SUMMARY: When the guanine analogue, 5-amino-7-hydroxy-1-v-triazolo () pyrimidine (guanazolo), was sprayed on the leaves of tobacco or plants it reduced the number of local lesions and delayed or inhibited systemic spread of lucerne mosaic virus. Guanazolo was more effective when applied before inoculation, but had some effect if applied up to about the second day after inoculation. The compound was more effective in solution in 0.1% sodium bicarbonate than in aqueous suspension. With mechanically inoculated plants guanazolo watered on the soil around the plants was less effective than when sprayed on the leaves.

Incubated with the virus the compound did not affect infectivity. In concentrations up to 0.005 guanazolo usually caused negligible plant damage, but at higher concentrations produced a slight yellowing and distortion in the younger leaves with general stunting if treatments were prolonged.

The virus-inhibitory activity of guanazolo was reversed by adenine, guanine and possibly by hypoxanthine, but not by xanthine, uric acid, theobromine, theophylline, caffeine, uracil or thymine.

The triazolo analogue of adenine severely damaged plants and had only slight virus inhibitory activity. The hypoxanthine analogue caused no plant damage. It was less effective than guanazolo in tobacco and but more effective in reducing the number of local lesions produced in beans. Thiouracil, methyl-thiouracil and propylthiouracil were ineffective against lucerne mosaic virus. Thiouracil caused fairly severe plant damage.

Guanazolo had slight or negligible effects on spotted wilt virus in tomato, potato viruses and in potato, and tobacco and pea mosaic virus in peas. Applied as a leaf spray at 0.01 concentration guanazolo delayed or prevented systemic movement of cucumber mosaic virus from mechanically inoculated cucumber leaves, but had no effect when watered on the soil. However, watering the compound on the soil gave some control when the virus was introduced by aphids.


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