Alleviatory activities in mycorrhizal tobacco plants subjected to increasing chloride in irrigation water

The effects of presence and absence of arbuscular mycorrhizal (AM+ and AM-) fungus (AMF) Glomus intraradices on agronomic and chemical characteristics of field-grown tobacco (Nicotiana tabacum L.) Virginia type (cv. K-326) plants exposed to varying concentrations of chloride 10, 40, 70 and 100 mg Cl L-1 (C1-C4) were studied over two growing seasons (2012-2013). Mycorrhizal plants had significantly higher uptake of nutrients in shoots and number of leaves regardless of intensities of chloride stress. The cured leaves yields of AM+ plants under C2-C4 chloride stressed conditions were higher than AM- plants. Leaf chloride content increased in line with the increase of chloride level, while AMF colonised plants maintained low Cl content. AM+ plants produced tobacco leaves that contained significantly higher quantities of nicotine than AM- plants. AM inoculation ameliorated the chloride stress to some extent. Antioxidant enzymes like superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase as well as non-enzymatic antioxidants (ascorbic acid and glutathione) also exhibited great variation with chloride treatment. Chloride stress caused great alterations in the endogenous levels of growth hormones with abscisic acid showing increment. AMF inoculated plants maintained higher levels of growth hormones and also allayed the negative impact of chloride. The level of 40 mg L-1 in combination with arbuscular mycorrhizal can be considered as the acceptable threshold to avoid adverse effects on Virginia tobacco.