| Abstract: | Berseem clover (Trifolium alexandrinum L.) is an important crop in semi-arid regions; its herbage and seed yields are often reduced by water stress. Our objectives
were (i) to determine the effect of water stress, applied after a conditioning period, on water relations, proline accumulation
and plant dry weight, and (ii) to investigate if some physiological responses differed in varieties of berseem. Five cultivars
(Axi, Bigbee, Lilibeo, Sacromonte and Saniros) were grown in a controlled environment, and subjected to four irrigation treatments
(T1, T2, T3 and T4 referring to plants irrigated to field capacity every 1, 2, 3 or 4 d, respectively) during a conditioning
period (12 d). T1 treatment indicated the well-watered control, whereas T2, T3 and T4 treatments represented the conditioned
plants. Leaf water potential (Ψ), osmotic potential (Ψπ), relative water content (RWC), gravimetric soil water content (GSWC)
and leaf proline concentration were recorded during the conditioning period and a subsequent water deficit period (3 d) applied
at early flowering growth stage. The conditioned plants subjected to subsequent water deficit maintained higher values of
Ψ, Ψπ, RWC and GSWC, and lower values of leaf proline concentration. Reductions in parameter values were inversely related
to the water stress severity that plants had previously experienced. At the end of the experiment, T1 showed 42%, 58% and
31% lower values for Ψ, Ψπ and RWC, respectively, than those of T4. Conditioned plants were also shorter and accumulated less
leaf, stem and total dry weight. The conditioning treatments did not affect the relation between Ψ and Ψπ since conditioned
plants show similar values of Ψπ as the control at the same Ψ value. Thus, drought acclimation in berseem clover contributed
to water stress tolerance by the maintenance of tissue hydration. The berseem cultivars examined showed differences in plant
growth parameters, but they were very similar for physiological responses to water deficit. The main genetic difference was
recorded for turgor maintenance capacity.
This revised version was published online in June 2006 with corrections to the Cover Date. |
