Expression of wheat puroindoline-b reduces scab susceptibility in transgenic apple (Malus x domestica Borkh.)

Scab, caused by Venturia inaequalis, is the most serious disease causing economic losses in apple commercial orchards. In Europe, new races of scab have overcome the Vf gene, which is the main source of scab resistance used in apple breeding. Therefore, combining several defense mechanisms is necessary to obtain durable resistance. In this study, apple genotypes 'Ariane' and 'Galaxy', carrying or not carrying the natural resistance Vf gene, respectively, were transformed via Agrobacterium tumefaciens, with the gene encoding wheat puroindoline B (pinB), under the control of the CaMV35S constitutive promoter. PCR and RT-PCR analyses confirmed both the presence and the transcription of the transgene in 24 lines selected via resistance to kanamycin. These transgenic plants were further examined for the accumulation of PinB using enzyme linked immunosorbent assay (ELISA) assay and for resistance to two races of the fungal pathogen V inaequalis: the race I affecting only the susceptible cv. Galaxy and the race 6 which overcomes the resistance conferred by the Vf gene. A significant negative correlation between PinB content and disease susceptibility was observed among transgenic lines of 'Ariane' as well as transgenic lines of 'Galaxy', after inoculation with the race 6 of the pathogen. This resistance was not detected in transgenic lines of 'Galaxy' after inoculation with the race 1. This is the first report of a partial resistance in woody plants induced by the expression of wheat puroindoline alone or in association with a natural resistance gene. (C) 2004 Elsevier Ireland Ltd. All rights reserved.