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.