Effects of Acquisition Time and Viral Load of Source Plants on Infections of Two Tomato Begomoviruses in Bemisia tabaci

Tomato yellow leaf curl disease poses one of the most severe threats to tomato production worldwide. This disease is associated with a group of closely related tomato yellow leaf curl viruses. These viruses can be transmitted by the sweet potato whitefly (Bemisia tabaci) in a persistent-circulative mode. Virus particles can infect the midgut and filter chamber of whiteflies feeding on infected plants, circulate in the hemolymph, and eventually infect the primary salivary gland (PSG) of whiteflies. Later, the whiteflies feed on healthy plants, and viral particles are introduced into the plants through their saliva. Virus–vector interactions play a crucial role in the efficiency and dynamics of virus transmission. In this study, we assessed the effects of the acquisition time and viral load of source plants on infections of two tomato begomoviruses, tomato yellow leaf curl Thailand virus (TYLCTHV) and tomato leaf curl Taiwan virus (ToLCTV), in B. tabaci Middle East–Asia Minor 1. We found that more viruses were acquired and accumulated in the whitefly midgut and PSG before reaching a plateau when the acquisition time increased and when the source plant had a higher viral load. The midgut and PSG acquired and accumulated more TYLCTHV than ToLCTV with the same acquisition time and regardless of the viral loads in coinfected source plants. These results not only help us to understand virus–vector interactions but also help in developing integrated disease management strategies.