Growth, development and yield of potatoes
Experiments were conducted in growth rooms to study the photoperiodic response of Pentland Crown. In field experiments the effects of sprouting techniques and the possibility of mixing of different physiologically aged tubers and the use of plant growth regulator, pp333 were studied. Sprout growth of the tubers used for planting was studied during storage. Light interception in the photo-synthetically active range (PAR), was measured in the crop canopies. Relevant literature relating to the present investigation was briefly reviewed. Tuberization in Pentland Crown was stimulated by relatively short days, lower temperature and higher irradiance. Pp333 allowed closer plant spacing (61 x 20cm) without any visible crowding effect, further it increased the allocation of assimilated to the tubers, which resulted in higher tuber yields and with a higher proportion of medium sized tubers. Sprout growth was linearly related to the initial tuber weight and day degrees above 4oC from dormancy break. Storing tubers in the cold before planting increased the sprout number and thus the proportion of main stems in the field. Time to reach 50% emergence was not reduced with increases in physiological age over 80 day degrees above 4oC. Cold (tubers stored at 3+/- 1oC until a day before planting) delayed tuber initiation but once the tuber had been initiated then the effect of physiological age disappeared and further tuber or overall plant growth or development was no more affected by the physiological age of the seed tuber. Yields from mixing different physiologically aged tubers were not different from those expected. The major factor affecting the growth of the crop was the water supply. The overall photosynthetic conversion efficiency of the canopy (g dry weight MJ-1 was intercepted) was 3.42g in 1980 in absence of any apparent water stress while in 1979 it was only 2.24g due to winter stress.