Colonisation patterns of root tissues byPhytophthora nicotianae var.parasitica related to reduced disease in mycorrhizal tomato

Abstract

Tomato plants pre-colonised by the arbuscular mycorrhizal fungus Glomus mosseae showed decreased root damage by the pathogen Phytophthora nicotianae var. parasitica. In analyses of the cellular bases of their bioproteetive effect, a prerequisite for cytological investigations of tissue interactions between G. mosseae and P. nicotianae v. parasitica was to discriminate between the hyphae of the two fungi within root tissues. We report the use of antibodies as useful tools, in the absence of an appropriate stain for distinguishing hyphae of P. nicotianae v. parasitica from those of G. mosseae inside roots, and present observations on the colonisation patterns by the pathogenic fungus alone or during interactions in mycorrhizal roots. Infection intensity of the pathogen, estimated using an immunoenzyme labelling technique on whole root fragments, was lower in mycorrhizal roots. Immunogold labelling of P. nicotianae v. parasitica on cross-sections of infected tomato roots showed that inter or intracellular hyphae developed mainly in the cortex, and their presence induced necrosis of host cells, the wall and contents of which showed a strong autofluorescence in reaction to the pathogen. In dual fungal infections of tomato root systems, hyphae of the symbiont and the pathogen were in most cases in different root regions, but they could also be observed in the same root tissues. The number of P. nicotianae v. parasitica hyphae growing in the root cortex was greatly reduced in mycorrhizal root systems, and in mycorrhizal tissues infected by the pathogen, arbuscule-containing cells surrounded by intercellular P. nicotianae v. parasitica hyphae did not necrose and only a weak autofluorescence was associated with the host cells. Results are discussed in relation to possible processes involved in the phenomenon of bioprotection in arbuscular mycorrhizal plants.

Induced Resistance in Mycorrhizal Tomato is correlated to Concentration of Jasmonic Acid

“…There have been several reports on increased disease tolerance of plants to soil-borne pathogens on pre-inoculation with mycorrhizal fungi [4,6,13] . This study reports effectiveness of mycorrhizal fungi to control vascular wilt disease, after the establishment of the pathogen.…”

Les mycorhizes : un outil de protection des plantes mais non une panacée

“…La dégradation continuelle des arbuscules intraracinaires entraîne une augmentation d'activité chitinolytique dans les couches profondes des cellules corticales ce qui peut directement affecter l'intégrité cellulaire des parasites (Benhamou et al 1994;Dehne et al 1978). La présence d'isoformes de chitinase nouvellement synthétisées et différentes de celles synthétisées par les parasites ont été détectées dans des racines de tabac et de tomates mycorhizées et parasitées (Cordier et al 1996;Dumas-Gaudot et al 1992), un mécanisme de défense spécifique aux parasites induit par les parois cellulaires de l'hôte (Pozo et al 1998). En résumé, une colonisation mycorhizienne bien établie entraîne des changements considérables des mécanismes de défense de la plante pour contrer l'action de certains parasites (Guenoune et al 2001;Wyss et al 1991).…”

Flow cytometry as a tool to investigate nuclear senescence in symbiotic and pathogenic systems

“…Les (Lindermann, 1992;Hooker et al, 1994;Liu, 1995). In tomato plants, for example, arbuscular mycorrhizae significantly reduce root necrosis, decrease root infection by pathogens and reduce inhibition of plant growth (Caron et al, 1985(Caron et al, , 1986Cordier et al, 1996;Trotta et al, 1996 (Cowden and Curtis, 1981;Mazzini et al, 1983;Darzynkiewicz et al, 1984;Evenson et al, 1986;Sgorbati et al, 1986Sgorbati et al, , 1993Bonaly et al, 1987;Berta et al, 1990Berta et al, , 1996. This paper describes the use of these techniques in the investigation of nuclear senescence in roots of non-AM and AM tomato plants, infected …”