TABLE 1.

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

References	Albiski et al., 2012	Anithakumari et al., 2011	Haverkort et al., 1990	Lahlou and Ledent, 2005	Mane et al., 2008	Tourneux et al., 2003
Observations	Decreased root length.	Increased root dry mass.	Decreased stolon number.	Increased root depth, increased root dry mass (Remarka, Nicola and Monalisa), decreased root dry mass (Désirée), increased stolon number.	Decrease root dry mass (Ccompis), no effect on root dry mass (Sulla).	Increased root dry mass.
Cultivar	SY-C.1, SY-C.2, SY-C.3, SY-C.14, SY-C.28, SY-C.29, SY-C.31, SY-C.46, SY-C.52, SY-C.53, SY-C.54, SY-C.55, SY-C.56, SY-C.57, SY-C.58, SY-C.59, SY-C.60, SY-C.61	A random subset of the C × E diploid potato mapping population.	Radosa, Bintje.	Remarka, Dérirée (field and greenhouse); Nicola, Monalisa (field only).	Sullu (subsp. andigenum), Ccompis (subsp. andigenum).	Alpha, Waycha (subsp. andigenum), Luky (subsp. andigenum), Ajahuiri (Solanum ajanhuiri), Janko Choquepito (Solanum curtilobum), CIP 382171.10 (subsp. tuberosum × subsp. andigenum).
Culture method	In vitro	In vitro	Field and Pots.	Field (Remarka, Désirée, Nicola and Monalisa) Pots (Remarka and Désirée).	Field	Pots
Drought conditions	Six variations of growth media containing 0, 2, 4, 6, 8, or 10% (w:v) sorbitol to create graduated water potentials between -0.58 MPa (least sever water stress) to −2.5 MPa (most severe water stress).	Water potential of growth media lowered to −0.7 MPa by the addition of polyethylene glycol (PEG) for 7 weeks. 3 of 7 replicates were then allowed to recover for 4 weeks.	Irrigated to field capacity when soil moisture exceeded 100 kPa.	Rainfed in the field. Irrigated to field capacity when soil moisture dropped below −0.8 MPa in the pots.	Irrigated as controls until 45 days after planting when irrigation was completely suspended for 59 days (unclear if drought was terminal or intermittent).	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.
Control		Plants were grown in the same growth media in the absence of PEG. Water potential unclear.	Irrigated to maintain soil moisture levels at “near field capacity” constantly.	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.	Irrigated to maintain soil moisture between 0 and −0.02 MPa.	Irrigated to field capacity twice per week.