Two California strains of TSWV, one RB strain carrying the C118Y mutation (CA-C118Y-referred to as CA-RB throughout this paper) and one California WT strain lacking the mutation (CA-WT), were obtained from BASF Vegetable Seeds (Supplementary Table S1). Tomato seedlings (2 to 3 weeks old) were inoculated by mechanically rubbing the virus-containing sap of infected plant leaves onto tomato using carborundum-dusted leaves. Young leaves from TSWV-infected tomato stock plants were ground in an ice-cold mortar with approximately 5 to 10 ml of sodium sulfite solution (63 mg of sodium sulfite per 50 ml of tap water) as a buffer. The ground tissue was applied to plants using sterile cotton applicators by rubbing them onto tomato leaves sprinkled with carborundum to wound the leaf. The inoculated leaves were sprayed with distilled water to remove the remaining carborundum 10 min later. Control plants were mock inoculated with the buffer only. Tomato plants inoculated with the two strains were kept in separate mesh cages to prevent cross contamination.