Seed germination

In the case of the effect of seaweed extracts on seeds germination, several germination parameters such as germination percentage, germination index, mean germination time, germination energy and seedling vigor index should be taken into account (Hernandez-Herrera et al., 2014b; Castellanos-Barriga et al., 2017). Seaweed extract can also positively influence seed imbibition which can increase seeds germination (Castellanos-Barriga et al., 2017).

The increase of seed germination can result from the presence of plant hormones (indole 3-acetic acid and indole-3-butyric acid (IBA), gibberellins, cytokinins), vitamins, amino acids and micronutrients such as Co, Cu, Fe, Mo, Mn, Ni and Zn (Crouch and van Staden, 1993; Sivasankari et al., 2006; Hernandez-Herrera et al., 2014b). Mzibra et al. (2018) showed that seaweed polysaccharides can also act as biostimulants of seed germination and plant growth. Their polymeric structure allows them to act as water holders. Moreover, polysaccharides can increase the activity of germination enzymes and accelerate the seed metabolic activity (Hu et al., 2004).

Seaweed extracts are known to be bioactive at low concentrations - diluted as 1:1000 or more (Crouch and van Staden, 1993). Usually, lower concentrations of seaweed extracts show higher rates of seeds germination, while the higher concentrations can suppress germination (Sivasankari et al., 2006; Hernandez-Herrera et al., 2014b; Castellanos-Barriga et al., 2017). This negative effect can result from the inhibition of seeds' ability to imbibe water (Hernandez-Herrera et al., 2014b). Hernandez-Herrera et al. (2014b) showed that extracts produced from Ulva lactuca and Padina gymnospora and applied at lower concentrations (0.2 among 0.4 and 1.0%) enhanced germination of tomato seeds. The same concentration of Ulva lactuca extract (0.2%), obtained by hydrolysis of seaweeds with H2S04, was optimal for the germination of mung bean (Vigna radiata) (Castellanos-Barriga et al., 2017). The inhibition of seed germination may also result from the solvent used for the production of seaweed extract. The preliminary results of Choi and Choi (2016) showed that methanol extracts of Capsosiphon fulvescens and Monostroma nitidum completely inhibited germination of lettuce (Lactuca sativa L.). In contrast to methanol extracts, water extracts of these seaweeds slightly inhibited

Alga

Type of alga

Type of extract

Plant

Doses/active substance(s)

Effect of a product

Reference

Ascophyllum nodosum - Actiwave® product

brown

not specified

strawberry (Fra да ri a ananassa cv. Queen Elisa)

500 ml_/L of water/ kahydrin, alginic acid and betaines

  • • increase of the mineral nutrient uptake;
  • • increase of the vegetative growth, photosynthetic rate, leaf chlorophyll content, stomata density, the fruit production;
  • • increase of the plant biomass: the shoot and root dry matter;
  • • positively influence on the root- associated microbial biocoenosis

Spinelli et a I. (2010)

Ascophyllum nodosum - Acadian™ product

brown

water soluble, alkaline extract

strawberries - varieties Albion, Camarosa, Chandler, Festival

1,2 or 4 g/L/not specified

  • • increase of root and shoot growth, berry yield;
  • increase/stimulation of rhizosphere microbial diversity (increase of colony counts in soil samples) and physiological activity (increase

of metabolic activities of soil microbes)

Alam et al. (2013)

  • (1) Ulva lactuca,
  • (2) Caulerpa sertularioides,
  • (3) Padina gymnospora,
  • (4) Sargassum liebmannii
  • (Hand (2)
  • - green; (3) and (4)
  • - brown

autoclaving of seaweeds mixed with water at 121°C for 1 h

tomato (Solanum lycopersicum L.)

0.2, 0.4, 1.0%/macroelements

  • U. lactuca and P. gymnospora (0.2%) enhanced germination (lower mean germination time, high germination index and germination energy, greater seedling vigor, greater plumule and radicle length) and shoot length, root length and weight;
  • • height of the plant was higher for soil drench than the foliar spray application

Hernandez- Herrera et al. (2014)

  • (1) Sargassum wightii,
  • (2) Caulerpa chemnitzia
  • (1) brown;
  • (2) green

boiling of seaweeds in distilled water

cowpea (Vigna sinensis)

5,10, 20, 30, 40, 50, 100%/microelements and macroelements

  • • increase of shoot and root length, fresh and dry weight of seedlings;
  • • increase of chlorophyll, carotenoids, protein, amino acid, reducing sugar and root sugar content of shoot and root;
  • • increase of a and /3-amylase activities in V sinensis

Sivasankari et al. (2006)

Ulva lactuca

green

hydrolysis with H.S04 at 2, 4,

6,‘8 and 10% concentrations

mung bean (Vigna radiate)

0.2,0.4, 0.6, 0.8 and 1.0%/ carbohydrates, minerals and proteins

  • • increase at low concentrations (0.2%) of seed germination rates (lower mean germination time, high germination index, greater seedling vigour);
  • • increase of plumule, radicle, shoot and root length;
  • • increase of fresh and dry weight of mung bean;
  • • increase of protein, chlorophyll, total and reducing sugars content

Castellanos- Barriga et al. (2017)

Ascophyllum

nodosum

brown

aqueous alkaline extract

tomato, dwarf French bean, wheat, barley, maize

8 mL/L of water/betaines (y-aminobutyric acid betaine, S-aminovaleric acid betaine, glycinebetaine)

• increase of chlorophyll content in the leaves

Blunden et al. (1996)

Alga

Type of alga

Type of extract

Plant

Doses/active substance(s)

Effect of a product

Reference

Ecklonia maxima Kelpak product

brown

process called 'cold cell burst' (high pressure, low

temperatures)

tomato (Solanum lycopersicum

L.)

3 mL/L/phytohormones: auxins, cytokinins, carbohydrates, amino acids, vitamins: B1, B2, С, E, elements: N, P, K, Ca, Mg, Fe, Mn, B, Zn, Cu

  • • increase of the early and total marketable yield of fresh tomato;
  • • increase of the Ca concentration in the fruit tissue

Colla etal. (2017a,b)

  • (1 )Ulva rigida,
  • (2) Codium decorticatum,
  • (3) Fucus spiralis,
  • (4) Bifurcaria bifurcate,
  • (5) Gigartma sp.,
  • (6)

Chondra canthus acicularis

  • (1) and (2)
  • - green; (3) and (4)
  • - brown; (5) and (6)
  • - red

hot water method under neutral conditions

tomato

in vitro conditions:

0.2 mg/mL; greenhouse conditions: 0.1 mg/ml_/ polysaccharides

  • • increase of the seeds germination;
  • • increase of the plant biomass (shoots and roots);
  • • increase of the chlorophyll content

Mzibra et al. (2018)

A commercial seaweed extract from Ascophyllum nodosum

brown

not specified

strawberry plants cv. Camarosa

0.5 g/L of seaweed extract in combination with a commercial product of nitrophenolates/possible action due to the content of cytokinins, auxins and betaines

  • • increase of the marketable yield and fruit size,
  • • no significant impact on fruit juice pH, titratable acidity, total soluble solids content; fruit organic acid and carbohydrate concentration and on fruit color;
  • • enhancement of the total anthocyanin concentration

Roussos et al. (2009)

Ascophyllum nodosum - Goemar GA 14 product

brown

not specified

maize

(Zea mays L. cv. DEA)

  • 3.3 and 6.6 g/L of water/ phenolic compounds, mannitol, laminaran,fucoidan, alginates, auxin, gibberellins, substances with a cytokinin- like activity, cytokinins, abscisic acid,
  • 1 -amino-cyclopropane-l- carboxylicacid, betaines
  • • increase of the total fresh matter production of maize seedlings (increase of root and stem mass per plant) for 3.3 g/L;
  • • increase in stomatal resistance and a decrease in transpiration rate (for a dose 3.3 g/L);
  • • no significant effects on leaf number and plant height

Jeannin et al. (1991)

Ascophyllum nodosum - Goemar Spring Ci'tricos®

brown

not specified

trees of 'de Nules' clementine mandarin (Citms clementina Hort. ex Tanaka) and Navelina orange (Citms sinensis L.

Osbeck)

concentrations from 0.15% to 0.30% (full cover spray)

  • • increase of the yield of'de Nules' clementine mandarin;
  • • increase of the marketable fruit size

Fornes et al. (2002)

Ecklonia maxima

Kelpak® product, Ascophyllum nodosum - Goemar BM 86®

brown

not specified

apple trees cv. Gala Must, Golden Delicious, Jonagold Decosta, Elstar

200 and 250 mL/100 Lof water (Kelpak and Goemar, respectively)/Kelpak - auxins and cytokinins; Goemar - amino acids, phytohormones, vitamins, poligosaccharides, minerals: N, Mg, В

  • • improvement in fruit set and the size of apples;
  • • improvement in the distribution of apples in size classes;
  • • reduction of russeting;
  • • increase of the total nitrogen level in fruit;
  • • stimulation of the growth of shoots and leaves;
  • • improvement in flower quality and prolonged blooming time;
  • • no effect on the storage quality of apples

Basak

(2008)

Alga

Type of alga

Type of extract

Plant

Doses/active substance(s)

Effect of a product

Reference

Sea weeds extract

not

specified

not specified

strawberry cv. Honeoye

0.5% solution

  • • enhancement of root growth characteristics (root weight, total root length, diameter, surface area, volume and total number of root tips);
  • • had a positive influence on the colonization of roots by arbuscular mycorrhizal fungi
  • (Claroideoglomus claroideum and Funneliformis mosseae)

Sas Paszt et al. (2015)

  • (1) Codium iyengarii,
  • (2 )Jania capillacea,
  • (3) Solieria robusta,
  • (4) Stokeyia indica
  • (1) green;
  • (2) and (3) red;
  • (4) brown

ethanol extracts

chili

50% mortality of root knot nematode within 24 h at 10 mg/mL

  • • extracts from all seaweeds caused mortality of the root knot nematode - Meloidogyne javanica juveniles
  • S. indica a nd S. robusta extracts applied as soil amendments alone or with Pseudomonas aeruginosa, significantly suppressed infection of chili roots by root-infecting fungi Fusarium solani, Rhizoctonia solani and Macrophomina phaseolina

Sultana et al. (2008)

germination. It is supposed that the lipid and phenolic fraction of extracts may be the reason of germination hindering. The application of seaweed extracts in a greenhouse (pot experiments) or in the field trials should be preceded by the detailed germination tests aimed at the selection of the best algal extract produced from different seaweed species by different extraction methods with the use of a wide range of solvents. These tests also allow in choosing the optimal concentration of seaweed extract conditioning the largest shoot, root growth, fruit set and, finally, the product quality.

Shoot growth

The effect of seaweed extracts on the shoot growth was investigated by many authors. The complexity of numerous bioactive compounds in algal extracts may lead to their biostimulant activities of vegetables, fruits, flowers, crops and so on. Among them, plant hormones play an imperative role in the increase of cell size and cell division. For example, cytokinins are effective in shoot formation (Castellanos-Barriga et al., 2017). Another compound - betaines are organic osmolites that present a cytokinin-like activity. Their exogenous application in the form of algal extracts can increase not only the growth of shoots, but also roots and the chlorophyll content in leaves (Blunden et al., 1996). The plant growth can be also stimulated by seaweeds' polysaccharides and oligosaccharides through the enhancement of carbon and nitrogen assimilation and plant cell division (Castro et al., 2012).

Several commercial seaweed extracts, as well as those produced in laboratory conditions, exhibited a positive effect on the shoot growth. For example, Acadian™, a commercial product (water-soluble alkaline extract) from a brown seaweed Ascophyllum nodosum, applied in the field study increased strawberry shoot dry weight and also the leaf area (Alam et al., 2013). Tested by Ji et al. (2017) a commercial seaweed extract containing polysaccharide, alginate, increased the chrysanthemum shoot height, weight and leaf growth (length, width, area and weight) in a greenhouse. Another commercial product - seaweed extract from Ascophyllum nodosum (GoemarGA 14) applied foliarly in a greenhouse - increased maize shoot height and weight (Jeannin et al., 1991).

Root growth

The root system of plants is of great importance, taking into account the nutrients uptake and their transport in the plant (Ji et al., 2017). Seaweed extracts are known to enhance root development by the improvement of lateral formation and by the increase of the total volume of the root system and root length. Then, the vigorous root system can provide a larger surface area for nutrient and water uptake (Alam et al., 2013; Polo and Mata, 2017). The induction of the root growth can be due to phytohormones activity (auxin and gibberellin-like activities) which is involved in the regulation and improvement of the vegetal growth (Khan et al., 2009; Castellanos-Barriga et al., 2017; Polo and Mata, 2017). The application of seaweed extracts can also increase significantly the electrical conductivity of rhizospheric soil, which could be related to the mineralization of organic matter after the application of seaweed extract and consequently with the increase of the mineral nitrogen content in soil and increase of plant growth (Ji et al., 2017).

Literature data confirm that seaweed extracts increase not only the root length, but also the total root surface area, total root volume and number of roots as it was presented by Alam et al. (2013) who tested a commercial product - Acadian™ (Ascophyllum nodosum) in a strawberry cultivation. Similar effect showed seaweed extract containing alginate applied in a greenhouse on chrysanthemum (increase of the root dry weight, total root length, root surface area, root volume and root tip number) (Ji et al., 2017). Polo and Mata (2017) observed the increased root length of tomato at harvest after the application of Acadian, whereas foliar application of a commercial seaweed extract (Goemar GA14) increased maize root (Jeannin et al., 1991). The effect of seaweed extract on the root growth can also depend on the time of its application. Jeannin et al. (1991) suggested that the application of seaweed extract from Ascophyllum nodosum was generally most effective on maize root growth when applied during early vegetative growth.

Fruit set

The effect of seaweed extracts on fruit formation remains unclear, but it is supposed that it can result from the content of growth regulators (1,3-1,6 D-glucane, oligosaccharides known as laminarin)that can elicit the polyamine synthesis and stimulate cell division (Patier et al., 1993; Castro et al., 2012). The cell division during the early stages of growth along with the induction of flower formation can be influenced also by the seaweeds' phytohormones (cytokinins, auxins) and betaines (Roussos et al., 2009). Cytokinins and betaines were suggested as active compounds present in Ascophyllum nodosum extract that can be responsible for the increasing of fruit set - clementine mandarin and orange (Fornes et al., 2002). Colavita et al. (2011) found that the commercial extract from Ascophyllum nodosum (Goemar BM®) improved pears' fruit set, size and total yield by increasing the fruits' cell number early in the growth season. Gutierrez-Gamboa et al. (2018) examined the effect of seaweed extract on fruit set in a grapevine (Vitis vinifera L.) variety 'Carmenere'. The foliar application of Ascophyllum nodosum extract - especially in combination with micronutrients such as boron and zinc, before the beginning of flowering - improved fruit set, grapevine production and the content of phenolic compounds in fruits, which are classified as an elicitor

(Khan et al., 2012, Gutierrez-Gamboa et al., 2018). In the case of fruit set, the application time of seaweed extracts is of particular importance. Basak (2008) found that extracts from brown seaweeds, Ecklonia maxima and Ascophyllum nodosum, when applied to apples from the end of bloom until up to 4 weeks before harvest, improved fruit set and the size of apples. Grapevines ('Perlette') sprayed with the mixture of amino acids and seaweed extract (from Ascophylum nodosum) exhibited a significant increase in the berry setting, especially when applied at flowering, fruit setting and one month after fruit stages (Khan et al., 2012).

Product quality

The production of high-quality fruits by growers is forced by the increasing market competition (Colavita et al., 2011). This demand can be achieved by the reduction of the use of synthetic chemical products and the application of biological formulations, for example, seaweed extracts. Fruit quality parameters can be considered in terms of storability, ripening, firmness, sugar, nutrients and acid content, as well as external fruit quality parameters such as form, size, weight, length, diameter, thickness, color and so on (Nicola et al., 2009). Seaweed extracts, when applied as a foliar spray, can contribute to the supply of plant nutrients (Jeannin et al., 1991). Mineral content (e.g. calcium) is one of the major factors determining the quality and storability of fruits (Btaszczyk, 2008). For example, in the work of Col la et al. (2017a) it was shown that seaweed extract (Kelpak from Ecklonia maxima) enhanced the calcium, nitrogen and ascorbic acid content in tomato tissue. Grapevines treated with multiple spray applications of mixture of amino acids and seaweed extract at flowering and fruit setting stages showed higher levels of leaf N, P, К, B, Fe and Zn contents (Khan et al., 2012). The presence of bioactive compounds (e.g. amino acids, carbohydrates, peptides) in biostimulants of plant growth can increase the content of minerals in the fruit due to increased sink strength that influences the movement of substrates, including minerals, within the plant (Calvo et al., 2014).

Several authors reported a beneficial effect of seaweed extracts on the internal product quality. Btaszczyk (2008) showed that Go6mar BM 86 (from Ascophyllum nodosum) had a beneficial effect on the internal pears quality traits such as fruit firmness and titratable acidity during storage and maturation. Another trait of product quality is the content of soluble solids (the measure of sweetness). Grapevines treated with the mixture of amino acids and Ascophyllum nodosum seaweed extract exhibited significantly higher soluble solid concentrations, titrable acidity, total and reducing sugars than in the control group (Khan et al., 2012). Basak (2008) showed that the apples from the trees treated with seaweed extracts from Ecklonia maxima

and Ascophyllum nodosum (Kelpak and Godmar) had a little lower soluble solids content than the control group. But, after the storage, apples from the groups with seaweed extracts had better internal quality (a slightly higher firmness and significantly higher soluble solids content), but unfortunately they were more inclined to rot (Basak, 2008). Contradictory results were presented by Masny et al. (2004), who tested Kelpak and Godmar on strawberry. Both seaweed extracts reduced strawberry firmness (varieties 'Elkat' and 'Salut'). Also in the case of strawberry quality, Spinelli et al. (2010) did not find a significant increase of the studied parameters such as firmness, sugar content, titratable acidity and pH after the use of the biostimulant Actiwave® (from brown seaweeds). The same result was observed in the study by Roussos et al. (2009) - a commercial seaweed extract from Ascophyllum nodosum did not have a significant impact on strawberry juice pH, titratable acidity, total soluble solids, organic acid and carbohydrate concentration but they enhanced total anthocyanin concentration. In the case of vegetables, for example, cowpea (Vigna sinensis), seaweed extracts from Sargassum wightii and Caulerpa chemnitzia applied at low doses (till 20%) increased the chlorophyll, carotenoids, protein and amino acids, reducing sugar and total sugar content of shoot and root (Sivasankari et al., 2006).

In terms of external fruits and vegetables quality parameters, positive effects of seaweed extracts are reported. In order to achieve a larger fruit size, many plant growth-regulating compounds such as phytohormones (auxins, cytokinins and gibberellins) have been used in various crops (Guardiola and Garcia-Luis, 2000). Basak (2008) found that extracts from brown seaweeds Ecklonia maxima and Ascophyllum nodosum, applied before harvest, increased the average size of apples, depending on the fruit set, ameliorated the distribution of apples in size classes and reduced russeting. Moreover, these natural products increased the yield of marketable apples (diameter > 70 mm). Grapevines treated with the mixture of amino acids and Ascophyllum nodosum seaweed extract exhibited significantly higher berry size, weight, than in the control group (Khan et al., 2012). In the case of strawberry quality, Spinelli et al. (2010) observed increased yield and berry size after the application of biostimulant Actiwave® (from brown seaweeds). The commercial seaweed extract from Ascophyllum nodosum increased the marketable yield, fruit size, as well as strawberry color (Roussos et al., 2009). Seaweed biostimulants also have a positive effect on vegetables - for example, Acadian produced from seaweed Ascophyllum nodosum increased tomato fruit diameter (Polo and Mata, 2017); Kelpak, applied foliarly, improved the early and total marketable yield of fresh tomato (Colla et al., 2017a); extracts from Ulva lactuca, Padina gymnospora showed increased tomato weight (Hernandez-Herrera et al., 2014b); and so on.

 
Source
< Prev   CONTENTS   Source   Next >