Application of a high-speed breeding technology to apple (Malus × domestica) based on transgenic early flowering plants and marker-assisted selection

Abstract

Summary• Breeding of apple (Malus · domestica) remains a slow process because of protracted generation cycles. Shortening the juvenile phase to achieve the introgression of traits from wild species into prebreeding material within a reasonable time frame is a great challenge.• In this study, we evaluated early flowering transgenic apple lines overexpressing the BpMADS4 gene of silver birch with regard to tree morphology in glasshouse conditions. Based on the results obtained, line T1190 was selected for further analysis and application to fast breeding.• The DNA sequences flanking the T-DNA were isolated and the T-DNA integration site was mapped on linkage group 4. The inheritance and correctness of the T-DNA integration were confirmed after meiosis. A crossbred breeding programme was initiated by crossing T1190 with the fire blight-resistant wild species Malus fusca. Transgenic early flowering F 1 seedlings were selected and backcrossed with 'Regia' and 98 ⁄ 6-10 in order to introgress the apple scab Rvi2, Rvi4 and powdery mildew Pl-1, Pl-2 resistance genes and the fire blight resistance quantitative trait locus FB-F7 present in 'Regia'.• Three transgenic BC'1 seedlings pyramiding Rvi2, Rvi4 and FB-F7, as well as three other BC'1 seedlings combining Pl-1 and Pl-2, were identified. Thus, the first transgenic early flowering-based apple breeding programme combined with marker-assisted selection was established.

Early flowering and genetic containment studies in transgenic poplar

“…Arabidopsis flowering time genes Leafy (Schultz & Haughn 1991) and Flowering locus T (Blázquez & Weigel 1999) allow the hitherto most efficient early flowering induction in poplar (Weigel & Nilsson 1995, Rottmann et al 2000, Zhang et al 2010. Furthermore, it has been shown that transgenes can induce early flowering in trees more efficiently than cisgenes (Rottmann et al 2000, Zhang et al 2010, Flachowsky et al 2011, Tränkner et al 2010. Possibly, transgenes are less prone to "endogenous repressors" than cisgenes (Rottmann et al 2000).…”

“…-Flachowsky et al 2007), but not in poplar (Hoenicka et al 2008). BpMADS4 transgenic lines are currently being used for apple breeding (Flachowsky et al 2011). The apple gene MdFT2, homologous of FT gene, promoted early flowering in apple and poplar (Tränkner et al 2010).…”

“…The overexpression of BpMADS4 induce early flowering in birch (Betula pendula - Elo et al 2007) and apple (Malus × domestica Borkh. -Flachowsky et al 2007), but not in poplar (Hoenicka et al 2008). BpMADS4 transgenic lines are currently being used for apple breeding (Flachowsky et al 2011).…”

Mejoramiento genético acelerado de angiospermas perennes vía inducción floral por sobre-expresión del gen FT

“…Las semillas obtenidas de las cruzas se tamizaron con marcadores moleculares y se cruzaron con germoplasma comercial, siempre monitoreados por diagnósticos moleculares de la presencia del locus responsable de dicha resistencia. De esta manera, fue posible combinar ese tipo de genes en tan solo tres años, cuando por el método tradicional se hubiesen requerido más de 10 y una población de plántulas mucho mayor (Flachowsky et al, 2011;Le Roux et al, 2012).…”

“…El uso de potentes promotores constitutivos, como el del virus de mosaico de tabaco (35S), provoca la formación continua de flores que no son soportadas por la plántula y, como consecuencia, ocurre la caída de muchos frutos; también, se puede afectar la dominancia de crecimiento apical a favor de un mayor desarrollo de ramas y de un hábito de crecimiento tipo arbustivo (Flachowsky et al, 2011;Le Roux et al, 2012).…”