Phytophthora canker resistance in cacao: Role of peroxidase, polyphenoloxidase and phenylalanine ammonia-lyase

Peroxidase (PO) Polyphenoloxidase (PPO) and Phenylalanine ammonia-lyase (PAL) activities in stem extracts of six cacao clones (IMC 67, ICS 1, TSH 1188, P 18, SCA 6 and TSH 1076) were measured spectro-photometrically in (i) healthy tissues; (ii) tissues wounded with a 3-mm diameter cork borer and (iii) tissues inoculated with the canker pathogen Phytophthora palmivora. The results indicated significantly high (P < 0.05) activities of the three enzymes in extracts obtained from inoculated and wounded as opposed to those from healthy tissues. The activities of these enzymes were significantly higher in the extracts of IMC 67, low in TSH 1076, SCA 6 and P 18 and intermediate in TSH 1188 and ICS 1. There was no significant difference in enzyme activities among the genotypes TSH 1076, SCA 6 and P Is and also between ICS 1 and TSH 1188. Starch gel electrophoresis of PO indicated differences in banding pattern/band-intensity amongst IMC 67, ICS 1 and SCA 6 and also between inoculated and uninoculated stems. These results are discussed in relation to lignin and phenol metabolism associated with plant resistance to pathogen attack.