Genetic Diversity of Potato (Solanum tuberosum L.) Cultivars Grown in Lesotho as Determined by Morphological Markers

Irish Potato (Solanum tuberosum L.)is originated from Peru, Bolivia and Andes in the Western South America [1]. Peru is considered as the center of origin, diversity and its wild relatives [2,3]. They were domesticated in the Andes and Southern Peru approximately 10 000 years ago [2,4]. Potatoes were introduced by Spaniards from Peru to Spain during trading, after which it was introduced in Europe where it became an important food crop in Ireland. Southern and Eastern Asia also showed the most rapid expansion over the past century [5]. Since then, its world-wide distribution increased tremendously making it the fourth largest starchy food crop following wheat, rice and maize. China is now the largest potato producing country in the world with the total annual yield of 60 million tons on 4 million ha and productivity of 15 tons ha-1 [6]. Approximately 85% of this potato is produced in the Northern part of China because of low temperature and suitability for growing potato crop [7]. Irish Potato crop is an annual, herbaceous dicotyledonous commonly propagated vegetatively, although it can also be propagated through seeds known as true potato seeds. Nonetheless, it can be grown as a perennial in selected environments [8]. Morphologically, potato can be characterized by erect stem which grows up to a height of one meter with alternate compound leaves of three to five pairs of leaflets arranged in a downward position [9]. Potato can be distinguished by its ability to develop tubers under short days and cool nights, and knowledge of genetic diversity, identification and characterization of cultivars provides an informative tool for the detection of duplicates in the collection, effective extension, better characterization and use inbreeding programs [10]. In addition, characterization of potato genetic diversity is also important for tracing fraud, duplication, violation of cultivar protection, intellectual property right and ascertaining proper use of trademark [11,12].

In the past, morphological characterization was the most powerful tool in description, classification and evaluation of genetic resources. With time, morphological was superseded by biochemical and DNA-based molecular markers [10]. Nonetheless, morphological markers are still a powerful method where genetic distance of cultivars are far apart, and has a limitation where cultivars are closely related and share parentage In the beginning of the past century, characterization was accomplished in potatoes using morphological markers, even though these markers were complex and greatly influenced by the environment [13,14]. In morphological characterization, descriptor for potato is available and compiled by International Plant Genetic Resource Unit of Food and Agriculture Organization (1982) to guide throughout the process. Descriptor is based on morphological traits such as leaf, stem, flower and tuber characteristics. Data regarding morphological characterization are generated throughout the growing season as potato cultivars are growing under field conditions [15], after which appropriate statistical tool is applied for analysis and virtualization leading to better comprehension.

All potato cultivars grown by farmers in Lesotho are brought from South Africa, which in turn obtain them from overseas or breed them within the country. They are imported into the country of Lesotho without following proper protocols of evaluating for distinctness, registration and adaptability. No method of characterization of potato has been established to date. As a result, some cultivars are mistaken for others, fraudulence is committed by people who multiply the seeds and sell them without a license from the owner, retailers use a different name for the same cultivar to disguise as if they are the ones breeding them and lastly, some are not easy to distinguish by visual appraisal. At the end of the day, such closely related cultivars are mixed when planting, thereby losing their distinctness and other economically important traits. This study is therefore undertaken with the following objectives; (i) to estimate genetic distance among eight potato cultivars using morphological markers, (ii) to determine the discriminatory power of the different morphological markers in distinguishing potato cultivars.