| Salinity is one of major abiotic stresses and is a globally wide spread problem. It hampers plant growth and ultimately reduces yield. Induction of salinity stress tolerance in plants is one of principal objectives of agriculture research. The arbuscular mycorrhizal fungus(Glomus etunicatum) and acetyl salicylic acid has been reported to induce salinity stress tolerance in plants however rarely tested in tomato under salinity. In the present studies we focused to determine their role in tomato production under salinised conditions. 1. In the first experiment we studied effect of pretreatment(seed soaking) of tomato seeds with acetyl salicylic acid(54 mg?L-1) and arbuscular mycorrhizal fungus(G. etunicatum) spore solution on the germination of salinity stressed tomato seeds. The tomato seeds were soaked in acetyl salicylic acid and arbuscular mycorrhizal fungus spore solution for 12 h and then subjected to salinity stress in either peat moss medium in germination trays or on the wet filter paper in 18 cm Petri plates for 10 d under uniform conditions(dark, 26-22 °C; 90/80% humidity day/night respectively) in automated growth chamber. The results showed that the salinity delayed as well as reduced percent germination where as the arbuscular mycorrhizal fungus and acetyl salicylic acid treatments reversed the harmful effects to different extents. There were 84% comparative germination losses in the sole salinity treatment during same magnitude of time; 10 d in peat moss medium. The arbuscular mycorrhizal fungus and acetyl salicylic acid treatments rescued the process and reduced these losses to 28% and 54% respectively. The sole salinity rendered 43.5% fresh biomass losses over salinity free controls whereas the arbuscular mycorrhizal fungus and acetyl salicylic acid minimized this loss to 0, 13% respectively. Besides, the salinity induced reductions in the shoot and root lengths were also minimized to different extents in peat moss. In case of wet filter paper in petri dishes, on the 10 th day of sowing the final germination data showed that there was a significant(92.9%) reduction in seed germination in the sole salinity treatment as compared to the normal controls. However this extensive loss was minimized to 43.4% and 67.7%(from 92.9%) in the arbuscular mycorrhizal fungus and acetyl salicylic acid treatments, respectively. The seedlings of sole salinity treatment had single root filament whereas those of arbuscular mycorrhizal fungus treatment achieved highest mean number of sub-braches in the roots(3.0) followed by control(1.5) and acetyl salicylic acid(1.3) treatments. It was concluded that the arbuscular mycorrhizal fungus spores and acetyl salicylic acid in the studied concentrations significantly enhance tomato seed germination under moderate saline conditions.2. The second exepriment was designed to explore how the acetyl salicylic acid and Glomus etunicatum in combination or individually affect the growth of tomato seedlings under 200 m M and 300 m M Na Cl salinity stress conditions. It was recorded that the arbuscular mycorrhizal fungus and salicylic acid significantly improved seedling survival, fresh weight, height, stem thickness, number of leaves and leaflets and leaf length in 200 and 300 m M salt stress groups and significantly reduced the destructive effects of salinity to varying extents. The total chlorophyll contents were significantly reduced 20.6% and 29.4% in the 200 and 300 m M sole salinity treatments but the losses were subsequently reversed in these treatments and the total chlorophyll levels were 33%, 43.5% and 22.2 higher than the salt free controls in 200 m M salt stress category. In 300 m M Na Cl stress group, the losses caused by sole salinity were reduced to 6.22% and 0.94% in all treatments compared to the sole salinity treatment where the losses were 29.4%. In this category, acetyl salicylic acid +salinity was the best treatment that reversed the injurious effects of Na Cl and in this treatment total chlorophyll contents were 20.8% higher than the salt free controls. The salt stress severely affected the seedlings and was deleterious towards plant survival. There was no plant mortality in the salinity free controls however around 26 % and 58% seedlings died in 200 and 300 m M salt stress conditions. This loss was however reduced by arbuscular mycorrhizal fungus, acetyl salicylic acid and hybrid; treatments to 7.4, 0 and 33% in 200 m M salt stress, respectively. Similarly the survival damage was minimized to 14, 9.5 and 44% by arbuscular mycorrhizal fungus, acetyl salicylic acid and hybrid in 300 m M salt concentration. Salinity was highly injurious to roots and root activity. The 200 and 300 m M salt stress reduced the root activity by 28 and 73%, respectively, compared to the salinity free controls. However, arbuscular mycorrhizal fungus and acetyl salicylic acid completely nullified the deleterious effects of Na Cl in 200 m M group regarding root activity. Similar trend was observed in the 300 m M category, where arbuscular mycorrhizal fungus and acetyl salicylic acid and hybrid minimized the losses to 22 and 15% respectively but the AS treatment had more marked effect which totally removed the Na Cl injury in the given conditions.3. In the third experiment, the tomato seedlings were inoculated with G. etunicatum and exogenously sprayed with acetyl salicylic acid(0.30 m M) followed by salinity stress(150 m M) for ten days. It was observed that both G. etunicatum and acetyl salicylic acid(singly or in combination) were significantly effective to minimize the injurious effects of salinity by enhancing root morphological parameters(length, diameter, surface area, volume, tips, nodes, bifurcations and connections), photosynthetic parameters(net photosythesis Pn, stomatal conductance Gs) and chlorophyll contents compared to sole salinity treatment. The bio- inoculant Glomus etunicatum and chemical ameliorator acetyl salicylic acid notably up-regulated vegetative(fresh and dry weights) and reproductive growth(percent seedlings with flower buds and opened flowers, number of flower buds and opened flowers per seedling) of the plants as compared to the sole salinity treatment. The studied salt responsive genes(SOS1, Le NHX1, JERF3 and NAC1) were also regulated in roots and leaves which was consistent with enhanced salinity stress tolerance.4. In the fourth experiment, a pot based study in plastic tunnel was conducted to investigate the changes in root morphology, root activity, vegetative and reproductive growth, yield, fruit quality and some other physiological parameters of the tomato plants grown under moderate Na Cl stress(100 m M), pretreated with arbuscular mycorrhizal fungus(Glomus etunicatum) root colonization and acetyl salicylic acid as salinity ameliorative agents. The results revealed that both treatments significantly enhanced the fresh root weight and root morphological parameters; net length, surface area, volume, mean diameter, nodal count and number of tips to different extents as compared to those of sole salinity treatment at 90 days after transplantation. Both treatments; arbuscular mycorrhizal fungus alone and in combination with acetyl salicylic acid significantly enhanced the root activity level in terms of triphenyl tetrazolium chloride reduction(2.37 and 2.40 mg?g-1?h-1 respectively) as compared to the sole salinity treatment(0.40 mg?g-1?h-1) as well as the salt free control(1.69 mg?g-1?h-1). On the other hand, acetyl salicylic acid treatment alone also uplifted root activity(1.53 mg?g-1?h-1) which was significantly higher than that of sole salt treatment.It was observed that Glomus etunicatum root colonization and exogenous acetyl salicylic acid(0.3 m M) significantly up-regulated fruit size, number of fruits per plant and yield per plant to different extents as compared to the sole salinity(100 m M Na Cl) stressed plants. Highest per plant yield(1325.9 g?plant-1) after 60 days of weekly salt stress(100 m M Na Cl) was recorded in the FS(arbuscular mycorrhizal fungus + salinity) plants followed the AS(acetyl salicylic acid + salinity) and FAS(arbuscular mycorrhizal fungus + acetyl salicylic acid + salinity) treatments with 1188.3 g?plant-1 and 1180.8 g?plant-1, both being significantly higher than saline(434.7 g?plant-1) and none saline controls(1088.8 g?plant-1).In August, at 90 days of weekly salt stress(100 m M Na Cl) treatment, the sole salinity plants had mere 784 g?plant-1 yield, compared to the 1252.5 g?plant-1 in the salinity free controls. However, treatment FAS(arbuscular mycorrhizal fungus + acetyl salicylic acid + salinity), FS(arbuscular mycorrhizal fungus + salinity) and AS(acetyl salicylic acid + salinity), not only restored the per plant yield but also achieved higher yields than the salinity free control plants with 1614.5, 1489.3 and 1309.1 g?plant-1 yields, respectively. The improved plant performance was achieved due to the enhanced salt(Na Cl) stress tolerance associated with improved antioxidant enzyme system, enhanced chlorophyll, lycopene and proline contents, and healthier nutrient uptake and ion uptake balance. Therefore, synergistic use of arbuscular mycorrhizal fungus(G. etunicatum) and acetyl salicylic acid can be eco-friendly and economically feasible option for tomato production in marginally salt affected lands and suggests further investigations.Based upon these observations, it is suggested that, arbuscular mycorrhizal fungus(Glomus etunicatum) and acetyl salicylic acid have a positive role towards salt stress amelioration in indoor experiments(seed germination and seedling stages) as well as in field conditions(up to fruiting stages). To better exploit the potential of the bioinoculant(Glomus etunicatum) large scale studies should be conducted with aim to refine its role in practical agriculture. The function of chemical ameliorator; acetyl salicylic acid needs further validation in large scale field experiments involving different concentrations at suitable growth stages. The generated data may lead to development of novel, growth stage specific products. Thus it is inferred that both tested agents(arbuscular mycorrhizal fungus and acetyl salicylic acid) individually and in combination, confer salt(Na Cl) stress tolerance in tomato plants at all growth stages and can be suitable candidates in practical agriculture to be used in tomato production in moderately salinity affected soils. |
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