Transgenic peppers that are highly tolerant to a new CMV pathotype

The CMV (cucumber mosaic virus) is the most frequently occurring virus in chili pepper farms. A variety of peppers that are resistant to CMVP0 were developed in the middle of 1990s through a breeding program, and commercial cultivars have since been able to control the spread of CMVP0. However, a new pathotype (CMVP1) that breaks the resistance of CMVP0-resistant peppers has recently appeared and caused a heavy loss in productivity. Since no genetic source of this new pathotype was available, a traditional breeding method cannot be used to generate a CMVP1-resistant pepper variety. Therefore, we set up a transformation system of pepper using Agrobacterium that had been transfected with the coat protein gene, CMVP0-CP, with the aim of developing a new CMVP1-resistant pepper line. A large number of transgenic peppers (T(1), T(2) and T(3)) were screened for CMVP1 tolerance using CMVP1 inoculation. Transgenic peppers tolerant to CMVP1 were selected in a plastic house as well as in the field. Three independent T(3) pepper lines highly tolerant to the CMVP1 pathogen were found to also be tolerant to the CMVP0 pathogen. These selected T(3) pepper lines were phenotypically identical or close to the non-transformed lines. However, after CMVP1 infection, the height and fruit size of the non-transformed lines became shorter and smaller, respectively, while the T(3) pepper lines maintained a normal phenotype.