Potato (Solanum spp.) in an isohyperthermic environment III. Evaluation of clones

The potato is a new crop in isohyperthermic (hot tropical) environments. Locally available cultivars cover the at present limited hectarage. Superior high-yielding adapted cultivars must be identified. Thirteen experiments were conducted during four consecutive dry seasons from November 1983 to March 1987 at 14°N latitude in The Philippines. Monthly mean minimum air temperature always exceeded 20°C. A total of 97 clones from temperate and tropical sources were evaluated in one or more experiments. Seed tubers from some experiments were stored in cold storage and replanted the following cycle; this was repeated up to four times. All clones reached their maximum canopy cover 42–50 days after planting (dap). Tuberization occurred for all clones and generally started at 28 dap. Daylength of 11.5–12 h even at high temperature, favored rapid tuber initiation and bulking, causing rapid canopy decline. Non-heat-tolerant clones tuberized gradually and formed new above-ground shoots from many stolons. Tuber yields ranged from 35.6 to 1.9 t ha−1. Those clones giving superior yields were 378597.1, B71-240.2, ‘Desiree’, ‘Red Pontiac’, ‘Sequoia’, ‘Cosima’, MS35.22, 7XY.1, DTO-28, and DTO-33. When seed tubers were replanted for the fourth cycle, B71-240.2, Desiree, Cosima, MS1C.2 and MS35.22 proved stable. These clones have a combination of field resistance to viruses, long dormancy and good storability. Tuber size (small) and dry matter (low) need to be improved. Genetic differences were identified in ability to convert intercepted solar radiation (isr) into tuber dry weight (tdw). FOr 15 superior cultivars, tdw=0.004 isr + 1.1, with r=0.673. This was about 70% as efficient as in temperate climates. Superior clones have been identified which could further enhance yield and increase the area of lowland potato production.