Integration of Ty-1/Ty-3 and Ty-6 confers improved and durable resistance to highly pathogenic begomoviruses in tomato

Abstract Begomoviruses are among the most destructive pathogens of tomato worldwide, and the introgression of Ty -genes in tomato is a key strategy for disease management. However, a single Ty -gene often provides incomplete protection against highly virulent begomovirus species. Here, commercial tomato cultivars and breeding lines were inoculated with one of three begomovirus species that differed in virulence. The presence of Ty-1 , Ty-2 , Ty-3 , Ty-3a , ty-5 , and Ty-6 was validated using in-gene markers. Tomato plants carrying only Ty-2 were susceptible to all viruses, whereas those with Ty-1 were resistant to a less-virulent begomovirus, but susceptible to more-virulent viruses. Among the seven AVTO breeding lines, 1919 ( Ty-1 / Ty-1 , Ty-6 / Ty-6 ) and 1920 ( Ty-3 / Ty-3 , Ty-6 / Ty-6 ) were symptomless in most cases and the lowest viral DNA accumulation across all lines tested indicating strong begomovirus resistance. The resistance of 1919 was comparable to or greater than that of 1701, a line homozygous for Ty-2 , Ty-3 , ty-5 , and Ty-6 . Furthermore, F₁ plants derived from crosses between 1919 or 1920 and susceptible Moneymaker exhibited reduced disease tolerance, indicating the importance of homozygosity for Ty-1 or Ty-3 combined with Ty-6 . These results demonstrate that Ty-1/Ty-3 and Ty-6 integration in homozygous states can provide robust and broad-spectrum resistance to begomoviruses and is a valuable strategy for breeding durable resistant tomato cultivars.