Ecole Nationale Supérieure Agronomique de Montpellier ... - CIAM

Survival of European Stone Fruit Yellows Phytoplasma Outside Fruit
Crop Production Areas : a Case Study in Southeastern France
M. Yvon, G. Labonne and G. Thébaud
INRA, UMR BGPI, 2 place Viala, 34060 Montpellier, France
Keywords: ESFY, epidemiology, Cacopsylla pruni, Prunus spinosa, overwintering
ABSTRACT
The aim of the study was to assess the role of blackthorn (Prunus spinosa) in the
epidemiological cycle of ESFY and to search if an epidemiological cycle may exist
independantly of stone fruit orchards. A typical blackthorn hedge was chosen in an area free
of fruit orchards. A sample of 58 plants was tested for ESFY and 2 plants were detected
infected. Samples of the population of Cacopsylla pruni (vector of ESFY) found on the hedge
were taken at regular intervals from February to June and were tested for the presence of
ESFY. The proportion of reimmigrants (C. pruni arriving after overwintering to reproduce on
Prunus) infected remained stable during their 3 months of presence. Infected individuals were
also detected in the new generation. On overwintering sites (conifers in a montainous area
several km apart on the North-West), 2 C. pruni were detected infected by ESFY. From these
results it is suggested that an epidemiological cycle of ESFY can be achieved in wild
reservoirs of the phytoplasma even in the absence of Prunus orchards. On the other hand, the
blackthorn hedge do not seem to be a very efficient reservoir of ESFY.
INTRODUCTION
European stone fruit yellows phytoplasma (ESFY-P) damages mainly apricot (Prunus
armeniaca) and Japanese plum (P. salicina) crops, but can also be hosted by other Prunus
species, either cultivated (P. amygdalus, P. domestica), used as rootstock (P. cerasifera, P.
marianna) or wild (P. spinosa).
In the south of France, the desease on apricot trees (apricot chlorotic leaf roll) has been
noticed many years ago (Chabrolin, 1924) and is considered to be the first cause of decline of
this crop in some areas (Lemaire et al., 1998). During the last years, large apricot and
Japanese plum orchards were planted over previously uncultivated areas. In some cases a high
prevalence of ESFY has been observed in the new orchards. Thus the question of the arrival
of the first inoculum in these new areas arised.
The first inoculum can originate from planting material, from infectious vectors comming
from abroad or from wild reservoirs of phytoplasma which act as sources for the vectors.
Each of these 3 origins is possible : althought a strict certification scheme is used for Prunus
trees, infected plants are sometimes noticed in nurseries ; wild spontaneous or subspontaneous
Prunus reservoirs of ESFY phytoplasma were demonstrated (Carraro et al., 2002, Jarausch et
al , 2001) ; the vector has been identified as the psyllid Cacopsylla pruni (Carraro et al.,
1998). It is suspected to migrate between Prunus and conifers (Ossiannilsson, 1992 ; Lauterer,
1999) and to be infectious at the time it arrives on its Prunus host-plants (reimmigrants) to
reproduce (Carraro et al., 2001).
In this work, we search if an epidemiological cycle may exist independantly of stone fruit
orchards and can constitute a threat for new plantations. We investigated the infection status
of the psyllid population from a typical P. spinosa hedge far from any area of infected Prunus
orchards and then the status of infection of 2 populations at their overwintering sites.
MATERIAL AND METHODS
Location of the Blackthorn Plants
The study was carried out in the Languedoc plain, in an area of « garrigue» vegetation
and vineyards. The first stone fruit orchards were 25 to 30 km apart and they are grown under
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