Effect of gibberellic acid on a compactoid wheat

G. M. WRIGHT

Crop Research Division, Department of Scientific and Industrial

Research, Christchurch, New Zealand

The restoration of normal growth by gibberellic acid in many types of genetic dwarfing and virus stunting in plants has been reported. It stimulates growth of wheat and rye, and accelerates internode growth (Lona, 1956); in rye, no acceleration of flower formation has been found (Lang, 1957).

In a tetrasome compactoid line of wheat, described in a recent communication to "Nature", the application of gibberellic acid has produced a response in the early growth of upper internodes, earlier flowering, variable effects on fertility and possibly a slight reduction in ear density. The results are not conclusive, as too few plants were available, but they suggest a need for further work with earlier applications and higher concentrations.

Four plants in the glasshouse at the shot-blade stage (Feekes' scale, 8-9) were treated on September 11, 1957, with 5 or 10 micro gm of gibberellic acid per plant, applied by microloop to the first four tillers on each plant. There was no wilting after 22 hours, but after a further 24 hours the upper leaves of all tillers had wilted, wilting being more severe at the higher concentration. On September 18 the application was repeated on one plant at each dose (Feekes' scale 10.1). Five days later there were 18 ears emerging (through the side of the leaf sheath) in the treated plants, from 36 tillers, and only two of the 19 tillers on the two control plants had ears emerging. The commencement of flowering on each plant as expressed by the number of days after September 26 is shown in the table; also given are the average numbers of grains per spikelet, referring to the total production of grain in well-developed spikelets on each plant, and internode length, defined as the average length in mm of the top 14 internodes in the least dense of the later ears.



The correlation coefficient for initial dose and start of flowering was -0.92, and the correlation was lower for the later flowers; for the fifth flower it was -0.69. The production of grains in the glumes (Wright, in press) was not affected, but the effect on the total fertility of the plants was marked. Although the numbers of well-developed spikelets on the plants were similar, ranging from 109 to 131, the plants treated once were more fertile, and those treated twice were much less fertile than the controls (see the table).

No response in plant height or stem internode lengths, or in the density of the base of the ear, was established. It is probable that the treatment was too late to affect the rachis development of the early ears, but it is possible that the density of some of the later ears was affected, as shown in the table. The correspondin internode lengths for "average" ears of T. compactum and T. vulgare were 1.36 and 4.14 mm, and although the response to gibberellic acid in the compactoid wheat is doubtful, it does not, even if it is real, represent any substantial change towards normality.

(Received May 2, 1958)