Apple (Malus domestica Borkh.) a.k.a Malus pumila P Mill Jake Fleming Department of Geography, UW Madison jefleming@wisc.edu Image from bestapples.com Taxonomy Family: Subfamily: Genus: Section: Series: Species: Rosaceae Maloideae (with pears) Malus (40 sp.) Malus Malus domestica www.billnymanart.com A note on nomenclature: In his 2006 book The Story of the Apple, BE Juniper refers to both the domestic apple and the wild Central Asian apple as Malus pumila The USDA has also adopted this convention For clarity, and as Coart et al 2006 calls into question the hypothesis upon which this is based, I use the older names: Malus sieversii for the wild Central Asian apple and Malus domestica for the orchard apple Importance • World’s most important temperate fruit crop: 63 million tons/yr • Leading producers in 2004: China 18.7 Mtons (4 Mtons in 1990), United States Mtons, Russia, Germany, Japan Food and Agriculture Organization of the United Nations http://faostat.fao.org Malus domestica - the specifics • Woody, long-lived tree • Unlike congeners, extreme heterozygosity, does not breed true Single parental event yields massive variation in fruit color, size, taste, flower color, thorns, tree habit, so… • Cultivars must be vegetatively propagated – “instant domestication” • Perfect, self-incompatible flowers n = 17 Most congeners and cultivars 2n, some 3n, 4n Stories of Domestication • ‘Compilospecies’ – conventional wisdom until c 1990 Eurasian origin, somewhere/everywhere • Malus sieversii Roem – Vavilov 1930 Harris, Robinson, Juniper 2002 Central Asian origin • BREAKING!! Malus sylvestris Mill – Coart et al 2006 European origin? ‘Compilospecies’ hypothesis Hypothesis: Malus domestica arose from some combination of crabapples in Eurasia, with possible recent introgression in North America (Watkins 1995) • • • In Maloideae, hybridization between genera not rare (e.g Malus x Pyrus) In Malus, species boundaries fuzzy, some hybrids occur M domestica may (or may not) readily hybridize with sympatric congeners M sieversii hypothesis Hypothesis: Malus sieversii of Central Asia is the wild ancestor of domesticated apples Other species contributed little or nothing (Vavilov 1930) • As the Tien Shan Mountains rose and the Gobi and Taklamakan Deserts grew, ancestral Malus populations were isolated • Among a very diverse population making up as much as 80% of the forest, • Some wild fruits are indistinguishable from cultivars • Selection by bears? • Human-mediated dispersal along Silk Road trade routes (but not by current residents) (Juniper and Mabberley 2006) M sieversii hypothesis Hypothesis: Malus sieversii of Central Asia is the wild ancestor of domesticated apples Other species contributed little or nothing (Vavilov 1930) • As the Tien Shan Mountains rose and the Gobi and Taklamakan Deserts grew, ancestral Malus populations were isolated • Among a very diverse population making up as much as 80% of the forest, • Some wild fruits are indistinguishable from cultivars • Selection by bears? • Human-mediated dispersal along Silk Road trade routes (but not by current residents) (Juniper and Mabberley 2006) M sieversii hypothesis Hypothesis: Malus sieversii of Central Asia is the wild ancestor of domesticated apples Other species contributed little or nothing (Vavilov 1930) • As the Tien Shan Mountains rose and the Gobi and Taklamakan Deserts grew, ancestral Malus populations were isolated • Among a very diverse population making up as much as 80% of the forest, • Some wild fruits are indistinguishable from cultivars • Selection by bears? • Human-mediated dispersal along Silk Road trade routes (but not by current residents) (Juniper and Mabberley 2006) = Nuclear ribosomal ITS • No M sylvestris Robinson et al 2001 USDA collections, M sieversii Forsline et al 2003 Harris et al 2002’s matK duplication of 10 M sieversii accessions from Uzbekistan and Tajikistan (Robinson et al 2001) Forsline et al 2003 Other genetic support for M sieversii • Morphological + RAPD + sequence data (ITS1, 5.8S rRNA, ITS2, matK) – Forte et al 2002 • Isozymes DIA-2, AAT-2, PGM-1 and PGM-5 – Wagner and Weeden 1999 • Sampling? Strength of support? I don’t know… Forte, A.V et al 2002 Phylogeny of the Malus (apple tree) species, inferred from the morphological traits and molecular DNA analysis Russian Journal of Genetics 38: 1150-1160 Wagner, I and Weeden, N.F 2000 ISOZYMES IN MALUS SYLVESTRIS, MALUS DOMESTICA AND IN RELATED MALUS SPECIES Acta Hort (ISHS) 538:51-56 Morphological evidence for M sieversii • Floral morphology • Fruit morphology Juniper and Mabberley 2006 Molecular evidence against M sylvestris Hybridization b/w cultivars and sympatric European crab apple, M sylvestris, “almost absent” of 76 “wild” specimens Coart et al 2003 STRUCTURE BUT WAIT M sylvestris Hypothesis: Actually, M sylvestris, the European crab apple, is in some way ancestral to domesticated apples • Unlike M sieversii, M sylvestris is solitary, not notably heterogeneous, rare, and produces bitter, inedible fruit • Contrary to their own earlier work, Coart et al.’s JULY 2006 article shows M sylvestris to be much closer to M domestica than previous, using cDNA PCR-RFLP • 16 different chloroplast haplotypes based on: matK duplication, point mutation, restriction endonucleases (EcoRI, MseI) www.wikipedia.com Coart et al 2006 Coart et al 2006 Coart et al 2006 matK dupII Coart et al 2006 Also, • Greater chloroplast diversity of cultivars suggests some kind of hybridization • Geographic distribution of rare haplotypes suggests sylvestris x domestica hybridization Coart et al 2006 Coart et al 2006 Selected Sources • • • • • • • Coart, E.L.S., et al 2003 Genetic variation in the endangered wild apple (Malus sylvestris (L.) Mill.) in Belgium as revealed by amplified fragment length polymorphism and microsatellite markers Molecular Ecology 12: 845-857 Coart, E.L.S., et al 2006 Chloroplast diversity in the genus Malus: new insights into the relationship between the European wild apple (Malus sylvestris (L.) Mill.) and the domesticated apple (Malus domestica Borkh.) Molecular Ecology 15: 2171-2182 Forsline, P.L et al 2003 Collection, maintenance, characterization, and utilization of wild apples of Central Asia Horticultural Reviews 29: 1-62 Harris, S.A., J.P Robinson, and B.E Juniper 2002 Genetic clues to the origin of the apple TRENDS in Genetics 18(8): 426-430 Juniper, B.E and D.J Mabberley 2006 The Story of the Apple Portland: Timber Press, Inc Vavilov, N.I 1930 Wild progenitors of the fruit trees of Turkestan and the Caucasus and the problem of the origin of fruit trees Proceedings of the 9th International Horticultural Congress, London, pp 271-286 Watkins, R 1995 Apple and pear In Evolution of Crop Plants (Smartt, J and Simmonds N.W eds.) Longman 418-422 ... of the Apple, BE Juniper refers to both the domestic apple and the wild Central Asian apple as Malus pumila The USDA has also adopted this convention For clarity, and as Coart et al 2006 calls... nothing (Vavilov 193 0) • As the Tien Shan Mountains rose and the Gobi and Taklamakan Deserts grew, ancestral Malus populations were isolated • Among a very diverse population making up as much as 80%... the domesticated apple (Malus domestica Borkh. ) Molecular Ecology 15: 2171-2182 Forsline, P. L et al 2003 Collection, maintenance, characterization, and utilization of wild apples of Central Asia