Frangipani mosaic virus

A. Varma – Division of Mycology and Plant Pathology, Indian Agricultural Research Institute, New Delhi 110012, India

A. J. Gibbs – Research School of Biological Sciences, Australian National University, Canberra, Australia

Contents

Introduction

Described by Francki, Zaitlin & Grivell (1971).

Synonym

Temple tree mosaic virus. A virus with tubular particles 300 nm long and 18 nm in diameter. Sap transmissible. No vector known; is spread in cuttings of infected frangipani (Plumeria spp.). Restricted host range, grows best at 30-35°C.

Main Diseases

In Plumeria acutifolia the virus causes mosaic, ringspots, veinbanding and bronzing. In P. alba, it causes ringspots, leaf distortion and necrosis. No flower symptoms.

Geographical Distribution

Common in eastern Australia and northern India.

Host Range and Symptomatology

Host range not yet tested extensively, but seems restricted. More species become infected at temperatures above 25°C than below. At 35°C symptoms show in 3-6 days, at 22°C they take 2 weeks or more.

Diagnostic species

Datura stramonium. Chlorotic, necrotic or black lesions develop in inoculated leaves after 1-2 weeks in the glasshouse at 22°C. At 35°C, in controlled environment cabinets, similar symptoms develop in 3 days; one strain causes systemic necrosis along the veins and leaf margins.

Nicotiana glutinosa. At 22°C inoculated leaves develop chlorotic lesions in about 2 weeks. Not infected systemically.

N. tabacum (tobacco) cvs Samsun, Virginia Gold or White Burley. Rarely infected at 22°C. At 35°C all strains induce bright chlorotic or necrotic ringspots in inoculated and systemically infected leaves.

N. clevelandii x N. glutinosa. Not infected at 22°C. At 35°C inoculated leaves develop faint chlorotic lesions which become necrotic or develop ringspots. Not infected systemically.

Propagation species

Nicotiana glutinosa. Inoculated leaves give a good yield after 2-3 weeks at 22°C.

Assay species

Datura stramonium is the most reliable assay species.

Strains

Three distinct strains from different provenances have been distinguished by the symptoms they produce. They are the Adelaide strain (Adel) (Francki et al., 1971), and the Allahabad (Ald) and Delhi (Del) strains (A. Varma & A. J. Gibbs, unpublished data). Leaves of D. stramonium kept at about 22°C develop faint chlorotic lesions after inoculation with strain Adel, necrotic lesions after inoculation with strain Ald, and chlorotic lesions, later becoming black, after inoculation with strain Del. At 35°C symptoms developed more quickly and spread more: strain Adel gave necrotic lesions, strain Ald gave lesions with chlorotic haloes or ringspots, and strain Del gave spreading black necrotic ringspots and systemic veinal and marginal necrosis. N. tabacum cv. Virginia Gold was susceptible at 22°C to strain Del only, showing chlorotic and necrotic local lesions. At 35°C in the same tobacco cultivar, strain Adel gave faint necrotic ringspots, strain Ald gave bright necrotic ringspots and strain Del gave large ringspots both in inoculated and in tip leaves.

Transmission by Vectors

No vector is known.

Transmission through Seed

Not transmitted through seed of D. stramonium or N. tabacum cv. Samsun.

Serology

Particles of the virus are strongly immunogenic. They give flocculent precipitates in tube precipitin tests, and form one band of precipitate in gel diffusion tests.

Relationships

Properties, serological relationships and particle morphology place the virus in the tobamovirus group. The particles of frangipani mosaic virus are morphologically indistinguishable from those of other tobamoviruses. The Adel, Ald and Del strains are serologically closely related to each other. All three strains are related distantly to cucumber virus 4, cucumber green mottle mosaic virus, and an isolate of sunn-hemp mosaic virus from Queensland, Australia (but not one from West Africa); and even more distantly to TMV-type strain, TMV-U2 strain, tomato mosaic virus and ribgrass mosaic virus. (A. J. Gibbs & A. Varma, unpublished data; Franckiet al., 1971). There was no detectable serological relationship with Sammons’ opuntia virus even though comparisons of coat protein composition indicate a close affinity (Description No. 184).

Stability in Sap

Very stable. Sap from infected D. stramonium was not infective after heating to 95°C for 10 min, and lost 90% of its infectivity in 10 min at 90°C. The sap was still infective after 10 weeks at room temperature, and at dilutions up to 10^-5.

Purification

The virus is easily purified from infected leaves of frangipani or N. glutinosa by several methods. The following methods give good yields:

1. Francki et al. (1971), based on McLean & Francki (1967) and Francki & McLean (1968). Homogenise infected leaves of N. glutinosa in 1.5 volumes of 0.2 M Na₂HPO₄, clarify by adsorption with charcoal and DEAE cellulose and filter through Celite. Sediment the particles by centrifuging at 44,000 g for 90 min. Resuspend pellets in distilled water and emulsify with equal volume of chloroform. Centrifuge at 12,000 g for 10 min. Collect aqueous layer and sediment the particles by centrifuging at 16,000 g for 30 min. Repeat chloroform extraction and sedimentation.

2. Based on Varma, Gibbs & Woods (1970). Triturate infected leaves mechanically with 2 ml/g of neutral phosphate-ascorbate buffer (equal volumes of 0.1 M disodium hydrogen phosphate and 0.05 M ascorbic acid). Add a quarter volume of chloroform, emulsify, centrifuge at 8000 g for 10 min, collect supernatant fluid and centrifuge for 1 h at 75,000 g. Resuspend the pellets in a small quantity of the buffer. Further purify by rate zonal centrifugation at 45,000 g for 75 min in gradients of 10-40% sucrose.

Properties of Particles

In dilute solutions the virus sediments as a single component with sedimentation coefficient (s_{20, w}) of 188 S (R. D. Woods, unpublished data).A₂₆₀/A₂₈₀: 1.21.

Particle Structure

The virus has rod-shaped particles about 300 nm long and 17 nm wide. The preparations also contain shorter particles (Francki et al., 1971) (Fig.6).

Particle Composition

 Nucleic acid: The particles contain c. 5% RNA.Protein: Each subunit of the coat protein of strain Adel contains about 158 amino acid residues: Ala, 14; Arg, 11; Asx, 17; Cys, 1; Glx, 16; Gly, 9; His, 1; Ile, 11; Leu, 13; Lys, 4; Met, 0; Phe, 7; Pro, 4; Ser, 14; Thr, 13; Trp, 5; Tyr, 5; Val, 13 (Francki et al., 1971). Of the other tobamoviruses whose coat proteins have been analysed, Sammons’ opuntia virus has a composition most similar to that of frangipani mosaic virus..

Relations with Cells and Tissues

In the cytoplasm of infected parenchymatous cells of D. stramonium leaves, the particles of frangipani mosaic virus aggregate as microcrystals of various shapes and sizes. Particles were not seen in mitochondria, chloroplasts or nuclei although these organelles are not of normal appearance.

References

1. Francki & McLean, Aust. J. biol. Sci. 21: 1311, 1968.
2. Francki, Zaitlin & Grivell, Aust. J. biol Sci. 24: 815, 1971.
3. McLean & Francki, Virology 31: 585, 1967.
4. Varma, Gibbs & Woods, J. gen. Virol. 8: 21, 1970.