Efficient Transmission of ‘CandidatusPhytoplasma prunorum’ Is Delayed by Eight Months Due to a Long Latency in Its Host-Alternating Vector

Abstract

Understanding at which spatiotemporal scale a disease causes significant secondary spread has both theoretical and practical implications. We investigated this issue in the case of European stone fruit yellows (ESFY), a quarantine vector-borne phytoplasma disease of Prunus trees. Our work was focused on the processes underlying disease spread: the interplay between the life cycles of the pathogen ('Candidatus Phytoplasma prunorum') and of the vector (Cacopsylla pruni). We demonstrated experimentally that C. pruni has only one generation per year and we showed that, at least in southeastern France, C. pruni migrates between conifers in mountainous regions (where it overwinters) and Prunus spp. at lower altitude (where it breeds). In acquisition-inoculation experiments performed with C. pruni over its period of presence on Prunus spp., both immature and mature C. pruni were hardly infectious (0.6%) despite effective phytoplasma acquisition and multiplication. We demonstrated that most immature vectors born on infected plants reach their maximum phytoplasma load (10(7) genomes per insect) only after migrating to conifers and that, after a life-long retention of the phytoplasma, their transmission efficiency was very high (60%) at the end of winter (when they migrate back to their Prunus host). Thus, most transmissions occur only after an effective latency of 8 months, following vector migrations and overwintering on conifers in mountainous regions. From this transmission cycle, we can infer that local secondary spread of ESFY in apricot orchards is marginal, and recommend that disease management strategies take more into account the processes occurring at a regional scale, including the role of wild Prunus spp. in ESFY epidemics.

Opportunities for Napier Grass (Pennisetum purpureum) Improvement Using Molecular Genetics

“…The development and deployment of management practices to guard against any disease in a particular geographical area is guided by quantitative information on the existing levels of disease risk, definitive identification of the pathogen and a clear understanding of the factors that correlate strongly with disease/pathogen risk within a defined host population [145]. Although most of the viruses infecting Napier grass do not appear to cause any severe disease symptoms and productivity losses, there have been some reports on the effects of the potyvirus (Is 16840) identified in Ethiopia [146] and an insect-borne virus identified in Uganda [147] which need to be investigated more thoroughly, especially in terms of potential productivity loss, as they were reported to cause stunting in infected plants.…”

Incidence and distribution of ‘Candidatus Phytoplasma prunorum’ and its vector Cacopsylla pruni in Spain: an approach to the epidemiology of the disease and the role of wild Prunus

“…In June, young adults (emigrants) move to refuge trees to overwinter. Cacopsylla pruni acquires the phytoplasma within 2–4 days and is infective for the rest of its life, after a latency period of approximately 3 weeks (Carraro et al ., ; Labonne & Lichou, ; Thebaud et al ., ).…”

Psyllid Vectors of Plant Pathogens

“…Cacopyslla picta and C. melanoneura are confi rmed vectors of 'Candidatus Phytoplasma mali' in different geographical regions (Jarausch et al 2003, Tedeschi et al 2002 while C. pruni is the only identifi ed vector of 'Candidatus Phytoplasma prunorum' (Carraro et al 1998, Jarausch et al 2001, Thébaud et al 2009.…”

“…In order to obtain healthy psyllid populations for laboratory use, standardized plant material from tissue culture or from seedlings was used, e.g., from Malus cultivars Golden Delicious or Royal Gala for C. picta and C. melanoneura cultures (Jarausch et al 2004, Mayer et al 2008 or from Prunus cultivars P. marianna, P. salicina or P. cerasifera for C. pruni (Carraro et al 2004, Thébaud et al 2009), respectively. For subsequent acquisition and transmission trials, colonies were directly installed on infected Malus or Prunus cultivars under similar culture conditions.…”