Effects of cultural practices, Verticillium nubilum and locality on coiled sprout and yield of early potatoes

SUMMARY Treatments reported to affect the incidence of ‘coiled sprout’ were studied in 1968 with the cultivar Arran Pilot in experiments near Falmouth, Cornwall (F), Rothamsted (R) and near Edinburgh (E). Most coiled stems occurred at E (37%) with similar proportions at R (19%) and F (16%). Seed tubers with the longest sprouts at planting produced most coils at all sites, those with shorter sprouts less and unsprouted seed least. When coiling was assessed on the number of plants, long- and short-sprouted seed tubers were about equally affected at R and E. Sprouts emerged within 45 days at E and 30 days at R. Longer sprouts did not emerge more quickly, but emergence was more than 1 wk later from unsprouted seed at R and only a few days later at E. Harrowing ridges after planting to decrease the depth of soil covering seed tubers hastened emergence by about 1 wk at R and decreased the incidence of coiling; it had little effect at E but tended to increase coiling at F. Seed tubers inoculated with Verticillium nubilum produced more coiled sprouts but this increase was not significant. The highest final yields were achieved at R (43-2 t/ha) where short-sprouted seed outyielded long-sprouted and unsprouted seed, but cultivation treatments and fungus inoculation had no effect. At E (21-2 t/ha) only herbicide treated plots gave a significant effect, outyielding harrowed plots by 8 t/ha. At F (18-2 t/ha) short-sprouted seed outyielded long-sprouted and unsprouted seed, and herbicide treated plots outyielded harrowed plots. When ware yields from individual plants with and without coils from long-sprouted seed were compared at R on 18 June, coiled plants gave about 30% and on 2 July 60% of the yield of non-coiled, but by 16 July 120% yield (20% more); similar trends were shown by short- and by long-sprouted seed at E.