Solanum ajanhuiri

Cultivated potatoes are taxonomically difficult, and cultivated potatoes have been classified very differently by different taxonomists. Indigenous primitive cultivated (landrace) potatoes are grown throughout mid to high (about 3000-3500 m) elevations in the Andes from western Venezuela to northern Argentina, and then in lowland south-central Chile, concentrated in the Chonos Archipelago. Landrace populations in Mexico and Central America are recent, post-Columbian introductions (Ugent, 1968). The landraces are highly diverse, with a great variety of shapes and skin and tuber colors not often seen in modern varieties. The taxonomic treatment of Solanum ajanhuiri used here follows Spooner et al. (2007) that divide cultivated potato species into four species: S. tuberosum, S. ajanhuiri Juz. and Bukasov, S. curtilobum Juz. and Bukasov, and S. juzepczukii Bukasov.

The widely used recent classification of Hawkes (1990) divided cultivated potato into seven species and seven subspecies. Hawkes’ (1990) treatment was not universally accepted. The Russian potato taxonomists Bukasov (1971) and Lechnovich (1971) recognized 21 species. Ochoa (1990, 1999) recognized nine species and 141 infraspecific taxa for the Bolivian cultivated species alone. Bukasov (1971), Lechnovich (1971), Hawkes (1990), and Ochoa (1990) classified potatoes as distinct species under the International Code of Botanical Nomenclature (ICBN) (McNeill et al., 2006). Dodds (1962), in contrast, treated the cultivated species under the International Code of Nomenclature of Cultivated Plants (ICNCP) (Bricknell et al., 2005). Dodds (1962) suggested that there was poor morphological support for most cultivated species, and recognized only S. ×curtilobum, S. ×juzepczukii, and S. tuberosum, with five “groups” recognized in the latter. “Cultivar-groups” (the current terminology) are taxonomic categories used by the ICNCP to associate cultivated plants with traits that are of use to agriculturists. The cultivar-group classification of Dodds (1962) was based on comparative morphology, reproductive biology, cytological and genetic data, and cultural practices. He contended that the morphological characters used by Hawkes (1956) to separate species exaggerated the consistency of qualitative and quantitative characters.

Ploidy level has been of great importance in the classification and identification of cultivated potatoes. Bukasov (1939) was the first to count chromosomes of the cultivated potatoes and discovered diploids, triploids, tetraploids, and pentaploids and used these data to speculate on their hybrid origins. In historical and current practice, identifications are frequently made only after chromosome counts are determined, and reidentifications made after chromosome counts do not match that expected for the species. The strong reliance on ploidy levels was clearly stated by Hawkes and Hjerting (1989, p. 389): “The chromosome number of 2n = 36 largely helps to identify S. chaucha, but morphological characters can also be used.”

Huamán and Spooner (2002) examined the morphological support for the classification of landrace populations of cultivated potatoes, using representatives of all seven species and most subspecies as outlined in the taxonomic treatment of Hawkes (1990). The results showed some phenetic support for S. ajanhuiri, S. chaucha, S. curtilobum, S. juzepczukii, and S. tuberosum subsp. tuberosum, but little support for the other taxa. Most morphological support is only present by using a suite of characters, all of which are shared with other taxa. These results, combined with their likely hybrid origins and evolutionary dynamics of continuing hybridization led Huamán and Spooner (2002) to recognize all landrace populations of cultivated potatoes as a single species, S. tuberosum, with the eight cultivar-groups: Ajanhuiri Group, Andigena Group, Chaucha Group, Chilotanum Group, Curtilobum Group, Juzepczukii Group, Phureja Group, and Stenotomum Group.

Other studies questioned the reality of even these artificial cultivar-groups. For example, the S. tuberosum L. Phureja Group was recognized either as a Cultivar Group or species (S. phureja) based on short-day adaptation, low tuber dormancy, and its diploid (2n = 2x = 24) nature. It was believed to consist of a variety of landraces widely grown in the Andes from western Venezuela to central Bolivia, and to have excellent culinary properties and other traits for developing modern varieties. Ghislain et al. (2006) examined the entire germplasm collection of the Phureja Group at the International Potato Center (CIP) with nuclear simple sequence repeats (nSSR, or microsatellite) to complement a prior RAPD study. The initial goal was to explore the use of these markers to form a core collection of cultivar-groups of potatoes. The nSSR data showed a very unexpected result in that it uncovered 25 unexpected triploid and tetraploid accessions. Chromosome counts of the 102 accessions confirmed these nSSR results and highlighted seven more triploids or tetraploids. Thus, these nSSR markers were good indicators of ploidy for diploid potatoes in 92% of the cases. Because the Phureja Group was defined partly on its diploid nature, and because the nSSR study showed over 30% of the CIP collection to be polyploid, they questioned the validity not only of the Phureja Group but of all cultivar-groups of potato.

Spooner et al. (2007) considerably expanded the nSSR study of Ghislain et al. (2006) through an extensive study of 742 landraces of all cultivated species (or cultivar-groups), and eight closely related wild species progenitors, with 50 nSSRs and the 241-bp plastid deletion marker generally distinguishing Andean from Chilean potato landraces. The data highlighted a tendency to separate three groups: 1) putative diploids, 2) putative tetraploids, and 3) the hybrid cultivated species S. ajanhuiri (diploid), S. juzepczukii (triploid), and S. curtilobum (pentaploid), but there are many exceptions to grouping by ploidy. Strong statistical support for this tree occurred only for S. ajanhuiri, S. curtilobum, and S. juzepczukii. In combination with recent morphological analyses of Huamán and Spooner (2002), and an examination of the identification history of these collections at CIP, they proposed a reclassification of the cultivated potatoes into four species (1) S. tuberosum, with two cultivar-groups (Andigenum Group of upland Andean genotypes containing diploids, triploids and tetraploids, and the Chilotanum Group of lowland tetraploid Chilean landraces), (2) S. ajanhuiri (diploid), (3) S. juzepczukii (triploid), and (4) S. curtilobum (pentaploid).

Solanum ajanhuiri is a hybrid cultivar between diploid forms of S. tuberosum L. (formerly classified as S. stenotomum Juz. and Bukasov) and the wild species S. boliviense Dunal (including S. megistacrolobum). Some clones of S. ajanhuiri are likely formed by backcrossing to S. tuberosum. Some clones named ‘Sisu’ are believed to be triploid hybrids with the tetraploid species S. acaule. (Huamán et al., 1980, 1982, 1983; Johns and Keen, 1986; Johns et al., 1987).

Landraces originally were distributed in the high Andean altiplano between southern Peru and central Bolivia, at elevations between 3700 and 4100 m. However, in Peru only the purple-skinned ‘Ajawiri’ is scarcely grown. In the International Potato Center genebank there are 10 cultivars of Ajanhuiri Group. These include ‘Jancko Ajawiri’, Laram Ajawiri’, ‘Jancko Yari’, ‘Wila Yari’, ‘Chañu Yari’, ‘Alka Yari’, and ‘Jancko Sisu Yari’ reported in Huamán et al. (1980). Others from Bolivia are ‘Chañu Ajawiri’, ‘Wila Palta Yari’, and ‘Wila Anckanche’ (Huamán and Spooner, 2002).