Date of Award

2009

Document Type

Thesis

Department

Environmental Science

First Advisor

Dr. Fatima AI-Ansari

Second Advisor

Dr. Shahina Ghazanfar

Third Advisor

Dr. Taoufik Ksiksi

Abstract

The utilization of indigenous forage species to replace the exotic ones could help in saving large amounts of water. The indigenous forage grasses Lasiurus scindicus and Panicum turgidum have been ranked among the plants that could tolerate drought during vegetative and reproductive stages and are currently being successfully used as fodders under experimental conditions in the UAE and in some parts of the world. However, there are no enough information about their dormancy and the environmental factors affecting their seed germination. In this study, the innate dormancy, light and temperature requirements, drought and salinity tolerances and the impact of dormancy regulating chemicals on seed germination of the two species were assessed. In addition, the impact of storage and maternal habitats on the dormancy and germination requirements of the two species were assessed.

Fresh seeds of L. scindicus were collected during May 2007 from natural populations around AI-Ain and from an experimental field station in AI-Dhaid on April 2004. Seeds of P. turgidum were collected from the Zaranik nature protection area in the eastern part of Lake Bardawil, Egypt. Seeds were tested for germination after collection (fresh) and after different periods and conditions of storage. Seeds were also tested in different concentrations of salinity and polyethylene glycol 6000 (PEG-6000) that produced different levels of osmotic pressures. Most of the germination experiments had been done at different temperatures and light conditions.

Seeds of P. turgidum showed great innate dormancy. No germination occurred for the fresh harvested seeds of P. turgidum. The ability of a considerable fraction of P. turgidum seeds to maintain dormancy ensures the buildup and persistence of a soil seed bank which is considered vital for a species in the unpredictable environments of deserts. Germination of seeds stored for five years was significantly greater in dark than in light at 15-25°C, but the reverse was true at the higher temperatures (35 and 40°C). Salinity significantly reduced germination at 100 mM NaCI and completely inhibited it at 200 mM. Optimum germination was achieved at 30°C. Seed germination of P. turgidum was most salinity tolerant at 35°C. Similarly, germination rate decreased with the increase in salinity, but increased with the increase in temperature.

Fresh seeds of L. scindicus didn't show great innate dormancy and attained fast germination. Non-saline treated seeds of L. scindicus germinated well in a wide range of temperatures and in both light and dark.

Even though there was no germination occurred for P. turgidum seeds treated in higher salinities (200 mM NaCI and more), significant proportions of the seeds recovered their germination (about 30%) when transferred to distilled water. Overall optimal recovery germination was at moderate temperatures, compared to both lower and higher temperatures. The recovery germination from different saline solutions depended on temperature of incubation.

Seed germination of L. scindicus decreased with the increase in NaCI concentrations. Tolerance to salinity during germination is dependent on temperature; salinity tolerance was greater at the moderate temperatures (20-30°C), compared to both lower and higher temperatures. Germination rate decreased with the increase in salinity, but increased with the increase in temperatures. Recovery germination decreased with the increase in temperature, but decreased with the increase in salinity. Germination rate of the recovered seeds was much faster compared to saline or non-saline treated seeds.

All of the studied chemicals, except thiourea, did not succeed to improve germination of non-saline treated seeds of both L. scindicus and P. turgidum, compared to the control. The salinity-induced germination reduction in P. turgidum was completely alleviated by the application of Gibberellic Acid (GA3), partially alleviated by the application of fusicoccin, kinetin and thiourea, but not affected by nitrate. In L. scindicus, the germination inhibition was completely alleviated by fusicoccin, GA3, nitrate and thiourea, but partially alleviated by kinetin. Germination was completely inhibited by the application of ethephon in the two species.

Seeds of L. scindicus were more drought tolerant than those of P. turgidum. Seeds of L. scindicus germinated to 30% in -0.7 MPa, while those of P. turgidum completely inhibited in -0.5 MPa. This indicates that the toxicity effect would be the main cause of salinity intolerance in L. scindicus. The lower recovery germination in the seeds of this species, compared to that of P. turgidum, further supports this hypothesis.

Seeds of L. scindicus from natural habitats germinated to higher level and rate, compared to those collected from plants grown in experimental conditions and received more watering. Seeds of the natural habitats have light brown or dark brown colors. Dormancy and germination requirements differ between the two colors.

The temperature requirements during germination differed among P. turgidum seeds stored for different periods.

Seeds of L. scindicus stored for three months germinated significantly greater at higher (20-35°C), than at lower temperature (15°C). However, after 2 years of storage, there was no difference in final germination between all temperatures.

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