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 spectrophotometrically in (i) healthy tissues; (ii) tissues wounded with a 3-mm diameter cork borer and (iii) tissues inoculated with the canker pathogen Phytophtkora patmivora. The results indicated significantly high {P < 0.05) activities ofthe 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 18 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.
An assessment of canker incidence in six cocoa clones revealed IMC 67 to be least susceptible and TSH 1076 most susceptible among the clones tested (ICS 1, IMC 67, P 18, SCA 6, TSH 1076 and TSH 1188). These results were confirmed by greenhouse studies on budded plants using artificial inoculation. IMC 67 with the smallest canker lesion size was found to have the highest value (3.75 N/m2) for extra‐xylary tissue hardness while TSH 1076 with the largest lesion size had the lowest value (1.9 N/m2). Bark moisture content determination also showed lowest values for IMC 67 and highest for TSH 1076. Bark hardness and moisture content were highly correlated with canker resistance.
Anacardium occidentale gum exudate was analyzed for physicochemical, spectroscopic and rheological characteristics. Physicochemical analysis revealed that the gum is mildly acidic, ionic, extremely rich in carbohydrate and calcium. GCMS spectrum revealed the presence of some carboxylic acids, ketone and alkanes. The FTIR spectrum of the gum closely resembled those of other polysaccharides. Scanning electron micrograph revealed the presence of pores containing particles with irregular shapes. The average value of intrinsic viscosity of the gum was 3.28 dL/g, which compared favourably with those obtained for some plant gums. From the Huggins, Kraemer and Power law models, it was deduced that there is absence of molecular association and that the conformation of the gum is more rod like. Viscosity of the studied gum was found to be greatly influenced by the presence of urea, K+, Ca2+ and Al2+. Anarcadium occidentale gum exhibited a non-Newtonian property with characteristics dilatant and shears thickening properties.
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