GrainGenes

II. 8. The germination of immature barley seeds.

J. G Coors and T. E. Haus, Colorado State University, Fort Collins, Colorado 80523

It is often desirable to decrease the time for a generation cycle of barley in genetic or plant breeding studies. To this end immature seeds of Steptoe (C.I. 15229) and Betzes (C.I. 3398) were harvested at 12, 16, 20, and 24 days after pollination. The germination was determined for all combinations of kiln drying at 36 and 40°C for two, four, and six days, or no drying. Half of the seed was stratified for five days at 5°C. Hull effects were determined by the use of an isogenic line of Betzes for naked seeds developed by R. F. Eslick and E. A. Hockett, Montana State University.

Time of Harvest

Harlan and Pope (1922) reported that barley seeds were capable of germination as early as six days after pollination if the seed was stored for several months while connected to the culm. Germination of fresh seeds was poor. In the present study, the seeds of all three cultivars were able to germinate at all times of harvest if provided with the proper combination of stratification and drying. There were indications that harvest prior to 12 days after pollination would have been beneficial in order to avoid the development of inhibitory mechanisms.

From 12 to 16 days, seeds were adversely affected by drying at 40°C. From 16 to 20 days, the germination of untreated seeds dropped drastically. Determination of the moisture content revealed that the layers of the seed coat were completed in this period. (Harlan 1920, Wellington 1956). By 20 days, naked seeds were stimulated by the higher temperature of drying, and this stimulation did not appear to be due to the benefits of desiccation alone.

Stratification proved beneficial both before and after the likely formation of the seed coat, and, by 24 days, stratification had become the most effective single means of promoting germination.

Cultivars

There were both varietal differences and differences attributable to the presence or absence of hulls. The hulls reduced germination at all times of harvest Nonetheless, the hulls of Steptoe and Betzes seeds did offer protection at the early stages of development to the drying treatments and, possibly, to stratification.

Steptoe did not germinate well following any treatment. Moisture content and germination patterns of Steptoe suggested a four or more day lag in development when compared to the Betzes lines. The possible presence of less volatile or more temperature sensitive inhibitors in the hulls confused analysis without comparison to naked Steptoe seeds.

Stratification

There was a slight reduction in germination after stratification of naked seeds at 12 days after pollination. The hulls of Betzes and Steptoe seeds apparently prevented any harm, and, in fact, stratification of dried seeds with hulls dramatically increased germination at this time, indicating that stratification may have had a role in addition to that of increasing the efficiency of respiration (Nikolaeva 1967, Mayer and Shain 1974, Taylorson and Hendricks 1976).

Stratification alone did not overcome the inhibitory influences of the hulls. For naked seeds, the primary benefits to stratification occurred after the likely formation of the seed coats at 16 to 20 days after pollination. Desiccation and stratification at 20 and 24 days were thought to be acting in a similar manner.

Drying Duration

Increasing the duration of drying significantly increased germination of naked seeds before stratification, but not after. The benefit was possibly derived from desiccation. Betzes seeds with hulls responded in both instances because of the likely volatilization of inhibitors in the hulls, as well as the desiccation of the caryopsis. Steptoe appeared to be more sensitive to the drying temperature than the drying duration, and only at 24 days did longer durations increase germination.

Drying Temperature

Drying at 40°C was harmful at 12 and 16 days after pollination. This effect was attributed to the detrimental combination of heat and high moisture content causing the denaturation of enzymes and, in the case of seeds with hulls, to a stimulation of inhibition by the hulls. Drying at 36°C was beneficial to seeds with hulls at the earlier stages of development if stratification followed the drying treatments. At 20 days, drying at 40°C stimulated the germination of naked seeds and suppressed the germination of seeds with hulls. These effects did not appear to be influenced by the duration of drying or desiccation. By 24 days, the temperature sensitivity had lessened.

Practical Application

Table 1 summarizes the results of the experiment in relation to the desired goal of reducing the time from pollination to seed germination. The experiment suggests further possibilities which would reduce the time from pollination to germination. The harvest of seed prior to 12 days may avoid the repression of germination by inhibitory substances in the hulls. Drying at temperatures lower than those investigated in this experiment, at the earlier stages of development, may decrease the damage caused by high temperature and not restimulate inhibition by the hulls. There is some evidence that stratification could be eliminated if the proper drying duration and temperature could be determined.

Table 1. Optimum treatment combinations to minimize the time from pollination to germination.

References:

Harlan, H. V. 192Q. Daily development of kernels of Hannchen barley from flowering to maturity at Aberdeen, Idaho. J. Agric. Res. 19:393-430.

Harlan, H. V., M. N. Pope. 1922. The germination of barley seeds harvested at different stages of growth. J. Hered. 13:72-75.

Mayer, A. M., Y. Shain. 1974. Control of seed germination, Ann. Rev. Plant Physiol. 25:167-193.

Nikolaeva, M. G. 1967. Physiology of deep dormancy in seeds. National Science Foundation, Washington, D. C.

Taylorson, R. B., S. B. Hendricks. 1976. Aspects of dormancy in higher plants. Bioscience 26:95-101.

Wellington, P. S. 1956. Studies on the germination of cereals. 2. Factors determining the germination behavior of wheat grains during maturation. Ann. Bot. 20(n.s.):481-500.

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