Relationships between the number of stems produced by a potato seed tuber and its weight

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Abstract
SUMMARY: The relationships between the number of stems per tuber and tuber characters measured before planting were studied using a wide range of tuber weights of the varieties Désirée and Maris Piper. The effects of the storage temperature of the seed tubers and the site of growth on these relationships were then investigated over 3 years.Linear relationships between the numbers of stems per tuber and tuber weight accounted for more of the variation in numbers of stems than linear relationships established using tuber shape or sprout measurements. The linear relationships had positive slopes and intercepts, showing that small seed tubers produce more stems per unit weight than large seed tubers. There was little evidence of non-linear effects.On average over all treatments, using ten plant samples, single linear relationships between above-ground stems and tuber weight accounted for 64 % of the variation in above-ground stems with D6sire'e and 58 % with Maris Piper. When separate regression lines were fitted for each treatment the best models in each variety accounted for about 86 % of the variation in above-ground stems. The best model with Désirée had parallel lines showing that the advantage, in terms of stem production, of small seed over large seed increases in environments favouring stem development. The relationships for each treatment are used to show how the stem density established can vary when planting tubers at the recommended spacing.Seed tubers of comparable weight, planted at different sites, gave different numbers of stems suggesting that the optimum spacing may vary from one site to another.It is suggested that breeding varieties for yield stability might be aided by selectingfor low variation in the relationship between the number of stems per tuber and tuber weight.