Relationship between calcium levels and cocoa stem canker caused by morphological forms of Phytophthora palmivora

The effect of calcium on stem canker development in cocoa as caused by three isolates of Phytophthora palmivora were examined using seedlings grown in sand and water culture as well as in a nutrient film. At leaf calcium concentration varying from 0.12 to 0.26% increase in calcium level resulted in increase in resistance of stems to infection by P795 an MF4 isolate from Cameroun correlation coefficient (r) to 1.20%, there was a significant increase in susceptibility of seedlings to infection by the same isolate (r 0.89). There was no significant difference in seedling reactions at calcium concentration varying from 0.12 to 0.26% and 0.1-1.4% when inoculated with P255 and P40 respectively (MF1 isolates from Costa Rica and Malaysia). A macerating enzyme was produced by P255. Although enzyme activity was significantly inhibited at 10mM Ca++, studies with other Phytophthora isolates suggested that this macerating enzyme appeared only to have localized significance, if any, in the pathogenesis of stem canker and pod rot of cocoa.