THE INFLUENCE OF THE MYCORRHIZA GLOMUS-ETUNICATUM ON DROUGHT ACCLIMATION IN SAFFLOWER AND WHEAT

A study was done to determine the effects of vesicular-arbuscular myco rrhizal (VAM) colonization on drought acclimation of host plants. Saff lower (Carthamus tinctorius L. cv. S555) and wheat (Triticum aestivum L. cv. Anza) were grown under environmentally controlled conditions wi th or without the VAM fungus, Glomus etunicatum Becker and Gerd., and were either acclimated (by pre-exposing plants to a 10-11 day drought period) or unacclimated to drought. Plants from all treatments were th en exposed to drought for 9 days, and plant water status and root wate r uptake were measured. To minimize interactions between drought and P uptake, growth periods were adjusted so that acclimated and unacclima ted plants were similar in size when measurements were made. When whea t was acclimated to drought, osmotic adjustment occurred (leaf solute potentials of leaf tissue rehydrated to full turgor were approximately 0.5 MPa lower in acclimated than unacclimated plants); in safflower, osmotic adjustment was minimal when plants were acclimated. Consequent ly, acclimated wheat plants were able to tolerate drought better than unacclimated plants, and maintained higher leaf water potentials and r elative water contents as soil water was depleted. For both safflower and wheat, acclimated plants had higher water use efficiency, and ther efore produced more biomass when water availability was limited, than unacclimated plants. However, mycorrhizal colonization did not affect osmotic adjustment, plant water status, water use efficiency or water uptake in either plant species, and therefore had no effect on drought acclimation or resistance.