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Cisgenic 'gala' containing the scab resistance gene from Malus floribunda 821 and the fire blight resistance genes from m. 'Evereste'

Gessler, C., Vanblaere, T., Parravicini, G., Broggini, G. A. L.
Acta horticulturae 2014 no.1048 pp. 43-49
Agrobacterium, Erwinia amylovora, Malus floribunda, Venturia inaequalis, apples, crop production, crossing, cultivars, early selection, field experimentation, flowering, fungicides, genes, genetic markers, genotype, marker-assisted selection, mildews, orchards, organic production, powdery mildew, progeny, regulatory sequences, seedlings, transgenic plants, weather
Apple production in temperate climates with wet springs needs a relevant input of fungicides to control apple scab, caused by Venturia inaequalis, and powdery mildew, caused by Podophaera leucotricha. Additionally, if weather conditions are particularly warm and wet around flowering time, fire blight caused by Erwinia amylovora, may cause severe damage to the orchards. Breeding has produced many scab-resistant cultivars overwhelmingly based on the resistance from Malus floribunda 821 (Rvi6/Vf) (Bus et al., 2011) and some mildew resistant genotypes, and the breeding of fire blight resistant cultivars is in progress. Resistant cultivars are commonly used in organic production, however, to date have made little global impact. Marker assisted selection has increased breeding efficiency, i.e., allowing early selection of seedlings with pyramided resistance genes from progeny crosses. If the development of markers for MAS was the primary goal of genetic analysis in the 1990s, now the identification and cloning of resistance genes is the main goal. The first and until now sole resistance gene that has been cloned into a susceptible apple cultivar is the HcrVf2 gene responsible for the Rvi6 scab resistance. As products derived from genetically modified plants are contested by a large proportion of the European public mainly because of potential unwanted/unknown effects of the target gene as well as the presence of the selectable marker gene(s), we opted for the cisgenic approach producing a GM 'Gala' cultivar in which the apple endogenous HcrVf2 gene with its own regulatory sequences were inserted by Agrobacterium transformation, followed by a subsequent elimination of the selectable marker genes. In this paper we describe some lines which are currently under field testing and report preliminary results on the insertion of fire blight candidate genes putatively responsible for the fire blight resistance in the ornamental apple cultivar 'Evereste'.