Molecular selection in apple for resistance to scab caused by Venturia inaequalis

Abstract

Large-scale marker-assisted selection requires highly reproducible, consistent and simple markers. The use of genetic markers is important in woody plant breeding in general, and in apple in particular, because of the high level of heterozygosity present in Malus species. We present here the transformation of two RAPD markers, which we found previously to be linked to the major scab resistance gene Vf, into more reliable and reproducible markers that can be applied directly to apple breeding. We give an example of how the use of such markers can speed up selection for the introduction of scab resistance genes into the same plant, reducing labour and avoiding time-consuming test crosses. We discuss the nature and relationship of the scab resistance gene Vf to the one present in Nova Easygro, thought to be Vr.

Molecular markers linked to the apple scab resistance gene Vbj derived from Malus baccata jackii

“…Scab resistance was evaluated under glasshouse conditions at Agroscope FAW Wädenswil. The progeny seedlings were inoculated with a suspension of V. inaequalis field conidia (4×10 5 conidia/ml) as described by Gianfranceschi et al (1996). Assessment of susceptibility and resistance was performed macroscopically after 10-12 days and rated in six classes (Chevalier et al 1991) DNA extraction, bulked segregant analysis and RAPD amplification DNA was extracted as described by Dellaporta's protocol (Dellaporta et al 1983), with minor modifications following Koller et al (1994).…”

“…The RAPD fragments associated with the resistance were transformed into more consistent sequence-characterised amplified region (SCAR) markers as previously described by Gianfranceschi et al (1996). Plasmids were purified (Wizard Minipreps, Promega, Madison, Wis., USA), and the inserted fragments were sequenced on an Applied Biosystems 373 automated sequencer, using the ABI PRISM dye terminator cycle sequencing kit.…”

“…Cheng et al (1995) already concluded that the pedigree of cv. Nova Easygro was incorrect and Gianfranceschi et al (1996) demonstrated that the scab resistance gene present in Nova Easygro was not Vr, but Vf. Patocchi et al (2004) proved that the accession GMAL 2473 cannot be cv.…”

“…This strategy should delay, or even prevent, the breakdown of the resistance genes. However, breeding for more than one resistance gene can hardly be achieved without the use of molecular markers, which greatly facilitate the identification of favourable genetic combinations during the selection process (Gianfranceschi et al 1996).…”

Vr 2 : a new apple scab resistance gene

“…The popularity of Vf has encouraged many researchers to study this resistance. This has led to the discovery of several molecular markers linked to Vf (Koller et al 1994;Gianfranceschi et al 1996;Tartarini 1996;Tartarini et al 1999). These markers were later used to begin the positional cloning of the gene (Vinatzer et al 1998;Patocchi et al 1999a, b;Vinatzer et al 2001) resulting in the cloning of the first apple scab resistance gene (Barbieri et al 2003, Belfanti et al 2004.…”