The occurrence of Apple stem grooving virus and Apple stem pitting virus in pome fruit producing regions of South Africa

Abstract: Apple stem grooving virus (ASGV) and Apple stem pitting virus (ASPV) are known to infect pome fruit in all pome fruit producing regions of the world. As infection with these viruses causes yield reduction, has a negative effect on fruit quality and reduces orchard longevity, they are of significant economic importance. The South African Deciduous Fruit Plant Certification Scheme regulation states that no trees infected with these viruses are permitted for certified plantings. A survey in which ASGV and ASPV was detected was performed in South African pome fruit regions. A total of 9063 samples were tested for the presence of ASGV with DAS-ELISA over three testing seasons from September 2011 to December 2013. ASGV infection rate in 2011 and 2012 was 3.3% and 0.8%, respectively, with a significant increase to 19.4% in 2013. Seventy seven of these ASGV infected samples as well as randomly chosen additional samples were tested for ASPV with RT-PCR during two active testing seasons between September 2011 and December 2013. Samples from pome fruit trees that showed visual symptoms associated with ASPV, including apple stem pitting, apple epinasty and -decline, pear red mottle, pear stony pit, quince sooty ring spot and fruit, observed during block inspections were included. From the 77 selected samples, a total of 24.7% of ASGV infected samples were also infected with ASPV. Single infection of ASGV and ASPV occurred in 57.7% and 15.6% of the 77 selected samples respectively. Four pear samples that showed visual symptoms of stony pit and fruit deformation were found to be infected with ASPV. Coat protein genes of a large proportion of ASGV and ASPV isolates were sequenced and indicated that South African isolates have multiple worldwide origins.