Disease resistance in cocoa germplasm: witches' broom disease.
1993
Hardwick K. | Penman D. | Collin H. | Isaac S.
Reports on research aimed at developing chemical analyses to quantify each hyphal growth phase during the progress of Witches' broom disease and in different levels of disease severity. The analyses evaluated were based on fungal-specific mannan, chitin, sterols and lipids. Mannan concentrations and mannan: chitin ratios differed significantly between phases, but uninfected host tissue had high mannan levels and thus mannan is unsuitable measure of fungal biomass. Previous chitin analyses were too insensitive. A new GC based method with some x 1500 increased sensitivity has been developed. It is capable of measuring nanogram levels of fungus in sub-milligram portions of cocoa. The fungal sterol, ergosterol, often used to measure fungal biomass in diseased plants, is not present in healthy cocoa tissue. It is easily quantified by GC, and evaluation of its potential for fungal quantification in diseased cocoa is underway. The possibility of using other sterols and lipids, including ones already found to differ between hyphal phases, is also being evaluated.
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