Pythium F induce a minor but ubiquitous disease in tomato soilless cultures [Lycopersicon esculentum]

An immunoenzymatic staining procedure was used to assess the level of Pythium spp. colonization on the root surface of tomato plants growing in commercial hydroponic cultures. Sampling was performed with roots free of distinct necrosis or other symptoms. It was shown that 40% of the root segments on average were colonized by Pythium spp. Hyphae formed loose or dense mycelium networks on the root epidermis. The frequent occurence of the minor pathogen, Pythium F in soiless cultures was pointed out because it represented 82% of all the Pythium spp. isolates. It was observed by ultrastructural and cytochemical studies that, under such cultural conditions, Pythium F penetrated the cortical root areas and induced stricking alterations within the walls and the cytoplasmic contents of the invaded host cells. These host cell damages led to tomato yield losses although the roots looked macroscopically healthy. The ubiquitous occurrence of Pythium F and its pathogenic abilities can be of relevance, since such a minor pathogen can have a key impact in soilless cultures