COAT PROTEIN GENE-MEDIATED PROTECTION IN LACTUCA-SATIVA AGAINST LETTUCE MOSAIC POTYVIRUS STRAINS

Lettuce mosaic potyvirus (LMV) can be very destructive on lettuce crop s worldwide. The LMV strain 0 (LMV-0) coat protein (CP) gene was engin eered for expression in plants. It was introduced into three susceptib le cultivars of Lactuca sativa using an improved procedure for transfo rmation and regeneration of lettuce, by co-cultivation of leaf explant s with Agrobacterium tumefaciens. Several transformants accumulated de tectable levels of LMV CP. The R1 progeny of twelve RO transformants ( four plants per cultivar) with T-DNA integration at one single locus, was studied for protection against LMV. The progeny from five RO trans formants showed resistance to LMV-0, with the effectiveness of resista nce depending on the development stage of the plants at the time of in oculation. The R1 and R2 progeny from one of these RO transformants, C ocarde-9a, were more extensively analysed. The homozygous but not the hemizygous R1 plants displayed protection to LMV-0. The R2 progeny fro m one homozygous R1 plant were shown to be resistant to infection by L MV-0 and other LMV strains. As previously observed in other cases of p otyvirus sequence-mediated protection, a phenomenon of recovery was ob served in some plants, as well as complete resistance. However, this r ecovery phenotype was not always maintained, as opposed to the previou s described cases, leading to a late progression of viral infection.