حامد اشراف

In order to evaluate three species of mycorrhizal fungi (Glomus clarum, Glomus fasiculatum and Glomus mosseae) and drought stress (80, 55 and 30 percent of field capacity) on characteristics of grass genera, Lolium perenne, Poa pratensis, Festuca aurandiancea and Agropyron elongatum, a factorial experiment based on randomized complete block design was carried out in the greenhouse using a cylindrical pots. According to the results, Lolium showed the highest root colonization with G. mosseae while Poa showed the lowest colonization with G. clarum. Drought stress reduced the root colonization of Festuca and Lolium in all mycorrhizal treatments, but increased the root colonization of Agropyron and Poa with G. clarum and G. fasiculatum. At highest level of stress, G. fasiculatum and G. mosseae increased the chlorophyll and carotenoid contents of grass genera, more than 38 percent. Grasses symbiotic with G. mosseae showed the highest relative water content and lowest electrolyte leakage and malondialdehyde content compared to grasses symbiotic with other species of mycorrhizae. In general, mycorrhizal fungi could reduce the adverse effects of drought stress on grass characteristics, but the tendency to symbiosis and that’s influence on the grass genera under stress, were different.

Turfgrasses are the most important ground covers with high dining leg strength that rarely replacement can be found for them in landscape. Limitation of water resources especially in arid and semi-arid regions is one of the main challenges in turf management. Mycorrhizae symbiosis with plants is one of the ways to reduce the adverse effects of drought stress.
In order to investigate the effects of three species of mycorrhizae fungi (G. clarum, G. fasiculatum, G. mosseae and Non fungi) and drought stress (80, 55 and 30 percent of field capacity) on the biochemical characteristics of turfgrass species, Poa pratensis and Agropyron elongatum, a factorial experiment based on randomized complete block design was carried out in the greenhouse of the Faculty of Agricultural Sciences, University of Guilan in 2015. Following the establishment of turfgrass that lasted about 60 days, drought stress was applied. The traits of ascorbate peroxidase (APX), peroxidase (POD) and catalase (CAT) activity and malondialdehyde, proline, total protein of leaves and root colonization percent were studied.
According to the results Agropyron showed the highest root colonization with G. mosseae while Poa showed the lowest colonization with G. clarum. Drought stress reduced the root colonization of Agropyron and poa with G. mosseae but increased the root colonization of them with G. clarum and G. fasiculatum. Drought stress increased the activities of antioxidant enzymes, proline, malondialdehyde and total protein in the leaves of studied grasses. Mycorrhizal fungi, especially under drought stress increase the activity of antioxidant enzymes and proline content, but decreased the malondialdehyde content. There were significant differences between fungi species and grass species in terms of impact on the above mentioned traits. So that Agropyron with G. mosseae but Poa with G. clarum showed the highest leaf APX activity. In the highest level of stress grasses symbiotic with G. mosseae had the highest POD activity while under mild stress condition highest enzyme activity was observed in leaves of grasses symbiotic with G. fasiculatum. Grass response to mycorrhizal fungi species at different levels of drought stress on CAT activity was different. In moderate stress conditions Agropyron symbiotic with G. mosseae had a highest CAT activity, while in the highest level of stress Agropyron symbiotic with G. fasiculatum had a highest enzyme activity but in Poa in both moderate and severe stress the highest enzyme activity was related to grasses that had not been inoculated with mycorrhizae fungi. G. mosseae caused the proline content of grass leaves at the highest level of drought stress more than 130 percent compared to without mycorrhizae situation increased, but malondialdehyde more than 32 percent decreased. In moderate stress this rate was respectively 70 percent increase and 25 percent decrease.
The effect of mycorrhizal fungi species on the activity of antioxidant enzymes in leaves of studied turfgrasses under drought stress was different However, in general, mycorrhiza symbiosis with increases of antioxidant activity and proline could reduce the amount of lipid peroxidation in leaves of studied turfgrasses. In this regards the G. mosseae was more effective.

Effects of different Paclobutrazol concentrations (0, 250, 350 and 450 mgL-1) and plantlet density (80, 100 and 120 plantlet/m2) on minituber production per plantlet in potato cultivar ‘Sante’ were investigated in a factorial experiment based upon a randomized complete block design of 4 replications. Paclobutrazol (Cultar with 250 g/L of active ingredient) was used as foliar application at early stolon initiation. The results indicted that Paclobutrazol increased chlorophyll a and b contents of the leaf tissue as well the ratio of the tuber fresh mass to shoot fresh mass. Paclobutrazol significantly reduced the internode,s, stem and stolon length, also reduced stem diameter. While plantlet density increased internode, stem and stolon length, yet reduced tuber fresh mass to shoot fresh mass ratio. The interaction between the two factors was significant on internode, stem and stolon lengths. The study clearly showed that Paclobutrazole is effective in suppressing excessive vegetative growth in high plantlet densities. It could also improve the minituber average weight through an increase of assimilation to the minituber and as well an increase of chlorophyll a and b contents of the leaf tissue. Means related to weight and number of minituber production were recorded as 3.27, 3.74 and 5.69, 6.16 in control and Paclobutrazol treatments, respectively. In total, for producing the highest numbers of minituber of higher weights, it is recommended to apply higher plantlet densities along with lower concentrations of Paclobutrazol