ln previous studies, genetic differences between populations from different habitats, and even within populations, have been found in Hordeum spontaneum C. Koch (Nevo et al., 1984, 1986a, 1986b; Nevo, 1992). It has also been found that freshly harvested caryopses enclosed in their dispersal units do not germinate in a range of temperatures, in light or dark, unless they have been stored under dry conditions and a high temperature of 35-40°C for about 70 days. However, separated embryos as well as naked caryopses and uncovered embryos do germinate (Gutterman, Come and Corbineau, in preparation; Gutterman, 1992, 1993).
In the present set of experiments no germination was found, even after more than 73 days of wetting, of freshly harvested caryopses (grains) of Hordeum spontaneum in their spikelets (the dispersal unit) which were harvested on 3 May, 1992 near Sede Boker in the Negev Desert Highlands. In the same experiment, separated embryos germinated to 77%.
Thirty days of dry storage in 35-40°C, in comparison with natural summer dry storage, significantly increased the germination of naked caryopses collected near Sede Boker (from 7 to 32%), after the first 5 days of wetting.
When caryopses enclosed in dispersal units from three populations were compared, the highest germination (72-74%) was observed in those collected from a population on the north-facing slope of Nahal Oren, Mount Carmel, which is the most humid habitat tested. The lowest germination (30-45%) was observed in those collected near Sede Boker, where the desert conditions are the most extreme. An intermediate result (53-64%) was observed in those collected on the south-facing slope of Nahal Oren on Mount Carmel. The tested caryopses were wetted for 8 days after 74-85 days of dry storage in natural summer conditions at Sede Boker or in constant 35-40°C. At the same time, caryopses from dispersal units stored in -18°C were wetted. The highest germination (26-51%) after 2-3 days was from those collected on the north-facing slope of Nahal Oren on Mount Carmel and the lowest was observed in those collected near Sede Boker (16-37%). The same phenomenon was repeated in the experiments of 11 January 1993, from dispersal units stored under natural conditions, as well as on 8 March 1993, in constant 35-40°C and 5-20°C. The same pattern of germination was found on 21 November, 1992. This occurred after 2-8 days of wetting of separated embryos, after dry storage in -18°C.
From the above it seems that, in addition to genetic factors, environmental conditions during dry storage of the mature dispersal units are also important as germination regulators. Notably, the germination of seeds from the xeric south-facing slope of Nahal
Oren was intermediate between the mesic, north-facing slope and the desert, Sede Boker population, which are 200 km apart, whereas the two slopes on Nahal Oren are separated by only 0.5 km. This suggests that genetic factors underlie the above results.
References:
Gutterman, Y. 1992. Ecophysiology of Negev Upland annual grasses. pp. 145-162, 361. In: G. P. Chapman (ed.) Desertified Grassland: Their Biology and Management. Linnean Society Symposium Series 13, Academic Press, London. 361 p.
Gutterman, Y. 1993. Seed Germination in Desert Plants. Springer, Berlin Heidelberg New York. 253 p.
Nevo, E. 1992. Origin, evolution, population genetics and resources for breeding of wild barley, Hordeum spontaneum, in the Fertile Crescent. In: P. R. Shewry, (ed.) Barley Genetics, Biochemistry, Molecular Biology and Biotechnology. Biotechnology in Agriculture 5:19-43.
Nevo, E., A. Beiles, Y. Gutterman, N. Storch, and D. Kaplan. 1984. Genetic resources of wild cereals in Israel and vicinity: II. Phenotypic variation within and between populations of wild barley, Hordeum spontaneum. Euphytica 33:737-756.
Nevo, E., A. Beiles, and D. Zohary. 1986a. Genetic resources of wild barley in the Near East: Structure, evolution and application in breeding. Biological Journal of Linnean Society 27:355-580.
Nevo, E., A. Beiles, D. Kaplan, E. M. Golenberg, L. Olsvig-Whittaker, and Z. Naveh. 1986b. Natural selection of allozyme polymorphisms: A microsite test revealing ecological genetic differentiation in wild barley. Evolution 40:13-20.