EFFECTS OF MYCORRHIZAL INFECTION ON DROUGHT TOLERANCE AND RECOVERY INSAFFLOWER AND WHEAT

The influence of arbuscular mycorrhizal fungi on drought tolerance and recovery was studied in safflower (Carthamus tinctorius L.) and wheat (Triticum aestivum L.). Plants were grown with and without the mycorr hizal fungus, Glomus etunicatum Becker & Gerd., in nutrient-amended so il under environmentally-controlled conditions to yield mycorrhizal an d nonmycorrhizal with similar leaf areas, root length densities, dry w eights, and adequate tissue phosphorus. When drought stress was induce d, mycorrhizal infection did not affect changes in leaf water, osmotic or pressure potentials, or osmotic potentials of leaf tissue rehydrat ed to full turgor in either safflower or wheat. Furthermore, in safflo wer, infection had little effect on drought tolerance as indicated by the level of leaf necrosis. Mycorrhizal wheat plants, however, had les s necrotic leaf tissue than uninfected plants at moderate levels of dr ought stress (but not at severe levels) probably due to enhanced phosp horus nutrition. To determine the effects of infection on drought reco very, plants were rewatered at a range of soil water potentials from - 1 to -4 MPa. We found that although safflower tended to recover more s lowly from drought after rewatering than wheat, mycorrhizal infection did not directly affect drought recovery in either plant species. Dail y water use after rewatering was reduced and was correlated to the ext ent that leaves were damaged by drought stress in both plant species, but was not directly influenced by the mycorrhizal status of the plant s.