News Update on Wheat genotypes : Nov 2021

Changes in antioxidant activity in sub-cellular fractions of tolerant and susceptible wheat genotypes in response to long term salt stress

Effects of long term, medium level (electrical conductivity of extract (ECe)=6.85 dS m−1) sodium chloride (NaCl) salinity were studied in tolerant (Kharchia 65) and susceptible (HD 2687) wheat genotypes. NaCl salinity caused decrease in relative water content (RWC), chlorophyll (CHL), membrane stability index (MSI) and ascorbic acid (AA) content, and increased the contents of hydrogen peroxide (H2O2), thiobarbituric acid reactive substances (TBARS) (measure of lipid peroxidation) and activities of superoxide dismutase (SOD), its various isozymes, ascorbate peroxidase (APOX) and glutathione reductase (GR) in wheat genotypes Kharchia 65 (tolerant) and HD 2687 (susceptible). Salinity tolerant wheat cv. Kharchia 65 showed less decline in RWC, CHL, MSI estimated in whole tissue than salt sensitive HD 2687. Kharchia 65 also exhibited less decrease in AA content, less increase in H2O2, TBARS contents and higher increase in SOD and its isozymes, APOX and GR in all sub-cellular fractions than salt sensitive HD 2687. H2O2, TBARS contents and AA contents were higher in chloroplastic fraction. Chloroplastic fraction showed higher total SOD, APOX and GR activity, followed by mitochondrial fraction in case of total SOD and GR, while cytosolic fraction was in second place in case of APOX activity. Though Mn–SOD activity was highest in mitochondrial fraction, but residual activity was also observed in cytosolic fraction. Cu/Zn–SOD and Fe–SOD were observed in all the sub-cellular fractions, however, the activities were higher in chloroplastic fraction for both the isoforms. Total Cu/Zn–SOD activity, sum of activity observed in all the fractions, was higher than other SOD isoforms. Susceptibility of HD 2687 to long-term salinity stress seems to be due to relatively less induction of SOD isozymes, no induction in chloroplastic and mitochondrial APOX and cytosolic GR and decrease in chloroplastic GR under salt stress resulting in higher oxidative stress in the form of H2O2 and TBARS contents and decrease in MSI and CHL. [1]

Root Respiration and Carbohydrate Status of Two Wheat Genotypes in Response to Hypoxia

To investigate root respiration and carbohydrate status in relation to waterlogging or hypoxia tolerance, root respiration rate and concentrations of soluble sugars in leaves and roots were determined for two wheat (Triticum aestivum L.) genotypes differing in waterlogging-tolerance under hypoxia (5% O2) and subsequent resumption of full aeration. Root and shoot growth were reduced by hypoxia to a larger extent for waterlogging-sensitive Coker 9835. Root respiration or oxygen consumption rate declined with hypoxia, but recovered after 7 d of resumption of aeration. Respiration rate was greater for sensitive Coker 9835 than for tolerant Jackson within 8 d after hypoxia. The concentrations of sucrose, glucose and fructose decreased in leaves for both genotypes under hypoxia. The concentration of these sugars in roots, however, increased under hypoxia, to a greater degree for Jackson. An increase in the ratio of root sugar concentration to shoot sugar concentration was found for Jackson under hypoxic conditions, suggesting that a large amount of carbohydrate was partitioned to roots under hypoxia. The results indicated that root carbohydrate supply was not a limiting factor for root growth and respiration under hypoxia. Plant tolerance to waterlogging of hypoxia appeared to be associated with low root respiration or oxygen consumption rate and high sugar accumulation under hypoxic conditions. [2]

Root and Shoot Growth of Wheat Genotypes in Response to Hypoxia and Subsequent Resumption of Aeration

Understanding plant responses to hypoxiand subsequent resumption of aeration is important for breeding tolerant genotypes. The growth response of six wheat genotypes (Triticum aestivum L.) to hypoxiand subsequent recovery was evaluated. Plants were grown for 14 and 21 d in nutrient solutions flushed with air (aerated control) or with a mixture of 02 and N2 (hypoxia) or hypoxia for 14 d followed by aeration for 7 d (recovery). Shoot and root growth was inhibited by hypoxia, with roots being more sensitive. Stomatal conductance (gs) was reduced beginning 5 to 7 d after hypoxia. The adverse effect of hypoxia was most severe for Bayles and FL302, intermediate for BR34 and Coker-9766, and least for Gore and Savannah. Hypoxia enhanced formation of aerenchyma in roots, to a greater extent for Gore and Savannah. Aerenchyma became more conspicuous with duration of hypoxia. Seven days after resumption of aeration, shoot growth recovered completely for Gore and Savannah but only partially for Bayles, FL302, BR34, and Coker-9766. The number and length of crown roots increased to the value of the controls for all genotypes, whereas seminal root length was restored only in Bayles, Gore, and Savannah. Stomatal conductance recovered within 5 d for Savannah and 10 d for Gore but never recovered for Bayles, FL302, BR34, and Coker-9766. Breeding for hypoxia tolerance could be facilitated by selecting genotypes that develop more crown roots and more aerenchyma in those roots, maintain stomatal opening under hypoxic conditions, and resume seminal root growth and opening of stomatafter termination of hypoxia. [3]

Response of Bread Wheat to Sowing Dates and the Genotypes in Morocco

A field study was conducted to determine the effects of sowing date on the growth and yield of different bread wheat genotypes in two locations of Morocco (the plain of Saïs; Douyet and the Atlas Montaigne; Annoceur). The trial was conducted using a randomized complete block design with three replications in 2011/2012 and 2012/2013. The chosen dates were: 1st and 15th November in Douyet; 1st and 15th December in Annoceur and three bread wheat varieties (Achtar, Mehdia and Arrehane). Results revealed that seedlings in 1st November in the Saïs region and 1st December in the Atlas Montaigne increased grain yield for 11.15% compared to seasonal sowing, and any delay in bread wheat sowing might reduce wheat yield. The variety Arrehane surpassed the two other varieties Mehdia and Achtar in both growing seasons and at both locations with an average of 10.95% and 21.05% for grain yield, and for all components measured; number of spike m-2, 1000-grain weight, number of grains per spike, plant height and harvest index.[4]

Physio-biochemical Responses of Wheat Genotypes under Drought Stress

Tolerance strategies under water deficit conditions involve many physiological and biochemical responses which help crops to cope with drought stress. To study wheat response to stress, twenty Iranian wheat genotypes were evaluated in two separate field experiments during 2009-2010 growing season. Each experiment was conducted as randomized complete block design with three replications. The moisture level in one experiment was 100% field capacity while 45% field capacity was applied at the second experiment. Several biochemical (catalase, peroxidase, superoxide dismutase, ascorbate peroxidase and lipid peroxidation) and physiological indices (relative water content, relative water protection, stomatal resistance, chlorophyll and canopy temperature depression) were measured. Drought stress increased activities of lipid peroxidation, relative water protection, relative water content, stomatal resistance, chlorophyll and canopy temperature depression significantly at the pre-anthesis stage (Z34). Higher antioxidant activities, relative water content, relative water protection, chlorophyll, stomatal resistance and canopy temperature depression, and lower lipid peroxidation were observed in tolerant genotypes. The results demonstrated positive correlation of antioxidants with relative water content, relative water protection, chlorophyll, stomatal resistance and canopy temperature depression, and negative correlation with lipid peroxidation. Relative water protection and superoxide dismutase were suitable indices for screening and classifying tolerant genotypes. The results suggested that a combination of traits such as higher antioxidant activity, stomatal resistance and water retention capacity lead to wheat drought tolerance and the cultivars Kavir and Bahar were the most and least tolerant genotypes, respectively. [5]

Reference

[1] Sairam, R.K. and Srivastava, G.C., 2002. Changes in antioxidant activity in sub-cellular fractions of tolerant and susceptible wheat genotypes in response to long term salt stress. Plant Science, 162(6), pp.897-904.

[2] Huang, B. and Johnson, J.W., 1995. Root respiration and carbohydrate status of two wheat genotypes in response to hypoxia. Annals of Botany, 75(4), pp.427-432.

[3] Huang, B., Johnson, J.W., NeSmith, D.S. and Bridges, D.C., 1994. Root and shoot growth of wheat genotypes in response to hypoxia and subsequent resumption of aeration. Crop Science, 34(6), pp.1538-1544.

[4] Bendidi, A., Daoui, K., Kajji, A., Bouichou, L., Bella, M.B., Ibriz, M. and Dahan, R., 2016. Response of bread wheat to sowing dates and the genotypes in morocco. Journal of Experimental Agriculture International, pp.1-8.

[5] Aliakbari-Sadeghabad, A., Dadkhodaie, A. and Hasheminasab, H., 2016. Physio-biochemical Responses of Wheat Genotypes under Drought Stress. International Journal of Plant & Soil Science, pp.1-12.

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