Improving okra performance through pollinator attractors

ABSTRACT

The vicinity of natural areas can enhance availability of pollinators and crop productivity. Considering the global reduction of pollinators and the global food insecurity, innovative strategies to enhance pollination and crop yield are important. Thus, we investigated the efficacy of using colored attractors of pollinators to improve okra yield. The use of pollinator attractors led to a significant increase in the length, volume, and weight of okra in comparison to plants without attractors, and notably larger when compared to plants without pollinator access. Although uncertainties remain regarding scalability and optimal implementation, our results emphasized the opportunity of the colored attractors, a low-cost intervention, to boost food productivity and alleviate food insecurity.

Key words
innovation; Abelmoschus esculentus ; yield; pollination

INTRODUCTION

The proximity of natural areas to cultivated lands can enhance crop productivity (Berger et al. 2023). The greater availability of pollinators is one of the causes (Klein et al. 2020), since it is common that cultivated plants require pollination services to food production (Murphy et al. 2022). Presently, the cultivation of highly productive plants depends on pesticides to control insect pests (Davidar and Carr 2015), but the same pesticides can affect negatively pollinating insects and contribute to pollinators decline in world (LeBuhn and Luna 2021), and crop yield losses (Sponsler et al. 2019).

Simultaneously, around 783 million people worldwide face chronic hunger (United Nations Environment Programme 2024). This relevant situation suits critical for science, technology, and innovation to create benefits for people from food productive systems (Fears and Canales 2023). Therefore, techniques as the modification of non-floral resources, habitats and floral characteristics (Mallinger and Prasifka 2017, Requier and Leonhardt 2020, Garratt et al. 2023) are crucial to maintain or increase crop yield. In this context, Suárez et al. (2022) tested the use of Christmas balls colored with ultraviolet attractive colors to increase pollinators and boosted effective fruiting in acerola orchards by 230%. This intervention, with a remarkably low-cost investment, offered a stimulating approach to fostering innovation, with potential to enhance agricultural productivity, and to mitigate global hunger (Tomich et al. 2019).

The okra Abelmoschus esculentus (L.) Moench is a malvaceous plant of African origin that was introduced during the colonial period in Brazil. It has great socioeconomic function, remarkably on small farms both for food supply and income generation (Adelabu and Franke 2023). Its flowers are hermaphrodites and commonly undergo autopollination, as well as cross pollination (Klein et al. 2020). Its fruit has high nutritional value, with a significant content of dietary fiber, as well as other nutrients such as magnesium, phosphorus, and zinc (Bawa and Badrie 2016). Pollination positively affects seed number, weight, length, shape, and nutritional quality of its fruits (Angbanyere and Baidoo 2014). Considering the vital role of pollination in agriculture, the chronic hunger worldwide, and the recognized nutritional value of okra, we employed pollinator attractors in okra cultivation to test the hypothesis that they could boost okra yield.

METHODOLOGY

This study was conducted in an okra plantation in Jequitibá, MG, Brazil, a region characterized by a seasonal tropical savanna climate, type Aw, according to the Köppen classification. The region average annual temperature is 22.1 C (± 5°C), and the average annual precipitation 1,340 mm. The rainy season starts in September and the dry one in May. In the okra plantation, the soil was tilled once to remove spontaneous plants from the area, and then tilled again to break up the clods and loosen the soil. The 52 rows each had 100 holes manually made and filled with cow manure. Planting was done with 1 kg of Santa Cruz 47 seeds, staggered between December 15 and 20, 2022. Urea fertilizer was applied 15 days later, and on February 18, 2023.

The sampling plants were determined by chance considering the spacing between sampling sets as 10 m. The first treatment consisted of seven sets of four plants that were not experimentally influenced (28 plants in total). The seven sets were spaced approximately 5 m between crop rows, and the four plants within each set were all within a 1-m radius. These plants were freely pollinated by wind, gravity, and organisms of the agroecosystem. One floral bud on such plant was marked with tape, and after 15 days the total buds could be checked for qualitative evaluation of fruit formation. The formation of okras was registered and, when formed, collected, and evaluated in the laboratory. Since buds and subsequently flowers had free access to pollinators in this treatment, it was called permitted pollinators or PER (Fig. 1a).

Figure 1
Pictures illustrating (a) the treatments permitted pollinators access; (b) excluded pollinators; (c) attractors of pollinators; (d) the position of the analyzed measures in okras of a plantation in the municipality of Jequitibá, MG, Brazil.

Another seven sets of four plants, obtained in the same manner, comprised the second treatment. This treatment excluded pollinator access to floral buds using a 1-mm mesh nylon mosquito screen. Thus, effective fruiting could be affected by the exclusion of pollinator organisms, and the treatment was called excluded pollinators or EXC (Fig. 1b).

In the third treatment, the pollinator attractors were used. They consisted of two 8-cm diameter Christmas balls, painted with an ultraviolet blue paint, Colorgin Luminosa (Sherwin-Williams do Brasil, Brazil). The aerosol paint has high chemical stability according to the manufacturer, with no significant toxicity. The balls were affixed near the floral bud of a central plant in each plant set. The same plant arrangement of anterior treatments was made, and this treatment was called attracted pollinators or ATR (Fig. 1c). All the marked plants were revisited and checked for fruit formation 15 days later. The presence of fruit was recorded, and in the harvested fruits weight (g), length (mm), volume (cm3), equatorial diameter (mm), and polar diameter (mm) were measured (Fig. 1d).

Potential pollinating insects were registered by qualitative observations on okra flower visitors. Our approach involved capturing images after casual observations of the flowers. Taxonomic identification was done at the lowest level as possible to enrich our understanding of the potential effects of attractors.

Using Statistica 13.3 software (license JPZ804I376009FA-9), the dependent variables effective fruiting, weight, length, volume, equatorial diameter, and polar diameter of okra were evaluated for the three treatments, PER, EXC, and ATR. To avoid problems with normality and no linear relationship between variables and the treatments, due to some uncomplete data, we used a one-way analysis of variance assisted by generalized linear model (GLM). The generalization of the linear model permits to work with any type of distribution of residuals. Here, the GLM was computed using the maximum likelihood parameters estimation, with sigma-restricted parametrization, and the type VI sums of squares method. For all studied variables, Eq. 1 was used:

$Y_{ij}=\mu +T_i+e_{ij}$ (1)

where:Y_ij: the dependent variable (effective fruiting, weight, length, volume, equatorial diameter, and polar diameter); μ: the overall mean; T_i: the fixed effect of PER, EXC, and ATR treatments; e_ij: the residual error term of model considering normal distribution with mean 0 and variance σ² (N (0,σ²)).

Posterior comparisons among treatments were conducted using 95% confidence intervals.

RESULTS

Qualitative observations of pollinators enabled the identification of bees, butterflies, wasps, houseflies, and beetles. The two hymenopteran European honeybee Apis mellifera (Linnaeus, 1758), and stingless bee Trigona cf. spinipes (Fabricius 1793), and the coleopteran cucurbit beetle Diabrotica speciosa (Germar 1824) were the most common insects (> 90% of observations) in flowering plants.

Effective fruiting was the same for plants of PER and ATR treatments, but it was about 22% lower in EXC treatment, when pollinators had their access excluded from the flowers (F_{(2, 18)} = 4.650; p = 0.024; Fig. 2a). The weight of okra was equal between PER and EXC treatments, but it was higher in the ATR treatment, as expected by hypothesis. Okras obtained from ATR had 38% higher weight in relation to those obtained from PER and 94% higher than those obtained from EXC (F_(2,87) = 5.551; p = 0.005; Fig. 2b). Regarding to the okra length, those collected from ATR were 24% larger than those from PER, and 70% larger than those collected from EXC treatment and the plants from PER treatment had okras 36% larger than those from EXC (F_(2,87) = 9.896; p < 0.001; Fig. 2c). For volume measurement, okras from ATR were 26% larger than okras from PER and 77% larger than okras from EXC, with okras from PER 40% larger than those from EXC (F_(2,87) = 5.682; p = 0.004; Fig. 2d). There were no differences in polar (F_(2,87) = 8.907; p < 0.001; Fig. 2e) and equatorial (F_(2,87) = 5.459; p = 0.005; Fig. 2f) diameters between okras from ATR and PER, but okras from EXC were 20% smaller.

Figure 2
Presentation of variables obtained from the treatments PER (free pollinators access), EXC (excluded pollinators), and ATR (attractors of pollinators) in an okra plantation of the municipality of Jequitibá, MG, Brazil: mean of the (a) effective fruiting of okra flowers, (b) the weight, (c) length, (d) volume, (e) equatorial, and (f) polar diameter of okras. Dispersion measures around means represent confidence intervals of 95%.

DISCUSSION

Nesting sites, floral resources, and spatial and temporal heterogeneity are crucial for maintaining pollinators in landscapes and enhance fruit production and quality (Martínez‐Núñez et al. 2022, Hulsmans et al. 2023). Conversely, pollinator biodiversity continues to decline worldwide, posing risks to food production (Stout and Dicks 2022). Thus, the creation of techniques for safeguarding and rejuvenating pollinators is of utmost importance to ensure food provision (van der Niet et al. 2023), and our results indicated that pollinator attractors may boost okra 24% in length, 26% in volume, and 40% in weight compared to those from flowers normally accessible to pollinators. When compared to okra obtained without pollinator access, these differences increased to 70, 77, and 94% respectively.

Considering a producer in Brazil achieving the yield of 15 ton.ha^-1 and experiencing a 40% increase in okra weight, their productivity would rise to 21 ton.ha^-1. Brazil has seen a significant increase in the number of people experiencing food insecurity, rising from 19 to 33 million between 2020 and 2022 (Rede PENSSAN 2022). So, this gain of 6 ton.ha^-1 is an encouraging step towards addressing global food insecurity and its consequences. From the producer’s perspective, to attract pollinators can enhance financial gains: the price paid for okra at some of the main trading points in Brazil, e.g., Companhia de Entrepostos e Armazéns Gerais de São Paulo (available at https://ceagesp.gov.br/guia-ceagesp/quiabo), adjusts according to the seasonality, length, and fruits’ quality. On April 1, 2024, the average price fluctuated between US$ 0.89 and US$ 1.91 per kg. This implies that a producer who harvests 15 ton.ha^-1 should aim for a gross profit ranging from US$ 13,350 to US$ 28,650 per hectare, but, considering the gains with attractors, the profit can jump to $18,690 going up to US$ 40,110.

Our findings demonstrate positive impacts on fruit yield and financial gains for producers, but they are dependent on pollinators existence in agroecosystem. This underscores the importance of preserving natural areas, which serve as habitats and resources for pollinators (LeBuhn and Luna 2021). The National Resources Conservation Service of the U.S. Department of Agriculture advocates methods to boost native bee populations, e.g., preserving riparian vegetation, implementing cover cropping, reducing insecticide usage (Xerces Society Pollinator Resources and U.S. Department of Agriculture, 2005). The European Union has also issued a guide and recommends, e.g., enhancing habitats, providing food sources, and creating nesting sites (Keenleyside and Underwood 2020). In Brazil, for at least 20 years, similar actions have been recommended, e.g., the diversification of crops, the improvement of food sources and nesting sites (Imperatriz-Fonseca et al. 2006), and they are included in more recent studies (BPBES and REBIPP 2019). Such efforts inherently produce significant gains in the production of food reliant on pollinators and may contribute to the increased availability of pollinators in the presence of attractors.

The cost-effectiveness of the innovation used in this study renders it suitable for widespread adoption, potentially driving technological advancements in agriculture (Tomich et al. 2019). Nonetheless, uncertainties persist regarding the scalability of attractors, including questions surrounding the optimal size and quantity needed to enhance pollination, as previously pointed by Suárez et al. (2022). However, albeit further research is needed to elucidate its full potential, it is plausible to assert that colored attractants for pollinators represents an innovative approach to boost okra yield, a plant of high nutritional value (Bawa and Badrie 2016), and cultivated in practically all of Brazil.

CONCLUSION

The use of pollinator attractants, developed with non-toxic ultraviolet paint, allows for an increase in the length (24%), volume (26%), and weight (40%) of okra. This increase is even greater when compared to okra obtained in the absence of pollinators, reaching a 94% gain in weight. Such gains illustrate the potential to increase food production, boost financial gains for producers, and encourage the preservation of habitats and resources for pollinators, as even with the presence of attractants, pollinators need to be available in the landscape for these beneficial effects to be realized.

ACKNOWLEDGMENTS

Authors thank to Pró-Reitoria de Pesquisa e Pós-Graduação of Universidade Federal de São João del-Rei for scholarship funding for Correa RLS.

• How to cite: Correa, R. L. S., Carvalho, E. C. M., Latini, A. O., Dias, I. P., Reis, G. J. and Silva, M. L. A. (2025). Improving okra performance through pollinator attractors. Bragantia, 84, e20240139. https://doi.org/10.1590/1678-4499.20240139
• FUNDING
  Not applicable.

DATA AVAILABILITY STATEMENT

The data of this study are available on request from the corresponding author.

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Edited by

• Section Editor:
  Gabriel Constantino Blain https://orcid.org/0000-0001-8832-7734

Publication Dates

• Publication in this collection
  03 Feb 2025
• Date of issue
  2025

History

• Received
  24 June 2024
• Accepted
  10 Dec 2024