Response Two Tomato Cultivars to NaCl Stress in the Presence and Absence of Mycorrhiza

To investigate the beneficial effect of mycorrhizal symbiosis on plant under saline conditions, two tomato cultivars; i.e. Castle Rock; relatively salt-sensitive, and Super Strain B; relatively salt-tolerant, were sown in mycorrhiza-inoculated autoclaved soil mixture (2 composted field soil: 1 sand: 1 perlite v/v/v). Seedlings were grown for 21 days before transplanting to 5 L pots containing the same autoclaved soil mixture. Non-mycorrhizal treatments had an autoclaved inoculums. Salinity treatments were started after 2 weeks of establishment stage. Salinity levels were adjusted by adding 7.4 and 14.28 mg NaCl to the soil mixture in each pot to achieve 6.0 and 10 dS·m^-1 in soil saturated paste extract, respectively. Control soil had 1.7 dS·m^-1 salinity level. Each plant was given 25 mg of soluble fertilizer (NPK; 20:20:20) every week and irrigated with water to maintain adequate moisture. Leachate from each pot was collected and added back to soil in the same pot. The growth temperatures were 25/18 °C day/night with 16 hours photoperiod at PAR ranging from 550–650 µmol photon min^-2sec^-1. The plants were grown in four replicates for a month before sampling and harvesting the shoots. Growth parameters including fresh weight, dry weight and plant height were recorded. Samples taken from the third fully expanded terminal leaf from the top of the plant were tested for ion leakage. All growth parameters were reduced by the higher salinity levels in both cultivars. However, the sensitive cultivar was more dramatically affected than the tolerant cultivar. Preliminary results suggest that the influence of mycorrhiza is complex; only in tolerant cultivar, mycorrhiza seems to have overall positive effect on growth. At high salinity level, there seems to be no positive effect of mycorrhiza on either of the cultivars. The negative impact of salinity was reflected in higher ion leakage from leaf tissues in both the cultivars. Furthermore, the mycorrhizal plants had lower ion leakage in both the cultivars.