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skin is purplish or red. Often, they are mottled or striped with red or purple, especially below the eyes. The flesh is yellow.
Studies have shown there is a high correlation between the yield of tubers on the one hand and plant height, tuber size, and number of tubers on the other.
Horticultural Varieties. More than 100 varieties have been recognized; there are probably more. One reported in Colombia is var. pilifera, slender, long, deeply furrowed, and white, sometimes with pink-purple ends. Another, var. lineovaculata, in Colombia, Peru, and Bolivia, is white, streaked and spotted with red. Others may be yellow, orange, reddish violet, or dark purple, often stippled with bright red or purple dots and lines.
Color variants are recognized by a number of native descriptive names, among them in Peru are yana-añu (black), puca-añu (red), yurac-añu (white), sapullu-añu (yellow), and muru-añu (spotted).
Collections are maintained at Quito (INIAP, Santa Catalina), Ayacucho, Junín, and Huancayo.
Daylength. The plant seems to require 12-hour days (or perhaps less) for tuber formation, although it has successfully developed tubers outdoors in Vancouver, Canada (in October when daylight was less than 12 hours),
and under glass in southeast England.
Rainfall. The crop requires heavy rainfall; in its native range it receives between 700 and 1,600 mm. It seems to thrive in misty and cloudy weather.
Altitude. Mashua grows best between 2,400 and 4,300 m above sea level along the Andean cordillera. However, altitude may not be an important factor, considering its productivity in Canada, England, and New Zealand.
Low Temperature. It will tolerate light frost and is unaffected by temperatures as low as 4°C. In many parts of its range, it is regularly exposed to mild frosts.
High Temperature. Unknown. Probably above 20°C.
Soil Type. Mashua grows in soils ranging from pH 5.3 to 7.5. While it is tolerant of alkaline conditions, it performs best in fertile, organic soils. Good drainage helps inhibit soil fungi infestations.