Investigating the Role of Three Species of Arbuscular Mycorrhizal Fungi on Growth, Acid Phosphatase Enzyme Activity and Phenolic Compounds in Zinnia Plant under Drought Stress Conditions

This experiment was conducted to study the effects of three identified isolates of Arbuscular mycorrhizal fungi (AMF) on growth, acid phosphatase enzyme activity and phenolic compounds (phenol, flavonoid and anthocyanin) of zinnia plants (Zinnia elegans L.var. Magellan Red) under water stress conditions. A factorial (two factors) experiment was planned based on a completely randomized design (CRD) with six replications at the greenhouse of Vali-e Asr University of Rafsanan, Rafsanjan, Iran. The factors included five AMF inoculation (no mycorrhizae as control, Rhizophagus irregularis, Rhizophagus intraradisces, Funneliformis mosseae, mixture of three species) and four irrigation levels (100% FC as control, 80% FC, 60% FC and 40% FC). Seedlings with four true leaves were transplanted into 1.2 L pots and immediately inoculated with each of the above symbionts. The plans were irrigated with distilled water for 50 days to obtain certain amount of infection, then four irrigation regimes were achieved for four weeks. Vegetative growth traits (leaf number, peduncle diameter, petal length, shoot and root dry weight) were reduced significantly with increasing drought stress level. Drought stress reduced chlorophyll index (SPAD) and phenolic compounds concentration. Inoculation with AMF prominently improved growth, acid phosphatase enzyme activity, chlorophyll index and phenolic compounds under drought stress, so that  under  40% FC,  R. irregularis, R. intraradisces, F. mosseae, and a mixture of them  increased acid phosphatase enzyme activity by 58, 52, 61, 53 percent, respectively, compared to the control. In conclusion, it is suggested that AMF inoculation improves drought tolerance of zinnia plants at least in part through the enhanced uptake of slowly diffusing mineral ions such as phosphorus.