ISHS Acta Horticulturae 381: International Symposium on Natural Phenols in Plant Resistance
A CRUCIAL ROLE OF PHENOLIC METABOLISM IN RESISTANCE OF CARNATIONS TO WILT DISEASES |
| Author: | Gerard J. Niemann |
| Keywords: | Dianthus caryophyllus L., Fusarium oxysporum f.sp. dianthi, cell wall, dianthalexins, dianthramides, gum, phytoalexins |
| DOI: | 10.17660/ActaHortic.1994.381.76 |
| Abstract:
The mechanisms of resistance of carnations to vascular pathogens like Fusarium oxysporum f.sp. dianthi race 2 and Phialophora cinerescens seem to a large extent based on the metabolism of phenolic constituents of the host. The most important resistance component is the ability to confine the pathogen in the vascular region of the infection site. Localisation of the invading organism is caused by the accumulation of a large array of phenolic phytoalexins, modification of walls of surrounding cells and occlusion of colonised vessels by phenolic-incrusted gums. Xylem parenchyma cells play a key role in the necessary metabolic activities involved. The dianthramide phytoalexins probably retard the growth of the invading pathogen, which is subsequently encaged within barrier tissues made impermeable by infusion or apposition of phenolics, which polymerize into lignin-like constituents. Both degradation (of syringyl-) and synthesis of (guaiacyl-) lignin seem to occur at the same time. In addition, the fungal infection is accompanied by an increase in phenolic acids, probably esterified to cell wall polysaccharides, and by suberization of surrounding tissue. For F.oxysporum f.sp. dianthi race 2 the level of accumulation of the phytoalexins was found related to the level of resistance. Phytoalexin accumulation may be part of a more general xylem parenchyma activity and, thus, also be related to other responses such as gum formation. Such combined responses form a better explanation for the correlation found between resistance and phytoalexin accumulation than the fungitoxicity of those compounds in itself. Localisation of the pathogen is a general non-specific reaction. Resistant and susceptible responses may be found in the same plant. Early host reactions in a susceptible response may qualitatively be similar to those in a resistant one, but at a lower level and/or rate. A higher level of resistance is, therefore, determined by quantitative rather than by qualitative differences. | |
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