A VIRUS INHIBITOR IN PELARGONIUM SP.

Viruses are mechanically isolated directly from Pelargonium sp. with great difficulty. Pelargonium leaf curl virus (Smith, 1957; Kiviliaan and Scheffer, 1959), pelargonium vein netting virus (Kemp, 1966), pelargonium ringspot virus (Hollings, 1957c), tomato ringspot virus (Kemp, 1969), and cucumber mosaic virus (Kiviliaan and Scheffer, 1959) were not mechanically transmitted or were transmitted only with great difficulty to other herbaceous species. Transmission by grafting was, therefore, recommended (Smith, 1957; Kiviliaan and Scheffer, 1959). Transmission was successful with extracts prepared in 0.03 M sodium phosphate buffer, pH 8.0 (Reinert et al., 1960; Reinert, 1963), or 0.1 M phosphate buffer pH 7.0 with 0.025 M Na₂SO₃ (Kemp, 1966). Pelargonium leaf curl virus isolated from extracts prepared in 0.15 M phosphate buffer, pH 7.0–7.5 (Hollings, 1962).

In more recent work virus transmission was successful when Pelargonium leaves were ground in phosphate buffer containing 4% polyethylene glycol (PEG) (Hollings, 1971).

Attempts to isolate viruses from Pelargonium zonale with typical virus-like symptoms failed when extracts were prepared in phosphate buffer, pH 7.3, with or without 0.1% Na₂SO₃. The results were better when a dry inoculation method was used.

These results led us to postulate the presence of an inhibitor in Pelargonium. Pelargonium hortorum is known to contain inhibitors of potato virus X and TMV (Blaszcak et al., 1959). The effect of geranium tannin on TMV has been described (Cheo and Lindner, 1964). In these studies the inhibitors were effective when the juice was not washed from the inoculated leaf surface after rubbing.

The purpose of this study was to investigate the occurrence of an inhibitor of virus transmission in Pelargonium sap and determine how to overcome the effect of the inhibitor in mechanical transmission of viruses from Pelargonium.