SUMMARYData from nine experiments from 1973 to 1981 which examined the effects of physiological age on sprout and field growth of early potato varieties are reported. Length of longest sprout per tuber and all aspects of field growth were related to number of daydegrees > 4 °C experienced by the seed after onset of sprout growth (measured as the appearance of a 3 mm sprout). It is, therefore, suggested that this scale is an effective measure of physiological age. In Home Guard and Maris Bard, increasing age of seed tubers resulted in earlier emergence and tuber initiation, larger early leaf areas and increased early tuber yields. As growth proceeded young seed produced the largest and most persistent leaf areas and the yields surpassed those of older seed and in some experiments yields decreased with increasing age at the final harvests.Optimum ages for specific harvesting periods were determined from regressions of tuber yield on age. In both varieties, they decreased with delay in harvesting. However, optimum ages differed in the two varieties and the implications for production and storage of seed and testing of varieties are discussed.

SummaryThree experiments carried out in 3 years (1973–5) which examined the effects of length of sprouting period and temperature of sprouting on growth and yield of three early potato varieties are described. In Home Guard in 1973 at the earliest harvests, tuber yields increased with increase in length and temperature of sprouting period. At later harvests tuber yields decreased with increase in sprouting period especially at the higher temperature (13 rather than 8 °C) and increasing the temperature of sprouting reduced tuber yield. In 1974 length of sprouting period had few effects on yield at any harvest and increasing the temperature increased yields only at the first harvest. In Vanessa cold storage at 3 °C prior to entry to sprouting temperatures induced an earlier onset of sprout growth than continuous exposure to temperatures conducive to sprout growth. Long sprouting periods produced less sprout growth and at the earliest harvest lower tuber yields than all except the shortest period. Judged from the onset of sprout growth increases in length and temperature of sprouting generally increased tuber yields especially at early harvests. In Pentland Javelin sprout growth was very slow and tuber yields at early harvests decreased at both sprouting temperatures if sprouting began after mid-November. At later harvests effects of both factors were small.The implications of differences in the effects of sprouting periods according to variety and, in Home Guard, season, are discussed in relation to the provision of the most desirable sprouting environment and to variety testing. The similarity in the effects of lengthening the sprouting period and of increasing the temperature of sprouting suggest that temperature is the major causal factor in sprout growth and its effect on field growth. Sprouting periods may therefore be measured most accurately by accumulated day degrees > 0 °C and a close relationship between such a scale and tuber yields is demonstrated. The relevance of such scales for advice to growers is discussed.Tuber growth rates for Vanessa and to a lesser extent Home Guard in 1974 were extremely high, in excess of 10 t/ha/week for Vanessa. These high rates were associated with high levels of radiation received by coastal sites in May and June and are discussed in relation to the canopy structure of the varieties.

SummaryUsing data from four field experiments, comparisons were made between the drymatter percentages of several varieties harvested at different times during the growing season.There were negative quadratic relationships between tuber dry-matter percentage and tuber size in all varieties except Pentland Marble. The dry-matter percentage of particular tuber sizes varied according to the variety and the time of harvest. Failure to recognize the importance of tuber size and the time of harvest may easily distort differences in dry-matter percentage between varieties.There were significant positive correlations between the number of tubers produced by each variety on 25 June and four different variables representing the dry-matter percentage of tubers harvested on 10 September. Varietal maturity, assessed as persistence of the foliage, was not significantly correlated with any tuber dry-matter percentage variable in September.

No abstract

No abstract