First Report of Apple (Malus domestica) as a Host of ‘Candidatus Phytoplasma pruni’ in the United States

Abstract

In July - October of 2013-2015, more than forty blocks of Pennsylvania apple orchards from nine PA counties were surveyed for phytoplasma. Out of 218 apple samples submitted to Pennsylvania Department of Agriculture Plant Diagnostic Lab (PDA PDL) three mature trees from two farms in Adams County PA were found to be positive for Phytoplasma. Positive trees belonging to three different varieties showed abnormally small fruits, clumps of small leaves, leaf curl and premature reddening with the best symptoms showing in August-October. PDA PDL extracted total DNA from leaf mid-veins with a DNeasy Plant Mini Kit (Qiagen, Valencia, CA) according to manufacturer's instructions. Positive results were obtained when screened for presence of phytoplasmal DNA using a real-time PCR assay (Hodgetts et al. 2009). For analysis of the 16S rDNA genomic region, nested PCR was carried out with primer pair P1/P7 followed by R16F2n/R16R2 or P1A/P7A (Lee et al. 2004). For analysis of ribosomal protein genes, DNA was amplified in...