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The influence of the physiological age of microtubers on field growth and tuber yield in potatoes was studied with ´Superior´ variety, comparing the growth and tuber-yielding characteristics of microtubers with those of normal seed tubers (NST). Plants emerged earlier from the microtubers planted at the age of 33 weeks after harvest than from those planted at the age of 15 or 24 weeks after harvest, and the plant growth of the microtubers were slower than that of the NST. As compared with the NST, the microtubers produced less numbers of stems per plant but similar numbers of tubers per plant, resulting in about twice more numbers of tubers per stem. The microtubers were slower in tuber development and growth than the NST, and the microtubers at the age of 33 weeks showed a tendency of tuber development faster than those of 15 or 24 weeks. The microtubers yielded less than the NST, and the microtubers at the age of 33 weeks yielded more than those of 15 or 24 weeks. The yield rate of tubers over 20 g of the microtubers at the age of 33 weeks was 94%o, revealing a high yield rate of tubers proper for general field cultivation. Results from the present study and the fact that potato varieties have different periods of dormancy suggest that for each variety, the physiological age of microtubers proper for efficient field multiplication needs to be decided.
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