Amounts of winter or summer rain triggering germination and ‘the point of no return’ of seedling desiccation tolerance, of some Hordeum spontaneum local ecotypes in Israel.

Abstract

In this study we observed an important interrelationship between the ability of Hordeum spontaneum C. Koch (Poaceae) seeds to germinate after a small rainfall in winter and the dehydration tolerance of young seedlings after one, two or three weeks in dry conditions. In winter, local ecotypes of H. spontaneum started to germinate after only 10 mm of ‘rain’, when temperatures were mild, daily evaporation rates were low, and soil water content was 5.8%. In summer, however, germination was not triggered until at least 50 mm of ‘rain’ was received, at higher temperatures, evaporation rates and soil water content. The ‘point of no return’ is the earliest stage of germination or after germination at which dehydration will cause the death of the seedling and it depends on the duration in a dry environment, root length before desiccation and on the ecotype. Seedlings were stored in dry conditions for one, two or three weks and then rewetted. A higher percentage of seedlings which had developed roots of 5–20 mm long before desiccation, developed adventitious roots than that of seedlings with roots 1–4 or 40–50 mm long before desiccation. The strategy of regulating germination according to different amounts of rainfall, depending on the season, and seedling drought tolerance, are important survival adaptations in arid and semi-arid regions. These adaptations may enable the young seedlings to overcome drought periods between rainfalls.