Cachexia

Contents - Previous - Next

DESCRIPTION AND BACKGROUND

The citrus cachexia disease was named, described and first transmitted by Childs (1950). Xyloporosis, a condition affecting sweet limes, has been linked synonymously with cachexia. However, in a recent review by Roistacher (1988), cachexia is suggested as the preferred name, and xyloporosis is reserved for the specific condition or complex associated with sweet limes as originally described by Reichert and Perlberger (1934).

The viroid nature of cachexia was first suggested by Roistacher et al. (1983), when many similarities between cachexia and exocortis were described, i.e. both pathogens: are highly mechanically transmissible and are readily inactivated on tools by sodium hypochlorite; cannot be eliminated from budwood by thermotherapy; are readily eliminated from microshoot tips by shoot-tip grafting in vitro; and react best in indicator hosts held under warm conditions. Cachexia is now known to be viroid-induced. It is a low-molecular-weight RNA consisting of about 300 nucleotides (Semancik, Roistacher and Duran-Vila,1988).

The cachexia disease is found in most citrus growing areas of the world where exocortis is found. Since most commercial citrus cultivars are symptomless carriers and the pathogen is readily transmitted in buds and highly transmitted mechanically by tools (Roistacher, Nauer and Wagner,1980), the movement of this pathogen into new citrus-growing areas could present a problem, especially where mandarins, tangelos, tangors or C. macrophylla are grown as scions or rootstocks.

METHODS OF DETECTION Method 1: Field diagnosis

For photographs and a description of field symptoms of cachexia, see Childs (1959,1980) and Calavan and Christiansen (1965). The diagnostic symptoms in tangelo, mandarin or C. macrophylla are phloem discoloration by gumming, undulating stem pitting or bumps and projections on the bark, which fit into depressions in the wood. Gum spots are usually prominent in the bark and are readily seen by slicing sections through the bark with a knife (Figures 44 and 45). The presence of these typical symptoms on susceptible hosts in the field can be diagnostic for the disease since very few graft-transmissible diseases of citrus show these classical symptoms, especially in tangelos, mandarins, Rangpur limes or C. macrophylla.

Method 2: Indexing Parson's Special mandarin or Orlando tangelo

Parson's Special mandarin forced as a scion on a vigorous rootstock is the preferred indicator for the detection of cachexia (Roistacher, Blue and Calavan,1973; Vogel and Bov,1976). The Parson's Special mandarin seedling grows too slowly to be an effective seedling indicator (Roistacher, unpublished). However, if a bud from a seedling selection of Parson's Special mandarin is grafted on to a vigorous rootstock (such as rough lemon) and forced under warm conditions, growth is vigorous and symptoms may appear at the bud-union interface between six and 12 months after inoculation.

The choice of a sensitive clonal seedling of the Parson's Special mandarin is very important. There is variability among seedlings and some are more sensitive than others. At the Rubidoux indexing facility, a number of Parson's Special mandarin seedlings were tested for sensitivity to various isolates of cachexia. Seedling selections Nos 9 and 10 were found to be the most sensitive and these are currently recommended. If the Parson's Special mandarin is obtained as seed, seedlings should be grown and observed for uniformity and vigour. All slow-growing seedlings should be discarded and about ten of the larger and more uniform selections held. These should then be tested by forcing a bud from each of the selections as scions under a rootstock that has been inoculated with mild- and severe-positive cachexia, respectively. Alternatively it may be simpler to obtain selection Nos 9 or 10 as a clonal bud line.

Inoculated seedlings of Orlando tangelo or pathogen-free lemons or grapefruit as scions budded to Orlando tangelo as the rootstock can be used as indicators for indexing in the field. The Orlando tangelo as a seedling is preferred. The seedlings can be field-grown or preferably greenhouse-grown, "bud"-inoculated and removed to the field when convenient.

The procedures for indexing using Parson's Special mandarin forced on rough lemon rootstock in a greenhouse, or using tangelo seedlings for field planting, are as follows:

Collection of budwood. Four budsticks are collected from each of four quadrants of the field tree to be tested. Ensure that the collecting tool is disinfected in a 1 percent sodium hypochlorite solution between trees. Inoculum should be labelled, secured in a polythene bag and immediately placed in an ice chest. The budwood is later stored in a refrigerator at the plant laboratory.

Indicator plants. A minimum of four but preferably six plants should be used to test each candidate or selection. "Buds" (buds, blind buds or chip buds) cut from the various collected budsticks should be distributed equally among the indicator plants. Budwood should be refrigerated for possible future use.

For the Parson's Special index, rough lemon seedlings (or other fast-growing, vigorous seedlings) are grown one seedling per container, as a single shoot to about 1 m height. The Parson's Special mandarin selection Nos 9 or 10 or a selected seedling line held as a reserve plant in the greenhouse is used as the scion budwood.

Controls. Mild- and severe-positive controls, plus non-inoculated or self-inoculated negative control plants, should be included for each test or experiment. A minimum of four plants should be inoculated for each control treatment. Six or eight plants should be inoculated with the mild positive control since this will determine when the test can be terminated.

Inoculation. The Parson's Special mandarin bud is grafted to the rough lemon (or other vigorous stock) about 20 cm above the soil surface and, when wrapping the bud, the "eye" of the bud should be exposed for forcing. A minimum of two inoculum "buds" are then grafted anywhere in the rough lemon rootstock below the Parson's Special scion bud. Inoculum "buds" should be completely wrapped. The seedling is then bent at a point just above the Parson's Special scion bud, and the top of the bent seedling can be tied to the base of the plant or placed under the container (Figure 47). This bending aids the rapid forcing of the scion bud. Again, knives should be disinfected in a 1 percent sodium hypochlorite solution before moving to a new source of inoculum.

Tangelo seedlings are graft-inoculated with a minimum of two inoculum "buds" and these are completely wrapped. Knives should be disinfected in a 1 percent sodium hypochlorite solution before going to a new source of inoculum.

Inoculum survival. After two to three weeks, the budding tapes are removed from the inoculum, usually by cutting with a knife or razor-blade, which must be disinfected between plants in a 1 percent sodium hypochlorite solution. Inoculum survival is recorded and plants with dead buds should be regrafted, preferably with fresh material or with inoculum stored in the refrigerator (see methods for the collection and storage of inoculum tissue in Part II).

Where Parson's Special mandarin is used as the scion bud, the wrapping tape may be left on until the Parson's bud is well forced.

Post-inoculation care

Parson's Special mandarin index.. The Parson's Special scion is trained to grow as a single shoot or leader, and is staked and tied (Figures 47 and 48). After the scion reaches about 1 m, it is cut back about 10 cm above the bud-union and a single bud near the top of the cut-back area is then forced and trained to grow as a new single leader. This new growth is then staked, tied and grown to about 1 m high (Figure 48) in the same manner as the previous shoot. This procedure of growth, cut back and regrowth is repeated until the test is complete or until plants are removed to the field for further observation.

Plants should not be crowded on the bench (Nauer, Holmes and Boswell,1980). Adequate light is needed to maximize growth and symptom development. Each plant should have about 400 cm (20 x 20 cm) of growing room.

Seedling index. After survival of inoculum is verified, the seedlings should be cut back at about 25 cm from the soil surface. The new growth should be trained to a single shoot or leader by removing all newly developed side branches. The young inoculated indicator plants are held in the greenhouse until they are large enough for transplanting to the field (about 1 m tall). The field location should be as warm as possible for maximum symptom development (symptoms may develop poorly under cool temperature conditions). The young trees should be well watered, fertilized and given good care.

Plants in the field can be close planted, preferably at about 2 m apart.

Time for development of symptoms

Parson's Special mandarin index. Symptoms in plants inoculated with severe isolates of cachexia may appear six to nine months after inoculation. Those inoculated with mild isolates may take nine to 12 months or longer. If symptoms do not appear on plants inoculated with the mild isolates after 12 months, the plants should be moved to a warm field location and planted at intervals of 1-2 m. The young trees should be well watered and fertilized and given good care. Symptoms should be evident under the extended field index within one growing season (provided temperatures are warm or hot).

Seedling index to tangelo in the field. Symptoms may appear in eight to 18 months after field planting in seedlings inoculated with severe isolates. Those containing mild isolates may take two to six years, depending on the temperature and mildness of the isolate.

Temperature requirements. Plants under index for cachexia should be grown in as warm an environment as practical or possible. Recommended greenhouse temperatures are 32-40C maximum by day and 27-30C minimum at night. Symptoms induced by the cachexia viroid, similar to those induced by the citrus exocortis or other citron viroids, are best expressed in indicators under warm growing conditions.

Detection of symptoms

Parson's Special mandarin index. After six to eight months, when plants are at maximum growth, the control plants inoculated with the mild- and severe-positive inoculum can be examined for symptoms. Three-sided rectangular cuts are made across the bud-union as shown in Figure 46. This is done at two places on opposite sides of the bud-union; the bark is lifted back and the area examined for the typical gumming symptoms diagnostic for cachexia (Figure 46). Similar cuts can be made in the regrowth area surrounding the joint where the plant had been cut back. If no symptoms are evident at the bud-union or the first joint, the bark is replaced and securely rewrapped with budding tape. Plants can be re-examined in this manner every two to three months. Early symptoms will almost always appear at the bud-union or the joint at the first cut-back area and rarely in the portion of the stem above the bud-union or in the area between cut-back joints as shown in Figure 50.

Seedling index. When the bark peels easily or is "slipping", the mild-positive control plants are observed for symptoms. Cut three sides of a rectangle in the bark of the Orlando tangelo seedling or rootstock as shown in Figure 46. Ensure that knife blades are disinfected. Two or three such windows can be made, preferably in the lower parts of the trunk to observe symptoms. If no symptoms are seen, the bark should be replaced and wrapped with budding tape. This permits the peeled area to regraft and heal, leaving the trunk less damaged and available for more extensive bark cutting and peeling at future observation times.

Termination. When 75 percent of the mild-positive controls show definitive symptoms, the bark can be completely peeled from all of the test plants and examined for symptoms. The symptoms are then recorded and the test or experiment terminated. Symptoms on seedlings of Orlando tangelo in the field will resemble those in Figures 44 and 45. Symptoms for the Parson's Special mandarin will be as in Figure 49a or 49b. Symptoms will almost always appear at the bud-union or at the cut-back and regrowth areas (Figures 46, 49a and 50). However, with very severe isolates, symptoms may appear throughout the stem, as shown in Figure 49b.

MISCELLANEOUS

The parameters for bringing out the maximum symptom expression in the Parson's Special mandarin indicator scion have not been completely researched. High temperatures are definitely an important factor for inducing definitive symptoms more rapidly. Light intensity appears to be an important factor, but this has not been adequately tested. Alternating temperatures by moving the inoculated plants between hot and cool rooms has been tried with some success, but the precise parameters have not been determined (Roistacher, unpublished). Forcing the Parson's Special mandarin scion on larger stock plants may be helpful in inducing earlier symptom expression, and using larger pieces of inoculum has been suggested as a means of enhancing symptom development. Nauer and Roistacher (1984) evaluated 63 mandarin and mandarin hybrid seedlings to find a more rapid seedling indicator for cachexia, but found none that were reactive.

The use of Parson's Special mandarin and Orlando tangelo indicator plants as an index is a long-term process, and there is a distinct need for a more rapid indexing procedure for detecting this disease. With the recent discovery of the viroid nature of cachexia (Semancik et al.,1988), new techniques may be developed to shorten this time period. The PAGE technique is promising for locating the viroid band and could be a relatively rapid means of confirming presence or absence of viroids after therapy. Inoculated citrons grown under warm conditions should be used as donor plants for PAGE.. Mechanical inoculation of cucumber as a supplemental diagnostic technique is very rapid and should be tested and tried (Semancik et al.,1988; Duran-Vila et al., 1988). A most promising rapid future technique may be nucleic acid hybridization using cDNA probes. These techniques are illustrated in Part III.

CACHEXIA DETECTION

Summary
Graft transmission to Parson's Special mandarin

Indicator:
Parson's Special mandarin/rough lemon.

No. plants/test:
4 to 8 (grown one per container; mild- and severe-positive controls should be included).

Inoculum:
"Buds" (buds, blind buds or chip buds).

Plant growth:
Single shoot grown to 1 m and repeatedly cut back.

Temperature:
Hot: 32-40C day, 25-30C night.

First symptoms:
Severe isolates: 6-8 months.
Mild isolates: 9- 12 months or longer.

Symptoms:
Gum in scion just above the bud-union and also at the cut-back joint of the new growth area.

REFERENCES

Calavan, E.C. & Christiansen, D.1965. Variability of cachexia reaction among varieties of rootstocks within clonal propagations of citrus. In Proc. 3rd Conf. IOCV, p. 76-85. Gainesville, Univ. Fla. Press.

Childs, J.F.L.1950. The cachexia disease of Orlando tangelo. Plant Dis. Rep., 34: 295-298.

Childs, J.F.L.1959. Xyloporosis and cachexia. Their status as citrus virus diseases. In Wallace, J.M., ed. Citrus virus diseases, p. 119124. Richmond, Univ. Calif. Div. Agric. Sci.

Childs, J.F.L.1980.Cachexia-xyloporosis. Vol. 1. In Bov, J.M. & Vogel, R., eds. Description and illustration of virus and virus-like discuses of citrus. A collection of colour slides. Paris, I.R.F.A. SETCO-FRUITS.

Duran-Vila, N., Pina, J.A., Ballester, J.F., Juarez, J., Roistacher, C.N., Rivera-Bustamente, R. & Semancik, J.S.1988. The citrus exocortis disease: a complex of viroid-RNAs. In Proc. 10th Conf. IOCV, p. 152-164. Riverside, IOCV.

Nauer, E.M., Holmes, R.C. & Boswell, B.S.1980. Close spacing in the greenhouse inhibits lime seedling growth. Hort Sci., 15(5): 591 -592.

Nauer, E.M. & Roistacher, C.N.1984. Evaluation of seedlings of 63 citrus cultivars for cachexia detection. In Proc . 9th Conf. IOCV, p. 353-356. Riverside, IOCV.

Reichert, I. & Perlberger, J.1934. Xyloporosis, the new citrus disease. Bull. Agr. Res. Sta. (Rehovat), 12: 1-49; Huclur, 7: 163167, 172,193-202.

Roistacher, C.N. 1988. The cachexia and xyloporosis disease of citrus - a review. In Proc . 10th Conf: IOCV, p. 1 16- 124. Riverside, IOCV.

Roistacher, C.N., Blue, R.L. & Calavan, E.C.1973. A new test for cachexia. Citrogr., 58:261 262.

Roistacher, C.N., Gumpf, D.J., Nauer, E.M. & Gonzales, R.1983. Cachexia disease: virus or viroid. Citrogr., 68: 111- 113.

Roistacher, C.N., Nauer, E.M. & Wagner, R.C.1980. Transmissibility of cachexia, dweet mottle, psorosis, tatterleaf and infectious variegation viruses on knife blades and its prevention. In Proc. 8th Conf IOCV, p. 225-229. Riverside, IOCV.

Semancik, J.S., Roistacher, C.N. & Duran-Vila, N.1988. Viroid RNA associated with cachexia (xyloporosis) disease of citrus. In Proc. 10th Conf. IOCV, p. 125-135. Riverside, IOCV.

Vogel, R. & Bov, J.M.1976. La nouvelle technique d'indexation de la cachexie-xyloporose: son utilisation en Corse. Fruits, 31: 93-96.

FIGURE 44 A window in the trunk of a field tree of Ellendale mandarin showing severe symptoms of gumming on the bark and trunk typical of severe cachexia. Note the areas of gum in the cut-back section (Australia)

FIGURE 45 The trunk portion of a field tree of Parson's Special mandarin as a rootstock under a grapefruit scion with the bark cut away to show the brown gum-stain. This tree was inoculated with a severe isolate of citrus cachexia viroid (Central Calitornia)

FIGURE 46a Parson's Special mandarin as a scion budded to rough lemon as the rootstock with a window cut into the bud-union showing severe symptoms in the Parson's Special mandarin. Note that the gumming occurs only in the Parson's Special mandarin and not in the rough lemon rootstock (greenhouse grown, Riverside, Calitornia)

FIGURE 46b The first mild gumming symptom usually seen in an exploratory cut into the budunion area

FIGURE 47 Bending the rough lemon seedling just above the scion bud aids in the forcing of the Parson's Special mandarin scion bud

FIGURE 48 Growth of a Parson's Special mandarin scion as a single shoot or leader. Nob careful staking and tying

FIGURE 49 Symptom reaction on Parson's Special mandarin after the bark is completely peeled a) Mild

FIGURE 49 Symptom reaction on Parson's Special mandarin after the bark is completely peeled b) Very severe

FIGURE 50 The appearance of symptoms of gum in the Parson's Special mandarin occurs only at the cut-back joint area, but no symptoms show in the stem above or below the area surrounding the joint

Satsuma dwarf

DESCRIPTION AND BACKGROUND

The family of virus diseases called satsuma dwarf is found primarily in Japan and consists of satsuma dwarf virus (SDV), navel infectious mottle virus (NIMV), citrus mosaic virus (CIMV) and natsudaidai dwarf virus (NDV). All are related serologically, are transmitted to herbaceous hosts and are caused by strains of the same virus.

The dwarfing problem of satsumas wax first noted in the early 1930s in Shizuoka prefecture. Yamada and Sawamura (1952) showed it to be infectious and named it dwarf disease of satsuma, popularized to satsuma dwarf. A slide and text description of the disease is given by Tanaka (1980).

Except for its presence in Turkey (Azeri,1973), the disease has not been reported outside Japan. It is very probable that the disease is present in mainland China, and there is no reason why the disease could not develop anywhere citrus is grown if infected budwood is introduced and cool temperatures prevail. Miyakawa (1969) found 18 species of citrus plus seven hybrids and two related genera to be susceptible when they were bud-inoculated.

Satsuma dwarf is caused by a virus 26-27 nm in diameter. The virus has been purified and characterized (Tanaka and Imada,1974). Particle size, reactivity to sesame (Sesamum indicum) and citrus, and serological relationships with related viruses. i.e. NIMV, CIMV and NDV, suggest close relationships within this family (Imada,1984). Despite the similarity of particle size and morphology of SDV and citrus infectious variegation virus (CIVV), the differential reaction to sesame and lack of serological relationship to CIVV antiserum suggest that SDV is not closely related to CIVV (Imada,1984). The satsuma dwarf family of viruses are all readily mechanically transmissible to sesame.

SDV can be readily transmitted mechanically on tools. However, the primary means of spread is by humans through propagation of infected budwood and spread through the soil (Izawa,1966; Tanaka, Yamada and Kishi,1971; Tanaka1980; Koizumi et al.,1988).The soilborne soil borne nature of this virus disease of citrus may be an important aspect of its epidemiology since, once a site is infected, the disease may be permanently established. There is no evidence for aboveground vector transmission.

Koizumi et al. (1988) found SDV in a non citrus host, China laurestine, a tree often used as a windbreak in satsuma orchards in Japan.

Since tristeza and the severe seedling-yellows tristeza viruses are endemic in Japanese citrus, it is probable that most satsumas carry the tristeza virus. This makes it difficult to index for SDV by bud transmission to tristeza-sensitive index plants. Mechanical inoculation to sesame indicator plants is effective and can be used for indexing.

The availability of antisera for SDV enabled Kuhara et al.. (1981) to use ELISA for mass screening of CIMV in field trees. They were able to test 53 000 trees and found that 38 percent were infected. In order to eliminate the threat of nationwide contamination by this virus, 17 410 field trees and 120 000 nursery trees were destroyed. ELISA is now used extensively in Japan as an index for the satsuma dwarf family of viruses.

METHODS OF DETECTION Method 1: Field diagnosis

Trees in the field are stunted or dwarfed (Figure 51 a), shoots are short and leaves are small and boat- or spoon-shaped (Figure 51 b). The boat- or spoon-shaped leaf is characteristic of the disease both in Japan and in Turkey. The malformed leaves are usually observed in the spring flush and not on other flushes of growth.

Method 2: Graft transmission to indicator plants

Since severe CTV is present in almost all satsuma trees in Japan, any budwood imported from Japan which is suspect for SDV or related viruses will also probably contain CTV. It is therefore desirable, and perhaps necessary, to eliminate the CTV in order to test for SDV CIMV, NIMV or NDV by graft transmission. This can be done by "filtering out" the tristeza virus by inoculation into trifoliate orange seedlings. Buds from test trees or plants are first graft-inoculated into a seedling of a trifoliate orange, the seedling is then cut back and the new growth forced. If SDV is present, the leaves on the new growth will usually show psorosis-like symptoms of flecking and mottle within four to six weeks. These symptoms may not persist as the leaves mature and harden.

The use of supplemental lighting to enhance growth of trifoliate seedlings is recommended (see section on lighting in Part II). Procedure for graft transmission for detection of SDV and related viruses is as follows:

Inoculum tissue. "Buds" (buds, blind buds or chip buds) are taken from pre-inoculated trifoliate orange filter plants, or directly from suspect trees in the field.

Inoculation. A minimum of two inoculum "buds" are grafted to the lower part of the indicator seedlings. The seedling can be cut back about 20-25 cm above the soil surface at the time of inoculation, or two to three weeks after inoculation at the time inoculum survival is recorded.

Indicator plants. Natsudaidai, citron, sour lemon, Dweet tangor, mandarin or satsuma are used as seedlings. Grow three seedlings per container; inoculate two, leaving one as a negative control.'

Controls. If possible, SDV-positive tristeza-free controls should be included in each test; preferably the mildest-reacting available source plus a severe source should be used. A non inoculated or self-inoculated negative control must always be included in every index test.

Inoculum survival. Cut the wrapping tapes two to three weeks after inoculation. Dip the razor blade or knife in a 1 percent solution of sodium hypochlorite disinfectant when going from plant to plant.

Temperature requirements. The satsuma dwarf complex of viruses are cool-temperature-dependent for optimum symptom expression, and temperatures should be maintained as cool as possible. Night temperatures in the indexing facility should not exceed 18C. Day temperature must not be too warm and should not exceed 26C. A temperature of 28/23C (maximum day/minimum night) will mask symptom expression (Tanaka et al.,1969).

Symptoms. In general, the symptoms induced in indicator plants by the satsuma dwarf family of viruses (without the presence of CTV) are similar to those induced by infectious variegation (see Infectious variegation, Figures 64-67). Young leaves will show psorosis-like leaf patterns of flecking, mottle, chlorosis and perhaps some mild shock reaction within four to six weeks. The characteristic symptoms may not persist and may fade as the leaves harden. Mature leaves may show leaf curl and crinkle. Line patterns and misshapen leaves are common.

Miyakawa (1969) induced a non-persistent mottle in leaves of the young flush in almost all plants of the 27 citrus species, hybrids and related genera he tested.

Symptoms induced on leaves of satsuma seedlings under cool conditions will be typically boat- or spoon-shaped with occasional crinkle (Figures 51 b and 52a). Symptoms may appear in six to eight weeks after inoculation (Figure 52b).

Method 2: Transmission to herbaceous hosts

Although cowpea and the common red kidney bean are good indicators for the satsuma dwarf family of viruses, white sesame is the preferred indicator plant. The following inoculation procedure is essentially that of Tanaka (1980):

Inoculum tissue. Soft young shoots under 10 cm are collected from trees or plants to be tested. Tissue from field collections should be put in polythene bags and immediately placed in an ice chest. It not advisable to collect tissue when temperatures are too warm.

Preparation and buffers. Sap is prepared by triturating young leaves in a cold mortar kept on ice using a two- to tenfold volume of 1/15 M Sorensen phosphate buffer solution at pH 7.0.

Inoculation. The leaves of the sesame plant are dusted with 500-mesh carborundum and rubbed with absorbent cotton or swabs dipped in the sap. After inoculation, leaves are rinsed in tap water. Five plants can be grown per container; a minimum of four are inoculated and one left as a non-inoculated control. Preferably two containers with a total of eight inoculated plants should be used per index test.

Post-inoculation care. Inoculated plants should be kept below 25C for at least eight hours after inoculation. Greenhouse temperatures should be maintained relatively cool (20-25C).

Time for first symptoms. Symptoms should appear within seven to 14 days, depending on temperature.

Symptoms. Necrotic local lesions on inoculated primary leaves (Figure 53), vein clearing, vein necrosis, curling, malformation and necrosis and spotting on secondary leaves (Figure 54).

Method 3: ELISA

Good antisera are available to SDV, and ELISA has been widely used in Japan for SDV and CIMV indexing. Specific procedures for ELISA are given in Part III. The ELISA technique was extremely helpful in the large-scale detection and eradication of citrus mosaic virus in Japan (Kuhara et al.,1981). It should not be used as the only method for the indexing of budwood from critical primary foundation trees or from shoot tip grafted or heat-treated plants to be used for producing primary trees. However, ELISA can be used in conjunction with mechanical or graft transmission indexes to ensure that the important foundation or mother block budwood is free of pathogens.

MISCELLANEOUS

Studies by Tanaka (1972) indicate that transmission by sap inoculation from citrus to citrus was very poor. He achieved 6/64 transmissions showing symptoms for SDV and 3/81 for NDV. The poor response to mechanical inoculation precludes this as a routine method for indexing.

SATSUMA DWARF DETECTION

Summary
• Graft transmission to citrus

Indicators:
Seedlings of Natsudaidai, citron or lemon if tristeza is not present; Dweet tangor or mandarin seedlings or satsuma/trifoliate if tristeza is present.

No. plants/test:
4 (3 plus 1 control in each of 2 containers); or 1 per container of satsuma/trifoliate.

Inoculum:
"Buds" (buds, blind buds or chip buds).

Plant growth:
Allow full flush to develop without trimming.

Temperature:
Very cool not to exceed 26C maximum day, 12-18C minimum night.

First symptoms:
4 to 6 weeks.

Symptoms:
Similar to those of infectious variegation, i.e. psorosis-like leaf patterns in young growth, leaf curl and crinkle in mature leaves.

• Transmission to herbaceous hosts

Indicator:
White sesame (Sesamum indicum).

No. plants/test:
8 (3 plus 1 control in each of 2 containers of 5 plants each).

Inoculum:
Soft, young shoots.

Inoculation:
1 / 15M Sorensen phosphate buffer, pH 7.0. Leaf rubbed with carborundum.

Temperature:
Cool - below 26C.

First symptoms:
7-14 days.

Symptoms:
Primary leaves: necrotic local lesions. Secondary leaves: vein clearing, necrosis, curl, malformation.

REFERENCES

Azeri, T.1973. First report of satsuma dwarf virus disease on satsuma mandarins in Turkey. Plant Dis. Rep., 57: 149-154.

Imada, J.1984. Purification and some properties of natsudaidai dwarf virus. Bull. Fruit Tree Res. Stn. Ser. E (Akitsu), 5: 55-59.

Izawa, H.1966. Investigation on withering disease of Citrus unshiu Markov. in Gamagori district, Aichi Pref. Bull. Aichi Hort. Exp. Sta., 5: 1-9.

Koizumi, M., Kano, T., leki, H. & Mae, H.1988. China laurestine: a symptomless carrier of satsuma dwarf virus to accelerate natural transmission in fields. In Proc. 10th Conf. IOCV, p. 348-352. Riverside, IOCV.

Kuhara, S., Koizumi, M., Yamaguchi, A. & Yamada, S.1981. A nationwide campaign for certification of early satsuma "miyamato wase" for citrus mosaic by means of ELISA. In Proc . Int. Soc. Citriculture,1981, 1: 441-444.

Miyakawa, T.1969. Susceptibility of Citrus spp. and the other related plants to the satsuma dwarf virus (SDV). Ann. Phytopathol. Soc. Jap., 35: 224-233.

Tanaka, H.1972. Mechanical transmission of viruses of satsuma dwarf and natsudaidai dwarf from citrus to citrus. Ann. Phytopathol. Soc. Jap., 38(2): 156- 160.

Tanaka, H.1980. Satsuma dwarf. In Bov J.M. & Vogel, R., eds. Description and illustration of virus and virus-like diseases of citrus. A collection of colour slides. Paris, I.R.F.A. SETCO-FRUITS.

Tanaka, H. & Imada, J.1974. Physalis floricluna, a good production host for satsuma dwarf virus. Plant Dis. Rep., 58(4): 602-605.

Tanaka, H., Kitajima, H., Yamada, S. & Kishi, K.1969. Influence of environmental factors on symptom appearance of satsuma dwarf. 2. Relation of the appearance of the spoon-shaped leaf symptom to temperature. Bull. Hort. . Res. Sta. Japan Ser.B,9: 175 179.

Tanaka, H., Yamada, S.-l. & Kishi, K.1971. Symptoms and occurrence of navel orange infectious mottling and natsudaidai dwarf. Bull. Hort. Res. Stu. .Japan Ser. B (Okitsu), 11: 141-147.

Yamada, S. & Sawamura, K.1952. Studies on the dwarf disease of satsuma orange, Citrus unshiu Markov. (Preliminary report). Hort. Div. TokaiKinki Agr. Exp. Sta. Bull., 1: 61 -67.

FIGURE 51a A satsuma dwarf virus-infected tree in the field (right) showing typical stunting and dwarfing (Japan)

FIGURE 51b A branch from an infected field tree of satsuma mandarin showing typical spoon- or boat-shaped leaves (Japan)

FIGURE 52a Symptoms on leaves from a satsuma seedling induced by graft inoculation with buds from an infected tree in the field. Typical spoon- or boat-shaped leaves with occasional crinkle are seen (Japan)

FIGURE 52b Graft-inoculated satsuma seedlings inoculated with SDV. Non-inoculated control plant is on the left. Note the smaller-sized plants and spoon-shaped leaves. Photo taken by M. Miyakawa eight weeks after inoculation (Japan)

FIGURE 53 Necrotic local lesions on inoculated cotyledons of a sesame plant inoculated by sap containing SDV (Japan) (Photo: M. Miyakawa)

FIGURE 54 Necrosis of the upper portions of the leaves of a systemically infected sesame plant (Japan) (Photo: M. Miyakawa)

continue


Contents - Previous - Next