Study the effect of different irrigation regimes and biofertilizers on morphological characteristics, essential oil and phenol and flavonoids contains in fennel (Foeniculum vulgare Mill.)

Drought stress, permanent or temporary, limits the growth and the distribution of natural vegetation and the production of cultivated plants more than any other environmental factor. Water deficit stress has changed plants ‘metabolism significantly, by attenuating the growth, photosynthesis, and ultimately yield of the plants. The recent global trend in production of medicinal plants is in favor of sustainable agriculture. One of the efficient practices of sustainable agriculture is the application of biological fertilizers for quantitative and qualitative yield improvement in medicinal plants, such as fennel, which is of great significance in food, pharmaceutical, and cosmetic industry. Fennel (Foeniculum vulgare Mill.) is an umbelliferous plant. Due to the high potential of West Azerbaijan province, especially Mahabad region, the present study was conducted to investigate the effect of biofertilizers on the increase of water tolerance in fennel.

In order to investigate the effect of different irrigation regimes and biofertilizers on the quantitative and qualitative characteristics of fennel, an experimental experiment was conducted in 2020 in an agricultural farm in Mahabad city. In this experiment, four irrigation regimes (irrigation after 60, 90, 120 and 150 mm evaporation from Class A evaporation pan) in main plots and inoculation of seeds with biofertilizers (including control, inoculation with mycorrhiza, azotobacter  and phosphate Fertile 2) were placed in subplots. In this study, plant height, number of sub-branches, number of umbrellas and umbrellas per plant, number of seeds per umbel, thousand kernel weight, biological yield, grain yield, essential oil content, phenol and flavonoid content were measured. The data obtained from the experiment were analyzed using SAS 9.2 software. The means obtained were statistically compared using Duncan's test at a level of 5% probability.

Based on the results of the analysis of variance of the data, a significant difference was observed between the levels of the irrigation regime in terms of the effect on all the studied traits at the level of 1% probability. Effect of biofertilizer on the number of branches, number of umbrellas per plant, number of umbrellas per umbrella, on thousand kernel weight, biological yield, grain yield, percentage of essential oil, total phenol content and flavonoids at a probability level of 1% and on plant height, number of seeds per umbel and flavonoid content were significant at 5% probability level. Among of irrigation with biofertilizer interaction treatments in terms of effect on plant height, number of sub-branches, number of umbrellas per plant, number of umbrellas per umbrella, number of seeds per umbrella, grain yield, essential oil percentage and phenol content at a probability level of 1% and in terms of effect on thousand kernel weight there was a significant difference at the level of 5% probability. The results showed that the highest plant height, number of sub-branches, number of umbrellas per plant, on thousand kernel weight and grain yield were allocated to irrigation regime after 90 days and seed inoculation with mycorrhiza, Also, the highest percentage of essential oil and total phenol content in the irrigation regime was observed after 120 mm of evaporation and inoculation of seeds with mycorrhiza. The results of mean comparisons also showed that although grain yield decreased with increasing severity of water deficit stress, but in all irrigation regimes, the use of biofertilizers significantly increased grain yield compared to the control treatment. Also, the use of biofertilizers under irrigation regime stresses after 120 and 150 mm of evaporation was able to show higher grain yield than the control treatment in irrigation regimes after 60 and 90 mm of evaporation. In this study, water deficit stress increased the percentage of essential oil in fennel plant. Also, the use of mycorrhiza in irrigation regimes after 60 and 90 and the use of mycorrhiza and Azotobacter in irrigation regimes after 120 and 150 mm of evaporation significantly increased Essential oil percentage compared to control treatment.

In this study, the most suitable quantitative and qualitative characteristics of fennel were obtained in the irrigation regime after 90 mm, so the irrigation regime is recommended to achieve the maximum quantitative and qualitative characteristics of fennel in the study area. The results also showed that the application of Mycorrhiza and Azotobacter biofertilizers in both normal irrigation and water deficit conditions can improve the quantitative and qualitative properties.