Hossein Nastari Nasrabadi; Seyyed Farhad Saber Ali
Abstract
Introduction: Melon (Cucumis melo L.) is one of the most important vegetables in Cucurbitaceae family and one of the most important economic crops in the Torbat-e Jam city (Longitude: 60 ̊48', latitude: 35 ̊31', altitude: 928 m). Growth and yield of agricultural crops are affected by biotic ...
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Introduction: Melon (Cucumis melo L.) is one of the most important vegetables in Cucurbitaceae family and one of the most important economic crops in the Torbat-e Jam city (Longitude: 60 ̊48', latitude: 35 ̊31', altitude: 928 m). Growth and yield of agricultural crops are affected by biotic and abiotic environmental stresses. Cold stress can be one of the most important environmental factors reducing crops yield. Cold acclimation in plant is a complex process involving many morphological, physiological and biochemical changes, including a significant reduction in tissue hydration during cold hardening. Melatonin (MEL, N-acetyl-5-methoxytryptamine) is a conserved substance, which has been discovered in all living organisms, from bacteria to mammals. MEL regulates the growth of root, shoot, and explant, activates seed germination and rhizogenesis, and delays leaf senescence. In addition, the most frequently mentioned functions of MEL are related to various abiotic stresses such as drought, radiation, low/high temperature, heavy metals, and salinity stresses. Materials and Methods: In order to investigate the effect of PEG priming and melatonin on cold stress resistance of melon seedlings, a factorial experiment was conducted in a completely randomized design with three replications in Torbat-e-Jam University. In this experiment polyethylene glycol 6000 was used to produce drought stress at three levels (0, 0.18 and 0.58 MPa) and melatonin was used at two levels (0 and 200 μmol). When melon seedlings were at 4 leaf stage, the amount of polyethylene glycol was added to the irrigation solution for a week and to prevent drought stress, drought stress was increased for 3 days and increased one third of the required concentration daily. Recovery was performed for three days after drought stress and during this period melatonin was added to the irrigation solution at the required concentration. Seedlings were then exposed to cold stress (T0: non-stress and T1: cold conditions). Control plants were kept in greenhouse conditions. Results and Discussion: Comparison of the mean results showed that there was an increasing trend in proline production by increasing drought stress. The highest amount of proline (0.80 µmol g-1 FW) was recorded at the highest level of drought pretreatment with no melatonin and without cold stress (D2M0T0), and then a decreasing trend in proline production was observed. The results showed that melatonin significantly increased leaf relative water content compared to the control. Interaction effects of drought pretreatment and temperature showed that there was a trend of decrease in relative water content by increasing drought pretreatment. Ghanbari and Sayyari (8) reported that drought pretreatment stress maintains relative water content of tomato seedlings under cold stress conditions. Drought pretreatment significantly reduced the amount of chlorophyll a and total chlorophyll. The results showed that the highest levels of drought pretreatment stress (D2) and melatonin (M1) maintained chlorophyll a under cold stress conditions. Results showed that the amount of chlorophyll b was decreased by drought pretreatment stress, but it increased by melatonin application in all compounds. Based on the results, it was found that only simple effects of treatments at 1% of probability level had significant effects on soluble sugars content. Comparison of the mean simple effects of drought pretreatment showed that under drought stress the amount of soluble sugars increased significantly and the highest sugar content was recorded at the highest drought stress level. The amount of soluble sugars in plants under cold stress also increased significantly. Melatonin application also significantly increased the amount of soluble sugars. Kabiri et al. (19) reported that the use of melatonin increased soluble sugars in Moldavian balm seedlings under osmotic stress which is similar to this study results. It was found that melatonin significantly increased phenolic compounds under stress conditions and significantly decreased electrolyte leakage.
Hossein Nastari Nasrabadi; Seyyed Farhad Saberali
Abstract
Introduction: Melon (Cucumis melo L.) is one of the most important vegetables in Cucurbitaceae family and one of the most important economic crops in the Torbat-e Jam. Growth and yield of agricultural crops are affected by biotic and abiotic environmental stresses. Salinity stress can be one of the most ...
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Introduction: Melon (Cucumis melo L.) is one of the most important vegetables in Cucurbitaceae family and one of the most important economic crops in the Torbat-e Jam. Growth and yield of agricultural crops are affected by biotic and abiotic environmental stresses. Salinity stress can be one of the most important environmental factors limiting the yield of plants, especially in arid and semi-arid regions. It has been reported that by application of bio-fertilizers, root and shoot dry weight and nitrogen concentration in alfalfa increased under salt stress. Sarabi et al (44) in a study of different genotypes of melons under salinity stress reported that salinity stress increases soluble sugars and proline content and decreases photosynthetic pigments. Growth-promoting bacteria can help plants under stress conditions by stabilizing atmospheric nitrogen, increasing the accessibility of nutrients, and interfering by the production of plant hormones such as auxin, cytokinin, and gibberellins. Soliman et al. (49) also reported that growth-promoting bacteria increase the absorption of elements, especially nitrogen, in Acacia saligana. Basilio et al. (7) showed that growth-promoting bacteria increase plant height and yield of wheat. The use of salicylic acid to create plant reactions to environmental stresses has been suggested. Raghami et al (39) reported that salicylic acid improves vegetative indexes and photosynthetic pigments in eggplant under salt stress. It has been reported that salicylic acid treatment increased K in wheat under salt stress. Due to the expansion of saline soils as well as the reduction of fresh water resources, the purpose of this experiment is to better establish melon seedlings under adverse environmental conditions and to maintain and develop this valuable crop.
Materials and Methods: In order to study the effect of biological fertilizers and salicylic acid on physiological parameters and growth of Khatooni melon under salinity stress conditions, a factorial experiment was conducted based on completely randomized design with three replications in Torbat-e-Jam University. Salicylic acid treatment was selected at two levels, without (SA0) and one mM (SA1) salicylic acid. Bacteria treatments were including Azotobacter (B1), Azospirilium (B2), Azotobacter and Azospirilum (B3) and without inoculation (B0) and salinity treatments were prepared in five concentrations: control (S0), 50 (S1), 100 (S2), 150 (S3) and 200 (S4) mM of sodium chloride.
Results and Discussion: Interaction effects of salinity, salicylic acid and bacteria showed, proline content was increased by salinity stress. The highest of proline content was obtained by combination of 200 mM salinity, one mM of salicylic acid and Azetobacter + Azospirilum (S4 SA1 B3) and the minimum of it was recorded in contorol (S0 SA0 B0). Under salinity conditions, the accumulation of compatible solutions such as proline, glycine, betaine and other organic solutions in the plant occurs, which play an important role in protecting the plant against the harmful effects of stress. On the other hand, the increase in proline content by growth-promoting bacteria may be due to an increase in the absorption of nutrients, especially nitrogen, because proline has a nitrogenous structure.
Without salinity stress no significant difference observed between salicylic acid treatments on soluble sugars, but soluble sugars content were significantly increased by increasing salinity stress. The maximum and minimum of soluble sugars content were recorded in combination 200 mM salinity and one mM of salicylic acid (S4 SA1) and control (S0 SA0) respectively. Plants try to overcome salinity stress by producing organic compounds that are osmotically active such as soluble sugars.
It has been reported that the use of salicylic acid in eggplant and barley under salinity stress has increased the production of soluble sugars, which is consistent with the results of this study. In general, accumulation of proline and soluble sugars content might be due to increased synthesis and decreased degradation under stress conditions. According to the results, photosynthetic pigments and relative water content percentage (RWC %) were decreased under salinity stress. Simple effects of salicylic acid (SA1) and bacteria treatments especially combination of bacteria (B3) significantly improved Chlorophyll a, b, carotenoids and RWC. Sarabi et al. (43) reported that chlorophyll content, carotenoids and RWC were decreased in melon under salinity stress. Kheirizadeh Arough et al (29) reported that application of bio-fertilizers and nano zinc oxid increased content of chlorophyll a, chlorophyll b and carotenoids in Triticale under salinity conditions.
Conclusion: Based on the obtained results in this study, we can use Azotobacter and Azospirillum together for seed inoculation and spraying with salicylic acid for obtaining better growth and yield under salt stress.
Seyyed Farhad Saberali; Hossein Nastari Nasrabadi; Zahra Shirmohamadi Ali Akbar Khani
Abstract
Introduction: A rapid, complete, and uniform seed germination is important to establish a healthy seedling that is a critical key to successful crop production. Therefore, identification of effective factors on germination and plant response to various conditions are important to use an ...
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Introduction: A rapid, complete, and uniform seed germination is important to establish a healthy seedling that is a critical key to successful crop production. Therefore, identification of effective factors on germination and plant response to various conditions are important to use an appropriate agronomic managements. Temperature and water are the most important environmental factors controlling seed germination in plants. The crop growth models are among the most effective tools for using in crop management decisions. The response of seed germination to temperature and water potential can be simulated by thermal time, hydrotime and hydrothermal time models. Regarding the importance of watermelon production in Iran, this study was conducted to determine the cardinal temperatures of germination in watermelon plant, and also to quantify its germination in response to the temperature and water potential interaction. .
Materials and Methods: In order to investigate the effects of temperature and drought stress on seed germination and quantifying the germination responses; a factorial experiment was conducted with seven levels of temperature including 10, 15, 20, 25, 30, 35 and 40 °C and the six levels of water potential including 0, –0.25, –0.5, −0.75, –1.0, and –1.25 MPa, respectively. A Ψ of 0 MPa was obtained using distilled water. The negative Ψ levels were prepared by polyethylene glycol (PEG 6000; Merck, Germany) according to Michel and Kaufman (1973). For each treatment, four 25-seed replicates were placed in 9-cm petri dishes containing one disk of Whatman No. 1 filter paper, with 7 mL of test solutions. Cumulative germination percentage was transformed to probit regression against time log (Finney, 1971; Steinmaus et al., 2000), and the time taken for cumulative germination (tg) to reach subpopulation percentiles (10–90%) was estimated from this function according to Steinmaus et al. (2000). Then the germination rates (GR) were calculated as the inverses of the germination times for each percentile at each T or Ψ. The preliminary estimation of the parameters in the TT, and HT models were obtained by plotting GR versus T and Ψ for each percentile. Then using repeated probit analysis developed by Ellis et al. (1986), the exact parameters for the TT, HT and HTT models were determined for the whole seed population. All statistical procedure were done by SAS and Excel software, and the figures were drawn by SigmaPlot10 software.
Result and Discussion: The analysis of variance showed that the temperature, water potential and their interaction had significant effect on the germination percentage of the watermelon plant. Seed germination of watermelon was about 96 % under the optimal conditions. However, the germination ability was affected by the temperature and water potential of the seedbed. The results showed that the germination was decreased by decreasing water potential, at all temperature levels. The seeds of watermelon germinated over a range of water potentials from 0 to -1 MPa. Furthermore, the lowest germination loss associated with decreasing water potential observed at temperature range of 20-30 °C (compared to temperatures below and above this range). The maximum percentage of germination was recorded at 20-30 °C, while no seeds germinated at 10 and 40 ° C. The results also showed that the highest germination rate was obtained at 25 °C and the germination rate decreased at lower and higher temperature than this range. While watermelon seeds were grown under no water stress condition, the estimated base and ceiling temperatures of germination by a linear regression method were 10.7 and 40.0 °C, respectively. However thermal time model was used, but the base and the maximum temperatures were estimated as 11.5 and 40.1 °C, respectively. Furthermore, an optimum temperature of 25.2 °C was predicted by hydrothermal time model for watermelon germination. The results showed that the base temperature and median thermal time to germination were varied with changing water potential. The hydrotime analysis showed that the base water potentials was in a range from -0.45 to -1.23 Mpa, that differed with changing water potential. Watermelon seeds had higher base water potential and also required a longer hydrotime for germination under non-optimal temperature. Hydrothermal time analysis showed that seed germination responses to temperature and water potential might as well quantified by parameters derived from hydrothermal time models (R2= 0.90-0.92). The amount of hydrothermal time required to germinate was 40.5 MPa °C days on the suboptimal and supra optimal temperature ranges. The HTT model showed that the Ψb(50) increased by 0.09 MPa with every degree increase in temperature above optimum temperature.
Conclusions: The thermal time, hydrotime and hydrothermal time models well described germination time course of watermelon seeds in response to temperature and water potential.Thus, the estimated parameters of these germination models allowed us to characterize the germination behavior of watermelon seeds under varying environmental conditions and global warming.
