SOIL TEMPERATURE AS A FACTOR IN THE FRENCHING OF TOBACCO (NICOTIANA TABACUM L.)

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Abstract
Tobacco growing in a compost soil developed frenching symptoms consistently at 35 C and never at 21 C. Symptoms appeared as early as 8 days. After frenching set in a reversal of the temps. caused a decline of symptoms to complete disappearance on subsequent growth of frenched plants, and the appearance of symptoms on non-frenched plants. Tobacco vars. of cigar and cigarette types were equally susceptible. No relationship was found between frenching and the ions Cu, Zn, B, or Ca. Addition of N fertilizer failed to prevent or cure frenching. Plant tissue tests showed high amts. of NO3 in frenched leaves. H-ion concn. of the soil did not appear to be a factor, although low pH values delayed the onset of frenching symptoms. Plants grown at a root temp. of 35 C in soln. cultures failed to develop symptoms of frenching with or without addition of filtered soil extracts from a frenching soil. Air drying the soil destroyed its ability to cause frenching. Growing the plants in a soil with a lowered avg. moisture content lessened the symptoms of frenching on new growth.