ABSTRACT

A hydroponic experiment was conducted to study the morphological and physiological responses of selected sorghum genotypes to salinity stress at early vegetative stage with a view to screen salt tolerant genotypes. Nine sorghum genotypes viz. BD 687, BD 688, BD 689, BD 690, BD 691, BD 692, BD 693, BD 694 and BD 695 were grown in hydroponics with a full nutrient solution at 12 dSm−1 and control condition for fourteen days. Different morphological and physiological parameters viz. root length, shoot length, shoot dry weight, root dry weight, total dry matter, root shoot ratio, relative chlorophyll content and maximum photochemical efficiency of PSII (Fv/Fm) were recorded. Most of the parameters mentioned above showed significant variation due to salinity stress and also among the genotypes. The stress tolerance index for root and shoot lengths varied from 70-93, and 67-92, respectively. Root and shoot weights were greatly affected by the stress and the genotypes studied exhibited large variations in respect of tolerance indices that ranged from 62-78 and 62-93 for shoot and root dry weights, respectively. Leaf greenness expressed in SPAD values and Maximum photochemical efficiency of PSII (Fv/Fm) was varied due to the stress and among the genotypes. SPAD values and Fv/Fm in different genotypes ranged from 29.6-20.2, and 0.78-0.71, respectively under control and, 28.3-18.2 and 0.77-0.67, respectively under the stress. Based on the responses to the stress the genotypes BD 688, BD 690 and BD 693 appeared to be more tolerant compared to other genotypes studied.

Key words: Sorghum, salinity, genotype.

Introduction

 Salinity is one of the major environmental stresses limiting crop production of marginal agricultural lands in many parts of the world. Worldwide, it is an increasing problem and main obstacle to the crop productivity especially in areas where crops should be irrigated (Ahloowalia et al., 2004) because water contains high amount (about 30g NaCl/L) of salt. Salinity stress involves changes in various physiological and metabolic processes, depending on severity and duration of the stress and ultimately inhibits crop production (James et al., 2011). Effect of Salinity on plant growth is a complex syndrome that involves osmotic stress, ion toxicity, mineral deficiencies, physiological and biochemical perturbations and combination of these stresses (Hasegawa et al., 2000). Sorghum [Sorghum bicolor (L.)], a major grain and forage crop, was previously characterized as moderately tolerant to salinity, can tolerate up to 8.6 dSm−1soil salinity without any reduction to its yield (Maas et al., 1986). It is originated from Africa (Tari et al., 2013) and is a C4 carbon cycle plant belonging to the Poaceae (or Gramineae) family with high photosynthetic efficiency and productivity. It is one of the five major cultivated species in the world because it has several economically important potential uses  such as 55% as food (grain), 33% as feed (grain and biomass) and others are as fuel (ethanol production), fibre (paper), fermentation (methane production) and fertilizer (utilization of organic by-products) (Krishnamurthy et al., 2007). It is the only crop from which ethanol can be produced from grain (starch), juice (sweet sorghums) and biomass (lignocellulose). It also has biological nitrification inhibition activity which reduces the loss of N from the field. Based on the tolerance to soil salinity, the crops were ranked as sorghum>sunflower>sugar beet>maize> barley> linseed>chili> sweet potato> cowpea>groundnut. In Bangladesh, it would contribute enhancing food, nutrition and energy security in the country with higher productivity during the fallow period. There is a large genotypic variation for tolerance to salinity reported in sorghum (Sun et al., 2014). It is important to note that germination and early seedling growth are more sensitive to salinity than later developmental stages

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