First Report of Grapevine yellow speckle viroid 1, Grapevine yellow speckle viroid 2, and Hop stunt viroid Infecting Grapevines (Vitis spp.) in Nigeria

Abstract

Grapevine yellow speckle viroid 1 (GYSVd-1), Grapevine yellow speckle viroid 2 (GYSVd-2; genus Apscaviroid), and Hop stunt viroid (HSVd; genus Hostuviroid) are three of six viroid species documented globally from grapevines (Di Serio et al. 2017). These small plant-pathogenic, non-protein coding, circular RNAs may or may not elicit disease symptoms in grapevines depending on vagaries of the environment and their presence in mixed infection with other grapevine-infecting viruses. During 2016, surveys were conducted in the Northern Guinea Savannah agroecological zone of Nigeria to document the occurrence of grapevine viruses and viroids. A total of 318 leaf tissue samples belonging to five cultivars were collected during the survey across 28 vineyards. The samples were dried under CaCl₂ at room temperature, and then shipped under USDA-APHIS-PPQ permit to Texas AM MF576417–428) shared 96 to 100% identity with several HSVd GenBank isolates. The complete GYSVd-1 RNA derived in this study (365 to 367 nt; MF576399–407) shared 96 to 99% identity with several GYSVd-1 GenBank isolates. The complete GYSVd-2 RNA derived in this study (361 nt; MF576408–416) shared 97 to 99% identity with several GYSVD-2 GenBank isolates. No discernible symptoms were associated with the presence of all three viroid species in their source grapevines. To our knowledge, this is the first report of viroids infecting grapevine in Nigeria. Studies are ongoing to further elucidate the prevalence of all three viroids in Nigerian vineyards and their occurrences in mixed infections with other graft-transmissible agents of grapevine.