|Authors: ||A. Dewitte, L. Leus, J. Van Huylenbroeck, E. Van Bockstaele, M. Höfte|
|Keywords: ||Rosa, haustoria, development, physiological reactions, hydrogen peroxide, phytoalexins|
Fungal development of powdery mildew Podosphaera pannosa (Wallr.: Fr.) de Bary (syn. Sphaerotheca pannosa) on rose leaves depends on different resistance mechanisms present in attacked rose genotypes.
These mechanisms influence both mycelium formation and sporulation.
Two rose species (R. wichuraiana and R. laevigata) and 2 cultivars (‘Excelsa’ and ‘Gomery’) were selected to examine microscopically the interaction between fungal development and plant resistance mechanisms.
Differences in fungal development and resistance mechanisms were detected in all four rose genotypes.
Mycelium formation and sporulation were dependent on the proportion between normal haustoria, abnormal haustoria, papilla formation, physiological responses and intracellular induction of antifungal phenolic compounds (phytoalexins). Two different forms of physiological responses could be observed, with and without cell collapse.
Both were induced by H2O2 production of invaded cells, and were very important in limiting the formation of conidiophores.
The most important resistance mechanism was, however, the ability to inhibit normal haustorium formation, probably as a constitutive resistance mechanism.
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