Effects of mycorrhiza inoculation and different irrigation levels on yield, yield components and essential oil contents of fennel (Foeniculum vulgare Mill.) and ajwain (Trachyspermum ammi L.)

Fertilizers are the key components which provide plant nutrients'' needs in recent years (Omid Jangir & Sing، 1996; Kapoor et al.، 2007). In many cases، using chemical fertilizers has different negative environmental effects such as soil، water and air pollution، which increase environmental hazardous and production costs (Jangir & Sing، 1996; Kapoor et al.، 2007). Biological activities are markedly enhanced by microbial interactions in the rhizosphere of plants (Kapoor et al.، 2007). Many investigators have successfully used mycorrhiza to increase the availability of immobilized phosphate and thus minimize the use of mineral fertilizers. Arbuscular Mycorrhizal Fungi (AMF) can better enable a plant to withstand environmental stresses such as drought and salinity. AMF interacts with pathogens and other rhizosphere inhabitants which affect plant health and nutrition. More importantly، mycorrhizal fungi are capable of dissolving weakly soluble soil minerals، especially phosphate، by releasing acids or increasing CO2 partial pressure (Gupta et al.، 2002; Gosling et al.، 2006; Kapoor et al.، 2007). Therefore، they have the ability to enhance host plant uptake of relatively immobile nutrients particularly P، S and Zn. Limited water supply is also another major environmental constraint in the productivity of crop and medicinal plants. Moisture deficiency induces various physiological and metabolic responses such as stomatal closure، decline in growth rate and photosynthesis (Flexas and Medrano، 2002). The results of Baher et al. (2002) showed that greater soil water stress decreased plant height and total fresh and dry weight of Satureja hortensis.

In order to study the effects of mycorrhiza inoculation and different irrigation levels on the growth، quantitative and qualitative yield of fennel (Foeniculum vulgare Mill.) and ajwain (Trachyspermum ammi L.)، a field experiment was conducted as factorial based on randomized complete block design with three replications at the Agricultural Research Station، the Ferdowsi University of Mashhad، Iran during two growing seasons of 2009-2010 and 2010-2011. Mycorrhiza inoculation (with and without inoculation) and irrigation levels (1000، 2000 and 3000 m3. ha-1) were allocated to the first and the second factors، respectively. Several criteria such as yield components (including branch numbers per plant، umbel number per branch، umbellet number per umbel، seed number per umbellet and 1000-seed weight)، biological yield، seed yield، harvest index، essential oil content and essential oil yield of fennel and ajwain were measured.

Results indicated that the simple effects of mycorrhiza inoculation and irrigation levels on the biological and seed yields، harvest index (HI)، yield components، essential oil content and essential oil yield of fennel and ajwain were significant (p≤0. 01). The maximum biological yield of fennel (5. 3 g. m-2) and ajwain (4. 3 g. m-2) were observed in mycorrhiza inoculation. Mycorrhiza inoculation enhanced seed yield of fennel and ajwain up to 46% and 97% compared with control، respectively. The highest essential oil content of fennel (4. 2%) and ajwain (3. 0%) were obtained in mycorrhiza inoculation. The highest and the lowest seed yield of fennel and ajwain were observed in 3000 m3. ha-1 (1. 6 and 0. 9 g. m-2) and 1000 m3. ha-1 (1. 4 and 0. 7 g. m-2) irrigation levels، respectively. The maximum essential oil content of fennel and ajwain were obtained in 3000 m3. ha-1 (4. 0% and 3. 4%) and the minimum were for 1000 m3. ha-1 (3. 2% and 2. 9%). Interaction effects among mycorrhiza inoculation and different irrigation levels on the biological yield، HI and some yield components of fennel (such as branch number per plant، umbel numbel per branch، umbellet number per umbel and seed number per umbellet) and ajwain (such as umbellet number per umbel، seed number per umbellet and 1000 seed weight) scale fern number، seed number and 1000 seed weight of ajwain were significant (p≤0. 05). Inoculation with mycorrhiza، enhanced root development and resulted in the availability of moisture and nutrients، particularly phosphorus. On the other hand، these fertilizers are the cause of production of many growth regulators for the plant. The higher irrigation levels increased photosynthesis and dry matter production due to vegetative growth and photosynthesis area of the plants.