Light and temperatures of germination greatly affect germination of several Cucurbitaceae species. Environmental conditions prevailing at seed maturation time can affect dormancy and germination requirements. Citrullus colocynthis seeds have a deep dormancy. This perennial prostrate shrub grows all over the year in the arid Arabian deserts. We explored if seed dormancy and germination requirements of C. colocynthis depend on time of fruit collection. Matured seeds were collected at five different times during 2014/2015 year from a population around Dubai city. Fresh seeds were germinated at three temperature regimes in both continuous darkness and alternating 12 h light/12 h darkness. Impacts of seed storage and other treatments on germination were applied on seeds collected in March and exhibited deep dormancy. March collected seeds almost did not germinate in both light and dark at the three temperatures, but those of the other collections responded differently to both light and temperatures. At the lowest temperatures, seeds of all collections did not germinate in light, but those of June, October and December collections germinated in dark. There were negative correlations between final germination and seed length, width, mass and coat thickness. Physical scarification, water soaking and seed storage did not break dormancy of March collection. Germination of C. colocynthis is very sensitive to light and incubation temperature as well as to the environmental conditions associated with the time of seed maturation. It is important to investigate the effects of environmental factors prevailing during seed maturation under controlled conditions to understand exact reasons for unusual seed dormancy and germination requirements of C. colocynthis, which seems to be very sensitive to maternal environment.

Endemic species on mountains often have narrow altitudinal ranges and are more threatened at the higher altitudes, especially with climate changes. However, plants could use special microhabitats at the mountain tops as proper places for surviving the climate change (i.e., refugia). We assessed population attributes of three critically endangered endemic species (Primula boveana Decne ex Duby, Rosa arabica Crep., and Silene leucophylla Boiss.) in two growing seasons (2006/2007 and 2013/2014), differing in the received rainfalls in microhabitats at the high mountains of southern Sinai. Both P. boveana and S. leucophylla had very small population size, but significantly increased in the 2013/2014 growing season which received above average rainfalls. The population of R. arabica is the smallest (around 40 individuals) and did not increase, even after the increase in rainfalls. Whereas P. boveana is present in fewer sites and grew in small number of specific microhabitats, both S. leucophylla and R. arabica were recorded in most studied sites and habitat types. Unlike R. arabica, both P. boveana and S. leucophylla were recorded in caves and steep slopes and on the top of the mountains. This indicates that these sheltered mist microhabitats are the best for future conservation of these species after climate change.

In many species, seeds with different sizes show diverse responses in their requirements for temperature and light for optimal germination. In this study, the effect of seed size (i.e., small and large) on germination was tested in seeds of Brassica tournefortii Gouan, Lotus garcinii DC., and Salvadora persica L. from arid Arabian Desert habitats. The mean seed size of all three study species differs significantly between small and large-sized seeds. Differences were observed in seed germination between large and small seeds of B. tournefortii and L. garcinii. We found that the large seeds of B. tournefortii and L. garcinii showed a higher germination percentage at all tested temperatures than that displayed by the small seeds. However, both small and large seeds of S. persica germinated equally (100%) well under all tested incubation conditions. Our results show significant differences in germination percentage between the small and large seeds of B. tournefortii at 25/35 °C under a 12 h light regime. However, seeds of L. garcinii showed a significant difference in germination percentage at low temperatures (15/25 °C) under a 12 h light regime.

Background This is the first study on seed germination of Cucumis prophetarum in the Arabian Peninsula. Light and temperature as the main environmental factors and seed storage conditions greatly affect the germination of many Cucurbitaceae species. C. prophetarum is the perennial prostrate with woody rootstocks that grow throughout the year in the arid Arabian deserts. We examined the effects of seed storage conditions and sterilization by sodium hypochlorite (NaOCL) on germination of C. prophetarum seeds. Matured, fresh and field stored seeds were collected in March of 2016 and 2017 from a population in the United Arab Emirates. Fresh and the stored seeds (field, freeze, and room temperature) were germinated at three temperature regimes (15/25, 20/30 and 25/35°C) in both continuous darkness and alternating 12 h light/12 h darkness. Results The fresh and freeze stored seeds had higher germination percentage than the field and room temperature stored seeds. High germination was recorded in both lower and moderate temperatures (15/25 and 20/30°C) in light conditions. Sterilization of the seeds by NaOCl had a negative effect on the speed and germination percentage under all storage conditions, and it changes light and temperature requirements of seeds for germination. Conclusions Germination of C. prophetarum is sensitive to incubation light and temperature as well as to the seed storage conditions. The germination ability of stored seeds indicates that seed storage behaviour of C. prophetarum is orthodox. Light and temperature requirements for seed germination reflects a suitable place, habitat, and time for seedling emergence of C. prophetarum. The effect of NaOCl treatment on the germination may be associated with concentration and exposure periods of seeds. Therefore, we suggest that when using NaOCl for seed sterilization or to stimulate the germination, caution must be taken for using its concentration and exposure time, especially for species with thin and soft seed coats like C. prophetarum. Further studies on seed germination ecology would help to understand better the adaptive strategy of the C. prophetarum in the arid desert environments.