OBSERVATIONS ON THE BULKING AND DEVELOPMENT OF TUBER SIZE DISTRIBUTION IN MAINCROP POTATOES AT ROTHAMSTED IN 1964-75

Tuber samples taken at 2-week intervals from plots of cvs King Edward, Majestic and Pentland Crown in 1964-75 showed that the maximum bulking rates ranged from 1 to 5 tonnes/hectare/week. Maximum tuber numbers were usually produced by 11 weeks after planting and thereafter numbers declined. In September, about 70% of the tubers initiated were recovered, and between 24 and 52 % of the tubers had reached marketable size (> 4 cm). Tuber size distributions developed similarly in all years with all cultivars. During tuber initiation the distributions appeared as one population, and usually between 9 and 11 weeks after planting a second population of larger tubers developed. The population of small tubers later declined although in most years it was still present in September. This development fitted a model based on a mixture of two normal distributions and was determined by five parameters; the proportion of tubers in the small population and the means and standard errors of both populations.