The World of Apples

Wild apples

Malus sieversii (Ledeb.) M.Roem.

Asian wild apple

Description

Malus sieversii is a tree of 2 to 10 m, occasionally 14 m. Its leaves are ovate or broadly elliptic, 6–11 cm long and densely hairy beneath when young. The flowers are 3–3.5 cm across, with pinkish petals tinged rose in bud, and in Xinjiang they open in May. The fruit is yellowish green flushed with red, round or somewhat flattened, usually 3–4.5 cm across but sometimes 7 cm, and ripens there from August to October1. Trees and Shrubs Online gives the fruit as 3–8 cm2.

Wild trees are remarkably variable. Some are very spiny and others not at all; the flowers may be white, pink or, rarely, almost red; and the fruits differ in size, colour, texture and flavour, and in whether they hang on the tree into winter2. Trees growing on their own roots in the mountains of Central Asia can bear fruit more than 60 mm across, approaching the size of commercial apples3, and Robert Spengler gives a maximum of 8 cm4.

Carl Ledebour described the tree as a Pyrus in 1830, from specimens collected in 1793 by Johann Sievers on an early Russian expedition to the mountains of Central Asia2.

Range and habitat

The species is native to Xinjiang in China, Kazakhstan, Kyrgyzstan, Tajikistan and Uzbekistan5. It grows on mountain slopes, summits and valleys, where it is often the dominant tree of the forest1, usually at middle elevations of about 900 to 1,600 m3.

Little of the old fruit forest is left. In 2014 only a few small intact forests, none larger than several hundred hectares, remained in the Tian Shan on the border of Kazakhstan and China and in southern Kazakhstan, with smaller stands in Kyrgyzstan; the tree was also reported here and there in Turkmenistan, Uzbekistan, Tajikistan and north-eastern Afghanistan3. The populations were heavily over-harvested in the Soviet era3. The IUCN Red List assessed the species in 2007 as Vulnerable, with a decreasing population5. The Red List of Trees of Central Asia (2009) named the threats as farmland and development, the grafting of commercial varieties and hybridisation, and over-grazing, and reported that its habitat in Kazakhstan had shrunk by more than 70% in thirty years6.

Apart from people, bears and horses appear to be the main dispersers of its seeds2. Spengler argues that the large fruits of wild apples evolved to recruit large mammals as dispersers, many of which are now extinct4.

Relationship to the cultivated apple

The sequencing of the domestic apple’s genome, published in 2010, placed M. sieversii as the progenitor of the cultivated apple7. Later studies refined the picture. A large microsatellite study in 2012 confirmed it as the initial progenitor, but found that gene flow from the European crab apple, Malus sylvestris, has made today’s cultivated apple genetically closer to that species than to its Central Asian ancestor8. A genome survey of 117 wild and cultivated apples in 2017 traced cultivated apples to M. sieversii in Kazakhstan; the trees of Xinjiang, on the eastern side of the Tian Shan, turned out to be an isolated population that did not contribute directly. About 46% of the cultivated apple’s genome was probably derived from the Kazakh trees9. A haplotype-resolved genome of M. sieversii followed in 202010.

The wild trees are a resource for breeders. Between 1989 and 1996 four expeditions collected M. sieversii in Central Asia for the United States’ national collection, which grows a seedling orchard of it at Geneva, New York, and holds more than 170,000 seeds from collecting trips at −20 °C; a further 63,000 seeds from its own M. sieversii trees were offered for distribution after a popular book stirred demand11. Germplasm from Kazakhstan has been used to improve disease resistance, and samples resistant to apple scab, fire blight and drought have been found6. About 500 accessions, counting the closely related Malus kirghisorum and Malus turkmenorum, grow at Geneva2.

Where the sources disagree

  • Species or synonym. Plants of the World Online treats the name as a synonym of Malus domestica12. The Flora of China, the IUCN Red List and the 2022 revision of the genus keep it as a species1,5,13. A 2012 study cited earlier sequence data suggesting that the wild and cultivated apples form a single gene pool8.
  • Elevation. The Flora of China gives 1,200–1,300 m for western Xinjiang1, Trees and Shrubs Online 1,100–2,400 m2, and Cornille and colleagues typically 900–1,600 m3.
  • Countries. The IUCN Red List names five countries5; the 2009 Red List of Trees of Central Asia adds Turkmenistan6; Cornille and colleagues add north-eastern Afghanistan3; and Trees and Shrubs Online lists Iran as possible2.
  • The red-flowered form. Trees with purple-red flowers, leaves and fruit were described as Malus niedzwetzkyana in 18912. The IUCN Red List assessed it as a separate, Endangered species in 200714; Trees and Shrubs Online treats it as a form of M. sieversii2; the 2022 revision lists it as a synonym of M. sieversii13; and Plants of the World Online sinks it, with M. sieversii, into M. domestica12.
  • Red List criteria. The IUCN page gives the criteria as A2cde5, the 2009 report as A2acde6.

Sources

  1. Malus sieversii, Flora of China vol. 9, Gu Cuizhi and Stephen A. Spongberg, Flora of China, eFloras.org, 2003. Supports: the description (tree 2–10(–14) m, leaves, flowers, fruit 3–4.5(–7) cm, flowering in May and fruiting August to October, 2n = 34); habitat on mountain summits, slopes and valleys, often the dominant forest tree, at 1,200–1,300 m in W Xinjiang; treatment as a species, "believed to be the principal ancestor of commercially grown apples".
  2. Malus sieversii, Julian Sutton and Nick Dunn, Trees and Shrubs Online (International Dendrology Society), 2021. Supports: fruit 3–8 cm; the variability of wild trees (spines, flower colour, fruit size, colour, texture, flavour, fruit held into winter); description by Ledebour in 1830 from specimens collected in 1793 by Johann Sievers; habitat in mountain forests at 1,100–2,400 m; fruit forest now only remnants; bears and horses as the main seed dispersers apart from people (citing Juniper and Mabberley); about 500 accessions at the Geneva repository; Iran listed as a possible country; the red-pigmented f. niedzwetzkyana and the doubts about its status.
  3. The domestication and evolutionary ecology of apples, Amandine Cornille, Tatiana Giraud, Marinus J. M. Smulders, Isabel Roldán-Ruiz and Pierre Gladieux, Trends in Genetics 30(2): 57–65; Wageningen University repository, 2014. Supports: fruit approaching the size of commercial cultivars (more than 60 mm); intermediate elevations, typically 900–1,600 m; only a few small intact forests of no more than several hundred hectares in the Tian Shan, southern Kazakhstan and Kyrgyzstan, with sporadic reports from Turkmenistan, Uzbekistan, Tajikistan and north-eastern Afghanistan; over-harvesting in the Soviet era; the term "Asian wild apple".
  4. Origins of the Apple: The Role of Megafaunal Mutualism in the Domestication of Malus and Rosaceous Trees, Robert N. Spengler, Frontiers in Plant Science 10: 617, 2019. Supports: wild Tian Shan trees with fruits up to 8 cm across; the argument that large fruits evolved to recruit large, now largely extinct, mammals as seed dispersers.
  5. Malus sieversii, The IUCN Red List of Threatened Species 2007: e.T32363A9693009, Participants of the FFI/IUCN SSC Central Asian regional tree Red Listing workshop, Bishkek, Kyrgyzstan (July 2006), 2007. Supports: Vulnerable under criteria A2cde, assessed 1 March 2007, global scope; population decreasing; native to China (Xinjiang), Kazakhstan, Kyrgyzstan, Tajikistan and Uzbekistan.
  6. The Red List of Trees of Central Asia, Antonia Eastwood, Georgy Lazkov and Adrian Newton, Fauna & Flora International and Botanic Gardens Conservation International, 2009. Supports: M. sieversii Vulnerable A2acde in China, Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan and Uzbekistan; threats from agricultural expansion and development, grafting of commercial varieties and hybridisation, and over-grazing; habitat in Kazakhstan reduced by over 70% in the previous 30 years; germplasm collected in Kazakhstan in the 1990s used by the USDA to improve disease resistance, with resistance found to scab, fire blight and drought; M. niedzwetzkyana Endangered B2ab(iii,v).
  7. The genome of the domesticated apple (Malus × domestica Borkh.), Riccardo Velasco and others, Nature Genetics 42: 833–839 (abstract), 2010. Supports: phylogenetic reconstruction of the genus identified M. sieversii as the progenitor of the cultivated apple.
  8. New Insight into the History of Domesticated Apple: Secondary Contribution of the European Wild Apple to the Genome of Cultivated Varieties, Amandine Cornille and others, PLoS Genetics 8(5): e1002703, 2012. Supports: M. sieversii confirmed as the initial progenitor, but the cultivated apple now genetically closer to M. sylvestris; no domestication bottleneck; an earlier 23-gene study suggesting M. sieversii and M. domestica form a single genepool.
  9. Genome re-sequencing reveals the history of apple and supports a two-stage model for fruit enlargement, Naibin Duan and others, Nature Communications 8: 249, 2017. Supports: cultivated apples likely originating from M. sieversii in Kazakhstan; M. sieversii in Xinjiang an isolated ecotype not directly contributing to domestication; 46% of the M. domestica genome probably derived from Kazakh M. sieversii.
  10. Phased diploid genome assemblies and pan-genomes provide insights into the genetic history of apple domestication, Xuepeng Sun and others, Nature Genetics 52: 1423–1432, 2020. Supports: a haplotype-resolved genome of M. sieversii; M. sieversii recovering its population size after a first bottleneck.
  11. The vulnerability of US apple (Malus) genetic resources, Gayle M. Volk and others, Genetic Resources and Crop Evolution 62: 765–794; USDA GRIN, 2015. Supports: four expeditions to Central Asia to collect M. sieversii between 1989 and 1996; a seedling orchard of M. sieversii at Geneva, New York; more than 170,000 seeds from collecting trips stored at −20 °C; 63,000 "Botany of Desire" seeds distributed after the success of Pollan's book.
  12. Malus sieversii (Ledeb.) M.Roem., Plants of the World Online, Royal Botanic Gardens, Kew. Supports: the name treated as a heterotypic synonym of Malus domestica (Suckow) Borkh.; the authority (Ledeb.) M.Roem..
  13. A revision of the genus Malus Mill. (Rosaceae), Jing-chao Li, Jian-quan Liu and Xin-fen Gao, European Journal of Taxonomy 853: 1–127, 2022. Supports: M. sieversii accepted as one of 26 wild species, with M. niedzwetzkyana and M. chitralensis among its synonyms.
  14. Malus niedzwetzkyana, The IUCN Red List of Threatened Species 2007: e.T63477A12681555, Participants of the FFI/IUCN SSC Central Asian regional tree Red Listing workshop, Bishkek, Kyrgyzstan (July 2006), 2007. Supports: M. niedzwetzkyana assessed as a species, Endangered under criteria B2ab(iii,v), in 2007.