NAME OF THE ORGANISM: Ilarvirus PNRSV (prunus necrotic ringspot virus) (PNRSV0)

Evaluation continues

Listed as 'Prunus necrotic ringspot ilarvirus (PNRSV)' in EPPO Standard PM 4-30 Certification scheme for almond, apricot, peach and plum; with testing recommended. However, in the preliminary excel file submitted by the European Commission, one country commented that the pest 'seems to be quite frequent in nursery and it has a low nuisance level on fruit plants'. As this could affect the RNQP status, a full assessment is performed. In the responses to the questionnaire, PL supported deregulation based on the pathway criteria.
Remark: The assessment performed covers the given host species as well as interspecific hybrids with other Prunus species.

Candidate

Prunus necrotic ringspot virus occurs worldwide and infects many cultivated Prunus species (Hammond, 2011), such as almond - Prunus dulcis (e.g. Mekuria et al., 2003), apricot - Prunus armenica , sweet and sour cherry, P. avium and P. cerasus (e.g. Oliver et al., 2009, Rouag et al., 2009), plum - P. domestica (e.g. Rouag et al., 2009; Jakab-Ilyefalvi et al., 2011), Japanese plum - P. salicina (e.g. Wood & Fry, 1984), and peach (e.g. Topchiiska, 1982; Uyemoto et al., 1992). PNRSV was also found in many wild Prunus spp. like black cherry (Prunus serotina) and cherry laurel (P. caroliniana) and in rose, where it is one of the causes of rose mosaic disease (Horst & Cloyd, 2007). The natural host range also includes herbaceous hosts like hops (symptomless) and cucumber, where chlorotic local lesions, systemic necrosis and severe stunting may occur (Fulton, 1995).
PNRSV is a variable virus consisting of isolates linked to various symptoms in different host species and cultivars (Howell & Mink, 1988; Moury et al., 2001; Oliver et al., 2009; Kamenova & Borisova, 2021; Chirkov et al., 2023).
Infected propagation material is an important pathway (Scott et al., 1989)
Once established PNRSV is easily spread by infected pollen - by wind, bees or thrips - and is also seed transmitted, which can lead to PNRSV-infected seedling rootstocks (e.g. Greber et al., 1991; Kryczynski et al., 1992; Amari et al., 2007; Tayal et al., 2024). Preventing mother stocks to flower prevents infection by pollen.
The Fruit SEWG concluded that plants for planting was a significant pathway.

Yes

General: PNRSV can cause diseases in nurseries which reduced bud take tree growth, tree survival, and uniformity in nursery operations (Saunier, 1972; Topchiiska, 1993 – cited from Hammond, 2011), and death of buds and roots, reduced growth of fruit (10-30%) and fruit yield (20-60%), delay in fruit maturity (Saunier, 1972), diminished fruit quality, and increased susceptibility to winter injury in orchard trees (Nemeth, 1986; Scott et al, 1989; Uyemoto & Scott, 1992). Successful commercial budding can be lower in combinations where scion and rootstock carry the virus (Lang & Howell, 2001). Many of these symptoms however, were described at a time when it was more difficult to study the whole virome of plant species. New techniques revealed presence of many previously unknown viruses of which their impact on or addition to symptom development is unknown or under investigation (e.g. James et al., 2018; Koloniuk et al., 2018; Hou et al., 2020; Fontdevila Pareta et al., 2023; Khalili et al., 2023).
Prunus persica & Prunus armeniaca
Single virus infection by PNRSV significantly affected tree growth and fruit yield (Uyemoto et al, 1992). When peach cultivars were bud-inoculated with PNRSV, the trees developed foliar chlorotic rings and necrosis during the virus year after inoculation. Twig dieback, bark necrosis, root sprouts and trunk cankers developed during subsequent years. Symptoms on inoculated trees resembled those of the slow-decline disease prevalent in central Georgia orchards, particularly the extensive bark necrosis and longitudinal trunk cankers (Wells et al., 1986).
PNRSV affected apricot and pollen germination (by ca. 58%) and delayed germination (Amari et al., 2007). Pollen of peach can also be affected by PNRSV: infection resulted in distorted shape, reduced viability, and germination of pollen grains, but the effect was cultivar dependent (Tayal et al., 2024).
PNRSV has been observed to cause extensive economic losses to peach (Prunus persicae) and apricot (P. armaniaca) trees in Egypt. Symptoms are mostly expressed as necrotic ringspots on leaves, bud failure and poor quantity and quality of fruits (Abdel-Salam et al., 2007).
In peach, PNRSV, together with prune dwarf virus (PDV, another pollen dispersed ilarvirus), causes synergistic effects on growth reduction and yield losses. The resulting disease, peach stunt (PSD) is a frequently reported disease in the Mediterranean area (Myrta et al. 2003). Typical symptoms of PSD include stunting, shortening of internodes, reduction in fruit yield and vegetative growth, defoliation of leaves, rosetting, leaf chlorosis, gummosis, bark splitting, delay in bud break, as well as an increase in water sprouts production. Mixed infection could be more harmful than individual infections as PSD was associated with an 80% mortality in stone fruits in Morocco (Srhiri et al.1998; for review see Tayal et al. 2024). Uyemoto et al. (1992) reported that a double infection with PNRSV and PDV leading to peach stunt disease reduced fruit production, trunk diameter and tree height by ca. 30, 23 and 12% respectively over 3 years. In another publication, peach trees infected with PDV and PNRV were reported to display bark splitting and increased watersprout (sucker) production. Fruit yields were reduced by up to 60% in trees infected with both PNRSV and PDV (Scott et al., 2001).

Medium

No

Candidate

PNRSV infection can cause symptoms in various Prunus spp. PNRSV symptoms can vary depending on the time passed since the initial infection, species and cultivar, additional virus infection etc. Symptoms can vary between lethal infections (e.g. Lang et al., 1988) to symptomless (e.g. Pérez Sánchez et al., 2017). Due to pollen transmissibility, PNRV infected trees pose a serious risk for trees at the same production site. This became e.g. apparent in Austria in a propagation stock intended for the production of certified stone fruit material in the mid-1990s. The explosive spread of PNRV in sweet and sour cherry via pollen from single trees led to the uprooting of the plantation after a few years, despite regular ELISA testing and clearance of positive trees (Riedle-Bauer, unpublished).

Candidate

Inclusion in a certification scheme.
Propagation material plays relevant role for dissemination.
Serological and molecular detection methods available.

Candidate

Propagation material is a relevant source of infection, the pathogen is widespread, economic damage are reported in many cases.