Genetic analysis of potato (Solanum species) genotypes using morphological and molecular markers

Abstract

English: Genetic analysis of 53 potato genotypes representing seven of the 13 potato species that are frequently used in the varietal development of potato was examined using morphological and molecular markers with main objective of analyzing their genetic distance and evolutionary relationships. These genotypes were obtained from the Ethiopian National Potato Research Program and the ARC-Roodeplaat Vegetable and Ornamental Plant Institute of South Africa. These species are collections from the major diversity centres of potato, i.e., Peru, Argentina, Mexico and Bolivia. They include both wild and cultivated diploid and tetraploid genotypes. Of the 53 genotypes only 15 genotypes consisting 11 advanced breeding clones and Ethiopian converted commercial tetraploid varieties were examined morphologically. As a result a genetic distance ranging from 0.46 to 1.68 was computed. This clearly indicates the phenotypic diversity existing .among them and the diverse genetic background of their parental materials. A direct positive correlation was found between stem height and weight of tuber and days to flowering and days to harvesting as previously reported and negative associations between number of tubers per plant and average weight of a tuber and leaflet width and days to flowering. AFLP and SSR analysis of these genotypes together with 38 other genotypes of different species supported the phenotypic diversity result with a genetic distance value ranging from 0.28 to 0.70 for AFLP and 0.28 to 0.78 for SSR. As expected the genetic distance computed using molecular data are more conservative in their estimate than those computed using morphological data. Furthermore, AFLP and SSR data revealed that Solanum stenotomum and Solanum sparsipilum might be the putative ancestor of the cultivated potato Solanum tuberosum subsp. andigena as previously hypothesized. However, the grouping of species based on DNA does not always indicate ancestry but is rather a result of introduced traits from wild species. This data clearly indicated those species that have contributed genes to potato cultivars thus far developed. Hence, with the use of morphological markers that are heritable and stable genetic distance could be successfully studied. This, however, does not rule out the major drawbacks of morphological markers caused by the low level of heritable and stable characters. In conclusion, this study has revealed the relevance of employing morphological markers together with molecular markers to determine genetic distances for potato breeding. Although there were differences in the ranges of genetic distances calculated using the different markers, there was a remarkable correlation between the relationships of the different genoptypes based on these distances. Hence, DNA marker systems with high multiplex ratio like AFLP and high diversity index like SSR can be an excellent component to the morphological and conventional markers that are currently used to estimate genetic diversity or distance and evolutionary relationships for potato.

Afrikaans: Genetiese analise was uitgevoer op 53 aartappel genotipes verteenwoordigend van sewe uit 13 aartappel spesies wat in variëteit ontwikkéilng gebruik word. Die doel van hierdie studie was die vergelyking van genotipes op morfologiese en molekulêre vlak, die bepaling van genetiese afstand tussen genotipes en daaropvolgende evolusionêre verwantskappe tussen hulle te ondersoek. Plant materiaal is ontvang vanaf die Ethiopiese-Nasionale-Aartappel- Navorsing-Program en die LNR-Roodeplaat Groente en Sierplant Instituut van Suid-Afrika en is verteenwoordigende versamelings van die hoof diversiteits bronne van aartappel naamlik Peru, Argentinië, Mexiko en Bolivia, insluitend wildetipes, gekweekte diploïedes en tetraploïedes. Net 15 van die 53 genotipes, afkomstig van ontwikkelde teellyne en Ethiopiese tetraploïede variëteite was morfologies ondersoek. Daar is vasgestel dat die genetiese afstand tussen genotipes wissel tussen 0.46 tot 1.68. Dit dui op 'n breë diversiteit en asook die ouermateriaal waaruit hulle ontwikkel is. 'n Positiewe korrelasie is gevind tussen stamhoogte en gewig van knolle asook die hoeveelheid dae tot bloei en oes van knolle. 'n Negatiewe korrelasie is gevind tussen die hoeveelheid knolle per plant en gemiddelde gewig van knolle asook blaartjie wydte en dae tot bloei. AFLP en SSR analise van hierdie genotipes tesame met 38 ander genotipes verteenwoordigend van verskillende spesies het die hoeveelheid fenetiese diversiteit ondersteun met 'n genetiese waarde van 0.28 tot 0.70 vir AFLPs en 0.28 tot 0.78 vir SSR analise. Soos verwag, is die genetiese afstande afkomstig vanaf molekulêre data meer konserwatief as ooreenkomstige waardes deur morfologie bepaal. AFLP en SSR data het ook verder getoon dat Solanum stenotomum en Solanum sparsipilum die moontlike voorouer van die gekweekte variëteit Solanum tuberosum subsp. Andigena is. Alhoewel, die verwantskappe aangetoon deur DNA analise nie altyd 'n aanduiding van afkoms is nie maar eerder a.g.v. ingeteelde eienskappe vanaf wildetipe spesies. Hierdie data gee dus 'n duidelike aanduiding van die spesies gebruik in die ontwikkeling van gekweekte ontwikkelde lyne. Dus, met behulp van stabiele morfologiese eienskappe kan betroubare genetiese afstande tussen genotipes bepaal word. Nieteenstaande, is die gebruik van morfologie bemoeilik deur lae vlakke van duidelike oorerwing en stabiliteit. Ten slotte, hierdie studie dui die belangrikheid van die gebruik van morfologiese eienskappe tesame met molekulêre eienskappe om genetiese,afstande in aartappels te bepaal. Alhoewel daar gevind is dat verskillende merkers verskillende genetiese afstande getoon het, is gevind dat daar 'n merkwaardige ooreenstemming is tussen die verwantskappe soos deur die verskillende merkers aangetoon. DNA merker sisteme soos AFLPs, met veelvoudige lokus herkenning, en SSRs, met hoë diversiteits· indeks, is ideaal geskik vir gebruik saam met morfologiese en konvensionele merkers soos tans gebruik om genetiese afstande en verwantskappe te bepaal in aartappels.