A series of field experiments were carried out to investigate the effects of differences in the previous history of the
mother crop, sprout number, sprout development and in the
environment in the early stages of post -emergence growth on
stem and tuber production.
1. There was no effect of sprouting in the winter preceding
the production of the mother crop, or burning off the mother
crop on sprout, stem or tuber production in the current season
in either Arran Pilot or Majestic.
2. Delay in setting up previously cold -stored tubers to
sprout resulted in an increase in sprout and mainstem number in
both varieties. Early- sprouted tubers showed a greater degree
of lateral- branch development of the sprout and mainstem than
late -sprouted tubers. The response in tuber number and yield
varied from year to year but, on average, late -sprouting
produced more tubers than unsprouted seed: 10% more in Arran
Pilot and about 3% more in Majestic. Late- sprouted seed
usually produced more tubers than early- sprouted seed. Where
crops matured naturally, yields at harvest in both sprouted and
unsprouted seed were similar. In 1965 tuber bulking rates in
unsprouted seed were not constant and appeared to show changes
in rate associated with the pattern of foliage growth and the
prevailing weather conditions.
3. Efforts to induce differences in the number and type of
lateral branches on the sprout and thus stem and tuber
production in Arran Pilot, by clipping off the apex of the
sprout at different stages of development, were not successful.
An increase in an index of sprout development (the number of
lateral branches + sprouts per tuber) led to an increase in
stem numbers at ground level and tuber number but the relationship was not a close one. It was difficult to induce lateral - branch development of the sprout in Majestic. Although an
increase in the number of lateral stems led to an increase in
tuber number this was not as large as an increase per stem as
from a unit increase in mainstem number.
4. It was clear from the results of a planting date experiment and a shading experiment that differences in tuber number
occurred irrespective of changes in mainstem number. It was
suggested that these differences were brought about by
differences in the environment, particularly soil water content,
light intensity and air temperature, at the time of tuber
5. It was argued that differences in the response in tuber
number to sprouting from year to year could be related to
differences between the treatments in 1) lateral -branch
development of the sprout at planting, and 2) the environment
at tuber formation.