Drought tolerance in potatoes
By Marg Land
June 30, 2008 – Scientists are
studying potato varieties from the cold, dry Andean Altiplano in order
to engineer new drought-resistant crops of potato, as well as other
June 30, 2008 – Climate change is expected to exacerbate drought events throughout the world, resulting in large-scale ecosystem alteration and failure of drought-sensitive crops. In addition, periods of drought vary from year to year in severity and length, making it difficult for plants to adapt to more severe conditions. Many modern varieties of potatoes are considered to be drought-sensitive. However, evolution and cultivation in the cold, dry Andean Altiplano gave rise to a number of potato varieties that could tolerate drought. Scientists are studying these varieties to identify the genes and molecular mechanisms of drought tolerance in order to engineer new drought-resistant crops of potato, as well as other Solanaceous vegetables.
Dr. Roland Schafleitner and his colleagues, Raymundo Oscar Gutierrez Rosales, Luz Rosalina Tincopa Marca, and Merideth Bonierbale, are examining the genes for drought tolerance traits in several native Andean potato landraces. Dr. Schafleitner, of the Germplasm Enhancement and Crop Improvement Division, International Potato Center in Peru, recently presented this work at a symposium on the Biology of Solanaceous Species at the annual meeting of the American Society of Plant Biologists in Mérida, Mexico.
From tiny dark blue tubers to huge tan bakers, potatoes come in an astonishing variety of colors and sizes, reflecting their genetic variety as well as their long history of cultivation. Potato was first domesticated in the Peruvian Andes over 7,000 years ago and was carried to Europe in the late 16th century, becoming such an important food source that a failure in the crop caused by blight in Ireland triggered a famine. It is a member of the Solanaceae or nightshade family, which also includes tomato, eggplant, tobacco, and chili peppers.
Drought first causes stomatal closure, reducing CO2 uptake for photosynthesis, reducing plant growth and yield. Plants vary in the types and speed of responses to drought conditions, depending on their genetic and ecotypic backgrounds, but a number of drought responsive genes are conserved across plant taxa, especially genes involved in osmotic adjustment, detoxification, and cell communication and signaling. Schafleitner and his co-workers studied two Andean potato clones, SA2563 and Sullu (Solanum tuberosum) L. subsp. Andigena (Juz, Bukasov) under field conditions and used microarrays to to identify genes that are up- and down-regulated under drought conditions.
The scientists identified about 2000 genes that were differentially regulated under drought conditions. Many of these genes contribute to the increased drought tolerance of the two clones under investigation. Up-regulated genes included transcription factors and cell signaling-related genes such as kinases and phosphatases, which regulate numerous functions, including metabolic changes and cell defense functions.
Solute concentrations were increased, lowering osmotic potential, to induce uptake of water from drying soils. Increased expression of lipid transfer genes and fatty-acid and wax synthase genes suggested the reinforcement of cell membranes and cuticles. Genes for cell wall components were also upregulated, as were biosynthetic genes for antioxidants such as flavonoids and anthocyanins, which function in cell protection and detoxification under oxidative stress.
Many of the ancient potato landraces were adaptations to different environmental conditions such as different soils, temperature, altitude, and drought. Preservation of these varieties and knowledge of their genetic and adaptive histories are of paramount importance as farmers around the world cope with changes in temperature and water availability and struggle to maintain a food supply for growing populations.
The International Potato Center in Lima, Peru maintains the world's largest collection of tubers in the interest of conserving the genetic diversity of potato as well as investigating traits such as resistance to various insects and diseases, as well as to cold, heat and drought. The results of this research are used for screening and breeding efforts in crop improvement. The knowledge gained from these efforts can also be applied in crop and yield improvement efforts for other members of the Solanaceae.