Fig 1.
Virus seed transmission cycle.
(1) Plant viruses reach seeds either by direct invasion of the embryo from the parental plant via the suspensor, and/or indirectly by infecting pollen grains or ovules, which lead to an infected embryo after fertilization. (2) Infected seeds may (i) directly germinate; (ii) remain for long periods of time in the soil; or (iii) be dispersed to long distances. In any of these 3 scenarios, infected seed will produce infected seedlings after germination. (3) Infected seedlings (and adult plants) from infected seeds will be sources of primary inoculum allowing virus dispersion through vectors. The picture represents aphids, which transmit 30% of plant viruses. (4) The cycle can be closed in 2 ways: (i) Viruses from infected seedlings/adult plants may again reach seeds leading to a second round of seed transmission, allowing virus persistence in the absence of vectors. (ii) Plants infected by vectors can produce infected seeds. Constructed using BioRender.