| چکیده انگلیسی مقاله |
Introduction: Citrus is highly sensitive to water and soil salinity. About 13 percent decrease of citrus yield per each 1 dS m -1 increase in salinity above 1.4 dS m-1. Arbuscularmycorrhizal (AM) fungi are probably distributed in most soils and approximately 90% of higher plant species examined interact with AM fungi.AM growth hyphae increased root level, water absorption efficiency and nutrient distribution specially phosphorus and zinc. More biomass and less proline content in citrange "carrizo" inoculated with Glomusintraradices in compare with non-inoculated treatment under different salinity levels. Two symbiosis AM (Glomusmosseae and Paraglomusoccultum) through growth improving, photosynthetic rate and root structure could reduce adverse effects of salinity under 100 mM sodium chloride concentration. We analyzed the impact of two mycorrhizal fungi under salinity stress. Our objectives were to determine how AM symbiosis can alleviate adverse effect of salinity and which of our mycorrhizal fungi show better results. Materials and Methods: Seed of Flying dragon were sterilized by immersion in 70% alcohol for 4 min, rinsed 5 times with distilled water and germinated in jiffy pots at 27ºC. 25 g of fungi (Glomusmosseae and Paraglomusoccultum) per pot were used while non-AM fungi treatments received the same weight of growth media. The experimental design conducted in a completely randomized design as a factorial form. First factor was four levels of salinity (0, 50, 100 and 150 mMNaCl) and the second factor was two different genotypes of mycorrhizal fungi. Six replicates of each treatment were applied. Control treatments were irrigated with distilled water. Shoot and root dry weight were measured. Concentration of proline was measured by the method of Bates et al (3). AM colonization was estimated in according to with Hashem et al (14) with using light microscopy. Relative water content (RWC) was measured by Wu and Xia (28). The sucrose and glucose were determined by Wu et al (29) method. Na+, K+ and Ca+ concentrations in leaves were measured by using atomic absorption spectrometer. The data were analyzed by two factor ANOVA using JMP 7 software. Least significant difference (LSD, α< 0.05) was used in order to compare the significant difference between treatments. Results and Discussion: The highest colonization occurred in control treatmentin which inoculated with Paraglomusoccultum, andthe lowest colonization was in 150 mM treatment of NaCl that inoculated with Glomus mosseae. Salinity cause more remarkable decrease on colonization of Glomus mosseaethanParaglomusoccultum. This indicated that each different mycorrhizal species had different potential during salinity. Salinity had reduced leaf number, relative water content stem diameter, leaf area index, root and shoot dry weight, regardless of the inoculation with AM fungi. Byincreasing salt levels, stem diameter and leaf area index (LEI) remarkably decreased, but colonized seedlingespecially in low salt concentration partly displayed better condition. In LEI and stem diameter, according to the results of mycorrhizal inoculation, even in high salinity (150 mM) had shown significance difference (Table 1). During increasing of salinity level, sucrose content in inoculated treatments decreased, while in un-inoculated ones it was reverse. Only in 100 mM sodium chloride treatments observed different significant between two AM fungi. In addition, the inoculated AM fungi had higher concentration of glucose than un-inoculated treatments. Proline concentration was increased 22℅ and 32℅ in G. mosseaeandP.occultum,respectively. Although proline content increased with salinity intensity, no significant differences were observed between two AM fungi. In high salinity treatments (100 and 150 mM), proline content has been shown significantly difference in compare with no AM fungi inoculation (Table 2). Compared to the control treatment, Na+ but not K+ concentrations were markedly increased under 100 mM sodium chloride. With comparing two different AM fungi, no significant difference were found in K+, Na+, Ca+ ,K+/ Na+ and Ca+/ Na+. Under the non salinity and salinity conditions, AM symbiosis notably decreased the Na+ concentration in compared with non-inoculated treatments.Salinity significantly decreased the ratio of K+/ Na+ and Ca+/ Na+. Leaves of AM seedlings have shown higher K+/Na+ and Ca+/Na+ ratios than the non-AM inoculated seedlings at three salinity levels. A reduction in mycorrhizal fungi colonization in citrus plants grown under saline condition was expected since it has been shown that AM fungi may be influenced by salinity during spore germination. This is consistent with other results. According to the results colonization rate of two AM fungi displayed different results, suggesting that P.occultumcontained a better colonization than G. mosseae. Significant increase in growth parameters, namely, height, diameter, root length, and leaf area was more evident for the seedlings inoculated with G. fasciculatum and G.mosseae. Salinity reduces the water potential of the roots, causing reduction in growth rate, along with a suite of metabolic changes similar to those caused by water stress. From the present results it can be deduced that the reduction in plant growth due to increased salinity can be attributed to the osmotic effects of salts. Osmotic stress is a problem stemming from salt stress, and the resulting decrease in chemical activity causes cells to lose turgor. Conclusions: Under salt stress, plant growth and biomass would be slowed down. The reasons may be the non-availability of nutrients and the expenditure of energy to counteract the toxic effects of NaCl. However, mycorrhization was found to increase the compatibility of the host plant by enhancing its growth. Several researchers have reported that AM fungi-inoculated plants grew better than non-inoculated plants under salt stress. Conclusion based on various studies on the effect of several mycorrhizalinoculums on the seedling growth, it was clear that AMfungi could be infected effectively, and their shoot and rootgrowth, especially fibrous root growth, was significantlyimproved, compared with the control. For alleviating the adverse effects of salinity in Flying Dragon rootstock, inoculating with mycorrhizal fungi is suggested. However, in respect of AM symbiosis, the fundamental pertinent mechanism pathways are still not completely clear. |