Improvement of some morphological, biochemical and postharvest characteristics of Gerbera jamesonii ‘Dune’ with application of humic acid and mycorrhizal fungus

Abstract In order to investigate the effect of humic acid and mycorrhiza on cut flower of Gerbera cv. Dune, an experiment was performed as a completely randomized design with two factors and three replications in hydroponic conditions. First factor was included: humic acid in 4 concentrations of 0 (control), 500, 1000 and 2000 mg/l as drench and the second factor: two levels of mycorrhizal fungi (without mycorrhiza and with mycorrhiza) were applied by root inoculation. Indicators such as leaf number and leaf area, root volume, fresh and dry weight of flowers, vase life, chlorophyll a, b and total chlorophyll, total soluble sugar and some postharvest traits such as petal ion leakage and petal malondialdehyde were measured. The results showed that humic acid and mycorrhizal fungus improved the morphological and biochemical properties of gerbera. Concomitant use of humic acid at a concentration of 1000 mg/l and mycorrhizal fungus on the difference between leaf length and root volume, fresh and dry weight of flowers and vase life almost doubled compared to the control. Application of humic acid and mycorrhizal fungus significantly increased total chlorophyll content and soluble sugar content. Application of humic acid and mycorrhizal fungus reduced ion leakage and malondialdehyde.   Introduction Gerbera (Gerbera jamesonii) is a rosette, herbaceous, perennial plant belonging to the Asteraceae family. The leaves have long petioles up to 15 cm long. The flower diameter in wild gerbera is 7-10 cm and in hybrid plants is 15-25 cm. Gerbera is a day-neutral plant and flowers better in more light intensity. This plant flowers from late spring to late autumn and even early winter (Rashidi, 2009). Humic substances are obtained from the decomposition of soil organic matter, peat, lignin, etc., and their actions are similar to auxin and cytokinin. These substances improve the absorption of some elements by being placed in the cell membrane, which can to maintain the stability of the membrane (Balazadeh and Hassanpour Asil, 2014). Humic acid increases the length and weight of roots and the number of lateral roots (Ambreen and Khetran, 2014). Due to its cytokinin-like properties, humic acid delays the decomposition of chlorophyll and protein in leaves and senescence in flowers. These compounds play an essential role in the metabolism of carbohydrates and their transfer to the growing buds, thereby increasing the dry matter in flowers and their longevity (Hosseini Darvishani and Chamani, 2013). In many plants, the root system of the plant is symbiotically connected with different species of fungi, and they form a complex association called mycorrhizae (Alizadeh, 2011). Mycorrhizal fungi in the hydroponic system lead to the expansion and development of the roots, which increase the yield of the product. Three main groups of ornamental plants that are suitable for symbiosis with mycorrhizal fungi have been identified, including pot plants, biennial and perennial plants, and ornamental plants grown under hydroponic conditions (Crisan et al., 2017). Considering the positive effects of mycorrhizal fungi and humic acid on the quantitative and qualitative traits of plants, this study investigated the effects of different concentrations of humic acid were investigated on some growth, flowering, and post-harvest characteristics of gerbera flowers in symbiosis with mycorrhizal fungi in hydroponic conditions.   Materials and Methods To perform this experiment, tissue-cultured plantlets of gerbera (Gerbera jamesonii ‘Dune’) were used. These plants were grown in pots of size 20 (volume 7 liters, height and diameter of pots 19 and 24 cm, respectively) under soilless conditions (a mixture of 65% peat moss, 30% perlite, and 5% cocopeat). The daily temperature of the greenhouse was 20-25/13-16ºC (day/night), and the light intensity was 400-500 µmol.m-2s-1. This research was carried out in a factorial trial based on a completely randomized design with three replications. Each replication contained three pots with one plant in each pot. The experimental factors included: four concentrations of humic acid (0, 500, 1000, and 2000 mg/l) as a drench, two-week intervals for three months, and the second factor: two levels of mycorrhizal fungi (with or without mycorrhizal inoculation). The culture medium was inoculated with a mixture of three types of mycorrhizal fungi, including Rhizophagus fasciculatus, Diversispora versiformis, and Funneliformis mosseae. Inoculation was done at the time of planting plants in pots and in the root zone. Sixty grams of inoculum (including soil, fungal spores, hyphae, and mycorrhizal roots) were added to half of the pots (plants inoculated with mycorrhizal fungi). The same amount of autoclaved inoculum was added to the rest of the pots (plants without mycorrhizal inoculation). At the end of the experiment, parameters were measured, such as leaf number and leaf area, root volume, fresh and dry weight of flowers, vase life, chlorophyll a, b, and total chlorophyll, total soluble sugar, and some postharvest traits such as petal ion leakage and petal malondialdehyde. Statistical analysis of data was done with SAS Ver. 9.2, and the comparison of means was done with Tukey's multiple range test.   Results and Discussion The results showed that humic acid and mycorrhizal fungus improved the morphological and biochemical properties of gerbera. A comparison of means showed that the length of leaves and leaf area increased with the increase of humic acid in plants inoculated with a mycorrhizal fungus. The highest root volume was observed in the concentrations of 1000 and 2000 mg/l of humic acid in inoculated plants. Increasing the concentration of humic acid led to a significant increase in the flower fresh and dry weight of inoculated plants so that the highest flower fresh and dry weight was observed at a concentration of 2000 mg/l of humic acid in inoculated plants. The results showed that by increasing the concentration of humic acid up to 1000 mg/l, the vase life of gerbera flowers increases, but at higher concentrations, a decreasing trend was observed. The use of mycorrhizal fungi also increased the vase life of the flowers. The application of humic acid (up to 1000 mg/l) and inoculation with mycorrhizal fungi led to an increase in the amount of total chlorophyll. In non-inoculated plants, the concentrations of 1000 and 2000 mg/l of humic acid caused a significant increase in total soluble sugar compared to the control. Also, the application of humic acid and mycorrhizal inoculation reduced ion leakage and malondialdehyde of flowers during the vase life period. Due to the formation of complexes with mineral ions, humic substances cause the absorption of more elements and, as a result, increase the amount of photosynthesis in the plant, thus increasing the growth of the aerial parts of the plant (Abbas and Hammad, 2017). It should be noted that the hormone-like property of humic acid in plants accelerates the growth of roots leading to the growth of aerial parts and the improvement of the flowering characteristics of the plant (Youssef et al., 2004).   Conclusion From the results obtained, it can be concluded that the use of treatments with humic acid and mycorrhizal fungi improves some parameters of the plants, including the morphological, physiological, biochemical, and post-harvest characteristics. According to the results, among different concentrations of humic acid, the concentration of 1000 mg/l of humic acid with mycorrhizal fungi inoculation had the highest effect on improving the measured traits.