Bioactive effect of cyanobacteria and calcareous algae mixture in bioassays and on potato growth and yield¹

Efeito bioativo da mistura de cianobactérias e algas calcárias em bioensaios e no crescimento e na produtividade da batata

ABSTRACT

The growth-promoting effect of the micronized calcareous algae Lithothamnion sp. is related to the presence of humic acid and its bioactive auxin-like effect, characteristic of humic substances, whereas the plant growth-promoting effect of the microalgae (cyanobacteria) Arthrospira platensis (Spirulina platensis) has been attributed to the presence of L-amino acids and polyamines in its biomass. The present study aimed to identify the possible synergistic bioactive effect of a mixture of both sources (micronized Lithothamnion and A. platensis biomass) in bioassays and in the field, with foliar application, on organic potato (Solanum tuberosum L.) cultivation. Four bioassays were carried out to evaluate the root growth of Vigna radiata, as well as the expansion of Solanum lycopersicum hypocotyls, Cucumis sativus cotyledons and V. radiata hypocotyl-radicle axis. Subsequently, a field experiment was conducted in an organic system with foliar application to potato plants. The bioassays showed the bioactivity of the calcareous algae and of the cyanobacteria, and their combination, promoting biometric and metabolic changes, increasing the potato yield and tuber sugar content. Thus, the mixture of micronized Lithothamnion with A. platensis biomass can be a novel natural input to sustainably improve potato growth and yield.

KEYWORDS:
Lithothamnion sp.; Arthrospira platensis; Solanum tuberosum L

RESUMO

O efeito promotor de crescimento da alga calcária micronizada Lithothamnion sp. está relacionado à presença de ácido húmico e seu efeito bioativo semelhante à auxina, característico das substâncias húmicas, enquanto o efeito promotor de crescimento vegetal da microalga (cianobactéria) Arthrospira platensis (Spirulina platensis) foi atribuído à presença de L-aminoácidos e poliaminas em sua biomassa. Objetivou-se identificar o possível efeito bioativo sinérgico da mistura de ambas as fontes (Lithothamnion micronizado e biomassa de A. platensis) em bioensaios e no campo, com aplicação foliar, no cultivo orgânico de batata (Solanum tuberosum L.). Quatro bioensaios foram conduzidos para avaliar o crescimento da raiz de Vigna radiata e a expansão dos hipocótilos de Solanum lycopersicum, dos cotilédones de Cucumis sativus e do eixo hipocótilo-radícula de V. radiata. Posteriormente, foi conduzido um experimento de campo, em sistema orgânico, com aplicação foliar, em plantas de batata. Os bioensaios mostraram a bioatividade das algas calcárias, das cianobactérias e de sua associação, promovendo mudanças biométricas e metabólicas, aumentando a produtividade da batata e o teor de açúcar nos tubérculos. Assim, o Lithothamnion micronizado associado à biomassa de A. platensis para o crescimento de batata pode ser um novo insumo natural para melhorar a sua produção de forma sustentável.

PALAVRAS-CHAVE:
Lithothamnion sp.; Arthrospira platensis; Solanum tuberosum L.

INTRODUCTION

The development of natural-based inputs can provide an efficient means of increasing crop yield. Potato is the world’s third most consumed food, with a global production of 383 million tons (FAO 2023). Thus, developing novel nature-friendly agricultural practices is essential to ensuring food safety.

Biofertilizers, natural substances that act on plant metabolism, are bioactive, agrotoxin-free and capable of promoting increased yield (Brasil 2020). Recently, the Brazilian legislation classified them as bioinputs (Brasil 2024).

This reflects a growing demand, extending to large production areas, for more sustainable techniques and good practices that can reduce production costs by decreasing the use of chemical inputs by conventional but innovative farmers (Vidal et al. 2021).

In addition, research on natural plant growth-promoting sources is increasingly relevant for improving the yield, quality and sustainability of agricultural production in a changing environment. Examples include the use of free L-amino acids to improve potato yield (Röder et al. 2018) and mitigate the effects of oxidative stress in soybean (Marques et al. 2021), microalgae associated with humic acid to enhance onion growth and yield (Gemin et al. 2019), algae extract to increase the growth of bean and maize under salt stress (Hussein et al. 2021), and chlorophyte microalga extracts to benefit common bean (Marques et al. 2023) and melon (Marques et al. 2025).

Macroalgae are classified into three major groups according to their pigmentation: Chlorophyta (green), Phaeophyta (brown) and Rhodophyta (red) (Freitas et al. 2022). Lithothamnion sp., a red alga, contains calcium (±31.93 %), magnesium (±3 %), humic substances (±10 %) and free amino acids (0.15 %), exhibiting proven bioactivity in several plants (Amatussi et al. 2020, Ramos et al. 2023).

While Brazilian regulations classify Lithothamnion sp. as a mineral fertilizer, based only on its mineral fraction (Brasil 2018), it can also be considered a biofertilizer (Brasil 2020) in the bioinputs class (Brasil 2024), if its bioactivity is demonstrated.

Lithothamnion sp. application has shown positive effects on root development, thereby increasing bell pepper (Evangelista et al. 2016) and melon yield (Negreiros et al. 2023), and inducing phytoalexin accumulation in bean and soybean (Faria et al. 2022). In onion, it increased plant growth, nutrient content and yield (Mógor et al. 2021).

The bioactivity of micronized Lithothamnion sp. (micrometer scale particles) has been attributed to its highly bioactive humic acid content (Amatussi et al. 2020). Humic substances combined with the microalgae chlorophyte Scenedesmus subspicatus have shown to increase plant growth and yield (Gemin et al. 2019), as well as to improve onion storage and post-harvest quality (Gemin et al. 2022). The foliar application of a mixture of Lithothamnion sp. and the cyanobacterium Arthrospira platensis (Spirulina plantensis) promoted onion growth, biochemical changes and yield gains (Amatussi et al. 2022).

Microalgae have demonstrated plant growth-promoting effects, including mitigating the harmful effects of water shortage in common bean (Marques et al. 2023) and oxidative stress under high salinity in melon (Marques et al. 2025). These effects are attributed to bioactive compounds such as proteins, polyamines, cytokinins and free L-amino acids (Mazepa et al. 2021, Cordeiro et al. 2022, Mógor et al. 2022a).

The cyanobacterium Arthrospira platensis has also shown a plant growth-promoting effect on various crops, including red beet (Mógor et al. 2018), lettuce (Mógor et al. 2017), red spinach (Mala et al. 2017), Petunia x hybrida (Plaza et al. 2018) and radish (Godlewska et al. 2019). Bioassays show that the cytokinin-like activity may be related to polyamines in A. platensis biomass (Mógor et al. 2017), and the presence of trans-zeatin and isopentenyl adenine, contributing to plant growth promotion in treated plants (Plaza et al. 2018).

However, the combination of different algae sources may exhibit synergistic biostimulatory action, thereby contributing to designing the next generation of plant growth-promoting sources for sustainable agriculture. In this context, the present study investigated the effect of the micronized calcareous algae Lithothamnion sp. combined with A. platensis in bioassays (to identify bioactivity) and in the field on potato growth and yield.

MATERIAL AND METHODS

As an initial step to identify possible bioactive properties of Lithothamnion sp. and Arthrospira platensis in plants, four bioassays were conducted: hypocotyl expansion of Solanum lycopersicum (Zhao et al. 1992, Stirk et al. 2002); cotyledon expansion of Cucumber sativus (Zhao et al. 1992, Stirk et al. 2002, Mógor et al. 2017); root emission with Vigna radiata (Tripepi & George 1991, Zhao et al. 1992, Amatussi et al. 2020); and hypocotyl-radicle expansion of V. radiata.

These bioassays were performed in March 2021 at the the Canguiri experimental farm of the Universidade Federal do Paraná (Paraná state, Brazil). The micronized calcareous algae Lithothamnion sp. sample was provided by NaturVita Bioagroindustria (Petrolina, Pernambuco state, Brazil) (Amatussi et al. 2020). Arthrospira platensis was cultivated in photobioreactors at the laboratory, then lyophilized (Mógor et al. 2017) and suspended in distilled water as described below:

The hypocotyl expansion bioassay of S. lycopersicum was performed in plastic germination boxes (Gerbox^®). Seeds were placed on pre-moistened germination paper (2.5 times the weight of the paper) in solutions with concentrations of micronized Lithothamnion sp. and A. platensis: control (distilled water only); Lithothamnion sp. (1.5 g L^-1); 1.5 g L^-1 of Lithothamnion sp. + 0.75 g L^-1 of A. platensis; 1.5 g L^-1 of Lithothamnion sp. + 1.5 g L^-1 of A. platensis; and A. platensis (1.5 g L^-1). The bioassay was conducted in a growth chamber at 22 ºC, in the dark, for 9 days, in a completely randomized design, with four replications. The length (cm) and volume (cm³) of tomato hypocotyls were evaluated;

Cucumis sativus seeds were previously germinated in a vermiculite bioassay with cotyledons. Once developed, the cotyledons were placed in plastic Gerboxes on germination paper moistened (2.5 times the weight of the paper) with solutions containing concentrations of Lithothamnion sp. and A. platensis: control (distilled water only); Lithothamnion sp. (1.5 g L^-1); 1.5 g L^-1 of Lithothamnion sp. + 0.75 g L^-1 of A. platensis; 1.5 g L^-1 of Lithothamnion sp. + 1.5 g L^-1 of A. platensis; and A. platensis (1.5 g L^-1). The bioassay was conducted in a growth chamber at 22 ºC, in the dark, for 9 days, in a completely randomized design with four replicates (n = 4). The length (cm) and volume (cm³) of the cucumber cotyledons were evaluated;

To evaluate the effect on root growth of V. radiata, seeds were sown in 144-cell plastic trays filled at a 1:1 ratio with a commercial substrate (Tropstrato^®) and commercial organic compost (Provaso^®) containing: C = 30.3 g kg^-1; N = 30.3 g kg^-1; P = 8.5 g kg^-1; K = 6.6 g kg^-1; Ca = 8.1 g kg^-1; and Mg = 4.1 g kg^-1. The trays were kept in a nursery with timed micro-sprinkler irrigation. At 10 days after germination, the seedling stems were excised and placed in microtubes containing the following solutions: control (water); Lithothamnion sp. (1.5 g L^-1); 1.5 g L^-1 of Lithothamnion sp. + 0.75 g L^-1 of A. platensis; 1.5 g L^-1 of Lithothamnion sp. + 1.5 g L^-1 of A. platensis; and A. platensis (1.5 g L^-1). The bioassay was conducted in a growth chamber at 25 ºC, under a 12-hour photoperiod (photon flux intensity: 0.52-0.56 mmol m^-2 s^-1) for 9 days, in a completely randomized design with four replicates (n = 8). The length (cm) and average diameter (mm) of V. radiata roots were evaluated;

The V. radiata seeds were soaked for 2 min in the following solutions: control (with water application); Lithothamnion sp. (1.5 g L^-1); 1.5 g L^-1 of Lithothamnion sp. + 0.75 g L^-1 of A. platensis; 1.5 g L^-1 of Lithothamnion sp. + 1.5 g L^-1 of A. platensis; and A. platensis (1.5 g L^-1). The seeds were placed in plastic Gerboxes on germination paper previously moistened (2.5 times the weight of the paper) with distilled water. The bioassay was conducted in a growth chamber at 25 ºC, for 5 days, in a completely randomized design, with four replicates (n = 4).

The length (cm), volume (cm³) and mean diameter (mm) of S. lycopersicum hypocotyls, C. sativus cotyledons and V. radiata roots and hypocotyl-radicle were determined using the WinRhizo Pro^® (Regent Instr^® Canada) software and an Epson^® (v700 PHOTO model) dual-lens scanner.

Based on the bioassay results, the potato growth and yield experiment was conducted in the organic horticulture area of the Canguiri experimental farm of the Universidade Federal do Paraná, in Pinhais, Paraná state, Brazil (25º25’S and 49º06’W), in August 2021. This region is on the first plateau of the Paraná state, at an altitude of 920 m. According to the Köppen classification, the regional climate is temperate (Cfb), with no defined dry season, cool summers, mild winters, average annual rainfall between 1,400 and 1,600 mm, and average annual minimum temperature between 17 and 18 ºC, with frequent and severe frosts (Embrapa 2013).

The chemical analysis of the 0-20 cm soil layer revealed the following average values: pH (CaCl₂) = 5.84; pH (H₂O) = 6.71; Al⁺³ = 0 cmol_c dm^-3; H + Al⁺³ = 2.93 cmol_c dm^-3; Ca²⁺ = 5.28 cmol_c dm^-3; Mg²⁺ = 3.05 cmol_c dm^-3; K⁺ = 1.32 cmol_c dm^-3; P (Mehlich) = 49.0 mg dm^-3; S = 33.49 mg dm^-3; C = 26 g dm^-3; V = 76.7 %; and CEC = 12.58 cmol_c dm^-3.

After the soil preparation, planting furrows were made using a micro tractor and spread homogeneously with 12.5 t ha^-1 of organic compost containing the following: C = 31.3 g kg^-1; N = 26.3 g kg^-1; P = 8.2 g kg^-1; K = 7.2 g kg^-1; Ca = 8.0 g kg^-1; Mg = 4.2 g kg^-1; and 50 kg ha^-1 of magnesium thermophosphate.

The experimental area was irrigated using a sprinkler system to maintain the soil moisture at 80 % of its water holding capacity, as measured by a tensiometer. The design was completely randomized, with four replicates of the following foliar applications (treatments): control (water); Lithothamnion sp. (1.5 g L^-1); 1.5 g L^-1 of Lithothamnion sp. + 0.75 g L^-1 of A. platensis; 1.5 g L^-1 of Lithothamnion sp. + 1.5 g L^-1 of A. platensis; and A. platensis (1.5 g L^-1). A total of six rows were established, with the first and last considered border rows, and 20 plots of eight plants each randomly distributed in the four central rows. Potato tubers of the ‘BRS Clara’ cultivar (Embrapa) were planted with spacing of 0.35 m between plants and 0.80 m between rows.

‘BRS Clara’, one of the most suitable cultivars for organic cultivation (Passos et al. 2022), is medium sized, with a semi-erect growth habit, moderately open leaves and average maturity of 100 days. The tubers have an elongated oval shape, smooth yellow skin and are moderately resistant to greening and resistant to powdery mildew (Phytophthora infestans), with average yield of 7.23 t ha^-1 in the spring (Pereira et al. 2013) and average total soluble solids content of 3.2 ºBrix (Virmond et al. 2014). The hilling-up procedure was performed at 25 days after planting (DAP). Applications started at 32 DAP, and occurred weekly, totaling eight applications until leaf senescence (84 DAP). The application rate was 400 L ha^-1 using a 10-L electronic sprayer (Kawashima^®), with constant pressure (40 psi). To avoid drift, a plastic barrier was used in all applications.

The relative chlorophyll index was measured in the field with a chlorophyll meter (N-Tester^®), which provided average values from 30 random readings taken on fully expanded leaves in the middle third of the plants (Mógor et al. 2013). The readings were taken on the three central plants of each plot (55 DAP).

Harvest was performed at 98 DAP, with the plants showing complete senescence. Three central plants from the plots were used for tuber mass quantification, and yield was calculated by extrapolating these values to a population of 40,000 plants ha^-1. Yield assessment followed the potato tuber size classification (Class I: > 70 mm; Class II-2: 50-70 mm; Class II-1: 42-50 mm; Class III: > 33-42 mm; Class IV: 28-33 mm; and Class V: < 28 mm). For calculations, only the commercial standard classes were used (I, II-1 and II-2). The total soluble solids content of the tubers was determined at harvest using a portable refractometer (EEQ9030), and the results were expressed in ºBrix.

For reducing and total sugars analysis, potato leaves and tubers were collected after the fourth and eighth application (55 and 98 DAP, respectively). Leaves and tubers (commercial standard classes at harvest) were collected, macerated in liquid nitrogen and stored (-20 ºC) for biochemical analysis. Leaf collections were performed between 9 and 10 a.m. (Mógor et al. 2022b).

The total sugars were quantified according to Maldonade et al. (2013), preceded by acid hydrolysis of the sample using 3,5-dinitro salicylic acid. The standard curve for reducing and total sugars was generated using glucose (5.5 mM). The values were expressed as µg of sugars per g of fresh plant material.

All data were evaluated for homogeneity and then submitted to analysis of variance (Anova). When significant differences were detected (p < 0.5), the Tukey test was applied. The statistical analyses used the Assistat^® 7.7 Beta software (Silva & Azevedo 2016).

RESULTS AND DISCUSSION

The bioactivity of micronized Lithothamnion sp., lyophilized Arthrospira platensis biomass and their combinations was characterized as follows: 1.5 g L^-1 of Lithothamnion sp. + 1.5 g L^-1 of A. platensis concentration stimulated the expansion of tomato hypocotyls, resulting in a 15 % increase in length and 27 % in volume (Figures 1a and 1b). This increase may be due to the presence of bioactive substances in the algae, such as humic acid in Lithothamnion sp. (Amatussi et al. 2020), L-amino acids (Mógor et al. 2018) and polyamines in A. platensis (Mógor et al. 2017).

Figure 1
Length (a) and volume (b) of Solanum lycopersicum hypocotyl expansion; length (c) and area (d) of Cucumis sativus cotyledons, grown on germination paper treated with concentrations of micronized Lithothamnion sp. (Lm) and Arthrospira platensis (Ap). Concentrations: control; Lithothamnion sp. (1.5 g L^-1); LAp1 (1.5 g L^-1 of Lithothamnion sp. + 0.75 g L^-1 of A. platensis); LAp2 (1.5 g L^-1 of Lithothamnion sp. + 1.5 g L^-1 of A. platensis); and A. platensis (1.5 g L^-1). Means followed by the same letter do not differ statistically (p < 0.5) according to the Tukey test. Bars indicate the standard deviation.

The length and volume of S. lycopersicum hypocotyls showed the bioactive effect of the Lithothamnion sp. and A. platensis combination at the highest concentration (1.5 g L^-1 of Lithothamnion sp. + 1.5 g L^-1 of A. platensis) (Figures 1a and 1b). The S. lycopersicum hypocotyls treated with 1.5 g L^-1 of Lithothamnion sp. + 1.5 g L^-1 of A. platensis showed a 15 % increase in length and 27 % in volume, when compared to the control.

Furthermore, the bioactivity of Arthrospira platensis was expressed in the C. sativus cotyledon bioassay, resulting in an 82.3 % increase in length (Figure 1c). A similar bioactivity was reported by Mógor et al. (2017), attributed to an increase in polyamine spermine, and a similar result was found with chlorophyte microalga (Scenedesmus obliquus), which exhibited a cytokinin-like effect (Navarro-López et al. 2020). By contrast, the Lithothamnion sp. application showed no significant effect in the cucumber cotyledon expansion bioassay (Figure 1c).

The V. radiata bioassay serves as an indirect assessment of auxin-like substances by expressing bioactivity through rooting (Amatussi et al. 2020). In V. radiata plants treated with Lithothamnion sp., rooting was 84 % higher than in the control (Table 1). By contrast, plants treated with A. platensis alone or in combination with Lithothamnion sp. did not develop roots.

Table 1
Average length (cm) and diameter (mm) of Vigna radiata roots and hypocotyl-radicle.

Treatments		Length (cm)	Average diameter (mm)
Root emission	Control	97.99 ± 3.70	0.97 ± 0.05
	Lithothamnion sp.	180.76 ± 20.52	0.68 ± 0.06
Hypocotyl-radicle emission	Control	267.98 a	1.034 ± 0.002 b
	Lithothamnion sp.	285.54 a	1.111 ± 0.084 ab
	LAp1	265.61 a	1.032 ± 0.017 b
	LAp2	255.36 a	1.163 ± 0.075 a
	Arthrospira platensis	272.46 a	1.104 ± 0.052 ab
	CV (%)	8.78	5.18

When algae extracts are applied to increase rooting, algae species with higher auxin-like activity are superior to extracts from species with lower activity (Lötze & Hoffman 2016), as observed in this study, when comparing the same concentration of Lithothamnion sp. and A. platensis. Solutions containing A. platensis did not promote root development in V. radiata. The effect of Lithothamnion sp. is attributed to its high bioactive humic acid content, which can exhibit auxin-like activity when applied to plants (Amatussi et al. 2020).

Treating V. radiata seeds with 1.5 g L^-1 of Lithothamnion sp. + 1.5 g L^-1 of A. platensis increased the mean diameter of the hypocotyl-radicle, showing the bioactive effect of micronized Lithothamnion sp. combined with A. platensis at the highest concentration (1.5 g L^-1 of Lithothamnion sp. + 1.5 g L^-1 of A. platensis) (Table 1). The hypocotyl-radicles of V. radiata in 1.5 g L^-1 of Lithothamnion sp. + 1.5 g L^-1 of A. platensis showed a 12.47 % increase, when compared to the control. However, the length did not differ between the treatments.

The results of these bioassays indicate that Lithothamnion sp. and A. platensis have different modes of action that may be complementary.

In the field experiment, the leaves of potato plants treated with Lithothamnion sp. and 1.5 g L^-1 of Lithothamnion sp. + 1.5 g L^-1 of A. platensis exhibited a higher relative chlorophyll index (Figure 2a), with 21 and 18 % increases, respectively, when compared to the control. Moreover, the higher chlorophyll content observed in the field resulted in higher tuber total soluble solids at harvest (Figure 2b), with 2 and 15 % increases in Lithothamnion sp. and 1.5 g L^-1 of Lithothamnion sp. + 1.5 g L^-1 of A. platensis, respectively, when compared to the control. Total soluble solids (ºBrix) can be used as an indirect measure of sugar content (mainly sucrose). Factors such as photosynthetic rate, carbohydrate status and plant hormone balance are essential in sugar accumulation in storage organs (Ševčíková et al. 2017).

Figure 2
Relative chlorophyll index (a) of potato leaves (55 days after planting - DAP) and soluble solids content (b) of tubers (98 DAP) in plants treated with foliar applications of micronized Lithothamnion sp. (Lm) and Arthrospira platensis (Ap). Concentrations: control; Lithothamnion sp. (1.5 g L^-1); LAp1 (1.5 g L^-1 of Lithothamnion sp. + 0.75 g L^-1 of A. platensis); LAp2 (1.5 g L^-1 of Lithothamnion sp. + 1.5 g L^-1 of A. platensis); and A. platensis (1.5 g L^-1). Means followed by the same letter do not differ statistically (p < 0.5) according to the Tukey test. Bars indicate the standard deviation.

Consequently, the accumulation of sugars is related to the increase in leaf area (Figure 3c) and the chlorophyll index (Figure 2a), as observed with Lithothamnion sp. applications alone and combined with both concentrations of A. platensis, thereby increasing leaf area.

Figure 3
Leaf dry mass (a), leaf area (b) and tuber fresh mass (c) (55 days after planting) of plants treated with foliar applications of micronized Lithothamnion sp. (Lm) and Arthrospira platensis (Ap). Concentrations: control; Lithothamnion sp. (1.5 g L^-1); LAp1 (1.5 g L^-1 of Lithothamnion sp. + 0.75 g L^-1 of A. platensis); LAp2 (1.5 g L^-1 of Lithothamnion sp. + 1.5 g L^-1 of A. platensis); and A. platensis (1.5 g L^-1). Means followed by the same letter do not differ statistically (p < 0.5) according to the Tukey test. Bars indicate the standard deviation.

The biometric variables evaluated at the onset of tuberization (55 DAP) demonstrated the effectiveness of Lithothamnion sp. on the initial growth of plants, particularly regarding biomass accumulation in leaves and tubers (Figure 3) and leaf area, when applied alone or combined with A. platensis (1.5 g L^-1 of Lithothamnion sp. + 0.75 g L^-1 of A. platensis and 1.5 g L^-1 of Lithothamnion sp. + 1.5 g L^-1 of A. platensis). A 33 % increase in leaf dry mass was observed in plants treated with Lithothamnion sp. The leaf area of plants treated with Lithothamnion sp. alone and in combination (1.5 g L^-1 of Lithothamnion sp. + 0.75 g L^-1 of A. platensis and 1.5 g L^-1 of Lithothamnion sp. + 1.5 g L^-1 of A. platensis) increased by 52.7, 50.2 and 68.3 %, respectively. The tuber fresh mass (Figure 3c) increased by 132 % in the plants treated with Lithothamnion sp., when compared to the control.

These results corroborate those of Amatussi et al. (2020), who observed increased leaf dry mass (11.4 %) in tomato plants treated with Lithothamnion sp., and Amatussi et al. (2022), who reported a 43 % increase in onion. Gemin et al. (2019) demonstrated that the combination of humic acid with microalgae increased the initial growth of onion plants, as a result of enhanced rooting, characteristic of the auxin-like effect of bioactive humic substances.

The field results showed that the combination of Lithothamnion sp. with A. platensis increased the sugar content (Figure 4a). The 1.5 g L^-1 of Lithothamnion sp. + 1.5 g L^-1 of A. platensis combination stimulated the source-drain transport, leading to a higher potato yield. Sugars present in the leaves were translocated to the tubers (1.5 g L^-1 of Lithothamnion sp. + 1.5 g L^-1 of A. platensis), thus promoting an increased yield at harvest (Figure 5b).

Figure 4
Total sugars, reducing sugars and non-reducing sugars (a) in potato leaves (55 days after planting - DAP); total sugars (b) in potato tubers (98 DAP) of plants treated with foliar applications of micronized Lithothamnion sp. (Lm) and Arthrospira platensis (Ap). Concentrations: control; Lithothamnion sp. (1.5 g L^-1); LAp1 (1.5 g L^-1 of Lithothamnion sp. + 0.75 g L^-1 of A. platensis); LAp2 (1.5 g L^-1 of Lithothamnion sp. + 1.5 g L^-1 of A. platensis); and A. platensis (1.5 g L^-1). Means followed by the same letter do not differ statistically (p < 0.5) according to the Tukey test. Bars indicate the standard deviation.

Figure 5
Average number of tubers per plant (98 days after planting - DAP; a) and average yield (t ha^-1; b) of potato tubers (98 DAP) in plants treated with foliar applications of micronized Lithothamnion sp. (Lm) and Arthrospira platensis (Ap). Concentrations: control; Lithothamnion sp. (1.5 g L^-1); LAp1 (1.5 g L^-1 of Lithothamnion sp. + 0.75 g L^-1 of A. platensis); LAp2 (1.5 g L^-1 of Lithothamnion sp. + 1.5 g L^-1 of A. platensis); and A. platensis (1.5 g L^-1). Means followed by the same letter do not differ statistically (p < 0.5) according to the Tukey test. Bars indicate the standard deviation.

Plants treated with 1.5 g L^-1 of Lithothamnion sp. + 1.5 g L^-1 of A. platensis and A. platensis (1.5 g L^-1) showed 50.2 and 38.8 % accumulation of total leaf sugars (Figure 4a). Reducing sugars (e.g., glucose and fructose) increased by 44.4 % in plants treated with the application of 1.5 g L^-1 of Lithothamnion sp. + 1.5 g L^-1 of A. platensis. Moreover, non-reducing sugars (e.g., sucrose) in plants treated with A. platensis were 92.8 % higher than in the control. At harvest (Figure 4b), tubers from the 1.5 g L^-1 of Lithothamnion sp. + 1.5 g L^-1 of A. platensis treatment exhibited a 66.3 % increase in total sugars, when compared to the control.

In potato cultivation, auxin is important in the initiation, growth and sprouting of potato tubers (Wadas & Dziugiel 2019), and is dependent on carbohydrate status (Kolachevskaya et al. 2019). In addition, the number of tubers per plant is a yield component in potato crops (Prajapati et al. 2016).

At harvest, 1.5 g L^-1 of Lithothamnion sp. + 1.5 g L^-1 of A. platensis and A. platensis (1.5 g L^-1)-treated plants exhibited 40 and 38 % increases in number of tubers (Figure 5a), respectively. Potato yield (Figure 5b) at 1.5 g L^-1 of Lithothamnion sp. + 1.5 g L^-1 of A. platensis (1.5 g L^-1)-treated plants was 82 % higher than in the control. Similarly, potato plants treated with foliar applications of the microalga Asterarcys quadricellulare obtained a higher sugar content, increased chlorophyll and greater potato yield (Cordeiro et al. 2022). These treatments act as stimuli for photoassimilate translocation from source (leaves) to sink (tubers) and showed an important role in increasing plant growth and yield.

The obtained results may be explained by a complex metabolic response enhanced by the algae combination. The synergistic effect of the calcareous algae and cyanobacteria mixture was demonstrated in 1.5 g L^-1 of Lithothamnion sp. + 1.5 g L^-1 of A. platensis, exhibiting an auxin-like effect (Table 1) due to the humic acid in Lithothamnion sp. (Amatussi et al. 2020, Ramos et al. 2023). In addition, the possible changes in polyamine metabolism, linked to increased plant growth and yield (Mógor et al. 2017, Chen et al. 2019), along with the cytokinin-like behavior observed following A. platensis biomass applications (Figure 1c), may have contributed to enhanced potato plant growth.

The positive effects on plant growth with the combined use of micronized Lithothamnion (Amatussi et al. 2020, Mógor et al. 2021) and Arthrospira platensis (Mógor et al. 2017) may be a synergistic blend of bioactive compounds that promotes growth and increases potato yield in an environmentally-friendly manner.

CONCLUSIONS

• 1. The bioactivity of micronized Lithothamnion L. and the Arthrospira platensis cyanobacteria was demonstrated in Solanum lycopersicum, Cucumis sativus and Vigna radiata bioassays. Foliar applications of the Lithothamnion sp. and A. platensis combination increased the growth of potato plants, stimulating their chlorophyll index, number of tubers, tuber sugar content and yield;

• 2. The beneficial effect of foliar application of micronized Lithothamnion (1.5 g L^-1) combined with lyophilized A. platensis biomass (1.5 g L^-1) on potato crops is a novel natural input to sustainably improve yield.

ACKNOWLEDGMENTS

The authors are grateful to Ely Cristina Negrelli Cordeiro (in memoriam), for her assistance with the study; and the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (Capes), for the doctoral scholarship awarded to the first author (Finance code 001).

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• Editor:
  Luis Carlos Cunha Junior

Publication Dates

• Publication in this collection
  04 Aug 2025
• Date of issue
  2025

History

• Received
  19 Feb 2025
• Accepted
  28 Apr 2025
• Published
  05 June 2025