b'Heat-ProofingOur Potato CropsAs climate warming turns up the heat, how will Canadian potato production be affected?BY: CAROLYN KING POTATO CROPS ARE known to be sensitive to high temperatures, says Xiu-Qing Li, a research scientist at Agriculture and Agri-Food Canadas (AAFC) Fredericton Research and Development Centre. Potatoes evolved high in the Andes of South America where conditions are relatively cool. So, they grow best at temperatures around 22 degrees Celsius, which makes Canada a great place for potato production, he says.But climate warming has already caused some very hot days in Canada. The highest temperatures recorded in most Canadian provinces in recent years were around 35 C or higher.Thats why Li and his research team have been examining how heat stress af-fects the growth, development and productivity of Canadian potato varieties. Their findings so far show rising temperatures could be a serious issue. The big question on researchers minds is how do we help our potato crops beat the heat?EVALUATING VARIETAL RESPONSESLi and several colleagues recently published the results from their greenhouse study where they assessed the effects of heat stress on 55 Canadian potato varieties. One set of the 55 cultivars was grown under a high-temperature regime of 35 C during the day and 28 C at night, and a second set was grown under ideal conditions of 22 C during the day and 18 C at night. The researchers measured plant height andXiu-Qing Li observes a small potato tuber, similar to the tubers produced by the leaf size, leaf chlorophyll content, and weight of the largest tuber.heat-stressed plants in his study, and an average-sized tuber grown under normal Until this study, very little was known about the responses of Canadian varie- conditions.PHOTO: AAFCties under high-temperature conditions. We have performed the first-ever large-scale evaluation of potato varieties fortuber was 93 per cent lower under the high-temperature conditions compared with their tolerance to heat stress, says Li. His study included two replicates of eachideal conditions. of the two treatments, and four plants of each variety within each replicate, for aThe varieties that performed best in terms of tuber weight under high temper-total of 880 plants, which generated lots of useful information. atures were Eramosa, Chieftain, AC Belmont, and Superior. And even Eramosa, the We have identified the relative heat tolerance and susceptibility of the 55most heat tolerant, had a 70 per cent reduction in tuber weight. varieties. We found significant variation in heat-stress responses among theThe worst performers were Russet Burbank, All Blue, Butte, AC Chaleur and varieties, he says. White Rose. Under heat stress, the All Blue, Butte, AC Chaleur and White Rose We demonstrated that most of the cultivarseven the relatively heat-toler- plants produced no tubers at all. Out of the eight Russet Burbank plants grown ant onesare very sensitive to heat stress. Overall, the plants grown under theunder heat-stress conditions, only one plant produced any tubers, and it had just high-temperature regime had much smaller leaves, taller plant heights, higherone little tuber weighing about one gram.estimated chlorophyll contents, and severely reduced tuber weights.Under normal growing conditions, when a potato plant conducts photosynthe-The cultivars that were relatively heat tolerant in terms of having the highestsis, its photosynthesis products are translocated from its leaves to its tubers and tuber weights, also had greater plant height and higher chlorophyll content understored there as starch. Modern potato varieties have been bred to be very efficient heat-stress conditions, compared with the control plants.at this, Li says. Under heat stress, the plant still conducts photosynthesis, but for some TUBER PRODUCTION DRASTICALLY REDUCED reason, the photosynthesis products mainly stay in the above-ground part of the The most concerning finding is that heat stress dramatically decreased tuber for- plant instead of going to the tubers. Perhaps the tubers have less ability to attract mation and tuber weight in all 55 varieties. On average, the weight of the largestthe photosynthesis products. Perhaps the translocation path has a problem. 44 SPUDSMART.COM WINTER 2020'