Frenching of tobacco in Australian soils and in soil leachates

Abstract

In Australia frenching occurred consistently in tobacco plants grown in sandy soils that tend to remain wet for long periods. At Katherine, N.T. and Manjimup, W.A., plants grown in soils taken from a depth of 0–6 in. frenched readily, but in soils from a depth of 6–12 in. frenching symptoms in plants were less severe, appeared later, or were absent. Cultivated soils were shown to cause frenching in tobacco plants more readily than uncultivated soils.

Under glasshouse conditions frenching occurred in "active soils" at a wide range of temperatures (18–45°C); high soil temperatures increased the severity and decreased the time to appearance of symptoms. Various minerals added to the soil did not influence frenching, but excess nitrogen delayed the onset of symptoms up to 3 weeks. Prolonged storage of active soils did not affect their ability to induce frenching symptoms in plants.

Frenching could not be transmitted from plant to plant by grafting, mechanical means, or dodder, but could be readily transmitted from active to inactive media by inoculation. Leachates of soil from Katherine and sand from Molonglo, A.C.T. induced frenching in plants. Severity of frenching was decreased by centrifugation, flocculation, or Seitz filtration of the leachates.

Heat and chemical sterilization of active media (leachates, soils, sand, and vermiculite) eliminated their ability to induce frenching in plants. A biological origin of frenching disorder is suggested.