Malus sieversii: a historical, genetic, and conservational perspective of the primary progenitor species of domesticated apples

Apples are one of the most valued tree fruit crops around the world. Currently, a few highly popular and economically successful apple cultivars dominate the commercial production and serve as main genetic contributors to the development of new apple cultivars. This limited level of genetic diversity, grown as a clonally propagated monoculture renders the apple industry vulnerable to the wide range of weather events, pests, and pathogens. Wild apple species are an excellent source of beneficial alleles for the wide range of biotic and abiotic stressors challenging apple production. However, the biological barriers of breeding with small-fruited wild apples greatly limit their use. Using a closely related wild species of apple such as Malus sieversii can improve the efficiency of breeding efforts and broaden the base of available genetics. M. sieversii is the main progenitor of the domesticated apple, native to Central Asia. The similarity of fruit morphology to domesticated apples and resistances to abiotic and biotic stresses makes it appealing for apple breeding programs. However, this important species is under threat of extinction in its native range. Preserving the wild apple forests in Central Asia is vital for ensuring the sustainable protection of this important genetic resource. The insufficient awareness about the complete range of challenges and opportunities associated with M. sieversii hinders the maximization of its potential benefits. This review aims to provide comprehensive information on the cultural and historical context of M. sieversii, current genetic knowledge for breeding, and the conservation challenges of wild apple forests.