Transmission, Field Spread, Cultivar Response, and Impact on Yield in Highbush Blueberry Infected withBlueberry scorch virus

Abstract

Scorch disease caused by Blueberry scorch virus (BlSV) spreads rapidly and radially from foci of infection. Healthy potted blueberry plants became infected when placed next to diseased field bushes from early May through mid-August. The aphid Fimbriaphis fimbriata, collected from infected field bushes, transmitted BlSV to healthy blueberry plants in controlled tests and was regarded as the most important means by which bushes in commercial fields became infected. The rate of spread in the symp-tomless cv. Stanley appears to be the same as the rate of spread in the cv. Pemberton, which exhibits blight and dieback. Most field bushes showed symptoms during the year following inoculation, but a few did not show symptoms until the second or third year. Many (30 out of 59) cultivars and selections infected with BlSV exhibited severe blighting of flowers and young leaves and dieback of twigs. Three cultivars showed only chlorosis of leaf margins. The virus was also detected in numerous cultivars (26 out of 59) that exhibited no symptoms, and they were considered tolerant of BlSV. The virus had no effect on germination of pollen from several cultivars. BlSV reduced yield in 'Pemberton', with the loss being related to the number of years bushes displayed symptoms. Yield was reduced by more than 85% in the third year of symptom expression. The virus did not significantly reduce the yield of six tolerant cultivars that were infected with the virus but displayed no symptoms.

Intraspecific Variation in Aphid Resistance and Constitutive Phenolics Exhibited by the Wild Blueberry Vaccinium darrowi

“…Managing the incidence of BlScV and BBSSV mainly occurs through insecticide applications to reduce aphid population densities, by rouging symptomatic plants and by planting clean root stock (Raworth, 2004). However, as BlScV has a latent period of 1-3 years before symptoms appear (Bristow et al, 2000), an infected plant could continue to serve as a source of inoculum. Therefore, simply rouging symptomatic plants does not represent an effective management strategy.…”

Seasonal variation in Blueberry scorch virus concentration in highbush blueberry and implications for disease monitoring and management

“…Blueberry scorch virus (BlScV), a Carlavirus, has been found in highbush blueberry, Vaccinium corymbosum L., in North America (Bristow et al 2000;Cavileer et al 1994;Martin and Bristow 1988) and Europe (Ciuffo et al 2005). The virus can cause blighting of stems, leaves and flowers, and significant yield reductions in susceptible cultivars (Bristow et al 2000).…”

“…The virus can cause blighting of stems, leaves and flowers, and significant yield reductions in susceptible cultivars (Bristow et al 2000). Symptom expression also varies with virus strain (Wegener et al 2006).…”

“…Symptom expression also varies with virus strain (Wegener et al 2006). BlScV is aphid-borne and has a non-persistent mode of transmission (Bristow et al 2000). Control of the aphid vectors and early detection and removal of infected plants is recommended to manage BlScV (British Columbia Ministry of Agriculture and Lands 2007).…”

“…Ericaphis fimbriata (Richards) (=Fimbriaphis fimbriata) (Remaudière and Remaudière 1997) [Hemiptera: Aphididae], the dominant colonizing aphid on highbush blueberry in southwestern British Columbia, Canada (Raworth 2004), has been regarded as the most important vector of BlScV in studies conducted in Washington, USA (Bristow et al 2000), although non-colonizing species may also be involved . Ericaphis fimbriata has a consistent population pattern among years and locations; populations increase exponentially throughout the spring to reach a peak of 0.8 to 16.1 aphids per leaf terminal (300 to 9000 aphids per bush) in late June or early July, and then decline rapidly due to reduced plant quality for the aphids and natural enemies (Raworth 2004;Raworth and Schade 2006).…”