Climate change and potatoes

Potato plants and potato crop yields are predicted to benefit from increased carbon dioxide concentrations in the atmosphere.[3] The major benefit of increased atmospheric carbon dioxide for potatoes (and other plants) is an increase in their photosynthetic rates which can increase their growth rates. Potato crop yields are also predicted to benefit because potatoes partition more starch to the edible tubers under elevated carbon dioxide levels.[1] Higher levels of atmospheric carbon dioxide also results in potatoes having to open their stomata less to take up an equal amount of carbon dioxide for photosynthesis,[1] which means less water loss through transpiration from stomata. As a result, the water use efficiency (the amount of carbon assimilated per unit water lost) of potato plants is predicted to increase.[1]

Potatoes grow best under temperate conditions.[4] Tuber growth and yield can be severely reduced by temperature fluctuations outside 5-30 °C.[5] The Intergovernmental Panel on Climate Change predicts global temperatures to increase between 1.1 and 6.4 °C by 2100.[6] The effect of increased temperatures on potato production in specific areas will vary depending partly on the current temperature of that area. Temperatures above 30 °C can have a range of negative effects on potato,[7] including:

• Slowing tuber growth and initiation.
• Less partitioning of starch to the tubers.
• Physiological damage to tubers (e.g. brown spots).
• Shortened/non-existent tuber dormancy, making tubers sprout too early.

These effects can reduce crop yield and the number and weight of tubers. As a result, areas where current temperatures are near the limits of potatoes’ temperature range (e.g. much of Subsaharan Africa,[1] will likely suffer large reductions in potato crop yields in the future.[4] At low temperatures potatoes are at risk of frost damage, which can reduce growth and badly damage tubers.[1] In areas where potato growth is currently limited or impossible due to risks of frost damage (e.g. at high altitudes and in high latitude countries such as Russia and Canada), rising temperatures will likely benefit potato crops by extending the growing season and extending potential potato growing land.[5]

Climate change predictions by the IPCC include likely changes to water resource availability across much of the globe.[6] In many areas water resources are expected to decrease, particularly in semi-arid areas.[1] Increases in extreme weather events including flash flooding are predicted, even in areas where overall average rainfall is predicted to decrease.[1]

Potatoes are sensitive to soil water deficits compared to other crops such as wheat,[8] and need frequent irrigation, especially while tubers are growing. Reduced rainfall in many areas is predicted to increase the need for irrigation of potato crops. For example, in the UK the amount of arable land suitable for rainfed potato production is expected to decrease by at least 75%.[9] As well as reductions in overall rainfall, potato crops also face challenges from changing seasonal rainfall patterns. For example, in Bolivia the rainy season has shortened in recent decades, resulting in a shorter potato growing season.[5]

As well as affecting potatoes directly, climate change is predicted to affect many potato pests and diseases. These include:

• Insect pests such as the potato tuber moth and Colorado potato beetle, which are predicted to spread into areas currently too cold for them.[1]
• Aphids which act as vectors for many potato viruses and will also be able to spread under increased temperatures.[10]
• Several pathogens causing potato blackleg disease (e.g. Dickeya) can grow and reproduce faster at higher temperatures and so will likely become more of a problem.[11]
• Bacterial infections such as Ralstonia solanacearum are predicted to benefit from higher temperatures and be able to spread more easily through flash flooding.[1]
• Late blight benefits from higher temperatures and wetter conditions.[12] Late blight is predicted to become a greater threat in some areas (e.g. in Finland [1]) and become a lesser threat in others (e.g. in the United Kingdom.[3])

Potato yields are predicted to decrease in some areas (e.g. Sub-Saharan Africa[1]) while increasing in others (e.g. northern Russia[4]), mostly due to changes in water and temperature regimes. At the same time potato production is predicted to become possible in high altitude and latitude areas where it would previously have been limited by frost damage. These changes in crop yields are predicted to cause shifts in the areas in which potato crops can be viably produced.[4] In some countries reductions in yields caused by increased temperatures and decreased water availability could be avoided to a high degree by shifting potato production areas.[4] A potential problem in shifting potato production is competition for land between potato crops and other crops and other land uses.

Potato requires frequent watering while tubers are growing to maintain yields. Due to decreasing water availability predicted in some areas (e.g. much of the United Kingdom), improving irrigation techniques and water capture is necessary to maintain potato crop yields without putting too much stress on water supplies. An example of an irrigation technique aimed at reducing water use which has been trialled on potatoes is Subsurface Drip Irrigation (SDI).[13]

Two main approaches are taken to create new potato varieties: ‘traditional’ plant breeding techniques and genetic modification. These techniques may play an important role in creating new cultivars able to maintain yields under stressors induced by climate change.

Traits that may be helpful in reducing negative impacts of climate on potato production include:

• Heat stress tolerance, in particular the ability to maintain tuber growth and initiation under high temperatures. Developing cultivars with greater heat stress tolerance is critical for maintaining yields in countries with potato production areas near current cultivars’ maximum temperature limits (e.g. Sub-Saharan Africa, India).[14]
• Drought tolerance. This includes better water use efficiency (amount of food produced per amount of water used) as well as potatoes that can be exposed to short drought periods and recover and produce acceptable yields. Deeper root systems could also be beneficial, as most commercial potato cultivars need frequent irrigation due to their shallow roots.[15]
• Fast growth/early maturation. Potatoes that grow faster could help adjust to shorter growing seasons in some areas[5] and also reduce the number of life cycles pests such as potato tuber moth can complete in a single growing season.
• Disease resistance. Potatoes with resistances to local pests and diseases could be helpful, especially in adapting to diseases spreading into new areas.

A major source of genetic material for creating new potato cultivars is the many species closely related to potato (Solanum tuberosum), many of which can be cross-bred with potato. There are also many varieties of Solanum tuberosum with potentially useful genetic material that are endemic to the Andes, the commercial potato's original habitat.[16]

Listed below are some examples of potato cultivars, hybrids and related species that have traits that may help reduce the negative direct and indirect impacts of climate change on potato production.

• Zahov - a heat tolerant polyploid hybrid between potato and several wild potato species.[7] Several wild potato species have been found to be more heat tolerant than Solanum tuberosum.[4]
• Kufri Surya – a heat tolerant, early maturing potato cultivar developed in India.[17]
• Solanum verrucosum – a wild potato species with genes that give it good resistance to late blight.[18]
• Sullu, an Andean potato variety with enhanced drought tolerance.[19]
• SpuntaG2 – a genetically modified variety of the Spunta potato cultivar, which is resistant to Potato Tuber Moth due to having the cry1Ia1 gene from Bacillus thuringiensis.[20]