Ecole Nationale Supérieure Agronomique de Montpellier ... - CIAM

infected and infectious in natural populations (Carraro et al., 2004). During the last six years,
the transmission properties of ‘Ca. P. prunorum’ by C. pruni have been intensively studied,
mainly by Carraro et al. (1998, 2001, 2002, 2004). They measured the proportions of infected
and infectious insects in orchards under their conditions; they demonstrated that the
phytoplasma was persistently transmitted; they characterized the minimum acquisition (4
days) and transmission (2 days) periods; they showed that the latency period lasted at least 2
weeks. However, two important points for the epidemiology of the disease remain unclear:
the persistence of the phytoplasma in its vector during the overwintering period and the
possibility of successful transmission by reimmigrants if they acquire the phytoplasma after
their return on an infected plant. These two points determine if transmission from infected
plants to healthy plants occurs within a year or between years, which is of major concern to
define the basic scale of ESFY epidemics and to improve its control since C. pruni migrates
between years.
The aim of this work was to obtain a clear demonstration of the cycle of the insect, to get
information about what happens to the phytoplasma in the vector during the overwintering
period, to assess the possibility of the reimmigrants to acquire and transmit the phytoplasma
during their reproductive period on Prunus, and to connect the biology of the vector to the
transmission processes to improve the knowledge on the epidemiology of ESFY. The
overwintering of C. pruni was investigated during the last years by searching for the insect,
mainly on conifers, in different places at a regional scale and by setting samples of C. pruni
on conifers. A real-time PCR method was designed and used to measure precisely the
evolution of the phytoplasma titer in different stages of the insect.
MATERIAL AND METHODS
Collecting of C. pruni
Reimmigrant C. pruni were collected on blackthorn (Prunus spinosa) hedges during the
months of February to May. The hedges are located in a plain at the north of Montpellier
(Languedoc-Roussillon, France) with “garrigue” and vineyard landscapes. The first stone fruit
orchards are 25 to 30 km away, and only a few Prunus trees are planted in private gardens in
the vicinity of the sites.
Overwintering C. pruni were searched on conifers (Abies, Picea, and Pinus) in the whole
Languedoc area. Samples were mainly collected either on the first line of a high plateau
25 km on the west at an altitude of 700 m (Séranne: site 1), or in the mountains 50 km on the
north-west at an altitude of 1300 m (Aigoual: site 2).
Samples of C. pruni were collected with a beating tray. The reimmigrants were collected
each week on a defined blackthorn hedge with a standardized protocol (20 P. spinosa
sampled). During the same period, overwintering C. pruni were searched on Abies sp. trees in
the site 1 (sampling of 20 min each time).
Life cycle of C. pruni
To complete the life cycle of C. pruni, adults of the new generation were obtained on
Prunus marianna ‘GF 8-1’ in climatic chambers and deposited during July and August on
conifers at site 1 on Abies sp., at site 2 on Picea abies and near the laboratory (site 3) on Pinus
halepensis. They were maintained on the shoots inside sleeve cages made of fine-meshed
tissue closed at both extremities until they were collected in February of the following year.
To test the hypothesis that some C. pruni could overwinter on P. spinosa plants,
experiments were made on a natural bush of P. spinosa where the psyllid was regularly
collected. A part of the bush was enclosed under two cages in December after the departure of
the new generation but before the arrival of the reimmigrants. Each cage enclosed a surface of
1.8 × 1.8 m. Two sticky blue traps (which had proven to be attractive for C. pruni) were set
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