The evidence for the participation of pectic enzymes in plant disease is reviewed, with particular reference to the part played by these enzymes in diseases of citrus fruits. The pectic enzymes of Penicillium digitatum, a pathogen of citrus fruits were compared with those of Penicillium notatum a related species which is non pathogenic, giving evidence that pectin transeliminase and arabanase might be involved in pathogenicity. The pectic enzymes produced by P.digitatum and two other citrus pathogens, Penicillium italicum and Aspergillus fonsecaeus, under various growth conditions were investigated. An indication was thus given that, in the case of P.digitaturn and P.italicum, pectin transeliminase was associated with maceration. The pectin transeliminases of Penicillium digitatum and Penicillium italicum were purified till they were electrophoretically homogeneous. In such a state of purity, they were still found to be capable of macerating orange rind tissue. Evidence of another macerating system (possibly endo-polygalacturonase) was found in the case of P.italicum. Pectin trans-eliminase was not considered to play a significant part in maceration in the case of Aspergillus fonsecaeus, though the nature of the macerating factor produced by this organism is not known at present. Pectin transeliminase and macerating factor were shown to be present in orange tissue infected with P.digitatum or P.italicum. The pectin transeliminases of Penicillium digitatum and Penicillium italicum were compared, and were found to have the same electrophoretic mobilities. They were found to differ only in their susceptibility to temperature, and when injected into oranges they were found to cause areas of softening. The significance of these results in the light of other work, is discussed; and suggestions are made for further research.
|Date of Award||1968|