Different theories of the evolution of I. batatas have been advanced by Japanese researchers, who consider it an autopolyploid derivative of I. trifida , and American researchers, who favor an allopolyploid origin involving I. trifida and an unidentified tetraploid parent. Introgression of traits from related species is normally prevented by crossing barriers between species. Some success has been reported through using massive numbers of crosses and embryo culture. However, introducing genes by this method is still generally not viable in a breeding program even though a few traits of considerable interest have been identified in related species. Crop Culture Ecology Sweetpotato is cultivated as a perennial in tropical and subtropical lowland agroecologies although it is well adapted to other zones and can be grown over widely different environments.
Storage roots are sensitive to changes in soil temperature depending on stage of root development.
Sweetpotato responds well to increasing moisture but is considered a drought-tolerant crop because it is deep rooted and capable of developing storage roots under very dry conditions. Excessive moisture inhibits storage root development in early growth stages and causes decay of storage roots in later growth stages. Sweetpotatoes grow best in a sandy loam, well-drained soil. They have been produced at altitudes in excess of 2000m and as far north as Canada. Cultivars Hundreds of cultivars and land races are used throughout the world and are unique to countries or to smaller regions within countries.