The evolution of Phytophthora infestans in France (Mating type, Metalaxyl resistance)

Abstract

Since 1993, more than 1400 samples have been tested to determine the mating type and the mefenoxam resistance. Since 2004, an evolution of the population is observed. I Mating type in North of France Before 2003 only 14 samples (by 783) have A2 strains in 1997 (11 in garden, 3 in fields). In 2003: 7 samples (4 on dumps, 3 in fields) have A2 strains: 6 % of the monitoring In 2004: 30 % of the sample are A2 (20 % of the fields visited) In 2005: 41 % of the sample are A2 (39 % of the fields visited) In 2006: 74 % of the sample are A2 (79 % of the fields visited) These A2 strains are observed in 81 % of the fields in Nord Pas-de-Calais, 89 % in Picardie, 96 % in Champagne Ardenne, 35 % in Normandy. Mating type in others regions The results are different: - Brittany: before 2005: only one or two A2 2005: 4 % of the sample are A2 2006: 43 samples, 9 % of A2, 10 % of fields with A2 - Aquataine: before 2005: the number of sample is very low 2005: 6 % of A2 2006: 8 samples, 25 % A2, 25 % offields - Alsace: 2005: 68 % A2 2006: 58 % A2 Conclusion: The number of A2 increases, particularly in North of France, the evolution is different according the regions. II Metalaxyl resistance North of France: 2004: 28 % resistants (on dumps 13 %, 37 % fields) 2005: 34 % resistants (on dumps 34 %, 65 % fields) 2007: only 7 samples on dumps (the 7 of June): 100 % resistants Others regions - Brittany: 53 % samples are resistant, 61 % fields - Alsace: 33 % samples are resistant, 33 % fields - Aquataine: 50 % samples are resistant, 93 % fields The metalaxyl resistance seems to increase particularly on dumps in North of France. Conclusion: the population is changing. What are the consequences on the epidemy?