Overcoming dormancy in malting barley

Abstract

The objectives of the project were to find means by which dormancy could be reduced or eliminated so that insights might be gained into the fundamental causes of dormancy and possibly ways to eliminate it under commercial conditions would appear. The treatments, usually applications of chemicals, were to be applied (a) to 'green grain', before it was dried; (b) to 'dried grain', during storage, and (c) to grain in the 'pre-steep period'. Treated samples of grain were stored, in parallel with untreated controls, at ambient temperatures. At intervals sub-samples were taken and tested for germinability.

The first experiments were to develop more reliable germination tests than those already available. These trials were successful, our 1 ml and 3 ml (agar) tests being superior to the 4 ml and 8 ml (paper) tests of the Institute of Brewing.

About a hundred different treatments were applied to dormant samples of grain in the 'green grain' and 'dry storage' periods. Only two treatments were beneficial. Applications of gibberellic acid stimulated germination as would be expected, since this substance is non- volatile. Spraying grain with sulphuric acid (0.5%) before drying also led to more rapid germination. Experiments indicated that it probably functioned by damaging microbes in the grains' surface layers. Some of the negative results obtained were also of interest. For example availability of oxygen during storage was not a necessary condition for a decline in dormancy.

Steeping samples of grain in various solutions for 6 h. then air-resting for 18 h. before testing showed that under these conditions dilute solutions of sulphuric acid, hydrochloric acid, phosphoric acid and various sulphur-containing compounds alleviated dormancy.

It was confirmed that antibiotics improved grain germinability. It was shown that microbes in the surface layers of grains consumed considerable amounts of oxygen and that the embryos of dormant grains need a more ready supply of oxygen to germinate than those from mature grains. Consequently we support the view that microbes in the surface layers of grain check germination, at least in part, by competing with the embryo for the oxygen.

Gibberellin contents were determined by bioassay and abscisic acid contents by capillary GLC (ECD), in mature and dormant sub-samples of three different lots of grain. We conclude that endogenous levels of these hormones are unlikely to be connected with grain dormancy.