The research team set out to test whether extracts from the seeds of this hardy savanna tree could control Colletotrichum capsici, the fungus responsible for cowpea anthracnose. In Cameroon, the disease is a major driver of yield losses estimated between 45 and 85 percent, and farmers typically respond with synthetic chemical pesticides. Those products, while effective, carry well-documented drawbacks: they can be costly for smallholder farmers, and their intensive use raises concerns about environmental contamination and risks to human and animal health. Biopesticides derived from locally available plants offer a biodegradable, low-toxicity alternative, and the desert date tree has a long history of biological activity, with prior studies attributing insecticidal, fungicidal, antimicrobial, and vermicidal properties to its bark, roots, and seeds.

The trials took place in Akonolinga, in agro-ecological zone V of Cameroon, a forest zone with bimodal rainfall where the sub-equatorial climate delivers roughly 1,633 millimeters of rain per year across two rainy seasons, with average temperatures of 23 to 27 degrees Celsius and humidity around 80 percent. The site, left fallow for four years, sits on acidic, lateritic, sandy loam ferralitic soils. Researchers from the study worked with two improved cowpea varieties supplied by the Institute of Agricultural Research for Development: V1, called Tiligré, a 70-day cycle variety, and V2, Lori 24-130, which is notably resistant to insect pests. Both varieties carry strong yield potential of 1,500 to 2,000 kilograms per hectare.

The experimental design was a split-plot layout with four replicates spread over 400 square meters. The two varieties formed the main plots, while five treatments occupied randomized sub-plots: an untreated control, an aqueous seed extract, an acetone extract, a methanol extract, and a synthetic fungicide containing 80 percent maneb. Each experimental unit measured roughly 3 by 2 meters and contained three rows sown at 80 by 40 centimeter spacing. The trials ran across two growing campaigns, in 2020 and 2021, allowing the team to assess consistency under natural field conditions.

Preparing the extracts was a hands-on process. Mature desert date fruits were collected beneath the trees, stripped of their outer layers by soaking, sun-dried, and crushed to obtain the kernels. The almond-like seeds were then milled into powder. For the aqueous extract, 500 grams of powder macerated in 5 liters of water for at least 24 hours, producing a 100 gram per liter solution that was filtered through muslin cloth and loaded into a backpack sprayer with powdered soap as a wetting agent to improve adhesion to plant surfaces. The organic extracts required macerating 500 grams of powder in 2 liters of acetone or methanol at 70 degrees Celsius for 48 hours, followed by filtration and concentration in a rotary evaporator until essential oils were obtained. All extracts were diluted at a rate of 7 milliliters per liter of water before application. The pathogen itself was confirmed by culturing infected pods on potato dextrose agar and examining the fungus microscopically, where C. capsici reveals its signature gray mycelial mass, black bristles protruding from conidial masses, and unicellular, hyaline, falcate conidia.

The results were striking. By nine weeks after sowing in the 2020 campaign, disease incidence in untreated control plots climbed to 75.38 percent for Tiligré and 76.01 percent for Lori 24-130. In plots treated with the aqueous extract, incidence fell to 20.91 and 28.24 percent respectively, while acetone extract plots recorded 22.75 and 29.28 percent. The synthetic fungicide still led with 14.6 and 14.19 percent. But in the 2021 campaign, the story shifted: the aqueous, acetone, and methanol extracts all outperformed the fungicide, recording incidence as low as 19.13, 19.25, and 17.93 percent for Tiligré, compared with 25.54 percent for the maneb treatment. Control plots reached 79.06 percent. All differences were statistically significant at P less than 0.001 across varieties, treatments, and their interaction.

Severity, the degree to which leaves, stems, and pods were attacked, followed a similar trajectory. In 2021 at nine weeks after sowing, aqueous extract plots recorded severity of just 10.6 percent for Tiligré and 20.48 percent for Lori 24-130, acetone plots 12.2 and 12.3 percent, and methanol plots 11.63 and 14.39 percent. Untreated plots suffered severity of 64.14 and 59.82 percent. The fungicide plots recorded 9.78 and 9.1 percent in 2020 and 27.03 and 9.47 percent in 2021, meaning the plant extracts matched or exceeded the chemical standard in the second season. The researchers suggest the mechanism likely involves biochemical compounds in the extracts forming complexes with polysaccharides and proteins on the outer layer of fungal cells, destabilizing cell membrane function and leading to pathogen death, though the precise mode of action remains unclear.

Yields told an equally compelling story. In 2020, aqueous extract plots produced 794.05 kilograms per hectare for Tiligré and 926.63 for Lori 24-130, compared with just 518.03 and 545.055 kilograms in control plots. Acetone and methanol extracts delivered similar gains, with acetone reaching 859.15 and 860.23 kilograms per hectare. In 2021, the pattern held, with aqueous extract plots yielding 852.97 and 935.79 kilograms per hectare and acetone plots 823.69 and 961.68, against control yields of 385.37 and 760.47. The fungicide still produced the highest yields in some plots, reaching 1,050.68 kilograms per hectare for Lori 24-130 in 2021, but the plant extracts closed much of the gap. Across both campaigns, the Lori 24-130 variety proved the most productive overall.

Multivariate analyses reinforced the picture. Principal component analysis captured 86.45 percent of total variability in 2020 and 91.27 percent in 2021 on the first two axes, consistently separating untreated control plots, which clustered near high incidence and severity, from treated plots, which grouped with favorable growth parameters such as leaf number, plant height, collar diameter, and high yield. Cluster analysis produced the same dichotomy, with control treatments isolated from all extract and fungicide treatments. The data show that the desert date seed extracts reduced disease and increased yields in the same way as the chemical fungicide during both campaigns.

The findings position Balanites aegyptiaca seed extracts as a viable component of integrated pest management for cowpea anthracnose. Because the tree is locally available across the Sahel and savanna zones, its seeds can be harvested, processed, and applied by the very farmers who need them, at a fraction of the cost of imported chemicals. The extracts are biodegradable and carry low toxicity for humans and the environment, addressing the core criticisms of synthetic pesticide overuse. As cowpea continues to feed millions across Africa’s arid and semi-arid belts, where few other crops thrive, a simple water-based extract from a desert tree could prove one of the most practical tools yet for keeping anthracnose at bay and harvests secure.

Subject of Research: agricultural science

Article Title: Bio-effectiveness of Balanites aegyptiaca (L.) Del. seed extracts against Colletotrichum capsici (Syd.) Butler & Bisby causal agent of anthracnose in cowpeas ( Vigna unguiculata (L.) Walps.) under natural conditions

Article References: Tize, T., Ngatsi, P. Z., Lontsi Dida, S. L., Njome Toka, A., Songwe Atindo, T., Ndongo, E. B., Sale Essome, C., & Ndongo, B. (2024). Bio-effectiveness of Balanites aegyptiaca (L.) Del. seed extracts against Colletotrichum capsici (Syd.) Butler & Bisby causal agent of anthracnose in cowpeas (Vigna unguiculata (L.) Walps.) under natural conditions. Innovations in Agriculture, 7, 1-9. https://doi.org/10.3897/ia.2024.131803

Image Credits: AI Generated

DOI: 10.3897/ia.2024.131803

Keywords: cowpea, anthracnose, Balanites aegyptiaca, biopesticide, Colletotrichum capsici, Cameroon, plant extracts, integrated pest management, food security, sustainable agriculture, Bio-effectiveness, Balanites