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H.S. Aldwinckle, P.L. Forsline, H.L. Gustafson, and S.C. Hokanson

Resistance to apple scab (Venturia inaequalis) in apple cultivar breeding has been derived mainly from the Vf gene from Malus floribunda 821, which introgresses horticulturally unfavorable characters. M. sieversii, now thought to be the primary progenitor of M. × domestica, grows wild in many diverse habitats in Central Asia and can have fruit quality comparable to commercial cultivars. Since 1989, four major collections of M. sieversii have been made in Central Asia, where scab is endemic. Some seed collections have been made from trees with superior fruit, that were not infected with scab. Over a 6-year period, 3000 seedlings from 220 wild M. sieversii trees representing 10 diverse ecosystems in Kazakstan, Uzbekistan, Kyrgyzstan, and Tajikistan have been inoculated with conidia of five races and two wild types of V. inaequalis. Suspensions (270,000 conidia/ml) were applied to 4- to 8-leaved seedlings, which were incubated for 48 h at 19°C with constant leaf wetness. Symptoms for three resistant reactions were assessed 2 to 4 weeks after inoculation: A = chlorosis with crinkling (Vf type reaction); B = stellate necrotic lesions (Vr type reaction), and N = large necrotic areas (uncharacterized resistant reaction). Results indicated that nearly 20% of the seedlings showed one or more of the resistant reactions. The range of resistance within seedling populations from each of the 220 single-tree sources ranged from 0% to 75%. Significant differences existed among seedlings from each of the ecosystems. Most resistance reactions appeared to be similar to those observed for Vr from “Russian seedling.” Resistant selections with superior horticultural traits may constitute a genepool for increased efficiency of breeding scab-resistant cvs. This genepool may also be useful to address the breakdown of resistance to V. inaequalis race 6.

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Shahrokh Khanizadeh, François Laurens, Yves Lespinasse, Yvon Groleau, Johanne Cousineau, Odile Carisse, and Jennifer DeEll

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Shahrokh Khanizadeh, Yvon Groleau, Audrey Levasseur, Odile Carisse, Djamila Rekika, Jennifer DeEll, Jean-Pierre Privé, Inteaz Alli, and Henk Kemp

`SuperMac' (Malus ×domestica Borkh) is being released as a replacement for `Spartan', which is presently being grown in Eastern Canada for its excellent shelf life. However, it is susceptibility to scab [Venturia inaequalis (Cke) Wint.], the most common apple disease. This new cultivar produces larger fruit than `Spartan' and is resistant to apple scab. It is very attractive (Fig. 1), has a pleasant taste and an excellent shelf life, and keeps very well and longer compared with the `Spartan'. `SuperMac' is a `McIntosh'-type apple. The tree is hardy to –30 °C, and the fruit and leaves are resistant to the common races of apple scab resulting from the presence of the V f gene derived from Malus floribunda 821.

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Shahrokh Khanizadeh, François Laurens, Yves Lespinasse, Yvon Groleau, Johanne Cousineau, Odile Carisse, and Jennifer DeEll

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A.G. Manganaris, F.H. Alston, N.F. Weeden, H.S. Aldwinckle, H.L. Gustafson, and S.K. Brown

Pgm-1, the gene responsible for variation in the most anodal isozyme of phosphoglucomutase in apple (Malus spp.), is shown to lie ≈8 centiMorgans from the gene Vf, which confers apple-scab resistance. The proximity of the marker and the ease by which allozymic forms can be resolved suggest that Pgm-1 will be useful for following the inheritance of scab resistance conferred by Vf.

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Shahrokh Khanizadeh, Yvon Groleau, Rong Tsao, Raymond Yang, Inteaz Alli, Robert Prange, and Robert Demoy

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Richard E. Durham and Schuyler S. Korban

DNA was extracted from leaves of various Malus genotypes and used to screen synthetic decamer oligonucleotide primers. Samples from the following two groups were bulked: 1) seven scab-susceptible apple cultivars, and 2) 15 scab-resistant apple genotypes derived by introgressive hybridization from the previous group of cultivars. A third sample consisted of DNA extracted from Malus floribunda Sieb. clone 821, the original source of apple scab resistance for all genotypes in the second group. A total of 59 primers from kits A, L, and R (Operon Technologies) were screened. Amplified fragments were obtained for 93% of the primers tested, while random amplified polymorphic DNA (RAPD) fragments were detected among samples for 76% of the primers. One primer, A15, amplified a unique band in both M. floribunda clone 821 and the bulked scab-resistant sample. This RAPD marker, designated OA15900, identifies an amplified, introgressed fragment that likely corresponds to a region of the genome that may serve as a modifier for the scab resistance gene block V, derived from M. floribunda clone 821.

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Janna Beckerman, James Chatfield, and Erik Draper

screened in the United States. When M. sieversii seed (collected in Central Asia) were raised in the United States, these seedlings had high levels of apple scab resistance that varied with the geographic region where the seedlings were screened; from 27

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Gayle M. Volk, Christopher M. Richards, Adam D. Henk, Ann A. Reilley, Patrick A. Reeves, Philip L. Forsline, and Herb S. Aldwinckle

. sieversii that offer apple scab resistance have been identified ( Boudichevskaia et al., 2009 ; Bus et al., 2005 ; Szankowski et al., 2009 ). M. orientalis individuals exhibiting apple scab resistance may offer novel candidate genes that could be of use

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R.L. Rusholme Pilcher, J-M. Celton, S.E. Gardiner, and D.S. Tustin

. Sansavini, S. Gessler, C. Patocchi, A. 2006 Mapping of the apple scab-resistance gene Vb Genome 49 1228 1245 Fisher, D.V. 1970 Spur strains of ‘McIntosh’ discovered in British Columbia, Canada