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Rhododendron ponticum, a common and widespread evergreen species of the Rhododendron genus, is 2-8 m long and has a vertical form. (Tutin et al. 1972) Its leaves are dark green and oblong-elliptic (Cross 1975). The funnel-shaped flowers are purple, lavender and pink (Burnie et al. 2004).
The thick leaf-litter layer created by Rhododendron on the forest ground breaks down slowly in some areas and may therefore endanger the natural bushes and trees by occlusion, and thus may result in a new or more restricted surface vegetation (Cross 1975). Studies in the literature indicated that Rhododendron ponticum is an invasive species on mixed forest ground, particularly in oak and beech forests andalso investigated the measures against Rhododendron ponticum invasion(Thomson et al. 1993; Erfmeier and Bruelheide 2004; Esen et al. 2004; Tyler et al. 2006; Harris et al. 2009).
Despite its damage to the endemic forest vegetation where it is an invasive species, Rhododendron ponticum has an aesthetic value in landscape architecture due to itsevergreen foliage and the purple and mauve tinted flowers that blossom in the spring. They are particularly effective when used in groups. In planting designs, in addition to their aesthetic effects, they can be utilized as hedges and border elements to create stimulant effects in slope stabilizations and roadway planting.
The present study aimed to support the seed cultivation of Rhododendron ponticum for its use in landscape planting designs. In this context, the success of germination of seeds obtained from different elevations was investigated.
MATERIALS AND METHODS
MATERIJALI I METODE
Rhododendron ponticum L. seed capsules were collected in November 2015, in the maturation season, from the origins at different altitudes in the Eastern Black Sea region in Turkey. Bulked seeds for each origin from at least 30 species were used. Information on the origins of the plants where the Rhododendron ponticum seed capsules were collected is presented in Table 1.
Seed capsules of Rhododendron ponticum, collected from different, were spread in a thin layer in the laboratory and dried at ambient temperature and humidity. Dried capsules were manually broken open and the seeds were removed. Before the seeds were sowed, it wasn’t applied any treatment for seeds to determine their viability, only healthy seeds were chosen. One thousand seed weights were determined using randomly selected seeds. The seeds were separated according to their origins in closed containers. Cold stratification pre-treatment at 2-4 °C in dark conditions was applied to the seeds for 3 months until February 2016 before sowing.
Germination experiments of Rhododendron ponticum seeds were conducted in the greenhouse with technological systems at 25 ± 2 ° C, 70 ± 2% humidity conditions. Soil, Peat, Soil + Sand (5:5), Soil + Sand (7:3), Peat + Sand (7:3) and Soil + Peat + Sand (4:4:2) media were prepared for germination in the study. Afterwards 3 x 100 seeds were planted in planting crates in the greenhouse in three repetitions for each elevation. The crates were covered with a polyethylene cover to provide suitable moisture until the germination process is completed.
Irrigation operation was conducted with the sprinkling method and equal amounts of water were provided for each crate. Weeds were removed from the medium during the study.
From the first day of germination, germinated seeds in each medium were counted at one-week intervals. At the end of the study after eight months of sowing in October 2016, measurements were conducted to determine the height and root length of the seedlings in the medium, based on the elevation they were obtained from during the diversion of the germinated seeds. The seedling height and the length of roots formed were measured as three repetitions by a type measure at 1 mm sensitivity and recorded as “cm”.
In the present study, multivariate analysis of variance was conducted to reveal the differences between the germinated seeds based on the altitude of collection and germination medium and the values obtained in the conducted measurements. Homogeneous subgroups were determined with the Duncan test. SPSS statistical software was used to conduct these analyzes.
RESULTS AND DISCUSION
REZULTATI I RASPRAVA
Randomly selected 8x100 seeds were weighed on a precision scale and 1000 seed weight was determined (ISTA 1996). Seeds collected from Zafanos provenance (592m) weighed 0.0764g, from Macka provenance (1234m) weighed 0.09444g and from Zigana provenance (1744m) weighed 0.0805g (Table 1). Cross (1975) states that Rhododendron ponticum produces hundreds of thousands of seeds every year with an average weight of 0.063g. Small seed size also increases plant proliferation potential by allowing seeds to spread over long distances (Higgins et al. 1996; Rejmanek and Richardson 1996).
Gutterman (1992) notes that seed germination is affected by environmental factors, such as light, temperature and salinity conditions, as well as the origin of the seed.Differences between germination of seeds based on provenance were reported in many species (for examples, see Vera 1997; Keller and Kollmann 1999; Andersen et al. 2008; Singh et al.2004; Vecchio 2012).