[Is there any point to eradicate Phragmanthera capitata parasitizing African rubber trees?]. / Faut-il éradiquer Phragmanthera capitata, parasite des hévéas en Afrique?

The effect of Phragmanthera capitata (Sprengel) Balle, an epiphytic Loranthaceae, on latex production of three clones of rubber tree, Hevea brasiliensis (Müll. Arg.), was studied in the industrial plantation of Mitzic, in Gabon. The 22-year-old trees, presenting the largest trunk circumference, were the most parasitized and at the same time the best producers of latex. At first, this would suggest that mistletoe parasitism could have a favourable effect on latex yield. However, an accurate statistical analysis showed that, in fact, parasitism had no significant effect on latex yield. These data, discussed in relation to the biology of flowering parasitic plants, suggest that there is no urgency to eradicate Phragmanthera capitata for the moment.

[Potential role of winter rape weeds in the extension of broomrape in Poitou-Charentes]. / Rôle potentiel des plantes adventices du colza d'hiver dans l'extension de l'orobanche rameuse en Poitou-Charentes.

In the Poitou-Charentes district, among the 82 species of winter rape weeds identified, 22 displayed a strong affinity for this crop (Brassica napus L.). In fields, 50% of these weeds were parasitized by Orobanche ramosa, playing the role of host plants. Greenhouse co-cultures (weed/Orobanche ramosa) showed that weeds non-parasitized in fields could be attacked by broomrape, developing a more or less complete cycle. In vitro co-cultures (weed/Orobanche ramosa) revealed that root exudates of non-parasitized weeds, in fields or in greenhouse co-cultures, could induce Orobanche ramosa seed germination, but not attachment. These weeds could play the role of false hosts.

A diffusible signal from germinating Orobanche ramosa elicits early defense responses in suspension-cultured Arabidopsis thaliana.

In plant/parasitic plant interaction, little is known about the host plant response before the establishment of the parasite within the host. In the present work, we focused on host responses to parasitic plant, O. ramosa in the early stage of infection. We used a co-culture system of A. thaliana suspension cells and O. ramosa germinated-seeds to avoid parasite attachment. We showed that O. ramosa induced H(2)O(2) generation and camalexin synthesis by A. thaliana followed by a drastic increase in cell death. We further demonstrated that a heat sensitive diffusible signal is responsible for this cell death. These data indicate that recognition of O. ramosa occurs before the attachment of the parasite and initiates plant defence responses.