RESPONSE OF SWEET-POTATO (IPOMOEA-BATATAS LAM) TO SHADING AT DIFFERENT GROWTH-STAGES

During 1990 and 1991 growth seasons at two locations in Peru four sweet potato cultivars were rested for their response to a short-term shading. The plants were subjected to artificial shade (42 % light reduction) for 1 month at different growth stages. A high genetic variability was found in the extent to which tuber and total biomass yield of sweet potato was affected by sub-optimal light conditions. One cultivar was completely tolerant to shade at all growth stages, whereas the others showed a yield decline between 20 % and 55 %. Generally tuber yield was most reduced when shade was imposed at the end of the growth season (fourth and fifth months) and the lease at its beginning (first and second months). Yield losses were due to a diminished biomass production and/or an altered assimilate partitioning within the plant. Tuber formation was affected rather than tuber initiation.