COMPARTMENTALIZATION OF DECAY IN CARNATIONS RESISTANT TO FUSARIUM-OXYSPORUM F SP DIANTHI

The anatomy of well-developed defense responses in carnation to Fusari um oxysporum f. sp. dianthi was studied in light of the compartmentali zation of decay in trees (CODIT) model. Compartmentalization of the fu ngus was achieved by occlusion of vessels with gums (wall 1) and circu mscription of the affected area with reaction zones (walls 2 to 4). Re action zones were characterized by thickening, lignification, and sube rization of parenchyma cell walls; suberization of fiber walls; and pr oliferation of xylem parenchyma cells bordering the reaction zone. A c ork layer was formed from the proliferating cells. Wall thickenings st ained for methyl ester groups (indicative of pectins or xylans) and li gnin aldehydes, but not for cellulose, callose, or lipids. Induced lig nin stained like cork rather than vessel or fiber lignin. Gums stained for pectin and lignin. Pressure exerted by proliferating parenchyma c aused the stem to burst. Cells at crack margins stained for lignin and suberin. No essential differences existed between vascular and extrav ascular reaction zones, which sometimes merged fluently. Compartmental ized tissues were replaced by vascular regeneration within the prolife rating xylem parenchyma on the side of the medulla. Defense responses focused for protection of regenerated cambium and xylem (wall 2) rathe r than the original cambium (wall 4), as in trees.