Interactions between mycorrhiza and powdery mildew of cucumber

Interactions between the arbuscular mycorrhizal fungus Glomus intraradices and the powdery mildew fungus Podosphaera xanthii were examined with cucumber as the host plant in pot experiments under greenhouse conditions. Plants were inoculated with mildew two weeks after seedling emergence. Plants were mycorrhizal or not, prior to mildew infection and were harvested two weeks after mildew inoculation. We found no influence of the cucumber — G. intraradices symbiosis on development of cucumber mildew in terms of numbers of colonies per unit area. Similarly, biomass and amount of energy reserves of G. intraradices as examined with signature fatty acids were unaffected by mildew. Both biotrophs caused growth depressions of the host plant. Plant carbon allocation is discussed in relation to biotrophs as sinks.