Published online by Cambridge University Press: 01 June 1997
Zoospore germination and in vitro growth of Phytophthora palmivora were studied in extracts obtained from healthy, wounded and inoculated cacao stem tissues. Extracts from wounded and inoculated stem tissues of IMC 67 (canker resistant genotype) significantly inhibited (P<0·05) zoospore germination and the growth of P. palmivora compared to healthy tissues and the controls. There was no significant difference in the percentage zoospore germination or the growth of the pathogen in the extracts obtained from P 18, SCA 6 and TSH 1076 (susceptible genotypes) and those of the controls, while extracts from ICS 1 and TSH 1188 (moderately resistant genotypes) gave intermediate effects. Also, germ-tube lengths were significantly shorter in IMC 67 extracts than in the controls, moderate in ICS 1 and TSH 1188 extracts and longest in P 18, SCA 6 and TSH 1076 extracts. Tests for antifungal compounds in extracts indicated the presence of phenols. The variation in inhibitory effects of cacao stem extracts on zoospore germination and in vitro growth of P. palmivora can be used as a criterion for selecting cacao genotypes resistant to canker.