Apricot chlorotic leaf roll in Roussillon: Specific detection of the pathogen, search for alternative host plants, attempts to determine infection periods and attempts to identify the insect vector

The Roussillon region in the south of France is one of the most heavily ACLR infected apricot growing areas in the world. A pluridisciplinary research program has been started using molecular biology tools to detect and characterize the pathogen associated with the disease, to discover alternative host plants, to determine infection periods and to identify the insect vector in 1994. Preliminary results of this program are presented here. A specific PCR detection method for apricot chlorotic leaf roll (ACLR) phytoplasmas has been developed and validated with a large number of field-collected samples confirming the epidemic situation in the Roussillon region. A search for alternative host plants has been started and ACLR infections have been found in wild seedlings of Prunus species. Bait plant assays have been conducted in two different diseased orchards during two vegetation periods to determine periods of natural transmission of ACLR. In order to identify the vectors, more than 7500 phloem-feeding insects belonging to the Homoptera have been collected in diseased orchards and surrounding areas by D-Vac aspiration. The collected insects have been individually tested by PCR for the presence of phytoplasmas. Furthermore, an exhausting inventory of Auchenorrhyncha present inside and around diseased orchards in the Roussillon region has been established.