Pome fruit breeding: Progress and prospects

Similarities between Malus and Pyrus include their polyploid origin, diversity, their prospects for interspecific hybridization and center of origin. Chimeras for enhanced fruit skin color and for increased or decreased russetting are common to both, as is a multi-allelic gametophytic incompatibility system. Resistance to the bacterial pathogen causing fire blight (Erwinia amylovora) is a breeding goal in both Malus and Pyrus. For fungal pathogens, resistance to apple scab (Venturia inaequalis (Cke.) Wint.) and to pear scab (Venturia pirina Aderh.) are priorities. Breeding strategies are common across pome fruits, and traditional breeding and genetic studies are being enhanced by increased international collaborations. The identification and use of molecular markers and marker-assisted selection is more advanced in Malus, with genetic maps for important cultivars and advanced selections being used in genetic improvement. Simple sequence repeats (SSRs) cross-amplify in Malus and Pyrus suggesting further advances in this area. Regeneration and transformation techniques are well established in Malus, and systems are being developed and optimized in Pyrus. Identification of genes is also progressing, with self-incompatibility alleles, allergens, and many other genes similar in apple and pear. Acceleration in both genetic improvement and the development of transgenic lines in pome fruits is being aided by research and by the development and use of new techniques.