Evaluation of Reference Genes for the Relative Quantification of Apple stem grooving virus and Apple mosaic virus in Apple Trees.

A SYBR Green(®)-based one step RT-qPCR assay was developed for the detection and quantification of Apple stem grooving virus (ASGV) and Apple mosaic virus (ApMV). The RT-qPCR assay employed seven plant-expressed genes-glyceraldehyde 3-phosphate dehydrogenase (GAPDH), 18S ribosomal RNA, ubiquitin, ribosomal protein S19, Rubisco, RNA polymerase subunit II and β-actin-as internal reference housekeeping genes in a relative quantification system in three apple cultivars (i.e. Idared, Champion, Fragrance). The average expression stability (M) found by GeNorm software suggest that GAPDH and S19 were the most stable reference genes. We propose employing GAPDH and S19 as housekeeping genes for accurate quantification of ASGV and ApMV in apple leaf samples. The detection limit for both viruses was found around 70 copies of viral genome by one-step RT-qPCR.