Spatial and temporal spread of Citrus tristeza virus and its aphid vectors in the North western area of Morocco

Abstract

First report of Citrus tristeza virus (CTV,Closterovirus) in Morocco datesback to 1961 in collections of citrus varieties. An exhaustive survey of citrus in the north of the country in 2009 revealed that CTV was spread all over the citrus production area. We attempted to evaluate the relative contribution of different aphid species in the spread of CTV disease in a Citrus reticulata orchard at the Loukkous region during 2 years (2012 and 2013). The overall CTV incidence estimated in the experimental site increased from 17.8% in 2012 to 31.15% in 2013. The most abundant aphid species colonising clementine trees was Aphis spiraecola and A. gossypii. Both aphid species reached their maximum peaks during the spring season. The rate of viruliferous aphids, estimated by real-time RT-PCR of single aphid, revealed that 35.4% of winged A. gossypii and 28.8% of winged A. spiraecola were viruliferous, confirming a high inoculum pressure in the area surrounding the experimental site. The aphid species Toxoptera citricida, which is able to transmit the aggressive isolates of CTV, was not found in the Loukkous region. The study of the spatial distribution of the CTV showed that in general, the disease was randomly distributed in the field. Overall, the results seem to indicate that A. spiraecola may be considered as the major aphid species contributing to CTV spread in our experimental conditions. The prevalence of mild strains in the region and the high level of aphid flight activity could explain the rapid evolution of CTV incidence in the experimental area.

Facultative symbionts associated with aphid populations in citrus orchards in northern Tunisia

“…citrus plants) distributed over a small geographical area and therefore subject to similar climatic conditions. In ad-dition, the two species share many natural enemies (Boukhris-Bouhachem, 2011;Limem Sellami et al, 2013), are frequently tended by ants (Kaneko, 2018;Karami-Jamour et al, 2018) and transmit the same viruses, such as citrus tristeza virus (CTV) (Elhaddad et al, 2016;Boukhris-Bouhachem et al, 2017). In our study, the two aphids differ in terms of symbiont composition, while they occupy very similar ecological niches.…”

“…In citrus orchards where the sampling was carried out, A. gossypii and A. spiraecola populations exploit similar niches (e.g. they feed on the same host-plant species, are attacked by the same natural enemies and are subject to similar climactic conditions) (Boukhris-Bouhachem, 2011; Limem Sellami et al, 2013;Elhaddad et al, 2016;Boukhris-Bouhachem et al, 2017). Thus, determining the presence of these facultative symbionts in A. gossypii and A. spiraecola also offer the possibility of testing the hypothesis that populations of these two aphid species are likely to host similar combinations of symbionts.…”

Fluctuations of aphid populations on grapefruit (Citrus x paradisi Macfad.)

“…Tena & Garcia-Marí (2011) considered that these two species are the most harmful to citrus in the Mediterranean region. Its importance on citrus fruits has been mentioned, among others, in Algeria (Lebbal & Laamari, 2016), in Morocco (Elhaddad et al, 2016), in Syria (Abo Kaf, 2005) and in Turkey . Whereas the weak infestation of A. nerii, M. persicae and M. euphorbiae on grapefruit in the studied orchard may be attributed to the competition from other species, particularly A. spiraecola.…”

Aphis spiraecola and Aphis (Toxoptera) citricidus differently manipulate plant metabolism to gain fitness in terms of population abundance or dispersal

“…Aphis spiraecola is polyphagous, feeding on Pyrus, Prunus, Malus, and Citrus spp. (Mostefaoui et al, 2014), and is a vector of Citrus tristeza virus and Citrus yellow vein clearing virus (Elhaddad et al, 2016;Zhang et al, 2018). Aphis citricidus is oligophagous, mainly feeding on members of the Rutaceae, and is the most efficient vector of Citrus tristeza virus (Brlansky et al, 2011).…”