بررسی انجام مطالعات فیزیولوژیکی در چهارگونه اکالیپتوس با هدف دسترسی به گونه های متحمل و مقاوم به تنش خشکی

Physiological reaction of different Eucalyptus species to drought stress can help to recognize effective mechanisms in drought tolerance selection of the best species for cultivation in dry area of Iran. This research was carried out to estimate drought resistance of four Eucalyptus species (Eucalyptus camaldulensis, E. microtheca,E. vimina/is and E. me/iodora) at gennination and seedling stages. Five potential osmotic levels (0, -0.1, -0.3, -0.6 and -1.2 MPa) treatments were used in five replications. Polyethylene glycol 6000 was used as diminutional osmosis in hydroponic culture in greenhouse. Radicule length, plumule length, vigour index, gennination percentage, germination speed and germination index were estimated at gennination stage. Pigments (total chlorophyle, chlorophyle a, b and carotene), soluble sugar, prolin, glycin betaine, turgor, leaf area, wet weight before stress, wet and dry weight after stress, dry weight of root and above ground, relative water content, leaf water content per unit leaf area, water saturation -different, specific leaf area, root to stem index, tolerance index, leafe area ratio, adaxial and abaxial stomata, lengh and width of abaxial and adaxial stomata and the content of sodium, potassium, calcium and magnesium in roots and stems were measured in growing stage on six mounth plants of Eucalyptus species. Proline and soluble sugar have important plane in osmotic regulation and osmotic protection so increase in content of these substance led to toletance of plant against osmotic stress. Decrease in pigments is caused by decomposition of enzymes activitiy. E.microtheca was the most tolerant species to drought stress, although it had the highest quantity of proline, soluble sugar, pigments, wet and dry weight, biomass, SLA and RWC, L WCA, the content of sodium, potassium in leaf and root and calcium in leaf and the number of adaxial and abaxial stomata and the lowest quantity of tolerance index. Increase of drought stress leds to increase in osmoprotectants and decrease of radicule length, plumule length, vigour index, gennination percentage, germination speed and germination index, pigments and growth parameters. Osmoprotectants have important plane in osmotic regulation and osmotic protection. So, increase in content of these substance led to toletance of plant against osmotic stress. Totally E. microtheca has strategies for stabling of relative water content and decreasing the osmotic potential under stress upto -1.2 MPa. Regards to studied parameters at germination and growth stages, we found that there are no relations between two stages and E. vimina/is and E. microtheca were the most tolerant species at germination and growth stages respectively. Regards to variety of Eucalyptus species we proposed such research on other species and eJ,ements, also extraction of Eucalyptus essential oil under drought stress is pprposed as another research. Key words: drought stress, Eucalyptus, vigour index, pigments, proline, glycin betain.