THE EFFECT OF DIFFERENT SHADE LEVELS ON GROWTH AND TUBER YIELD OF SWEET-POTATO .2. TUBER YIELD

Eight sweet potato cultivars (Ipomoea batatas Lam.) were grown under f our different light regimes (0, 26, 42 and 60 % light reduction (LR)) at two experimental sites of the International Potato Center (CIP) in Peru during the 1990 and 1991 growing season. Increasing shade diminis hed the tuber yield of five cultivars, two showed a tolerance for slig ht (26 % LR) and moderate (42 % LR) shade and one had the same yield i n full sunshine and slight shade. Shade mainly reduced the sink-size ( tubers m(-2)) of sweet potato and to a lesser extent the sink-strength . The growth of the plant top was hardly affected by shade; slight sha de even favoured shoot development of some cultivars. The plant top wa s the stronger sink under shade conditions and tuber yield was not onl y reduced by lesser assimilate production as a whole but also by an al tered assimilate partitioning.