| Autor: |
Sewify, G. H., Abul-Ata, A. E., Ammar, E. D., Elnagar, S. |
| Předmět: |
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| Zdroj: |
Journal of Phytopathology; Jul1989, Vol. 126 Issue 3, p257-271, 15p |
| Abstrakt: |
A comparative study between virulent and avirulent strains of Geotrichum candidum was undertaken in order to identify mechanisms for virulence of this pathogen on lemons. The initial development of virulent and avirulent strains during the 48 hours following inoculation, as measured by colony-forming units, was similar. However, only virulent strains produced actively developing soft rot lesions whereas avirulent strains produced arrested dry lesions. Microscopical examination indicated that disorganization and maceration of the exocarp tissue preceded the penetration of fungal hyphae at all inoculation sites. Degradation of pectic substances progressed with maceration. Ultrastructural examination revealed extoplasmic inclusions originated from projections of plastid membranes. Various tests for possible involvement of active defense mechanisms gave negative results. Production of endopolygalacturonase (PG) was significantly higher in virulent than in avirulent strains. When lemon fruits were treated at 80°C for 2 minutes, active lesions were also developed by avirulent strains. The PG of the virulent strain was more effective than that of the avirulent in causing maceration of the lemon albedo tissue and the heat treatment increased the rate of maceration with both enzyme preparations. It was suggested that the initial amount of PG produced in vivo and the sensitivity of the pectin in situ to this enzyme, are the main factors that govern virulence of G. candidum on citrus fruit. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
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