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The effects of boron and NaCl induced salinity on growth and mineral composition of the pear (Pyrus communis L.) rootstock OH × F 333 shoots cultured in vitro were investigated. Shoots were grown in vitro for seven weeks on a Murashige and Skoog medium containing two B concentrations (0.1 and 2 mM) combined with five NaCl concentrations (0, 10, 20, 40, and 80 mM). Τhe longest shoots were produced at 0.1 mM B and 80 mM NaCl, but highest number of shoots were produced at 0.1 mM B and 0 -20 mM NaCl. Inclusion of 20 and 40 mM NaCl in the culture medium significantly increased fresh mass of cultures compared to 0 mM NaCl for all B concentrations tested. The concentrations of P, K, Ca, Mg, Na, Fe, Mn and Zn of plants were affected by B and NaCl concentration of the medium.

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The in vitro response of two Prunus rootstocks: GF 677 (Prunus persica × Prunus amygdalus), and Nemared (Prunus persica) to increasing concentrations of KCl of the culture medium was studied. Shoots were grown in vitro for 8 weeks on an Murashige and Skoog medium supplemented with 0, 5, 10, 15, 20, 40 or 80 mM KCl. By increasing KCl concentration from 0 to 40 mM, the number of shoots per explant was not significantly affected for both rootstocks. However, Nemared rootstock formed more shoots per explant than GF 677 under respective KCl concentrations of the medium. Inclusion of 80 mM KCl in the medium resulted in a reduction of growth of both rootstocks. Sodium, Fe, Mn, and Zn concentration in tissues of Nemared rootstock were significantly higher than the respective values of GF 677.Additional key words: cell proliferation, ion toxicity, micropropagation. ⎯⎯⎯⎯Salinity is one of the most important environmental factors limiting plant growth. Salt stress can adversely affect plant survival, biomass and plant height. Upon exposure to salt stress, plants exhibit a wide range of responses at the molecular, cellular and whole plant level (Hasegawa et al. 2000). These include morphological and developmental changes (e.g. life cycle, inhibition of shoot growth and enhancement of root growth), adjustment in ion transport (uptake, extrusion and sequestration of ions, decrease in uptake of K + , Ca 2+ and Mg 2+ ) and metabolic changes (osmoregulation) (Xiong and Zhu 2002). Nutrient imbalances were observed in salt-stressed plants (Grattan and Grieve 1999). Rootstocks affect the nutritional status of the scion in vitro (Sotiropoulos et al. 2005) and proper choice of rootstocks can ameliorate the detrimental effects of salinity (Layne 1987). The objective of the present research was to study the effect of KCl induced salinity on growth and nutritional status of two Prunus rootstocks cultured in vitro.The explants employed were shoots of two peach rootstocks: GF 677 (Prunus persica × Prunus amygdalus), and Nemared (Prunus persica). The shoots were about 25 mm in length preserved from previous in vitro cultures and maintained in the growth room. Each shoot was transferred and grown in a 15 × 100 mm glass test tube containing 5 cm 3 of the Murashige and Skoog (1962; MS) culture medium supplemented with 1 g m -3 benzyladenine (BA). Six KCl concentrations were used: 0, 5, 10, 15, 20, 40 and 80 mM. These KCl concentrations were added to the standard MS medium containing already 20.04 mM K + and 5.98 mM Cl -. Therefore K + concentration (mM) of the treatments were as follows: 20. 04, 25.04, 30.04, 35.04, 40.04, 60.04, 10.98, 15.98, 20.98, 25.98, 45.98, and 85.98. The pH of the media was adjusted to 5.8 before autoclaving at 121 °C for 15 min. The tubes were maintained in the growth room at 22 ± 1 °C and 16-h photoperiod per day (cool white fluorescent tubes, irradiance of 45 μmol m -2 s -1 , 400 -700 nm). After 8 weeks in culture, the number of shoots, length of shoots, and fresh and dry mass of explants were measured. For determi...