Sweet potatoes do not generally twine, but twining can be induced by shade. Twining sweet potatoes were produced by selection and polycrossing. Frequency of climbing sweet potatoes increased in four successive populations from 0.7 to 33, 56, and 48%. Twining sweet potatoes produce normal storage roots, and can be selected for other characteristics. The foliage is modified. Most twiners have entire leaves, long, thin vines with long internodes, thin basal vines and underdeveloped crowns. Vine tops tend to grow vertically and twine in a counter-clockwise direction. Propagation of twiners under optimum conditions is restricted by the ease with which the thin stems wilt, and by reduced rooting. Most twiners are susceptible to "virus" disease. The clone, whether propagated from stems or from sprouts, is less vigorous than the seedling generation. Principal symptoms are small, rugose leaves and slow growth. After one or two generations it becomes impractical to continue. Twiners are still vigorous under test on supports and in relay with corn. Stable twining varieties should be useful in multiple cropping.


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