Asparagus virus 2

I. Uyeda
Department of Botany, Faculty of Agriculture, Hokkaido University, Sapporo 060, Japan

G. I. Mink
Washington State University, Irrigated Agriculture Research and Extension Center, Prosser, Washington 99350, USA

Contents

Introduction Main Diseases Geographical Distribution Host Range and Symptomatology Strains Transmission by Vectors Transmission through Seed Transmission by Grafting Transmission by Dodder Serology Nucleic Acid Hybridization Relationships Stability in Sap

Purification Properties of Particles Particle Structure Particle Composition Properties of Infective Nucleic Acid Molecular Structure Genome Properties Satellites Relations with Cells and Tissues Ecology and Control Notes References Acknowledgements Figures

Introduction

First reported by Hein (1963); virus described by Groschel (1976), Weissenfels, Schmelzer & Schmidt (1978) and Uyeda & Mink (1981).

Synonyms

Asparagus latent virus (Rev. appl. Mycol. 43: 3079)

Asparagus C-type virus (Rev. Pl. Path. 57: 891)

A virus with quasi-isometric particles c. 26-36 nm in diameter, which sediment as three or four components. Transmitted by mechanical inoculation of sap and through seed and has a wide experimental host range. Known to occur naturally only in asparagus. Reported in Europe, North America and Japan.

Main Diseases

Natural infection has been reported only from asparagus (Asparagus officinalis). Plants infected from seed show no obvious symptoms but vigour and productivity are reduced (Weissenfels & Schmelzer, 1976; Yang, 1979). Fronds of some experimentally inoculated plants show light green mosaic followed by recovery (Fujisawa et al., 1983).

Geographical Distribution

Reported from USA (Uyeda & Mink, 1981), Germany (Hein, 1963; Weissenfels & Schmelzer, 1976), The Netherlands (van Hoof, 1970), England (Paludan, 1964) and Japan (Fujisawa et al., 1983).

Host Range and Symptomatology

The virus is transmissible by inoculation of sap. Experimentally the virus infected 116 of 169 species in 27 of 34 families of dicotyledonous plants (Uyeda & Mink, 1981; Weissenfels et al., 1978). The virus also infected 2 of 3 species in 2 of 3 families of monocotyledonous plants (Weissenfels et al., 1978).

Diagnostic species

Chenopodium quinoa. Occasional chlorotic or necrotic spots in inoculated leaves. Mild mottle to severe necrosis in systemically infected leaves, depending on the isolate (Fig.1).

C. murale. Sunken necrotic local lesions (Fig.2). No systemic infection.

Nicotiana tabacum (tobacco) cv. Havana 423. Necrotic ringspots in inoculated leaves. Systemic necrosis followed by recovery (Fig.3).

Propagation species

Nicotiana tabacum cv. Havana 423 or cv. Xanthi-nc.

Assay species

Vigna unguiculata (cowpea) cv. California Blackeye and Phaseolus vulgaris (French bean) cv. Top Crop give red necrotic local lesions (Fig.4). Probably other cultivars also can be used.

Strains

Two strains, P and S, were distinguished by agar gel double diffusion serology (Fig.5) (Uyeda & Mink, 1981). In Washington State, USA, strain P was predominant and strain S was isolated only once. A European isolate was serologically and symptomatologically indistinguishable from strain P (Uyeda & Mink, 1981). A Japanese isolate reacted both with antiserum to strain P and with antiserum to strain S (Fujisawa et al., 1983).

Transmission by Vectors

No vector is known. The aphids Myzus persicae (Weissenfels et al., 1978; Uyeda, 1978; Fujisawa et al., 1983), Rhopalosiphum padi and Cavariella aegopodii (Uyeda, 1978) all failed to transmit the virus in a non-persistent manner.

Transmission through Seed

Transmitted through up to 60% of asparagus seeds. The virus was also transmitted through seed of N. tabacum cv. Samsun (36%), Zinnia elegans (22%) and Petunia hybrida (26%) (Fujisawa et al., 1983).

Transmission by Dodder

No transmission was obtained with Cuscuta campestris or C. californica parasitic on Nicotiana glutinosa, N. megalosiphon or N. tabacum (Weissenfels et al., 1978).

Serology

Moderately immunogenic. Antiserum with a titre of 1/256-1/1024 in the ring precipitin test was prepared by injecting 0.2-0.4 mg of formaldehyde-fixed virus intravenously several times at intervals of 2-3 days (Uyeda & Mink, 1981). The virus was readily detected in the spear of asparagus by single radial immunodiffusion (Uyeda, 1978).

Relationships

Asparagus virus 2 is a member of the ilarvirus group, being serologically related but not identical to elm mottle, citrus variegation, citrus leaf rugose and Tulare apple mosaic viruses (Uyeda & Mink, 1983). The three major nucleoprotein components of all these viruses sediment at very similar rates but not identically when centrifuged in sucrose density gradients in sister tubes (Uyeda, 1978). The ultraviolet absorption spectra of purified preparations of all these viruses are also similar. Asparagus virus 2 can be differentiated from these four viruses on Chenopodium murale, in which it produces local necrotic lesions without systemic infection, whereas elm mottle and Tulare apple mosaic viruses infect this species systemically, and citrus variegation and citrus leaf rugose viruses do not infect. Tobacco streak virus, another ilarvirus, is not serologically related to asparagus virus 2; the sedimentation and ultraviolet absorption characteristics of the purified virus are also distinct from those of asparagus virus 2.

Stability in Sap

In crude sap of C. quinoa, the virus has a thermal inactivation point (10 min) of 55-60° C, dilution end-point of 10^-3-10^-4, and retains infectivity for more than 2 days at 21-24°C (Mink & Uyeda, 1977).

Purification

Up to 2.5 mg of the virus was obtained by the following procedure (Uyeda & Mink, 1981). Triturate frozen infected tobacco leaf tissue (40-60 g) in a Waring Blendor for 2 min with 0.1 M neutral potassium phosphate buffer (2.5 ml per g tissue) containing 0.02 M disodium ethylenediamine-tetraacetate (EDTA). Add Triton X-100 (5 ml per 100 ml extract), and stir the mixture for 15 min at room temperature. Clarify the extract by treatment with chloroform (1 ml per 4 ml extract) and freeze overnight at -20°C. Concentrate the virus by two cycles of differential ultracentrifugation and suspend in 1 ml 0.01 M phosphate buffer containing 0.001 M EDTA, pH 7.2-7.4. Further purify the virus by rate zonal sucrose density gradient centrifugation. The purified virus, stored in 0.01 M phosphate buffer, pH 7.2-7.4, at 4°C, is stable for at least 1 month without significant loss of infectivity (Uyeda & Mink, 1981).

The virus may also be purified by chloroform-butanol clarification, differential centrifugation and rate zonal sucrose density gradient centrifugation (Fujisawa et al., 1983).

Properties of Particles

The virus particles sediment as three major components (NP1, NP2 and NP3) and one minor component (NPO) in 10-30% sucrose gradients (Uyeda & Mink, 1981). NP2 component was not always resolved in 10-30% sucrose gradients and when resolved it appeared as a diffuse zone.

Sedimentation coefficient, s_{20, w}: 104 S (NP1), 95 S (NP2), 90 S (NP3). Component NPO sediments faster than the other components but its sedimentation coefficient was not determined.

A₂₆₀/A₂₈₀: 1.31-1.36 (not corrected for light-scattering) (unfractionated virus).

Particle Structure

Components NP1, NP2 and NP3 are quasi-isometric particles with modal diameters of 32 nm, 28 nm and 26 nm, respectively (Fig.6) and are serologically identical. Component NPO consists of particles of two types, one 36 nm in diameter and the other a dimer of particles 28 nm in diameter (Uyeda & Mink, 1981; Fujisawa et al., 1983). The particles are unstable in 1% phosphotungstate, pH 7.0, unless fixed, but are well preserved in 2% uranyl acetate.

Particle Composition

No information.

Relations with Cells and Tissues

No information.

Notes

Another ilarvirus, tobacco streak virus, also has been isolated from asparagus (Brunt & Paludan, 1970; Mink & Uyeda, 1977). It causes systemic necrosis on C. quinoa very similar to that caused by some isolates of asparagus virus 2. The two viruses are best differentiated by serology, neither virus reacting with antisera to the other.

References

1. Brunt & Paludan, Phytopath. Z. 69: 277, 1970.
2. Fujisawa, Goto, Tsuchizaki & Iizuka, Ann. phytopath. Soc. Japan 49: 683, 1983.
3. Groschel, Ph.D. Thesis, Technischen Univ., Hannover, 1976.
4. Hein, Mitt. biol. BundAnst. Ld- u. Forstw. 108: 70, 1963.
5. Mink & Uyeda, Pl. Dis. Reptr 61: 398, 1977.
6. Paludan, Maanedsovers. PlSygd. 407: 11, 1964.
7. Uyeda, Ph.D. Thesis, Washington State Univ., 1978.
8. Uyeda & Mink, Phytopathology 71: 1264, 1981.
9. Uyeda & Mink, Phytopathology 73: 47, 1983.
10. van Hoof, Jversl. Inst. Plziektenk. Onderz., 1969: 90, 1970.
11. Weissenfels & Schmelzer, Arch. Phytopath. PflSchutz 12: 67, 1976.
12. Weissenfels, Schmelzer & Schmidt, Zentbl. Bakt. ParasitKde Abt. 2 133: 65, 1978.
13. Yang, HortScience 14: 734, 1979.

Figure 1

Systemic mottle in Chenopodium quinoa.

Figure 2

Necrotic local lesions in Chenopodium murale.

Figure 3

Systemic necrosis followed by recovery in Nicotiana tabacum cv. Havana 423.

Figure 4

Necrotic local lesions in Vigna unguiculata cv. California Blackeye.

Figure 5

Agar gel double diffusion serology test. Centre well contains antiserum to strain P. Peripheral wells contain strain P (P), strain S (S) and an isolate from Europe (EAV); healthy sap (H).

Figure 6

Virus particles (NP1 component) in 2% phosphotungstate, pH 7.0, after fixation with 4% formaldehyde. Bar represents 100 nm (courtesy of I. Fujisawa).