Graduate Thesis Or Dissertation
 

Evaluation of germination responses and early seedling development of selected medicago and hedysarum species

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/6w924d88h

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  • Germination strategies and early seedling development of selected Medicago and Hedysarum species were evaluated to identify plants with high potential for range rehabilitation in central Tunisia. Temperature (5°C to 25°C) and water stress (0 MPa to -0.8 MPa) affected the germination percentage of all Medicago and Hedysarum species. Water stress had a greater effect on percent germination than did temperature, however, the nature of the effect of water potential depended on temperature. Australian medics were more depressed by temperature extremes and low water potential than were Tunisian accessions. Optimum germination of Medicago polvmorpha var. Circle Valley and Medicago trucatula var. Jemalong was at 15 °C and 0 MPa. Germination was highly reduced at higher temperatures and water stress. Tunisian Medicago truncatula germinated better at lower temperatures (5 °C to 15 °C). Hedysarum carnosum germinated more completely at high temperatures. (15°C to 20°C). Medicago laciniata germinated well across a wide range of temperature but germination decreased as water stress increased. Rapid rates of root elongation are beneficial to plants in semiarid environments. High temperature accelerated rates of root elongation and low temperature retarded the rates. The degree of retardation varied with the species and the temperature range. Maximum root elongation occurred at 15°C and minimum root elongation occurred at 5°C. Medicago laciniata had the fastest root elongation rate at 5°C and 15°C . Medicago truncatula was equal to Medicago laciniata at 5°C. Hedysarum carnosum had rapid root elongation at 10°C and 15°C compared to 5°C. A Tunisian accession Medicago polymorpha had the slowest root elongation at all temperatures. A quantitative growth analysis was used to assess the effect of environmental conditions on the species performance over a period of 49 days. Mean relative growth rate (mRGR) varied among species. This variation suggested size hierarchies in relative performance among species. The largest plant, Tunisian Medicago truncatula had the largest mRGR and the smallest plant, The Tunisian Medicago polvmorpha had the lowest mRGR. The derived parameters, leaf area ratio (LAR) and unit leaf ratio (ULR), were not consistent with the size hierarchies obtained by mRGR. The Root to shoot ratio (R/S) varied among the species. The Tunisan Medicago truncatula had high root to shoot ratios at low temperature and its R/S ratio decreased at higher temperature. Slow growing species had high R/S ratio. Medicago laciniata was an exception, it produced low R/S ratio because of its long, and thin root system.
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