En 1997, le suivi de la résistance du Mildiou du à Phytophthora infestans aux phénylamides (métalaxyl) réalisé depuis 1981 a donné de nouveaux résultats, ainsi que celui des types de compatibilité sexuelle des souches, entamé depuis 1988. La résistance au métalaxyl mesurée au laboratoire concerne 10% des échantillons issus des régions du nord de la France et 44 % en Bretagne (soit plus que l'année précédente). Mais ces résultats de laboratoire ne sont pas transposables au champ. Pour la détermination des types A1 et A2, une nouvelle technique d'étude a été expérimentée. Par ailleurs, les résultats de 1997 confirment la présence sur tomates de souches A2 à côté des souches A1. Ils montrent la présence de souches A2 sur pommes de terre de plein champ dans le Nord (mais pas en Bretagne). On ne sait pas s'il s'agit d'une extension ou si le grand nombre de souches testées cette année a permis de mettre en évidence un phénomène déjà existant mais ignoré jusqu'ici. The close monitoring, since 1981, of resistance of Phytophthora infestans, late blight, to phenylamide (metaloxyl), and the monitoring of types of sexual compatibility, launched in 1988, produced some inte-resting new results in 1997.
Resistance to metalaxyl, measured under laboratory conditions, was detected in 10 % of samples from Northern France and 44 % of samples from Brittany (i.e. more than in the previous year). These laboratory results do not necessarily reflect the situation in the field however.
A new study technique for determination of A1 or A2 types was put to the test in 1997. Results confirmed the presence of A2 type alongside A1 type on tomato crops. A2 type was also found on potato crops in Northern France, but not in Brittany. For the moment, it is not clear whether these findings provide evidence of a real spread, or whether the testing of a greater number of strains merely brought to light a previously unknown phenomenon.
Key-words : potatoes, LATE BLIGHT RESISTANCE TO METALAXYL
The close monitoring, since 1981, of resistance of Phytophthora infestans, late blight, to phenylamide (metaloxyl), and the monitoring of types of sexual compatibility, launched in 1988, produced some inte-resting new results in 1997.
Resistance to metalaxyl, measured under laboratory conditions, was detected in 10 % of samples from Northern France and 44 % of samples from Brittany (i.e. more than in the previous year). These laboratory results do not necessarily reflect the situation in the field however.
A new study technique for determination of A1 or A2 types was put to the test in 1997. Results confirmed the presence of A2 type alongside A1 type on tomato crops. A2 type was also found on potato crops in Northern France, but not in Brittany. For the moment, it is not clear whether these findings provide evidence of a real spread, or whether the testing of a greater number of strains merely brought to light a previously unknown phenomenon.
