Production of Corn; Effects of Manganese Application on Plant Parameters

Introduction

Corn (Zea mays) is a cereal grain and used as a food source for both humans and animals. Micronutrients improve the yield and the crop quality for cereals, corn, beans, forages, and oil seeds [1]. The deficiency of micronutrients reduces performance and profitability in the plant [2]. Also, Maize is a major cereal crop in the world and has economic value in livestock [3]. The Mn deficiency reduced dry matter production and yield but induced susceptibility to drought and heat stress that produces pale green or yellow patches on younger leaves [4]. Manganese (Mn) involves in plant metabolic processes such as respiration, photosynthesis, amino acid synthesis and hormone activation [5, 6]. It was reported that Mn is an essential mineral micronutrient and co-factors for antioxidant enzymes [7]. Physiological activities such as enzyme activity, absorption, translocation and oxidative stress might occur due to excessive of the Mn concentration in plant tissue [8]. Manganese plays a key role in photosynthesis and photolysis (light splitting) of water molecules and provides energy for photosynthesis. Therefore, Mn deficiency impairs photosynthesis [9] and lignin biosynthesis in the root of plants, which increase soil- born fungi following the lignin-induced reduction of pathogenic infection [10]. The application of Mn provides the resistant capacity in plants against not only various soil-borne diseases but also fungal leaf diseases [11, 12]. Manganese deficiency also weakens fatty acid production, which induces non-stomatal water loss and the heat load on leaves and increased transpirational water loss and lower water-use-efficiency [13]. To date, few pieces of research were accounted on micronutrients function on corn plants [14, 15, 16, 17, 18]. However, the effects of Mn on the physiological parameters of corn plants and yield were not properly justified under low fertile soil condition. Therefore, this study was taken to know whether Mn improves in improving plant physiological functions and sustaining yield of the corn plant in sandy soil.

Methodology

Hybrid corn variety of L41 was used in this study. Two seeds were placed in a hole on a pre-prepared seedbed and the spacing of 25 cm X 75 cm in between two holes was applied. After that, a healthy seedling was maintained to grow for experimental purposes. The soil was a predominantly of BRIS soil that contains more than 90% of a sand particle with reduced soil physical and chemical properties. The BRIS soil encompasses carbon (3.82%), nitrogen (0.14%), phosphorus (0.1%), potassium (0.03%), calcium (0.34%), magnesium (1.01%), manganese (0.008%) and pH of 4.5. The compost, contains of carbon (27.5%), nitrogen (1.7%), phosphorus (1.5%), potassium (1.0%), calcium (2.3%), magnesium (1.3%), manganese (0.04%) and pH of 6.5, was mixed with BRIS soil. Plant tissue contains 35.2 mg kg-1 DM of Mn. Four Mn (0, 0.2, 1.5 and 3 ppm) treatments with five replicates were arranged according to the completely randomized design. Care of plants [19, 20, 21] and different cultural practices were followed according to the previous studies [22]. The concentration of Mn was chosen based on the lower, optimum and maximum level according to previous information [23]. The leaves were counted numerically. The plant height was measured from the soil surface to the leaf tip of the top of the final leaf emerged with a measuring ruler alongside. The weight of fresh leaf (FW) was measured just after detached from the plants then turgid weight (TW) was determined after leaf was incubated in distilled water for 24 h to obtain a full turgidity. Dry weight (DW) of the leaf, dried at 60°C for 24 h in an oven, was measured. The following reaction was used to measure relative water content according to the previous studies [24, 25, 26]. RWC (%) = [(FW-DW) / (TW-DW)] x 100 An SPAD-502 portable chlorophyll meter (Minolta, Japan) was used to acquire a rapid estimation of chlorophyll (Chl) content in leaves of corn plants [27, 28, 29]. Five plants were selected and the second uppermost collared-leaf was used to determine Chl content. There were five measurements from each plant and a total of 25 measurements were taken for each treatment. Data were taken at 11 am up to 1 pm to avoid wetness condition that affects Chl reading. A portable Junior-PAM Chl-monitoring meter (Walz, Germany) was used to quantify Chl fluorescence from leaves of corn plants [26]. A second uppermost collared-leaf was used for taking the data in between 11 am to 1 pm. The maximum fluorescence level was recorded in this experiment.Net photosynthesis rate (Pn) was measured using a CI-340 portable photosynthesis meter (CID Biosciences, Inc.) according to Khairi et al. [26]. These data were taken in between 11 am to 1 pm. Five measurements were taken for each treatment. Plant height, the number of leaves, length and weight of cob were determined after the yield produced. Cob weight was taken by using digital weight machine for each treatment. Data were analyzed for differences of mean value among treatments by one factor ANOVA procedure and T-test using Minitab-16 and MS Excel software. Differences at P < 0.05 were considered significant.

Results and Discussion

Plant height and leaf numbers were presented in Figure 1.

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Figure1: Effects of different concentrations of Mn on plant height (a) and leaf numbers (b).

Weekly-data showed that the height of corn plant increased with increasing time (Figure 1a). At week 4th, Mn did not affect plant height in both of Mn-treated and Mn-untreated corn plants. Plant height between control (Mn0) and a lower dose of Mn (Mn1) was almost similar throughout the growing period. On the other hand, Mn2 treatment significantly increased plant height compared to Mn1 treatment at week sixth (P ≤ 0.003) and week eighth (P ≤ 0.001) where control and Mn1 showed no difference. Similar results were observed in the case of Mn3 treatment. The plant height was similar when data were compared between week 6th and week 10th. It suggests that higher concentrations of Mn affect plant height [30]. At week 4th, Mn did not affect leaf numbers in Mn-treated and Mn-untreated plants (Figure 1b).

However, Mn2 significantly increased numbers of the leaf at week 8th (P ≤ 0.016) and week 10th (P ≤ 0.016). The effects of Mn3 on leaf numbers were similar to Mn2 treatments. This result suggests that Mn might increase leaf numbers of corn plant. Relative water content significantly (P ≤ 0.003) decreased in leaves of Mn-untreated plants compared to leaves of Mn-treated plants (Figure 2a).

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Relative water content increased with increasing Mn concentration and reached at the highest level when plants were treated with 3 ppm of Mn. The Mn2 treatment significantly (P ≤ 0.0002) increased RWC in plants compared to Mn0 treatment. Also, the RWC declined significantly (P ≤ 0.014) in plants when it was treated with Mn1 (0.2 ppm) compared to the Mn3 (3 ppm) treatment. Taken together, these results indicate that Mn2- treated plants might perform a better function related to the water content in the cell than Mn-untreated plants. Manganese plays a major role in improving stress tolerance through the increasing activity of Mn- superoxide dismutase. Higher RWC in Mn-treated plant improves fatty acid production [31]. Therefore, there is a possible that Mn deficiency plants showed susceptibility to both drought and heat stress. Because, Mn deficiency reduced the waxy content that increased transpirational water loss and lower water-use-efficiency [31].

We measured the net Pn and PAR rate in leaves of corn plants under different Mn conditions (Figure 2b). We found that Mn treatment significantly (P ≤ 0.0001) increased Pn rate in plants compared to Mn-untreated plants (Figure 2b, line graph). This result suggests that foliar application of Mn might affect net photosynthesis rate. In addition, Mn1 treatment significantly (P ≤ 0.012) increased PAR in plants than Mn0- treated plants (Figure 2b, bar graphs). In the case of Mn2 and Mn3, Pn and PAR significantly increased in plants than Mn-untreated plants, but Pn and PAR were insignificantly different among different Mn treatments. Taken together, it suggests that Mn increases plant photosynthesis rate and functions on light related reaction, example, light antenna complexes function in photosystem II where Mn is required for water oxidation, which plays a major role in photosynthesis [9]. Mn provides energy during photosynthesis through the splitting of water molecules in photosystem II [32] and damaged the photosynthetic apparatus [33], which finally might affect the production of dry matter and yield in plants. Whether the Mn application affected light related parameters, the chlorophyll (Chl) content, Chl fluorescence in leaves were determined at different growing stages. The Mn treatment affected Chl content (Figure 3a), however, Mn- treated plants presented different Chl accumulations in leaves under different observation times (Figure 3a).

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Figure 3: Effects of different concentrations of Mn on Chl content (a) and Chl florescence (b). In addition, Chl content increased significantly in leaves of Mn-treated plants at week 8th (P ≤ 0.013) and 10th (P ≤ 0.012) than in leaves of Mn- untreated plants. These results suggest that Mn application increases Chl content in leaves of corn plants and support that Mn might function on the light antenna in photosystem II. Previously, Jahan et al. [34, 35] stated that light-harvesting antenna of photosystem II increased chlorophyll content in Arabidopsis plants. In plants, Mn participates in the structure of photosynthetic proteins and enzymes [32]. Chl fluorescence is positively correlated with Chl content data. In addition, Mn application increased chlorophyll fluorescence in leaves of corn plants (Figure 3b). Mn- treated plants showed no difference (P ≤ 0.09) concerning Chl fluorescence accumulation during data taking time from 4th to 10th week but significantly higher than Mn- untreated plants (Figure 3b). These results indicate that Mn functions on Chl parameters probably through the photosystem II-water oxidizing system and photolysis of water molecules that provide energy for photosynthesis [9]. This result was consistent with Pn results in this study (Figure 2b). The yield and yield parameters were determined based on the weight and length of corn fruit, which were shown in Figure 4. The yield gradually increased with increasing Mn concentration (Figure 4a).

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The yield was lower than usual corn production due to the BRIS soil. Yield significantly increased in Mn-treated plants than Mn- untreated plants. In addition, different Mn concentrations differentiate corn yield where a higher concentration of Mn treatment significantly increased (P ≤ 0.013) corn yield compared to the lower Mn concentration treatment. This result was consistent with Pn data (Figure 2b) that higher Pn rate contributes in increasing yield of corn plants. Consequently, Mn2 and Mn3 showed better performance regarding cob yield. Besides, the length of corn plant was also higher under Mn2 and Mn3 treatments (Figure 4b) and showed insignificantly larger size than that of Mn- untreated plants and 0.2 ppm Mn- treated plants. These results also support that 1.5 ppm Mn supports plant tissues for better enzyme activity, absorption, translocation and utilization of other mineral elements [8].In conclusion, this study shows that the Mn application enhanced RWC, PAR, and Pn rate in corn plants. The 1.5 ppm of Mn application increased yield as well as increasing light related parameters, Chl content and Chl fluorescence and photosynthesis rate. Therefore, Mn at 1.5 ppm could be applied as a foliar spray on leaves for sustainable corn production.

Acknowledgements

This work was supported by the faculty of Agriculture, Biotechnology and Food Sciences, Universiti Sultan Zainal Abidin, Kuala Terengganu, Malaysia.