D. C. E. Wurr

The effect of calcium nutrition on the incidence of internal rust spot in the potato

Tubers produced by potato plants grown in vermiculite and supplied with either 0, 1 or 3 mM calcium chloride solution developed brown necrotic lesions of internal rust spot. Plants supplied with 9 and 27 mM calcium chloride solution did not show the symptoms and had a substantially greater concentration of calcium in the tuber dry matter. It is concluded that internal rust spot is a physiological disorder associated with a low concentration of calcium in the affected tubers.

The susceptibility of potato varieties to internal rust spot

In tubers of ten potato varieties the incidence of internal rust spot lesions increased and the calcium concentration decreased when the concentration of calcium chloride supplied to the plants fell from 9 to 1 mM. A simple linear model relating the probit transformation of internal rust spot incidence to tuber calcium concentration for each variety showed that there were substantial differences in varietal susceptibility to internal rust spot which were not related to tuber calcium concentration.

Effects of cold treatments on the sprout growth of three potato varieties

A period of storage at 2–3 °C followed by storage at higher temperatures more suitable for sprouting, gave a more rapid and greater total sprout development than that produced by continuous storage in sprouting conditions. The effect on the number of sprouts produced and the potential yield advantages to be gained from increasing sprout development by such a treatment are discussed.

Studies of the measurement and interpretation of potato sprout growth

Total sprout length and the length of the longest sprout were shown to be the most universally useful measurements to estimate sprout development in batches of potato tubers. A good estimate of sprout weight was also derived from measurements of total sprout length. There was a good linear relationship between total sprout length and initial tuber weight but the relationship varied considerably with the time of measurement and the temperature of storage. It is suggested that if sprout measurements are to be used to predict the field performance of a batch of tubers the changing pattern of sprout vigour with time needs to be more closely understood.

Studies of the growth and development of winter-heading cauliflowers

The winter-heading cauliflower varieties St Thomas, St Gwithian, St Agnes, Janavon, St Hilary, St Buryan, BB74605, St David and St Keverne were grown at Trefloyne, Tenby for 3 years from 1977 to 1980. Plants of all varieties were sampled periodically to determine the rate of curd expansion, the final number of leaves, the time of curd initiation, and the distribution of dry matter within the plant. The patterns of development of leaf area were similar in all varieties. Dry-matter distribution was similar for all varieties except for root growth; later-maturing varieties had a greater dry weight of root and a higher proportion of the total dry matter as root, than early varieties. Early rates of curd growth declined with later-maturing varieties and it is suggested that there may be a relationship between the time of curd initiation, root growth and the rate of curd growth. The mean total number of leaves formed before curd initiation varied from 49 to 102 depending on the variety and year. The earliest varieties St Thomas and St Gwithian took co. 120 days to reach 50% curd initiation and matured in 6–7 months from sowing while the late variety St Keverne took over 200 days to reach 50% initiation and more than 11 months to mature. The time interval between 50% initiation and 50% maturity increased with later-maturing varieties but on the basis of accumulated day degrees > 6 °C it declined with later varieties. The latter also matured more uniformly than earlier varieties when using an accumulated day-degree scale > 6 °C as a time scale. The results suggest that the low temperature threshold below which curd induction occurs may vary with variety. There was also evidence that the base temperature for curd growth is lower with later-maturing varieties.

The influence of some seed potato production techniques on basic tuber characteristics

The effects of the planting density of the seed potato crop, the date on which it was defoliated and the time at which it was lifted, on the weight, shape and number of eyes on progeny tubers in a given size grade, were small and were unlikely to be of practical importance. Size grade was both closely and linearly related to the number of eyes on a tuber and seemed to be a perfectly adequate practical method of grading seed tubers according to their number of eyes.