to be viruses or phytoplasma. Table 2 provides information on yield reduction caused by virus diseases in apple.
The National Clean Plant Network has recommendations for minimum testing standards for foundation and certification materials (test recommendations marked with an asterisk below are those acknowledged by the International Working Group on Fruit Tree Viruses (Acta Horticulturae 657:2004, pp. 575) and for which adequate testing exists with ELISA, PCR, or PT-PCR. Items identified as agents are graft-transmissible but are incompletely characterized.
| Group | Virus | Acronym | Symptoms | Transmission* | References |
|---|---|---|---|---|---|
| Capillovirus | Apple stem grooving virus | ASGV | Stem grooves, abnormal graft union | Me/Gr/Se | Uyemoto and Gilmer, 1971; Plese et al., 1975 |
| Ilarvirus | Apple mosaic virus | ApMV | Mosaic, mottling, necrotic ring spots | Me/Gr/Po | Gotlieb and Berbee, 1973; Wood et al., 1975 |
| Nepovirus | Tomato ringspot virus (apple union necrosis) | ToRSV | Mosaic or ringspots, rasp leaf, yellow bud or vein, ringspots and chlorosis | Me/Gr/Se/Po/Ne | Stouffer et al., 1977; Parish and Converse, 1981 |
| Sobemovirus | Apple latent virus | ALV (type II) | Latent infection | Me/Gr/Se/Po/In | Franki and Miles, 1985 |
| Trichovirus | Apple chlorotic leaf spot virus | ACLSV (ALV type I) | Chlorotic leaf spots or rings, stem pitting, stunning, line patterns, chlorosis | Me/Gr/Ne | Chairez and Lister, 1973; Dunez et al., 1975 |
| Foveavirus | Apple stem pitting virus | ASPV | Die back, inner bark necrosis, decline, epinasty, vein yellowing, latent infection | Me/Gr | Fridlund and Aichele, 1987; Kogenezawa and Yanase, 1990 |
| Phytoplasma | Apple rubbery wood | Causal agent is a phytoplasma and is included here because it was first investigated as a possible virus disease | Abnormal flexibility of stems and branches, shortened internodes, reduced or stunted annual growth, rootstock productivity, tree vigor and yield may be reduced | Me/Gr | NRSP-5 |
| *Possible transmission patterns:
Me = mechanical. Gr = grafting. Se = seeds. Po = pollen. In = insects. Ne = nematodes. |
|||||
| Apple Cultivars | Virus Strain | Yield Reduction (%) | References |
|---|---|---|---|
| Golden Delicious | Apple mosaic virus (AMV) | 46 | Baumann and Bonn, 1988 |
| Golden Delicious | AMV, rubbery wood disease agent (RW) | 21-67 | Baumann and Bonn, 1988 |
| Golden Delicious | RW | 46 | Wood, 1978 |
| Golden Delicious | Apple stem grooving virus (ASGV), apple stem pitting virus (ASPV), apple chloritic leaf spot virus (ACLSV) | 12 | Meijnske et al., 1975 |
| Golden Delicious | ASGV, ASPV, ACLSV | 30 | van Oosten et al., 1982 |
| McIntosh | AMV | 9 | Zawadzka, 1983 |
| McIntosh | RW | 8 | Zawadzka, 1983 |
| Red Delicious | AMV | 42 | Zawadzka, 1983 |
| Red Delicious | RW | 20 | Zawadzka, 1983 |
Web Resources:
- National Clean Plant Network – Fruit Trees
- Fruit Tree Clean Plant Network (formerly NRSP-5)
- Foundation Plant Services
- Microbe-Wiki
- Oregon State University
- West Virginia University, Apple Mosaic Virus and Latent Viruses
- West Virginia University, Apple Union Necrosis and Decline
References:
- Baumann, G., Bonn, G E., 1988. Einflub von Apfelmosaik und Gummiholzkrankheit auf Die Vegetative und Generative Leistung von Apfelsorten auf M 9 bis zum 13 Standjahr. (The influence of apple mosaic virus and rubbery wood on growth and cropping of apple trees on M 9 till the 13th orchard year.). Erwerbsobstbau 30:162-165.
- Chairez, R. and Lister, R.M. 1973. A comparison of two strains of apple chlorotic leaf spot virus. Phytopathology 63:1458-1464.
- Dunez, J., Marenaud, C. and Delbos, R. 1975. Bark split disease of prune trees and its association with strains of apple chlorotic leaf spot virus. Acta Hortic. 44:81-91.
- Francki, R.I.B. and Miles, R. 1985. Mechanical transmission of sowbane mosaic virus carried on pollen from infected plants. Plant Pathol. 34:11-19.
- Fridlund, P.R. and Aichele, M.D. 1987. Reactions of crabapples considered as potential apple pollinizers to latent virus infection. Fruit Var. J. 41:17-18.
- Gotlieb, A.R. and Berbee, J.G. 1973. Line pattern of birch caused by apple mosaic virus. Phytopathology 63:1470-1477.
- Koganezawa, H. and Yanase, H. 1990. A new type of elongated virus isolated from apple trees containing the stem pitting agent. Plant Dis. 74:610-614.
- Meijnske, C.A.R., van Oosten, H.J., Peerbooms, H. 1975. Growth, yield and fruit quality of virus-infected and virus-free ‘Golden Delicious’ apple trees. Acta Hortic. 44:209-212.
- Parish, C.L. and Converse, R.H. 1981. Tomato ringspot virus associated with apple union necrosis and decline in Western United States. Plant Dis. 65:261-263.
- Plese, N., Hoxha, E. and Milicic, D. 1975. Pathological anatomy of trees affected with apple stem grooving virus. Phytopathol. Z. 82:315-325.
- Stouffer, R.F., Hickey, K.D. and Welsh, M.F. 1977. Apple union necrosis and decline (tomato ringspot virus as possible cause). Plant Dis. Rep. 61:20-24.
- Uyemoto, J.K. and Gilmer, R.M. 1971. Apple stem-grooving virus: propagating hosts and purification. Ann. Appl. Biol. 69:17-21.
- van Oosten, H.J., Meijnske, C.A.R., Peerbooms, H., 1982. Growth, yield and fruit quality of virus-infected and virus-free ‘Golden Delicious’ apple trees, 1968-1982. Acta Hortic. 130:213-220.
- Wood, G.A., Chamberlain, E.E., Atkinson, J.D. and Hunter, J.A. 1975. Field studies with apple mosaic virus. N.Z. J. Agric. Res. 18:399-404.
- Wood, G.A. 1978. Effect of rubbery wood disease on growth and yield of ‘Golden Delicious’ apple trees. Orchardist N. Z. 51:66-67.
- Zawadzka, B., 1983. The effect of mosaic and rubbery wood infection on the growth and yield of apple trees. Zesz. Probl. Postepów Nauk Roln. 291:385-390.
Alan R. Biggs, West Virginia University