EFFECTS OF PLANTING MIXTURES OF DIFFERENT SIZES OF POTATO SEED TUBERSON THE YIELD AND SIZE OF TUBERS

In 1989 and 1990, small, medium and large seed tubers, cv. Desiree, we re planted 38 cm apart in experiments designed to measure the effects of different combinations of neighbouring plants on the yield and size of tubers from individual plants. Total yield, ware yield (> 150 g), numbers of tubers and numbers of stems increased as seed tuber size in creased. Also, decreasing the size of seed tubers decreased the number s of tubers in all sizes except those > 200 g. Competition from the tw o neighbouring plants on either side in the same row (first neighbours ) increased as the size of seed tubers increased and with all seed siz es yields decreased. For example, plants from large seed benefited fro m small seed planted as neighbours whereas, with plants from small see d, yield was decreased with neighbouring plants from large seed. Numbe rs of stems and tubers were not affected by neighbouring plants. Also yields were not affected by the two plants adjacent to the first neigh bours (second neighbours) or by the size of seed tubers planted in adj acent rows. Competition from first neighbours also affected tuber size distributions and, with small seed, increasing the competition decrea sed the number of tubers > 150 g and increased numbers < 50 g. Medium and small seed planted as neighbours of large seed increased numbers o f tubers, 150 g. When yields from plants produced by seed of each size with similarly sized seed planted as first neighbours (uniform popula tions) were compared with mixed populations, yields were always greate r from the mixed populations of different seed sizes planted alternate ly than from the means of uniform populations. Therefore in the mixed populations, there were larger gains from the larger seed than losses from the smaller seed.