On the Effect of Gibbellin Treatment with Potato Plant

Abstract

In 1958 years preliminary experiment, gibberellin treatments by rather lower concentrations had shown unfavourable effects on the tuber yield and starch content of potato plant (var. Irish Cobbler). These results had rather confirmed the observation of D. G. Morgan and G. C. Mees. Later on, E. C. Humphries in Rothamsted stated his result saying that it was quite sure that the gibberellic acid treatment could increase the leaf area, dry matter and tuber weight, although had had some questions if these effects could last by the maturity time. Following the results of Dr. Humphries, we wanted to repeat our field experiment with higher concentrations of gibberellin. The treatments, as illustrated in Table 1, included 50 ppm twice, 100 ppm once and twice splaying. Detailed comparison of results are made only between plots No. 1, 4 and 5 with the intention of avoiding complication. Gibberellin treatments have brought increases in plant height, leaf area and weights of stem and stolon, but on the other hand reduced the tuber weight and starch content as can be seen in Tables 2 and 3. Another noticeable difference brought by the Gibberellin treatment is the difference of mineral content. Nitrogen contents of treated plants have been strikingly reduced in any form and potassium increased reversely. As it is highly possible that mineral nitrogen in soil should be enough to meet the requirement of potato plant by the time of flower initiation that is about the very beginning of July, we would suggest that the Gibberellin treatment might bring some suppressing effect or inhibition on the nitrogen uptake by potato plant. As to the increase of potassium uptake we haven't any clear explanation at the moment but we might infer that it is closely related to the particular growth of stem and stolon. These particular growth or elongation of stem and stolon brought by the treatment might enhance the metabolic activity and anabolic cell function in these part, so that it could be unfavourable for the tuberization and accumulation of starch. This might be the reason of the delay of tuber formation and the increased formation of deformed tubers. Table 7 shows the slightly increased values of net assimilation rate and relative growth rate on the 1st measurment and the slight reduction of them on the 2nd and the increased leaf area ratios with the both measurements. Judging from these results, it might be possible to increase the tuber yield of potato by the Gibberellin treatment if reasonable nitrogen application could be done; even though, it is still quite doubtful for us whether we could expect an additive effect on the yield from the cooperating function of Gibberellin and nitrogen.