SOME PROPERTIES OF SEEDBORNE VIRUS HAVING AFFINITIES WITH NEPOVIRUSES, ISOLATED FROM BLACK LOCUST (ROBINIA PSEUDOACACIA) IN POLAND
H POSPIESZNY, N BORODYNKO and L ZIELINSKA
Institute of Plant Protection, ul. Miczurina 20, 60-318 Poznan
Backgroung and objectives
Slack locust trees (Robinia pseudoacacia) are widespread in Poland and infected with a several different viruses. We report here on some properties of the virus isolated from a natural infection of Robinia, distinct from other viruses reported from legumes in Poland.
Material and methods
In host range studies three to five young plants of each species were inoculated on at least two occasions in the year. From plants showing symptomless infection, back inoculations on Chenopodium quinoa were made. Seeds collected from virus-infected plants of Chenopodium quinoa and Robinia pseudoacacia were sown individualy and seedlings tested for the presence of virus by mechanical inoculation to Chenopodium quinoa or examined by electron microscopy. Virus was purified from infected Chenopodiurn quinoa by extraction in 0.2 M citrate buffer, pH. 7.2, containing 0.01 methylene diamine tetra-acetate and 0.4% mercaptoethanol, and clarification with chloroform, followed by precipitation with PEG-6000, high- and low-speed centrifugation and sucrose density gradient.
Results and conclusion
The virus had a narrow host range. When sap from virus-infected Chenopodium quinoa plants were used as inoculum, the following species developed systemic symptoms after mechanical inoculation: Chenopodium quinoa, Chenopodium amaranticolor, Beta vulgaris, Cucumis sativus and Tetragonia expansa. The following plant species were infected symptomlessly as determined by return inoculations to Chenopodium quinoa: Nicotiana tabacum cvs Samsun, Xanthi nc, White Burley, Lycopersicon esculentum and Pisum sativum. C. quinoa was useful as an indicator plant; 4-5 days after inoculation it showed systemic mottling. Virus was seedbome to 100% of C. quinoa and to about 25% of Robinia pseudoacacia. C. quinoa seedlings infected through seeds were markedly stunted when compared to the healthy ones. Purified virus sedimented in sucrose density gradients as three components. The absorption spectrum of top component showed a maximum at 280 nm and a minimum at 252 nm. For lower components Amax was at 260 nm and Amin at 241 nm.
The upper band was not infective and consisted of particles apparently devoid of nucleic acid. The next two bands were infective. Preparations made from C. quinoa contained much more top component than the two others. The particles of virus were isometric, ca 30 nm in diameter. In crude sap of C. quinoa some virus particles were found in tubules. In thin sections were found vascular bundles with scattered particles and tubular structures containing isometric virus particles. Virus failed to react to antisera against three nepoviruses which occur in Poland. The virus shared many properties with nepoviruses: (i) two types of particles -- penetrated (empty) and unpenetrated (full); (ii) its particles were frequently found within tubular structures; (iii) in sucrose gradients it sedimented as three components; (iv) it induced sympomless infection common for many nepoviruses; (v) it was transmitted by seeds.