Effects of Boron (B) doses and nitrogen sources (N) at different levels of soil pH on the control of clubrootwas investigated in transplants of chinese cabbage grown in pots containing field soil.. B dissolved in water was applied at 0, 5, 10, 20 and 30 mg.kg-1 of soil of pH 5.5, 6.2 and 7.3 on the day before transplanting. N sources tested (ammonium sulfate, urea and calcium nitrate) were applied to soil of pH 5.5 and 7.3. Seedlings were inoculated with a suspension of resting spores of the pathogen at transplanting and assessed for clubroot severity after 45 days. The disease was severe (70%) when the B dose was less than 10 mg.kg-1 and the pH less than 6.0, but milder (26%) when the B dose was 10 to 30 mg.kg-1 soil at pH values higher than 6.5. Clubroot was least severe when calcium nitrate was used in soil of pH 6.5. Clubroot severity correlated negatively with concentrations of N, Ca, Mg and B in the foliage. We conclude that use of 10 to 30 mg.kg-1 boron and calcium nitrate in soil of pH 6,5 or 7,3 was effective in reducing club root severity.
cultural control; gall; mineral nutrition; Brassica rapa var. pekinensis
