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 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)
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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)
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)
Bearington Bears catalog. $10.95
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 (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)
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
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
Wild apple: Malus sieversii
Domesticated apple: Malus domestica
Harris et al 2002
=
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
8 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”
3 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, 1
point mutation, 2 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
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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.