Application of Moroccan seaweed-based biostimulants -

Application of Moroccan seaweed-based biostimulants

This study assessed the effect of polysaccharide-enriched extracts (PEEs) derived from six Moroccan seaweeds on tomato growth, yield, and fruit quality. PPEs were applied to tomato plants as soil drench in a greenhouse experiment. The obtained results showed that all PEEs improved the growth, yield, and fruit quality of treated tomato plants. According to principal component analysis, the presence of SO₄, galactose, glucose, and maltose in the characterized polysaccharides was closely associated with their effect on plant growth, yield, and fruit quality parameters. PEEs obtained from Gelidium crinale, Schizymenia dubyi, Fucus spiralis, and Bifurcaria bifurcata exhibited the highest biostimulant effects and could be used as bioproducts for improved tomato yield and fruit nutritional quality.

Preparation of Polysaccharide-Enriched Extracts (PEEs)

Six polysaccharide-enriched extracts (PEEs) were obtained from different seaweed species collected from the Moroccan. The studied seaweed species included two red seaweeds (Gelidium crinale and Schizymenia dubyi), and two brown seaweeds (Fucus spiralis and Bifurcaria bifurcata). Polysaccharides were extracted by the conventional hot water method under neutral conditions followed by polysaccharide precipitation using ethanol. PEEs were characterized for their total sugars, reducing sugars and protein and sulfate contents. Tomato seeds (Solanum lycopersicum L.) were surface sterilized and sown in a depth of 1.5 cm on seedling trays filled with 25 g of peat moss. The trays were placed in a phytotron growth chamber at 26 ◦C, 16:8 h photoperiod, and 240 µmol/m²/s luminosity. After 4 weeks, uniform germinated seedlings (4–5 mature leaves) were transported to the experimental greenhouse and transplanted into pots of 5 L containing 5 kg of sterilized mixture of peat moss and sand (2:2 v/v). Pots were placed in a randomized complete block experimental design. Plants were adequately watered with tap water and fertilized when needed with a nutritive solution (Steiner 60%).

The four liquid PEEs formulations were prepared. Extracts were mixed with distilled water to achieve different concentrations, then autoclaved (121 ◦C for 15 min) and transported to the experimental greenhouse for plant treatments. The PEEs derived from B. bifurcata were prepared at 0.1 mg/mL and PEEs derived from G. crinale, F. spiralis, and S. dubyi were prepared at 0.02 mg/mL. The first PEEs treatment was applied 24 h after transplantation. Then two applications at intervals of 15 days each were carried out during the vegetative growth phase and one last application during the reproduction phase. For each application, 300 mL PEE was applied to each pot (100 mL per plant). Control plants were treated with an equal volume of distilled water.

Growth parameters were recorded every 15 days: plant height (cm) measured from the cotyledons to extreme growing tip using a meter scale, number of leaves (recorded until the leaf pruning stage), number of flowers and number of flower buds. Pruning consists of removing old leaves, basal leaves touching the ground, diseased leaves as well as leaves under the floral bouquet. It was carried out 90 days after transplantation and 20 days before the harvest stage in order to accelerate the ripening of the fruits, facilitate harvesting, and also ensure suitable aeration, sunstroke, and better ventilation between the plants.

Harvesting of fruits started at 115 days after transplantation; fruits were handpicked every week from April to May as they gradually achieved physiological maturity. After each harvest, yield parameters were recorded as: number of fruits per plant, fresh weight of harvested fruits per plant (g), and the equatorial diameter of each fruit (cm).

After each harvest, a representative sample of uniform unblemished fruits having similar size and color from each experimental pot was chosen for the determination of fruit quality parameters: The total soluble solids (TSS), TSS was determined by placing 1 to 2 drops of clear juice on the prism of a digital Pocket refractometer (ATAGO PAL-α Cat. No: 3840, Tokyo, Japan). Results were expressed in Brix degrees reflecting sugar concentration in the fruit. The prism of the refractometer was washed with distilled water and dried between samples; The titratable acidity (TTA), expressed as percentage citric acid, was determined according to the titration method and the acidity was calculated as a citric acid percentage (% of juice) by using the following formula:

The Titrable acidity (%) = volume of NaOH (mL) × acid factor × 100/Volume of juice (mL)            

Sugar-acid ratio, also called maturity index, was calculated by dividing total soluble solid (TSS) to titratable acidity (TTA) of the given sample under analysis:

The sugar acid ratio = Brix value /Percentage acid                               

For lycopene content fresh fruit samples (1 mg) were dissolved in 1 mL of distilled water and vortexed in a water bath at 30 ◦C for 1 h, then 8 mL of hexane: ethanol: acetone (2:1:1) was added. The samples were capped and vortexed immediately, then incubated out of bright light. After 10 min, 1 mL water was added to each sample and vortexed again. Samples were allowed to stand for 10 min to allow phases to separate and all air bubbles to disappear. Then the absorbance of samples was determined at 503 nm by spectrophotometry. The concentration of lycopene was calculated using the extinction coefficient:

Lycopene (mg/kg) = Abs503nm × 537 × 8 × 0.55/ 0.10 × 172        

Results

The lyophilized PEEs were characterized for their sulfate, protein, and carbohydrates (galactose, glucose, and maltose) content.

Cumulative data of vegetative growth parameters (stem length and number of leaves per plant) along with reproductive growth parameters (number of flowers and number of flower buds). Measurements were recorded at 15, 30, 45, 60, 75, 90, and 105 days after transplantation (DAT) of tomato plants under the effect of different treatments of polysaccharide-enriched extracts (PEEs) obtained from marine seaweeds. Length of stems was significantly higher in plants irrigated with PEEs compared to control plants from 15 DAT throughout the trial period. The number of leaves per plant increased significantly with PEEs treatments at 30, 60, and 75 DAT. PEEs obtained from G. crinale, S. dubyi and B. bifurcata at 60 and 75 DAT. Fruit set stage started at 45 DAT in plants treated with PEEs obtained from F. spiralis and at 60 DAT in plants treated with PEEs obtained from G. crinale, S. dubyi, and B. bifurcata, compared with control plants that started the fruit set stage at 75 DAP. It can be clearly deduced that the PEEs treatments stimulated the precocity of fruit set in the tomato plants.

The yield parameters of tomato plants subjected to different treatments of seaweed PEEs compared with untreated control plants. The application of all PEEs derived from G. crinale, F. spiralis, S. dubyi, and B. bifurcata significantly affected the yield of tomato plants, which increased by 33%, 47%, 90%, and 34%, respectively, compared to untreated plants. In addition, the number of fruits significantly improved in all PEE-treated plants. Other parameters such as the average diameter and average weight of fruits were also enhanced by PEEs application. The highest mean fruit diameters (33.90 ± 4.47 and 38.94 ± 3.79 cm) were recorded in plants treated with PEEs derived from G. crinale and S. dubyi, respectively. The mean diameter of control fruits was 27.39 ± 2.86 (cm). The mean fruit weight also significantly increased in plants treated with PEEs derived from F. spiralis, and S. dubyi, which were recorded as 30.74 ± 4.16, and 36.49 ± 6.84 (g), respectively.

Effect of PPEs on Fruit Quality Parameters

Fruit quality parameters were analyzed in red-matured tomato fruits after each harvest. The total soluble solids (TSS) indicating the sugar content, titratable acidity (TTA), and lycopene content of the fruits were analyzed. The highest increase in maturity index (ratio of total soluble solids and titratable acidity) and lycopene content (80% and 33 %, respectively) was obtained in fruits of tomato plants treated with S. dubyi PEEs compared with the control.

Conclusions

Based on the greenhouse experiment, results indicated that the application of PEEs extracted from seaweeds would be beneficial for the improvement of vegetative and reproductive parameters, including early flowering, fruit set precocity, yield, and quality of tomato plants and fruits. Additional collaborations are required between crop farmers, algae farmers, researchers, and governmental entities in order to develop environmentally friendly biostimulant products in the organic market.       

Reference:

Mzibra, A., Aasfar, A., Khouloud, M., Farrie, Y., Boulif, R., Kadmiri, I.M., Bamouh, A. and Douira, A., 2021. Improving Growth, Yield, and Quality of Tomato Plants (Solanum Lycopersicum L) by the Application of Moroccan Seaweed-Based Biostimulants under Greenhouse Conditions. Agronomy, 11(7), p.1373.