Exploring the genotype of the tea plant

Raising and exporting black tea is an activity of major importance in Africa today; Africa has become the world's second largest tea exporting region after India.

Tea has been grown in China for perhaps a millennium "by hand," with farmers seeking out and hand-selecting the tea bushes producing the best yield and quality of tea. Since tea growing reached the West in the 19th century, however, tea cultivation has rapidly incorporated techniques of genetics and, most recently, of molecular biology. While tea breeders continue to walk the fields daily to monitor the health of crops and to seek out the most promising bushes, the real action today is in the laboratory, where the breeder's skill is supplemented by work done at the molecular scale with instruments of enormous complexity and cost.

Pelly Malebe, a doctoral student in the SABINA network, has been swept up in this genetic revolution and is eagerly helping to help push it along. She works under the supervision of Prof. Zeno Apostolides at the University of Pretoria's Department of Biochemistry, riding the crest of an agro-technological revolution. The instruments of the present can not only analyze and compare the genes of the tea plants, but also allow biochemists to accomplish research feats undreamed of just a decade ago.

Pelly is a member of a research partnership between the University of Pretoria and Malawi, where the Tea Research Foundation of Central Africa (TRFCA) is located. Another of her SABINA colleagues is Nicholas Mphangwe, a Malawian who is actively involved in the TRFCA's breeding program. Their work carries considerable weight in Malawi, where the tea crop provides about nine percent of the country's foreign exchange and about five percent of the world's output.

The primary focus of Pelly's work is to locate and understand the sections of tea DNA that help the plant resist drought. Such a section is known as a marker, a gene or DNA sequence with a known location on a chromosome that can be used to identify the trait of interest in an individual or species. This is critical for tea, which prefers at least 50 inches of rain a year, and begins to drop its leaves when rainfall is not sufficient. Because Pelly is a native of the dry Limpopo province of South Africa, she is no stranger to drought, and her experience with dried-up crops and hungry farmers lends urgency to her work.

As a master's student at the University of Pretoria in 2009, Prof. Apostolides assigned her the task of searching for a genetic marker in tea plants that are relatively drought-hardy. She proved adept at picking up the complex techniques of tea genetics and was soon able to identify a putative marker for cultivars that show high resistance to drought. A cultivar is a plant selected by growers for certain traits and then vegetatively propagated by stem-cuttings so the next generation will have an identical genome. Virtually all food crops and ornamental plants sold today are cultivars that have been selected for certain traits; very few wild plants are used for commercial purposes.

Such activities are by no means unique to tea; the analysis of genetic variation is an essential part of most plant genetics and crop improvement programs. Knowledge of DNA sequences has become indispensable for basic biological research and in numerous applied fields such as diagnostics, biotechnology, and forensic biology. The type of analysis depends on understanding the plant's DNA and determining the precise order of the four bases (adenine, thymine, cytosine, and guanine) that function as the "letters" of the DNA alphabet (arranged in base pairs because of the double helix shape of DNA). The "words" that are formed by various arrangements of the letters determine the output, traits, and reproduction of the genome - for tea and every other organism, from virus to human. Any change in the spelling of these words is critical to DNA analysis as it might signify, for example, greater (or lesser) resistance to drought. By Alan Anderson.

Source: http://allafrica.com



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