THE MECHANISM OF RESISTANCE OF CARNATION TO WILT DISEASES
An overview is given of recent research on the mechanisms of resistance of carnation to wilt diseases and present ideas of possible mechanisms of defense are outlined. Emphasis is on Fusarium wilt caused by Fusarium oxysporum f.sp. dianthi race 2; however, wilt diseases caused by F. oxysporum f.sp. dianthi race 1 and by Phialophora cinerescens have not been excluded. The three fungi differ in pathogenesis, wilting caused by F.o. f.s. dianthi race 2 is due to xylem degradation, that by P. cinerescens to abundant gummosis and that by F.o. f.sp. dianthi race 1 probably to production of toxic metabolites. Resistance to F.o. f.sp. dianthi race 2 and P. cinerescens is partial and polygenic and relies on a complex system of host reactions. Resistance to F.o. f.sp. dianthi race 1 is more complete and could be of monogenic inheritance. All cultivars responded to inoculation with each of the three fungi with accumulation of dianthramide phytoalexins. The level of accumulation of the dianthramides was determined partly by the cultivar and partly by the invading pathogen. All fungi caused some degradation of lignin, but irrespective of the pathogen, each inoculated cultivar showed a unique pattern of demethylation and degradation of pectin, and degradation of lignin, and hemicellulose. Localization of the fungi within the xylem probably depends on an effective combination of accumulation of fungitoxic amides, occlusion of the colonized vessels with gums, lignification of surrounding cells and formation of phellem tissue. Susceptible and resistant responses may be found in the same plant and a higher level of resistance of a cultivar is determined by quantitative rather than by qualitative differences.
Niemann, Gerard J. (1992). THE MECHANISM OF RESISTANCE OF CARNATION TO WILT DISEASES. Acta Hortic. 307, 29-36
Dianthus caryophyllus L., Fusarium oxysporum f.sp. dianthi, Phialophora cinerescens, dianthramides, lignin degradation, phytoalexins