Salt Stress of Jeursalim Artichoke Plants in Relation to The Pre-soaking Tubers with Hydrogen Peroxide

Introduction

Jerusalem artichoke (Helianthus tuberosus L.) is a non- traditional tuberous crop ,which is recently introduced to Egypt for high nutritional and medicinal values. The tuber flesh of this plant  is a  rich source for nutrients and polysaccharides, particularly, inulin; that contains considerable levels of  fructose sweetener that could be utilized for human-being without any side effects on blood sugar level (Seljåsen and Slimestad, 2007). Its protein has high food value due to the presence of almost all essential amino acids ( Rakhimov et al., 2003). Tubers are considred a suitable livestock feed (Seiler and Campbell, 2004). In the last decades Jerusalem artichoke has been concidered as a biomass crop for ethanol because it produces high levels of carbohydrates ( Denoroy, 1996).

Salinity is one of the most important environmental stress variables that affects the growth and productivity of different crops (Lopez et al., 2002). The negative impact of salinity is increasing dramatically in the arid and semi-arid regions of the world where the majority of developing countries are located (Khan et al., 1999). Salinity not only exerts differences between average productivity and potential productivity, but also induces a marked drop the yield from year to year. It directly affects plant growth through its interaction with metabolic rates and pathways in plants (Rahimi et al., 2012).

Hydrogen peroxide (H₂O₂), produced naturally in plant cells under stress conditions, is characterized by high oxidative reactivity (Ogawa and Iwabuchi, 2001). Hydrogen peroxide is considered necessary for cell signaling, due to its important role in regulating oxidative stress (Rhee, 2006). Recently H₂O₂ has been regarded as a stress signaling molecule in regulating plant development and adaptation to abiotic and biotic stresses (Hung et al., 2005). Exogenous application of H₂O₂ at low concentrations (≤ 2.5 mM) had stimulatory effect on growth traits of plants, while the concentration up to 5 mM played an opposite role (Deng et al., 2012). Hydrogen peroxide is found to be involved in the acclimation and tolerance of plants grown under salt stress (Li et al., 2011; Wang et al., 2013). Therefore H₂O₂, at low concentrations, is considered one of the exogenous materials that used to induce the defense mechanisms in plant cells (Chen et al., 1993) and have  a central role in improving  plant  tolerance  to  environmental  stresses  such  as  salinity  (Azevedo Neto et al., 2005; Ashraf et al., 2013). Furthermore, H₂O₂ seems to be a “master hormone” that controls a variety of stress responses and plays a key role in primary plant metabolism (Ślesak et al., 2007).

This study was carried out to investigate the potential role of H₂O₂ to improve the performance of growth and productivity of Jerusalem artichoke plants under different salt stressed conditions.

Materials and methods

The present investigation was carried out during the two successive summer seasons on mid of April 2018 and 2019 at Soil Salinity Laboratory Research, Alexandria, Agricultural Research Center. Jerusalem artichoke tubers of Fuseau cv. were planted in cemented-butaminzed lysimeters (2*2*1m). Tuber seeds were planted in rows, 80 cm in wide, 2 m in length.

Four levels of saline irrigation water, namely, tap water as a control, 2000, 3500 and 5000mg/L, were used as a source of irrigation, keeping the soil moisture content near the field capacity (27.85%). The saline water was prepared by mixing tap water (0.68 dS/m) with sea water (46 dS/m) at certain ratios. The tuber seeds were partitioned in three parts, the first and second parts of tubers were soaked in liquid H₂O₂ solutions (100 and 200 mM) for 2h. before planting. The third part of tubers (soaked tubers in distilled water) was used as the control.

Before planting, the following fertilizers were added to the soil at rates of kg, 20 m³ organic manure /fed. plus 150 P₂O₅/fed.in the form of mono calcium phosphate, 15.5 % P₂O₅. Nitrogen fertilizer was added in the form of ammonium nitrate (33.5% N) at the rate of 300 kg ∕ fed. at three equal doses ; after 4, 8  and 12 weeks from planting date.  Potassium sulphate (48% K₂O) was applied at rate of 90 kg ∕ fed. in two equal doses after 8 and 12 week from the planting date. All other recommended agro-managements such as disease pests and weed control were performed whenever they appeared to be necessary.

The physical and chemical analyses of the experimental soil are presented in Table (1) according to (Page et al., 1982).

Table )1(. Physical properties and chemical analyses of the experimental soil

Vegetative characteristics were measured and recorded at the initial stage of flowering (150 days after planting). A random sample of three plants from each experimental plot was taken to estimate plant height (cm), number of main stems and plant fresh weight (kg).

At the harvest time (180 days old plants), each individual plant in the all treatment lysimeters was removed to measure the number of tubers, average tuber fresh weight (g)  and total tubers' yield / feddan(ton) .

Random samples of ten fresh tubers per treatment were used to determine their dry matter percentage, at 70 °C. Inulin content was determined in tubers according to the method of Winton and Winton (1958). Total carbohydrate were determined colorimetrically as in terms of gram of glucose/100g dry weight of tubers roots according the methods described by James (1995). In the digested dry matter of tubers nitrogen was determined according to the methods described by Pregl (1945) using micro-Kjeldahl apparatus. Meanwhile, phosphorus was determined colorimetrically following Murphy and Riley (1962). Potassium was determined against a standard using air propane flame photometer following Chapman and Pratt (1961). The concentration of N, P and K were expressed as percentage.

The experimental design used was a split-plot design with three replicates, where the four levels of saline irrigation water, namely, tap water as a control, 2000, 3500 and 5000 mg/L were arranged in the main plots, whereas, tuber seeds was soaked with hydrogen peroxide (0,100 and 200 mM) were arranged in the sub plots. Each sub plot contained 2 rows. Collected data from the experiments were statistically analyzed, using the analysis of variance method. Comparisons among the means of different treatments were assessed, using least significant differences (L.S.D) test procedure at p ≤ 0.05 level of probability, as illustrated by Snedecor and Cochran (1980) using Co-Stat software program.

Results and Discussions

1. Mean performances of vegetative growth parameters of Jerusalem artichoke crop

• The main effect of irrigation water salinity concentrations

The results given in Table 2 showed significant effects at p ≤ 0.05 on plant height and foliage fresh weight/plant characters during the two seasons. Evidently, increasing irrigation water salinity concentration from 500 mg/L up to 5000 mg/L negatively affected plant height and foliage fresh weight/plant characters during the two seasons of this study. Unlike, the number of stems per plant was not significantly affected under the salt-stressed conditions at p≤0.05. Plant growth, as revealed from the data of plant height and foliage fresh were more superior in the control treatment. As the salinity of irrigation increased up to 5000 mg/L, adversable effects were clearly manifested. These results falls in line with the data reported by Mahmoud (2012) on potato plants. The reduction in plant growth under salinity stress conditions is consistent with the fact that salinity induces accumulation of certain ions and deficiency of the others and lowers the external water potential in the cell (Salem et al., 2017). Furthermore, the reduction in plant growing may be due to the interruption in metabolic activities affected by the decrease of water absorption and disturbance in water balance (Fahad et al., 2015).

• The main effect of  soaked tubers in H₂O₂ concentration

The results of Table (2) showed that most of the studied vegetative characters were significantly affected p ≤ 0.05 with soaking tubers in H₂O₂ concentration treatments, except for No. of stems / plant. However, increasing H₂O₂ concentration exerted a significant positive effect on both plant height and foliage fresh weight/plant (g) traits during the two seasons. In this respect the highest mean values for plant height (cm) and fresh foliage weight/plant (g) were scored when the tubers soaked in 100mM H₂O₂ treatment, followed by with the soaking treatment of 200mM H₂O₂ treatment. In contrast, the lowest values were clearly noted in the control treatment. The results of Attia et al. (2017) showed that H₂O₂ priming can induce plants by modulating physiological and metabolic processes such as photosynthesis, proline accumulation detoxification, and that this ultimately leads to better growth and development.

• The effect of tested interaction

The 2-way interaction of saline irrigation and  H₂O₂ - soaked tubers (table 2) imposed significant effects on growth traits at p ≤ 0.05. In general, soaking tubers with H₂O₂ concentration treatment gave the best results for the characteristics of plant height at any given level of salt stress treatment. As mentioned earlier, the characteristic of foliage fresh weight (g) and No. of stems /plant was not affected by the two independent variables, this trait was also not affected by the interaction between these two variables (Table, 2). A number of studies on plants have demonstrated that the pre-treatment with an appropriate level of H₂O₂ can enhance abiotic stress tolerance through the modulation of multiple physiological processes, such as photosynthesis, and by modulating multiple stress-responsive pathways (Hossain and Fujita 2013; Wang et al., 2014).

2. Yield and yield components of Jerusalem artichoke crop

a- The main effect of irrigation water salinity concentrations

The documented results in Table 3 revealed clearly that total tuber yield and the corresponding its components e. i., number and weight of tuber /plant, average tuber weight as well as total yield/fed. were significantly affected (p ≤ 0.05) by irrigations water salinity concentrations during the two seasons of the growth. In this respect, highest records in tubers yield/fed. and their related characters that include i.e., average tuber weight, number of tubers/plant  and tubers weight yield/plant were clearly manifested in non-salt-stressed plants (control, 500 mg/L). With increasing the salinity levels of irrigation water, remarkable decrements on yield criteria were gradually noted, being the least at 5000 mg/L. As far as the total yield and its components are closely correlated with the vigorous of the vegetative growth. Therefore the reduction of the total yield and its components can be attributed to the fact that the vegetative characters were negatively affected by the high salinity of irrigation water (Table, 2). These results are in agreement with those reported by Elkhatib et al. (2004), Mahmoud (2012), Al-Hamdany and Mohammed (2014), Arafa and El-Howeity (2017) on potato. Abu-Muriefah (2015) attributed these results to changes in osmotic capacity due to reduction of water content in addition to the specific toxic effects resulting from the accumulation of sodium and chloride ions as observed in many plants. It was observed that salinity gradually reduced the size and number of marketable tubers per plant. In this respect, Ghosh et al. (2001) attributed the yield decrement in salt-stressed plants to the reduction of the tuber number per plant. It should be emphasized that the drop in yield, associated with salt- stress could be interpred to the nutritional imbalance, which consequently caused the inactivation of enzymes such as nitrate reductase (NR).

Table (2). Mean values of vegetative growth indices of Jerusalem      artichoke plants during 2018 and 2019 seasons

^* Significant at 0.05 level of probability.

1. The main effect of soaked tubers in H₂O₂ concentration

The results of Table (3) appeared that tubers yield/plant were significantly affected (p ≤ 0.05) by soaking tubers in H₂O₂ solutions during the two growing seasons. Regarding to the number of tubers/plant and total yield per feddan, the data showed that both traits were significantly decreased by soaking tubers in H₂O₂ with 100mM, only in 2019. The result obtained on the fresh tubers did not appear any significant variations along the H₂O₂-soaking treatments during both seasons. Similar results were recorded on wheat (Hameed et al., 2004), indicating that exogenous application of H₂O₂ provided more vigorous root system in wheat. H₂O₂ applied in low doses can increase roots weight and length (Narimanov and Korystov, 1997). Recently, has been reported that intensive root growth acted well for higher nitrogen uptake in wheat (Liao et al., 2004). More vigorous root grown will cause higher nitrogen uptake, creating better growth development of wheat plant. Niu and Liao (2016) showed that H₂O₂ mediates various developmental and physiological processes in plants. Also, the change of H₂O₂ level may impact metabolic and antioxidant enzyme activity related to plant growth and development (Barba-Espín et al., 2014).

Table (3). The average values of Jerusalem artichoke tuber yield and its     component characters as affected with water salinity concentrations, soaked tubers in H₂O₂ treatments and their interaction during the two study seasons

^* Significant at 0.05 level of probability.

1. The interaction effect of combined treatment

The interaction effect of two combined treatments exerted significant trend at p ≤ 0.05 on the number of tubers/plant and average tuber fresh weight traits during the two study seasons (Table, 3). In 2018, optimal results were realized when the tubers were soaked in 100mM H₂O₂ and irrigated with 500mg/L saline water, followed by water salinity concentrations of 2000 and 3500 mg/L, respectively. While the lowest positive results were at water salinity level of 5000 mg/L. As for the first season the significantly highest mean values for total yield / fed. were recorded with the saline irrigation , namely, 500 mg/L and 2000 mg/L , when the tubers were soaked in 100 mM H₂O₂ solution.

Table (4). The average values of Jerusalem artichoke tubers′ quality traits as affected with water salinity concentrations, soaked tubers in H₂O₂ treatments and their interaction treatments during the two study seasons

^* Significant at 0.05 level of probability.

Table (5). The averages of tubers′ mineral element contents as affected with water salinity concentrations, soaked tubers in H₂O₂ treatments and their interaction treatments during the two study seasons

^* Significant at 0.05 level of probability.

3. The performances of tubers′ quality and elemental composition
4. The main effect of saline irrigation water

The properties of tuber quality traits and the elemental composition of Jerusalem artichoke tubers are given in Tables 4 and 5. As for the tested water salinity irrigation concentrations, the results revealed that the tested tubers′ quality traits  expressed as total carbohydrate , inulin  and dry matter percentages and tuber elemental composition, including N, P and K content were significantly affected (p ≤ 0.05) with  increasing saline irrigation water during the two seasons. The results clearly showed a gradual decline in the mean values of the quality traits and tubers' elemental contents of nitrogen, phosphorus and potassium elements with increasing the level up to 3500 mg/L and severely dropped at the highest salinity exposure. Total dry matter production significantly decreased with increasing water salinity level. In contrast, Ghosh et al. (2001) illustrated that tuber N content increased by salt stress presumably due to the decrease in the carbohydrate content in the tubers. The decreases in K⁺ could be attributed to the antagonism of Na⁺ and K⁺ at uptake positions in the roots, the effect of Na⁺ on K⁺ transport into the xylem or the inhibition of uptake processes (Hu and Schmldhlter, 2005). In a saline environment, plants take up an excessive amount of sodium at the expense of K⁺ and Ghosh et al. (2001) illustrated that the decrease of dry matter production as a result of increasing salinity was relatively more pronounced in tubers than in the other parts of the plant. This result is consistent with El-Hedek (2013), who found a decrease in wheat plant phosphorus content with increased salt concentration in the soil.

b- The main effect of H₂O₂-soaked tubers

The results given in Table 5 indicated that except N% in 2018 & 2019 as well as K% in, 2019, no marked variations were detected at p ≤ 0.05. Regarding to the tubers quality, including; carbohydrate and inulin %, the results reported in Table 4 indicated that, only in 2018, significant differences were appeared between the 2 concentration levels of H₂O₂ 100 and 200 mM soaked-treated tubers. The results in Table 4 clarified that although the differences in the dry yield of tubers and P and K% between H₂O₂ –treated tubers along the all exposed salinity treatment did not impose any significant variations at p ≤ 0.05 different results were reported by Samah et al. (2012), indicating that the highest percentage of tubers dry matter was possessed when potato plants were sprayed with 40mM hydrogen peroxide.

• The effect of combined Treatments

The 2-way interaction of the combined treatment effects exhibited significant variations on total carbohydrate and nitrogen tubers content affected during the two growing seasons (Tables 4 and 5). Tubers potassium content was significantly affected only during the second season. The remaining estimated element P, inulin and dry matter percentage in tubers were not significantly affected by this interaction during the two growing seasons. In general, soaked tubers with H₂O₂ (100mM) generally gave the best values for the estimated elements and tubers′ quality traits, even if this increase was not significant in some cases.

Generally, it could be concluded that soaked Jerusalem artichoke tubers on concentration of 100mM hydrogen peroxide before   planting was promising to achieve better results and was effective to alleviate the adverse effects of irrigation water salinity on the vegetative growth criteria ad inducing progressive in increases in total tubers yield per feddan, and tubers′ quality characteristics.