Non-destructive observations of growth of single tubers on individual potato plants (cv. Pentland Crown) grown in field revealed a great variation in total numbers of tubers per plant, total tuber volume per plant, volumes of individual tubers and growth behavior of each tuber. The largest tuber at any one time was not necessarily the largest at the next time. No relationship was found between the duration of the grand period of growth of tuber and its growth rate. Some tubers increased in volume, stopped and then resumed growth. Mixtures of Naphthalene Acetic Acid 45 mg/l (NAA) + 6-Benzyl Amino Purine 4.5 mg/l (BAP) had a dual effect by increasing tuber number and tuber size per plant when applied via the leaves in different times. The mixture of NAA + BAP increased tuber number per plant at pre-tuberization by 39.1 % and at-tuberization by 13.1 % and decreased the number by 21.9 % at post-tuberization stage compared with control. The mean number of tubers per plant in pre-tuberization treatment was greater than that in at-and post-tuberization treatments by 27 % & 47 % respectively. The percentage increase in total volume of tuber per plant (yield) compared with control treatments were 14.8 %, 39.5 % and 13.8 % respectively. It is concluded that the application time with mixture of NAA + BAP to potato plants at-tuberization stage was the best to increase tubers yield
أ.د/ حماد نواف فرحان | Prof. Dr. Hammad Nawaf Farhan | 7129