The Pepper Bs2 Gene Confers Effective Field Resistance to Bacterial Leaf Spot and Yield Enhancement in Florida Tomatoes

By combining efforts in molecular biology, breeding, field trials, and pathology, we have investigated durable disease resistance to chronic bacterial leaf spot disease caused by Xanthomonas species. Previously we demonstrated that transfer of Bs2, a pepper gene and member of the common NLR resistance gene family, conferred effective resistance to bacterial leaf spot in tomatoes in Florida field trials. In these trials, we tested the impact of the gene as initially introduced into a California tomato cultivar, 'VF36', and the results demonstrated both significant reduction in disease severity and increases in yield compared to non-transformed lines. We have further investigated the impact of Bs2 by introducing the gene into a number of parent lines and hybrids in Florida breeding programs and testing them under Florida field conditions. A two-fold yield enhancement was typically observed in Bs2-containing Florida parent lines and hybrids over the near-isogenic non-transgenic versions. Some parent lines carried additional conventional resistances to Tomato yellow leaf curl virus, Fusarium crown rot, or Fusarium wilt, thus conferring protection against multiple pathogens afflicting fresh market tomato production in Florida. In one trial, strains occurred that were able to cause bacterial spot symptoms on Bs2-containing lines. However, the strains did not impact yield increases produced by the gene and were limited in space and time, not recurring in subsequent trials. Bacterial spot resistance conferred by Bs2 was achieved in the absence of any copper-based pesticides, providing an opportunity to eliminate the widespread use of ineffective copper compounds.