Improving resistance of different apple cultivars using the Rvi6 scab resistance gene in a cisgenic approach based on the Flp/FRT recombinase system

Abstract

Cisgenic apple plants of two different cultivars were developed by transferring the Rvi6 scab resistance gene of Malus floribunda 821, using a new transformation vector based on the Flp/FRT recombinase system. Transformation experiments on seven different cultivars resulted in 22 transgenic lines for the cultivars ‘Brookfield Baigent’, ‘Mitchgla’, ‘Novajo’, and ‘Pinova’, whereby 16 lines thereof were resistant to Venturia inaequalis strain 104 (race 1). Analysis of the transgenic lines revealed Rvi6 mRNA expression levels comparable to several traditional bred Rvi6 containing cultivars and identified four transgenic lines, harboring a single T-DNA insertion, as suitable for the production of cisgenic lines. The T-DNA insertion site of these lines was determined, and lines were subject to induction of the recombinase system. Two cisgenic lines originating from the cultivars ‘Brookfield Baigent’ and ‘Pinova’ were obtained for which the exact excision of the recombinase cassette was confirmed by sequencing the previously determined T-DNA integration site. Further investigations revealed both cisgenic lines as fully resistant to V. inaequalis race 1. Rvi6 mRNA expression of the cisgenic lines and traditionally bred Rvi6 harboring cultivars was still comparable. The transformation vector developed is useable for the production of cisgenic apple plants to a certain extent.