Study of salinity tolerance and its effect on some of the morphophysiological traits of Bassia (Bassia scoparia L.)

Introduction            Salinity is one of the major environmental factors which limits plants productivity and it is considered acting as the main source of yield reduction. The adverse effects of soil salinity in plants growth include ions toxicity, osmotic stress, nutritional dis-orders, and it also hampers the water uptake by the seeds and plants. Salt tolerance in plants is a multifarious phenomenon involving a variety of changes at molecular, organelle, cellular, tissue as well as whole plant level. In addition, salt tolerant plants show a range of adaptations not only in morphological or structural features but also in metabolic and physiological processes that enable them to survive under extreme saline environments. Bassia scoparia is a dicotyledonous annual herb and belongs to the Amaranthaceae family. Genetic diversity and resistance to drought stress of this plant has made it widely scattered in different regions which contains highly genetic diversity and great potential as fodder and can grow on salty, drought affected areas. The objectives of this study were to the effect of salt stress on growth response and some morphological and physiological traits of Bassia. Materials and methods                                     In order to study the effect of salinity on morphological and physiological traits of  Bassia (Bassia scoparia L.) an experiment was conducted in the randomized complete block design with four replications in 2014 at the Research Greenhouse in the Faculty of Agriculture, Ferdowsi University of Mashhad. Treatments included different levels of salinity (10, 16, 22, 28 and 34 dS.m-1 and non-saline water (1.4 dS.m-1) as the control.). The seeds were planted in plastic pots (with 23 cm diameter), filled with a mixture of leaf soil, sand and  loam soil (1:1:1; v/v). Salt solution was added to each pot containing sodium chloride, magnesium sulfate, magnesium chloride and calcium chloride in a ratio of 6: 2: 1: 1 with irrigation water after complete plant establishment. The type and ratio of solutes used in the saline solution is simulated based on Caspian Sea water and several saline rivers in Iran. Irrigation with saline water until complete seedling establishment (plant height were about 10 cm) was followed by non-saline water. After that, until the end of experiment (56 days after emergence, when plant height in control treatment was about 50 cm) irrigation was done with the desired salinity water treatments. At the end of the experiment after plants harvesting, different morphological traits of plants including plant height, fresh and dry weights of shoots, number of lateral branches, leaf area index were measured on all 5 plants in pots. One week before planting, physiological traits including chlorophyll index, stomatal conductance, membrane stability index, relative leaf water content, ash %, organic matter %, potassium, sodium and K/Na.  photosynthesis, transpiration were measured, and chlorophyll fluorescence indices including maximum fluorescence (Fm), minimum fluorescence (Fo), variable fluorescence (Fv) and maximum quantum yield (Fv / Fm) were measured in two vegetative (35 days after emergence and when plant height was approximately was 30 cm) and reproductive stages (49 days after emergence when plant height was about 45 to 50 cm). The youngest developed leaves were used to measuring  physiological traits. Analysis of variance  and comparison of means  using duncan's multiple range test at the 5% level of probability and stepwise regression analysis to determine relative share of traits were performed using SAS 9.1 software.   Results and Discussion The results showed that salt stress was significantly decreased plant height, leaf area, dry matter, number of lateral branches, Fo at the vegetative stage, stomata conductance, transpiration, ash %, organic matter %, potassium, sodium and K/Na. That there was no significant and positive correlation between fresh and dry weight with physiological traits and nutrients. Based on step-wise regression analysis, three traits of the number of lateral branches, leaf area and dry matter were only traits that were entered to the model and were justified 90 % of the dry weight changes. No relationship was observed between fresh and dry weight with physiological traits and nutrients.  Physiological traits were less affected by salinity in compared to morphological traits. According to the results, due to the saline nature of Bassia, most of morphological and physiological traits and its growth were better than non-stress conditions even in low and medium salinity. Conclusion The results confirmed the reports of high tolerance of Bassia to salinity, indicating that the use of non-destructive and physiological indices, especially chlorophyll fluorescence index, can be a reliable and rapid indicator in assessing plant salinity response. On the other hand, high tolerance of Bassia to salinity, allowing the use of saline water in the production of this plant as an economic plant or in green areas, is an important and determinant trait in its ability to compete with crops in saline soils. When it is present as an invasive plant.