Apple (Malus domestica Borkh.) a.k.a. Malus pumila P. Mill. Image from bestapples.com Jake Fleming Department of Geography, UW Madison [email protected].

Apple (Malus domestica Borkh.)

a.k.a. Malus pumila P. Mill.

Image from bestapples.com

Jake FlemingDepartment of Geography, UW Madison

[email protected]

Family: RosaceaeSubfamily: Maloideae (with

pears)Genus: Malus (40 sp.)Section: MalusSeries: MalusSpecies: domestica

Taxonomy

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.

www.billnymanart.com

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 6 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.

3 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

• 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)

Hypothesis: Malus sieversii of Central Asia is the wild ancestor of domesticated apples. Other species contributed little or nothing. (Vavilov 1930)

M. sieversii hypothesis

• 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)

Hypothesis: Malus sieversii of Central Asia is the wild ancestor of domesticated apples. Other species contributed little or nothing. (Vavilov 1930)

M. sieversii hypothesis

• 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)

Hypothesis: Malus sieversii of Central Asia is the wild ancestor of domesticated apples. Other species contributed little or nothing. (Vavilov 1930)

M. sieversii hypothesis

• 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)

Hypothesis: Malus sieversii of Central Asia is the wild ancestor of domesticated apples. Other species contributed little or nothing. (Vavilov 1930)

Bearington Bears catalog. $10.95

M. sieversii hypothesis

• 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 (adaptive?),

• 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)

Hypothesis: Malus sieversii of Central Asia is the wild ancestor of domesticated apples. Other species contributed little or nothing. (Vavilov 1930)

Bearington Bears catalog. $10.95

Geography of M. sieversii

Harris et al. 2002 Note: What’s up with this map?

Dispersal into Europe • Silk Road was operational by 2100 ybp. In

summer, went straight through Tien Shan• One big apple found in Ireland, 3000 ybp. What

is it? • Alexander the Great, 2300 ybp, fought mock

battles with apple projectiles. Must have been bigger than crabs.

• 2400 ybp, Celt-Persian contact?• 1300 ybp, Muslim empire, Central Asia-Spain

Molecular evidence

Harris et al 2002

Wild apple: Malus sieversiiDomesticated apple: Malus domestica

cDNA gene matK• Only 16 of 1341 characters informative• 18-bp duplication in M. domestica and 1 M. sieversii accession Other M. sieversii accessions tested only for duplication, did not have it

Nuclear ribosomal ITS

Robinson et al 2001

• No M. sylvestris

=

USDA collections, M. sieversiiForsline et al. 2003

Harris et al 2002’s matK duplicationForsline et al. 20038 of 10 M. sieversii accessions

from Uzbekistan and Tajikistan(Robinson et al 2001)

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

• Floral morphology

• Fruit morphology

Morphological evidence for M. sieversii

Juniper and Mabberley 2006

Hybridization b/w cultivars and sympatric European crab apple, M. sylvestris, “almost absent”

Coart et al. 2003

Molecular evidence against M. sylvestris

3 of 76 “wild”specimens

STRUCTURE

BUT WAIT. M. sylvestrisHypothesis: 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, 1 point mutation, 2 restriction endonucleases (EcoRI, MseI)

www.wikipedia.com

Coart et al. 2006

Coart et al. 2006

Coart et al. 2006

Coart et al. 2006

matK dupII

• Greater chloroplast diversity of cultivars suggests some kind of hybridization

• Geographic distribution of rare haplotypes suggests sylvestris x domestica hybridization

Also,

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.