TABLE 3.

A summary of the effects of drought stress on key physiological tuber traits in potato and the range of methodologies by which these variables were manipulated.

References	MacKerron and Jefferies, 1986	Martin et al., 1992	Painter and Augustin, 1976	Steckel and Gray, 1979	Tourneux et al., 2003	Jefferies and MacKerron, 1987	Jefferies and MacKerron, 1989	Jefferies and MacKerron, 1993	Lahlou et al., 2003	Lefèvre et al., 2012	Levy, 1986b	Luitel et al., 2015
Observations	Decrease in tuber number	No effect on processing quality, no effect on prevalence of internal or external defects	Increase in prevalence of misshapes	Reduced tuber dry matter	Decreased dry matter concentration (Up-to-Date and Troubadour), increased dry matter concentration (Alpha)	Decreased total dry matter, increased dry matter concentration.	Reduced tuber water content.	Reduced tuber dry matter concentration.	Reduced fresh tuber yield.	Increased tuber water content.	No effect on prevalence of misshapes, increase in prevalence of misshapes (Kondor).	Decreased tuber number.
Cultivar	Maris Piper	Russet Burbank	Russet Burbank	King Edward, Pentland Crown, Majestic, Maris Piper	Alpha, Waycha (subsp. andigenum), Luky (subsp. andigenum), Ajahuiri (Solanum ajanhuiri), Janko Choquepito (Solanum curtilobum), CIP 382171.10 (subsp. tuberosum × subsp. andigenum)	Maris Piper, Record, Désirée, Pentland Crown, Pentland Dell, Pentland Squire.	Maris Piper.	21 Commercial cultivars.	Remarka, Dérirée, Nicola, Monalisa.	21 Andean cultivars	Blanka, Kondor, Draga, Monalisa, Alpha, Désirée, Romano, unnamed clone, Cara.	Five CIP clones, the German cultivar NPI-106, Désirée.
Culture method	Greenhouse plots	Field	Field	Field	Pots	Field	Field	Field	Field (all), Pots (Remarka and Désirée).	Outdoor controlled plots.	Field	Field
Drought conditions	Twenty-two treatments with varying lengths (8 to 40 days) of total water deprivation at either 50% emergence, tuber initiation or small tuber stage.	Six treatments trickle irrigated with 30 mm when SMD reached 50 mm. Irrigation was removed and rain was excluded at various points during the season with varying severity.	Four water treatments. (1) Soil moisture was depleted to 25% before irrigation during early tuber set and then depleted to 65% before irrigation for the remained of the season. (2) Soil moisture was depleted to 65% before irrigation. (3) Soil moisture was depleted to 75% before irrigation. (4) Soil moisture was depleted to 85% before irrigation. How much water was given is unclear but assumed to restore field capacity.	Deprived of water by a mobile rain shelter from emergence to harvest, except for one bout of irrigation with 25 mm of water at the time of tuber formation.	Plants irrigated as controls until being subjected to either intermittent drought (gradual decline in water supply for 5 weeks, and 1 week with no water supply followed by full restoration of water supply) or terminal drought (same as intermittent drought but with no restoration of water supply) at tuberization.	Deprived of water by polythene sheeting laid over the plants from emergence to harvest.	Deprived of water by a mobile rain shelter from emergence to harvest.	Deprived of water by a mobile rain shelter from emergence to harvest.	Rainfed in the field. Irrigated to field capacity when soil moisture dropped below −0.8 MPa in the pots.	As control but irrigation stopped for 58, 86 days after planting.	Irrigated every 3 to 4 days to replace either 0.64 to 0.89 or 0.40 to 0.67 times water lost to evapotranspiration.	Irrigated once soon after planting, then total water deprivation.
Control		Three treatments trickle irrigated with either 20 mm of water when soil moisture deficit reached 30 mm, 30 mm when SMD reached 50 mm or 50 mm when SMD reached 50 mm.		Rainfed plus irrigation to field capacity when the soil moisture deficit reached 25 mm.	Irrigated to field capacity twice per week.	Rainfed plus trickle irrigation to maintain a soil moisture deficit of <30 mm.	Rainfed plus trickle irrigation to maintain a soil moisture deficit of <30 mm.	Rainfed plus sprinkler irrigation to maintain a soil moisture deficit of <25 mm.	Irrigated with 20 mm five times throughout the season in the field. Irrigated to field capacity when soil moisture dropped below −0.3 MPa in the pots.	Deprived from rainfall by a plastic rain shelter and 60 cm below-ground barrier. Drip irrigated to maintain a soil water potential between 0 and −0.02 MPa.	Irrigated every 3 to 4 days to replace water lost by evapotranspiration.	Rainfed and furrow irrigated when soil moisture dropped below 8% to maintain “ideal moisture conditions (8–16%)”.