The field trials were carried out in the locality of Akonolinga, located in agro-ecological zone V of Cameroon (forest zone with bimodal rainfall). The geographical coordinates of the site recorded using a GPS (Garmin model Etrex Legend HCX) are: 03°48.136'N, 012°15.518'E, for an average altitude of 671 m (accuracy of ± 3 m). The site was left fallow for four years with the previous crops: cassava, peanuts, cocoyam and plantain. The climate of Akonolinga is a sub-equatorial climate of the Congo-Guinean type, with two dry seasons alternating with two rainy seasons. The average rainfall is 1633 mm/year, divided into a major rainy season, from March to June, and a short rainy season, from September to November. The average annual temperature is relatively constant, around 23 to 27 °C. The average annual humidity is around 80%. The soil belongs to the group of ferralitic soils of acidic, lateritic, sandy loam and marshy rocks. It is characterized by outcrops of the hardened horizon in the form of slabs or gravel, which sterilize large areas of land (Moudingo 2007).

The plant material consists of the seeds of two improved cowpea varieties. The V1 variety: Tiligré (KVX-775-33-2G), whose development cycle is 70 days, and the V2 variety (Niébé Lori 24-130), very resistant to attacks by insect pests, supplied by Institute of Agricultural Research for Development (IRAD) of Maroua and the choice of these varieties is linked to their good yield potential (1500–2000 kg ha^-1) (Ouedraogo et al. 2011). As a biopesticide plant, the seeds of Balanites aegyptiaca (almonds) were used for the tests.

The split-plot experimental design with four replicates was used with two varieties constituting the main plots randomly in replication (V1: Tiligré) and V2: Lori 24-130) and five treatments represented sub-plots randomized within the main plot (T0: control; T-AqE: aqueous extract; T-AcE: acetone extract; T-ME: methanol extract; T-Fong: synthetic fungicide containing 80% of maneb). Each block is composed of 10 sub-plots, for a total of 40 experimental units. The experimental units, which measure approximately 3 m × 2 m, are separated from each other by paths of 0.5 m. The blocks, for their part, are 1 m apart from each other. Each experimental unit was made up of 3 rows, sown with a spacing of 80 cm × 40 cm, three seeds per plot (Lalsba and Drabo 2017; Traoré et al. 2019). The experimental design was spread over an area of 400 m².

The aqueous extract of Balanites aegyptiaca was prepared according to the method proposed by Zhang et al. (2018). The mature fruits are collected under the desert date tree. They were freed of their epicarps and mesocarps by soaking in water. After drying in the sun, the fruits containing the endocarp were crushed manually using a hammer against a stone to obtain the kernels. Using an electric mill, the almonds were crushed, and 500 g of almond powder were weighed using a precision balance from the “Sartoruis Ag Gottinguen” brand and macerated in 5 L of water for at least 24 hours (Gayathri and Sahu 2015). After filtration using a muslin cloth, the solution obtained with a concentration of 100 g L^-1 was poured into a 15 L backpack sprayer, to which 10 g of powdered soap was added as a wetting agent, to reinforce the adhesion of the products to the parts of the plant to be treated and limiting their leaching by rainwater. The mixture thus obtained is ready for the treatment of the 8 sub-plots concerned for this extract. The preparation of organic extracts was made by maceration of the almond powder of Balanites aegyptiaca seeds, at a rate of 500 g in 2 L (concentration: 250 g L^-1) of Acetone and Methanol at 70 °C for 48 hours. The products obtained were filtered using filter paper and concentrated in a Rota-vapor (Büchi R-200 Rotary Evaporator at 60 °C), until the essential oils were obtained. The extracts obtained were placed in a desiccator to eliminate the remaining solvent. Subsequently, they were weighed and stored in the refrigerator at 4 °C until use (Gata-Gonçalves et al. 2003). Balanites aegyptiaca seed extracts were diluted at a rate of seven (7) mL for 1 L of water, 35 mL for 5 L of water to treat the 8 sub-plots concerned (Dabiré-Binso et al. 2008). Fungicide with active ingredient 80% Maneb was used following the dose recommended by the manufacturer 3.33 g L^-1. The fungicide Plantineb 720 WP with active ingredient 80% Maneb was used.

The identification of pure isolate was made by observing the cultural and microscopic characteristic of Colletotrichum capsici and his comparison to a reference C. capsici isolate. In culture on PDA culture medium, C. capsici has a gray mycelial mass characterized by an absence of sclerotia. Under the microscope, the acervuli are made up of conidiophores producing conidia and numerous long, black brown to black bristles protruding from the conidial mass. The conidia are unicellular, hyaline, fusoid with rounded and slightly hooked ends, most often falcate. The identification key r described by Sérémé et al. (2001) was used.

Incidence is the proportion of diseased plants within a given experimental unit, independently of the severity of the attack on each plant; the number of plants attacked by diseases out of the total number of plants in the plot. The incidence is evaluated every two weeks interval from the first week of application of the treatments, on the 10 plants labeled randomly in each experimental unit (leaves, stems, pods) (Aroga 2007). The incidence is determined according to the formula of Tchoumakov and Zaharova (1990).

$\mathrm{I}(\%)=\frac{\mathrm{Npa}\times 100}{\mathrm{Npt}}$

Where I (%) : is the incidence of diseases in the plot expressed as a percentage, Npa: is the number of plants attacked by diseases in the plot and Npt the total number of plants in the plot.

Severity is the degree to which an organ or entire plant is attacked by a disease. Severity is assessed visually every two weeks interval as soon as the first symptoms of the disease appear, on the 10 plants randomly labeled in each experimental unit (leaves, stems, pods). (Aroga 2007). Severity is determined using the formula proposed by Tchoumakov and Zaharova (1990).

$\mathrm{S}(\%)=\frac{\sum \left(\mathrm{ab}\right)}{\mathrm{N}}\times 100$

Where: S (%) is the severity, is the sum of the products of the number of diseased or attacked plants (a) by the degree of infection (b) given in % and N is the number of sick or attacked plants.

The production parameters are measured considering the number of mature pods at 80 days after sowing (DAS) for the 2 varieties of cowpea per labeled plant and per experimental unit of each block. The grains obtained after shelling the pods were dried and weighed, then the weight was determined in each elementary plot according to the treatments and varieties. The values obtained were subsequently estimated per hectare using the formula from Zakari (2003).

$\mathrm{Yeild}\mathrm{k}\mathrm{g}/\mathrm{h}\mathrm{a}=\frac{\text{weight/plot (g)}}{\text{Surface parcellaire}\left({\mathrm{m}}^2\right)}\times \frac{10000{\mathrm{m}}^2}{1\text{ha}}\times \frac{1\text{kg}}{1000\text{g}}$

The data from field observations were subjected to one-way and two-way ANOVA using R software version 4.0.1. Then multiple comparisons of means were determined on data, and the Tukey test was used to separate them when the analysis of variance was significant. Principal component analysis (PCA) and cluster were performed using RStudio interface between varieties, treatments, epidemiological parameters (incidence and severity), and yield, with a view to detecting the correlation between varieties and treatments less susceptible to anthracnose.

In PDA medium, C. capsici has a gray mycelial mass characterized by an absence of sclerotia. This species of Colletotrichum produces rounded or elongated acervula. From these acervuli arise abundant septate brown-black bristles, having a lanceolate terminal cell or having the same diameter as the central cells, numerous small black dots corresponding to the fruiting bodies, isolated or in groups (the acervuli). Under the microscope, the acervuli are made up of conidiophores producing conidia and numerous long, black brown to black bristles protruding from the conidial mass. The conidia are unicellular, hyaline, fusoid with rounded and slightly hooked ends, most often falcate (Fig. 1).

Figure 1. 

Microscopic and macroscopic observation of the conidia of Colletotrichum capsici; A. Pure culture; B. Conidia.

During the 2020 and 2021 campaigns, a significant difference at (P < 0.001) is recorded between the different treatments for both varieties of cowpea. In 2020, the plot treated with aqueous (T-AqE) and organic extracts of B. aegyptiaca seeds reduced the incidence of anthracnose at 5, 7 and 9 weeks after sowing (WAS). However, at 9 WAS, the disease incidence rate is higher in the control plots (T0: 75.38% and 76.01%) respectively for V1 and V2 and lower in the plots treated with the aqueous (T-AqE: 20.91% and 28.24%) and acetone (T-AcE: 22.75% and 29.28%) extract, respectively for V1 and V2 during the 2020 campaign. Fungicide treatment (T-F: 14.6% and 14.19%) recorded lower disease incidence respectively for V1 and V2 (Table 1).

As for the 2021 campaign, the plots treated with aqueous (T-AqE: 19.13% and 20.81%); acetone (T-AcE: 19.25% and 22.21%) and methanol (T-ME: 17.93% and 24.15%) extract recorded the lower incidence of anthracnose compared to the control treatment which recorded the higher incidence (T0: 79, 06 and T0: 72.43%) respectively for varieties V1 and V2 (Table 1). Fungicide treatment (T-F: 25.54 and 37.6%) recorded a higher incidence of anthracnose than B. aegyptiaca seed extracts respectively for V1 and V2 at 9 WAS.]

A significant difference was recorded between treatments and varieties (P < 0.001) during 2020 and 2021 campaigns (Table 2). Thus in 2020 campaign at 7 WAS, the rate of anthracnose severity was more reduced in plot treated with B. aegyptiaca seeds extract (T-AqE: 22.7%; T-AcE: 25.24% and T-ME: 27.69%) compared to the control plot which recorded the highest severity (T0: 49.83%) for variety V1. For V2 variety at the same period, the rate of anthracnose severity in the control plot was higher (T0: 44.31%), compared to the plot treated with aqueous (T-AqE: 15.61%), acetone (T-AcE: 22.44%) and methanol (T-ME: 22.75%) extracts. But fungicide treatments recorded the higher rate of severity due to anthracnose (T-F: 19.63% and 18.8%) for V1 and V2 respectively. During the 2021 campaign at 9 WAS, plot treated with aqueous (T-AqE: 10.6% and 20.48%), acetone (T-AcE: 12.2% and 12.3%) and methanol (T-ME: 11.63% and 14.39%) extracts recorded the lower rate of disease severity compared to the control plot (T0: 64.14% and 59.82%), respectively for the V1 and V2 variety (Table 2).

During the two campaigns, a significant difference (P < 0.001) was recorded between the treatments × varieties (Table 3). In the 2020 campaign, plot treated with aqueous extract, acetone and methanol recorded a better yield respectively (T-AqE: 794.05 ± 3.33 kg.ha^-1 and 926.63 ± 1.67 kg.ha^-1); (T-AcE: 859.15 ± 4.52 kg.ha^-1 and 860.23 ± 1.04 kg.ha^-1) and (T-ME: 804.55 ± 2.91 kg.ha^-1 and 866.15 ± 1.82 kg.ha^-1) compared to the control plot (T0: 518.03 ± 3.25 kg.ha^-1 and 545.055 ± 1.95 kg.ha^-1) which recorded the lower yield, respectively for V1 and V2 (Table 3). During the 2021 campaign, the yield was higher in the aqueous extract treatments (T-AqE: 852.97 ± 1.85 kg.ha^-1 and 935.79 ± 2.09 kg.ha^-1), at acetone (T-AcE: 823.69 ± 1.78 kg.ha^-1 and 961.68 ± 1.56 kg.ha^-1) and methanol (T-ME: 658.77 ± 1.11 kg.ha^-1 and 885.74 ± 2.04 kg.ha^-1) compared to the control plot (T0: 385.37 ± 1.82 kg.ha^-1 and 760.47 ± 1.34 kg.ha^-1) which recorded the lower average yield respectively for the V1 and V2 varieties. At the end of the observations from the point of view of yield and other parameters evaluated, the most productive variety is the V2 variety (cowpea Lori 24-130).