Planting materials for warm tropic potato production: production and field performance of nursery-produced tubers

Abstract

S U M M A R YPotato production in the lowland tropics is constrained by lack of affordable supplies of planting material. Therefore, the potential to produce in situ tuber seed from true potato seed (TPS) seedlings and rooted stem cuttings under nursery conditions in the warm tropics was studied, and their yields were compared with those of the same materials obtained under cool conditions. Subsequently, their field performance in the warm tropics was evaluated.Tuber yield from TPS seedlings and rooted cuttings transplanted in nursery beds under warm conditions ranged from 50 % to < 20 % of that obtained in cool conditions, but reductions in tuber numbers were less marked under warm conditions. Survival of seedlings was less than that of stem cuttings, but tuber numbers of seedlings exceeded those of rooted cuttings by a factor of two or more (e.g. 700 m~2 for seedlings v. 224 m~2 for rooted cuttings). Low tuber number is physiologically inherent in cuttings, as is high tuber number in seedlings. Total tuber yields varied significantly amongst clones grown in the warm climate from rooted cuttings, not always in proportion to the number of tubers produced. Differences in tuber yield and tuber number were less marked between the two TPS progenies studied.The field comparisons highlighted the 30-40 % lower yield potential for warm-climate-produced nursery seed materials. Slower emergence and fewer stems apparently were in part responsible for this effect; however, neither tuber number harvested nor the proportion of marketable tubers was affected by site of production of seed materials. Cutting medium-sized warm-produced tubers (mean 23 g), the use of larger sized whole tubers (10-20 g v. 5-10 g) or increasing the planting density of 5 g tubers from 8-8 to 15-5 plants n r 2 significantly increased yields by 4-9, 2-25 and 3-5 t ha" 1 , respectively, but yields were not increased further by 20-40 g tubers nor by 22-2 plants m~2. Small seedling tubers (< 5 g) can potentially lead to high stem numbers per unit weight of tubers, but their success in plant establishment was hampered in warm climates, especially in the presence of soil pathogens. Cool-climate-produced seedling tubers and tubers from cuttings can compete physiologically with field-produced seed tubers when used as planting materials in the warm tropics. However, with few exceptions, no crop from tubers produced under warm conditions could match the performance of crops from similar cool-produced tubers when planted out in the warm tropics.