An Immunoenzymatic Staining Procedure for Filamentous Non-Inflated Sporangia Pythium in Soilless Cultures

Pythium spp. are minor pathogens in soil which are also responsible for severe root and stem rot on mature plants, especially in soilless cultures where the fungus can spread easily. Recent epidemiological studies conducted in Brittany (France) revealed the high frequency and the precocity of the colonization of tomato root systems by Pythium spp., even on symptomless roots. The frequent occurence of filamentous non-inflated sporangia Pythium isolates, according to the Plaats-Niterink key (1981), was noticed in selected greenhouses. Little is known about these Pythium isolates which have been shown moderately pathogenic in soil. A better understanding of their pathogenicity and their incidence in such cultures would prove useful in producing crops with limited and controlled treatments. Therefore, polyclonal antibodies were prepared against cell wall fraction of a filamentous non-inflated sporangia Pythium isolate, associated with root rot of tomato in soilless cultures. In ELISA tests, the antisera showed a high degree of sensitivity and specificity against their own antigens and those from closely related isolates (such as Pythium aquatile, Pythium coloratum. and other undeterminated isolates with filamentous sporangia). They reacted weakly with mycelial preparations of several fungi commonly found on tomato roots, such as Fusarium spp. or Trichoderma sp. An immunocytochemical staining test was developped in order to study the colonization of filamentous non-inflated isolates of Pythium in the presence of other fungi. The low cross reactivity of these antibodies with most fungi of tomato root flora allows the detection of Pythium in infected roots. Immunocytochemical staining methods, based on specific antibodies produced against Pythium spp., could provide a simple and efficient mean in further histological investigations.