Improvement of quantitative and qualitative characteristics of coriander using native zinc solubilizing bacteria and zinc sulfate under greenhouse condition

Introduction :

Coriander (Coriandrum sativum L.; Apiaceae), an aromatic annual herb, is known as an important medicinal plant. It has been recommended due to its significant nutritional and medicinal properties. The fresh shoots of this plant are used as a food condiment in many places in the world. However, the application of agrochemical fertilizers is a main source of soil, water and environmental pollution which can harmfully affect human health. Plant growth promoting bacteria (PGPB) can be considered as an effective way to meet sustainable agriculture by reducing agrochemical fertilizers usage (Bakhshandeh et al., 2015). Since a limited number of studies are available to investigate the effects of PGPB on coriander growth, thus, this study aimed to evaluate different treatments of zinc sulfate on coriander along with and without zinc solubilizing bacteria.

Two separate experiments were carried out under greenhouse conditions to study the effect of native zinc solubilizing bacteria (Burkholderia cepacia) and zinc sulfate (ZnSo4) on the emergence, some vegetative and phytochemical characteristics of coriander. The first experiment was conducted based on a completely randomized design to evaluate different methods of inoculation (non-inoculation as control, seed inoculation and soil inoculation). While the second was performed as a factorial experiment in a completely randomized design. The factors were two inoculation methods (non-inoculation as control and seed inoculation) and five treatments of ZnSo4 (99%) application (without application of ZnSo4 as control, 1.5 and 3 g/L for foliar application and, 5 and 10 mg/kg soil for soil application). Three replications were made in both experiments. The experiment was carried out under optimal conditions. The seedlings were harvested when they had six fully expanded leaves. Emergence characteristics, photosynthetic pigments, plant dry weight, phenol content, flavonoid content and antioxidant enzymes activity were measured in this study.

Based on the results obtained in the first experiment, the amount of all studied traits were remarkably increased by applying B. cepacia, except for antioxidant enzyme activity which was not significantly affected. Since there was no significant difference between the inoculation methods (soil and seed inoculations), thus, the seed inoculation method was selected as the best treatment for improving coriander growth in experiment I. In experiment II, the maximum emergence percentage and rate, chlorophyll a, b, total and carotenoids, phenol content in the leaves, flavonoid content in the leaves and root, guaiacol and superoxide dismutase enzymes activity increased by 16.5, 7.73, 9.63, 17.7, 3.94, 11.1, 3.24, 31.6, 23.5, 61.1 and 7.18% in the presence of B. cepacia as compared to the control (non-inoculation). While among the ZnSo4 treatments, higher amount of the studied traits was found in the foliar application at a concentration of 3 g/L and soil application at a concentration of 5 mg/kg soil. Furthermore, the interaction effect between the B. cepacia inoculation and ZnSo4 treatments was not statistically significant. In general, PGPB can improve plant growth and productivity in several ways: nitrogen fixation, solubilizing insoluble minerals such as phosphorus, potassium and zinc, plant hormone production, decreasing the inhibitory effects of biotic and abiotic stresses. The mechanisms mentioned above are fully described in Ahemad and Kibret (2014).

Our findings indicated that B. cepacia could be used in both inoculation methods (seed and soil inoculations) to improve the growth of coriander. Furthermore, foliar application at a concentration of 3 g/L and soil application at a concentration of 5 mg/kg soil by ZnSo4 along with B. cepacia inoculation were the best treatments for increasing quantitative and qualitative characteristics of coriander.