01648naa a2200253 a 450000100080000000500110000800800410001910000160006024500550007626000060013130000180013749000080015552009990016365000130116265000200117565000130119565300270120865300290123565300200126465300180128470000140130270000150131677300630133116439961993-05-14               bl uuuu     u00u1 u    #d1 aARIMOTO, Y.  aThe significance of the callus formation on citrus  c0  ap.374-379 v.1  vv.1  aTwo types of callus developed on damaged citrus. One was formed by infection of Diaporthe citri. Damaged cells swelled on the upper surface of tissue and callus was formed by the action of some wound hormones between healthy tissues and damaged cells. Damaged cells, including the invaded pathogen, were then separated by the formation of a corky layer. Thus the  citrus plant was protected from the spread of the pathogen. Another type of callus was formed by the action of ethylene. In a chamber with ethylene (100 ppm), callus, made of free cells, was produced at the base of the leaf and petiole, node of shoots and around the bud and thorn. The callus, made of free cells, induced tip dieback. The callus multiplied readily at the area of separation, but not at thebase of the separated organs. Therefore, both types of callus which were formed by the action of some wound hormones or by ethylene, may be responsible for the protecting reaction of citrus against damage by plant pathogens.  aethylene  aDiaporthe Citri  aMelanose  aAbnormal cell division  aAbnormal cell elongation  aSelf-protection  aWound hormone1 aHOMMA, Y.1 aMISATO, T.  tTokyo, Japan: International Society of citricultural, l981