A reliable system for the transformation of cantaloupe charentais melon (Cucumis melo L. var. cantalupensis) leading to a majority of diploid regenerants

An efficient system of transformation leading to a majority of transformed diploid plants from led explants of Cucumis melo L. var. Cantalupensis (cv. Vedrantais) was developed. Several regeneration protocols using cotyledon or leaf explants were analysed with particular emphasis on the regeneration efficiency and the ploidy level of the regenerated melon plants. The use o f leaf explants excised from 10 day-old seedlings, cultured in Murashige an d Skoog's medium supplemented with 1 mu M 6-benzylaminopurine (BAP) and 1 m u M 6-(gamma,gamma-dimethylallylamino)-purine (2iP), resulted in a high reg eneration frequency (73%). In these conditions, more than 84% of the regene rated plants were found to be diploid. Addition of an Agrobacterium-mediate d transformation step did not significantly change the percentage (81.8%) o f diploid plants regenerated. This protocol was successfully used to produc e diploid transgenic melon plants expressing the antisense ACC oxidase gene , encoding ACC oxidase which catalyses the last step of ethylene biosynthes is. Ethylene production and ACC oxidase activity of the leaf explants from transgenic plants was reduced by more than 80% as compared to the control u ntransformed tissues. This transformation/regeneration method could be rout inely used for the introduction of other genes of interest in melon. (C) 20 00 Elsevier Science B.V. All rights reserved.