NAME OF THE ORGANISM: Sobemovirus BSSV (blueberry shoestring virus) (BSSV00)

Blueberry shoestring virus (BSSV) infects all types of blueberry (e.g. V. corymbosum, V. angustifolium, V. darrowii) but infection rates appear to be higher in certain northern highbush cultivars (Acquaah et al., 1995; Hancock et al. 1986; Martin et al., 2012).
It is vectored by the Eastern blueberry aphid, Illinoia pepperi, in a persistent circulatory manner. The aphid is monoecious and overwinters as eggs on blueberry bushes (Ramsdell et al., 2017). The aphid is not yet present in the EU (De Jong et al., 2015; PESI, 2024). Since transmitted in a non-persistent manner, if introduced in the EPPO region, many local aphid species may transmit the virus.
The initial mode of spread is through infected, vegetatively propagated planting stock. After the stock is planted, transmission from infected bushes is mediated by the Eastern blueberry aphid (Ramsdell, 1987).
Epidemiological studies have shown that field transmission of BSSV by aphids begins when the first aphid population emerges in the spring and ends just before leaf drop in the autumn. The disease tends to spread down the row from bush to bush. In most plantings, bushes touch each other within the row (0.9—1.2 m apart) but not between rows (3 m apart). Aphids move from infected bushes to adjacent healthy ones as they feed (Ramsdell et al., 2017). Aphids can be transported longer distances by over-the-row mechanical harvesters. Such movement was tracked in a study in which a bush was exposed to rubidium and aphids were captured at regular intervals down the row, immediately following the harvester, and tested. Aphids with rubidium were detected up to 67 bushes from the point source (Isaacs et al., 2008; Ramsdell et al., 2017).

Yes

BSSV has a latency period of four years between infection and expression of virus symptoms in the field. Several symptoms are associated with BSSV, the most prominent and reliable symptom is elongated reddish streaks about 3-20 mm long on current-year and 1-year-old stems, especially on the side directly exposed to the sun, the discoloration normally disappears as the season progresses. Flower ‘breaking’ can occur when longitudinal pink streaks appear on the petals. Infected leaves can be elongated or straplike, hence the name shoestring (Lesney et al., 1978; Ramsdell et al., 2017). Infected bushes bear less fruit than healthy bushes. In addition, the fruit does not ripen normally and remains reddish purple instead of turning blue (Fig. 147). On actively growing bushes that have been infected for many years, the terminal third of the stems may be crooked. Infected bushes slowly decline over time and may be stunted (Ransdell et al., 2017). Symptoms vary in intensity depending on the environment and there have been reports were bushes can be asymptomatic for several seasons (Martin et al., 2012). Nine highbush cultivars were susceptible to the virus, whereas the cultivars ‘Blueray’ and ‘Atlantic’ showed field resistance to the disease (Acquaah et al., 1995; Saad et al., 2021).
BSSV is one of the most common viruses in the USA, affecting cultivated highbush blueberries (V. corymbosum). In 1981, an estimated 145,000 bushes on 4,000 ha were infected in Michigan, which resulted in bush and crop losses of more than $3 million, making it one of the most economically significant diseases of highbush blueberries. By 2008, the disease was still widespread in this state, particularly in old ‘Jersey’ fields. Yield reductions of up to 25% have been documented on infected hushes. In addition, a high percent of the fruit from infected bushes is reddish purple at maturity rather than the desired blue color, which lowers the fruit grade (Morimoto et al., 1995; Ramsdell et al., 2017; Saad et al., 2021).

Medium to Major

No

Since the virus is rare in the EU, it is difficult to state what the consequences would be. On the infected plants in Poland no symptoms were recorded.
It could spread to native Vaccinium spp.

Virus indexed material.
(since it was only reported once in the EU, plant material will be the main pathway into the EU)