Understanding plant virus vertical-transmission biology: A big, hairy, audacious goal

Understanding the biology of vertical transmission (from parent to progeny) of plant viruses is a big, hairy, audacious goal. Virus-infected seeds can insidiously enter a new territory and remain undetected for months, if not years; a single untraced primary source can then lead to epidemics, resulting in regional devastation and global economic loss. Vertical transmission of plant viruses is very difficult to study as it occurs in hard-to-access parts of the plant, over time, and usually manifests at low rates. Observations are generally destructive, often resulting in some orphaned scientific claims as it is difficult to repeat experiments; furthermore, meaningful time-course experiments are littered with challenges for creating quantitative data. Different viruses and plant systems have nuances that make generalizations difficult. A range of terms have been used to describe different aspects of vertical transmission of plant viruses, resulting in some confusion regarding the mechanisms involved and therefore how to manage the potential for transmission. Understanding the biology of vertical transmission of plant viruses would enable a paradigm change in their management, resulting in advanced regional and global biosecurity, food security, and economic resilience. In this review we outline the impacts of vertical, and horizontal, transmission of plant viruses, summarize transmission mechanisms, tabulate vertically transmitted plant viruses, explore biological and technological research complexities, discuss confusing historic terminology and provide a logic for potential future transmission nomenclature. Finally, using the biological knowledge at hand, simple measures and advanced virus detection methods, we provide some suggestions on how the management of plant virus vertical transmission may be improved to gain greater biosecurity.