Ty-2 and Ty-3a Conferred Resistance are Insufficient Against Tomato Yellow Leaf Curl Kanchanaburi Virus from Southeast Asia in Single or Mixed Infections of Tomato

Abstract

Tomato yellow leaf curl virus (TYLCV), a monopartite begomovirus that originated in the eastern Mediterranean, has spread worldwide, becoming a serious threat to tomato (Solanum lycopersicum L.) production. Southeast Asia is considered one of the hotspots for begomovirus diversity, and a wide variety of local begomovirus species distinct from TYLCV have been identified. In this study, the protection effect of introgressions of single TYLCV Ty resistance genes, Ty-2 and Ty-3a, in tomato was examined against inoculations of the bipartite begomoviruses Tomato yellow leaf curl Kanchanaburi virus (TYLCKaV) and Pepper yellow leaf curl Indonesia virus (PepYLCIV) isolated from Indonesia. Our findings suggest that Ty-2 in the heterozygous state was found to be ineffective against PepYLCIV and TYLCKaV, whereas Ty-3a in the heterozygous state was effective against PepYLCIV and partially effective against TYLCKaV. Quantification of viral DNAs showed correlation between symptom expression and viral DNA accumulation. Moreover, mixed infections of TYLCKaV and PepYLCIV caused notably severe symptoms in tomato plants harboring Ty-3a. In cases of mixed infection, quantifying viral DNAs showed a relatively high accumulation of PepYLCIV, indicating that Ty-3a loses its effectiveness against PepYLCIV when TYLCKaV is also present. This study demonstrates the lack of effectiveness of Ty resistance genes against single and mixed infections of distinct local begomoviruses from Southeast Asia.