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. / Graduation date: 1991
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/37967 |
| Date | 18 January 1991 |
| Creators | Jabbes, Mohamed |
| Contributors | Johnson, Douglas E. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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