A mutual titer-enhancing relationship and similar localization patterns between Citrus exocortis viroid and Hop stunt viroid co-infecting two citrus cultivars

Background Citrus exocortis viroid (CEVd) and Hop stunt viroid (HSVd) are commonly found simultaneously infecting different citrus cultivars in Taiwan. A crucial question to be addressed is how accumulations of these two viroids affect each other in an infected plant. In this study, we investigated the relationship between the two viroids at macroscopic and microscopic levels.