Efficacy of Intercropping Aromatic Plants and Spraying Volatile Oils on Population Density of The Main Pests Attacking Common Bean (Phaseolus Vulgaris L.) and Their Effects on Some Crop Parameters

INTRODUCTION

The common bean, Phaseolus vulgaris (Fam.: Fabaceae), is one of the most important edible leguminous crops widely grown in all geographical areas, including South America, Europe, and Africa (Bevilacqua et al., 2021). It is the second most important source of protein and the third most important source of calories in the human diet. It is a valuable source of carbohydrates, dietary fiber and phytonutrients, and provides neuroprotective properties (Jha et al., 2015). It serves as a critical plant protein source of vitamins, zinc, iron, and fiber for urban and rural areas, and it is a staple food crop in many developing countries due to its high nutritional value. It is cultivated for fresh and dry pods for local consumption and exportation (Abdou et al., 2019). Common bean is attacked by a vast array of insect pests such as flea beetles, leaf miners, stem fly, aphids, white fly, thrips, defoliators and spider mites in field conditionsand is causing considerable economic damage (Amit et al., 2017). The whitefly, Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae), is a highly polyphagous pest of many agricultural and horticultural crops. It causes extensive economic damage directly by feeding on the plant foliage, resulting in the weakening of plant growth and causing chlorosis (Perring et al., 2018). B. tabaci decreases the photosynthetic rate of a plant through excretion and accumulation of honeydew during feeding, thereby reducing plant growth and marketable produce (Sani et al., 2020). B. tabaci also acts as a super vector and transmits more than 300 deadly plant viruses (Kanakala and Ghanim, 2015). Another pest which causes damage to common beans, is the two-spotted spider mite, Tetranychus urticae Koch) Acari: Tetranychidae). This is a cosmopolitan pest mite species that feeds on a wide variety of plants (Liburd et al., 2020). This mite feeds by piercing leaf tissues and structures and infects the host plant, causing destruction of chloroplasts and consequently reduced chlorophyll (Ziaee and Nikpay 2016). Repeated application of pesticides, in addition to polluting the environment and degrading the natural environment, has caused B. tabaci to develop resistance to many pesticides (Ail-Catzim et al., 2015). Therefore, there is a need to develop biopesticides or natural enemies with biopesticides to control airborne and field vegetable pests and spider mites. Today, the latest control technologies and appropriate methods are used to ensure effective management of environmental problems both in vitro and in the field (Elnahal, et al., 2022). Natural plant products and their derivatives have great promise for the advancement of human well-being and the creation of sustainable food production systems. These products have been around for a while as insect repellents and antimicrobials (da Silva and Ricci-Júnior, 2020). In both developed and developing countries, there is a growing interest in using plant-based essential oils as an alternative to conventional pesticides. The global bio insecticide market is expected to reach $4.6 billion by 2025, up from $2.2 billion in 2020 (Mossa, 2016). Essential oils are complex mixtures of different bioactive chemicals, including monoterpenes, sesquiterpenes, and their oxygenated derivatives, that are volatile secondary metabolites of plants (Mossa, 2016). Multi-cropping is an additional technique for enhancing the agricultural ecosystem. It involves growing two or more crops in one field using ecological principles (Petrie and Bates, 2017). The primary distinctions between mono- and multi-cropping farming are the duration of the growing season and the biological and agronomic traits of the crops being grown. Multi-cropping lowers the number of pathogens and weeds as well as nutrient loss into deeper soil layers (Lizarazo et al., 2020). Therefore, the likelihood of reducing the need for pesticides and fertilizers increases with the strength of the ecosystem. In the meantime, mixed-cropping systems might produce more, have better grain quality, and be more resilient to pests and illnesses. (Meijuan Li et al., 2019). Thus, the aim of the current study was to assess the effects of intercropping sweet basil (Ocimum basilicum L.) and geranium (Pelargonium graveolens L.) plants and spraying their essential oils against the population density of major pests on common bean plants like B. tabaci and T. urticae. In addition, the best treatment for managing these pests should be selected from those that have been tried and proven, as well as the host's appropriateness, to ensure safe use within the framework of integrated pest management. Additionally, consider the impact of the tested treatments on common bean yield, fruit physical metrics, and growth characteristics.

MATERIALS AND METHODS

Experimental Design

                 The study was conducted at the Agricultural Experiment Station, Faculty of Agriculture, Cairo University, Giza, Egypt. In a randomized complete block design was applied, (RCBD) in two consecutive seasons of 2022 and 2023 to study the impact of intercropping sweet basil (O. basilicum L.) and geranium (P. graveolens L.) plants on the density of primary pests on common bean plants, P. vulgaris L. var. Morgan, in field conditions. The common bean seeds culture (P. vulgaris L. var. Morgan), purchased from the Horticulture Research Institute, Agric. Res. cent., Egypt, was planted in the first section of the experimental intercropping area during the last week of September 2022 and 2023 at a depth of 5 cm. Basil and geranium plants (15–20 cm in height) grown in plastic pots were purchased from the greenhouse nursery at the Agricultural Experiment Station when the seedlings were at the four to six true leaves stage, and they were transplanted in the field in October 2022 and 2023. The experiment included 12 plots, each measuring 1 m by 12 m, with 2 m between each two plots plot for the intercropping areas of geranium and sweet basil. Common bean plants were planted into two rows 40 centimeters apart. Each intercropping plot's outer boundaries were planted with sweet basil and geranium plants, spaced 30 cm apart from the common bean and 40 cm apart in rows (Ben Issa, et al., 2017).  Common bean solitary culture, common bean intercropping with basil, and common bean intercropping with geranium are the three planting methods that were alternately represented throughout the six plots of each (Figs. 1 and 2). The plots were hand-weeded and subjected to weekly flood irrigation, following the custom of the area. In every plot, green bean plants in the vegetative growth stage received 150 kg/ha of nitrogen fertilizer. There was not any pesticide used in the trials.  Essential oils of geranium and sweet basil, which were purchased from the National Research Center's oils extract section, were sprayed during the second phase of the experiment. To create O/W emulsion formulations, oils are typically mixed with an emulsifying agent to enable the oil to mix with water. This mixture is typically employed at a ratio of roughly 2 milliliters to 1 litter of water. Two sprays were applied to the treatment: the first on October 15 and the second on November 12. To avoid treatments that overlap, untreated rows were employed to divide the treated plots from one another. The prepared concentrate was sprayed into a 10-liter backpack sprayer right before each treatment. Every experimental plot was subjected to the same standard agricultural techniques.

                      Fig. 1. Schematic representation of the experimental area.

Identification of the essential oil by GC-MS:

         Gas chromatography-mass spectrometry (GC-MS) analysis was used to determine the chemical composition of basil oil and geranium oil. GC-2010 Shimadzu capillary gas chromatography was directly coupled to the mass spectrometer system, and the identification of the GC peaks corresponding to the components of the essential oil was based on computer matching with the NIST NBS54K library, direct comparison of the retention times and mass spectral data was done with those for standard compounds, and comparison of the fragmentation patterns of the mass spectra was done with those reported by Adams (1995).

Sampling technique:

            Ten leaves (upper, middle, and lower) were randomly selected from various plant levels and picked up from each treatment after three weeks of cultivation for common bean plants. The leaves were then kept in closed paper bags and brought to the Plant Protection Department's laboratory on the same day for analysis and identification using a stereomicroscope. For all treatments, the sampling was done at intervals of seven days up to ten weeks.

The analysis of chlorophyll content in the leaves was conducted as follows:

 A pigment used in photosynthetic processes and the source of colour for plants, chloroplasts create chlorophyll. By absorbing sunlight, it also makes it possible for photosynthesis to proceed effectively. Chlorophyll comes in a variety of forms; After 75 days, the amount of photosynthetic pigments (chlorophyll measured in mg/g.) in leaves was removed and concentrated. Chlorophyll content was recorded by SPAD (Soil-Plant Analyses Development) meter (SPAD model 502, Minolta Co, Osaka, Japan) (Shibaeva, et al., 2020).

Fig.2. A. Intercropping with geranium, B Intercropping with basil, and C. Sole culture of common bean plants

Yield and its components

            Over the course of the two ensuing fall seasons (2022 and 2023), the yield of common beans in each treatment was observed. Plant height and pod length (measured in centimeters) and the number of leaves and branches were determined. The following method was used to calculate the pods' total yield: At harvest yield of fruit per plant (g) was determined. After calculating the early yield per Fadden, the total yield was split into two groups: marketable yield (ton/fed) and unmarketable yield (ton/fed). From them, the overall yield was computed.

Statistical analysis

             Data were statistically analyzed by one-way analysis of variance as described by Snedecor & Cochran (1967). Mean values were tested for differences using Tukey’s test with P ≤ 0.05 level of significance for each season

RESULTS

1. Essential Oil Composition

      Tables 1 and 2 present the essential oil compositions extracted from the two aromatic plants using GC-MS. Thirteen elements were found in the geranium oil. Citronello (28.99%), Geraniol (14.8%), Alpha-Pinene (10.18%), Selinenol (9.69%), and Citronellyl Formate (9.60%) were the principal volatile components of geranium (Table 1). Eleven components were found in the sweet basil oil according to the predominant volatile constituents identified in basil were linalool (77.96%) and berneol (16.56%) (Table 2).

2. Effect of treatments on populations of B. tabaci nymphs.

              The weekly population of B. tabaci nymphs infesting common bean plants is displayed in Figs. 3 and 4. There was significant variation in the weekly populations of B. tabaci nymphs in the monoculture of common bean in the two seasons and all tested treatments. In the first season, B. tabaci nymphs were found in high populations during the third, sixth, and eighth sampling weeks. In the second season, however, high populations of this insect were found in monoculture during the second and fifth sampling weeks. There were significant variances in the population density of B. tabaci nymphs for intercropped basil during weekly sampling in the 2022 season and the mean of the 2023 season. In the second season, low populations of B. tabaci nymphs were seen in intercropped geranium and geranium oil. The mean numbers of B. tabaci nymphs in the first season were 2.1, 3.6, 2.65, 2.57, and 15.18 nymphs/plant, for the intercropped basil, basil oil, geranium, and monoculture, respectively; in the second season, those numbers were 5.29, 3.68, 1.46, 1.42, and 11.08 nymphs/plant. The population numbers of B. tabaci nymphs varied significantly between tested treatments during the two seasons.

Table (1): Chemical constituents of Geranium oil, (Pelargonium graveolens L.) by (GC/MS) analysis

Table (2): Chemical constituents of sweet basil oil (Ocimum basilicum L.) by (GC/MS) analysis

2. Effect of the tested treatments on populations of T. urticae Koch

          The effects of intercropping with basil, basil oil, and geranium and geranium oil on T. urticae eggs and adults were investigated. The mean adult populations of T. urticae varied significantly between the two seasons for every treatment (Figs. 5 and 6). The average number of T. urticae adults in the first season were 8.13, 2.1, 0.0, 2.2, and 19.6 adults /plant for intercropping with basil, intercropping with geranium, geranium oil, and monoculture, respectively. The mean number of T. urticae adults were 6.28, 0.48, 0.0, 1.64, and 22.36 adults /plant for intercropping with basil, intercropping with geranium, geranium oil, and monoculture, respectively, in the second season (Fig. 6 and Table 3). 

 Lower numbers of T. urticae adults appeared in two seasons of intercropping with geranium, but the highest number of adults was observed in monoculture. The population of T. urticae eggs seemed to high in the first week of the two seasons, and then progressively dropped during the studied periods in the mono culture. For every tested treatment, there was a highly significant difference in the mean number of T. urticae eggs between the weekly populations (Fig. 7 and Table 3). Near the end of the two seasons, the monoculture had the largest mean number of T. urticae eggs (28.6 and 29.45 eggs/plant) in the first and second seasons respectively. The geranium intercropping produced the lowest mean population of T. urticae eggs (Figs. 7, 8, and Table 3).

Fig. (3):  Effect of intercropping with basil and Geranium and their essential oils  on Bemisia tabaci nymph populations  during first seasons (2022).

Fig. (4) Effect of intercropping with basil and Geranium and their essential oils  on Bemisia tabaci nymph populations during second seasons (2023).  

Fig. (5): Effect of intercropping with basil and Geranium and their essential oils on Tetranychus urticae adult populations   during first season (2022).

Fig. (6): Effect of intercropping with basil and Geranium and their essential oils on Tetranychus urticae adult populations during second season (2023).

Fig. (7): Effect of intercropping with basil and Geranium and their essential oils on egg of  Tetranychus urticae populations during first season (2022).

Fig. (8): Effect of intercropping with basil and Geranium and their essential oils on egg of Tetranychus urticae populations during second season (2023).

3. Effect of the tested treatments on growth parameters and yield of common bean

a. Chlorophyll of all treatments of common bean

           Every treatment showed a significant impact on chlorophyll (Table 4). When comparing intercropped plants to treatments in the first and second seasons, there was a significant variation in chlorophyll content due the treatments comparing to the mono culture treatment (Table 4). Intercropped Basil had the maximum chlorophyll content. All treatments showed significant increase in chlorophyll, comparing to the mono culture treatment. The results obtained indicated that intercropped basil outperformed all other treatments in both seasons.

Table (3):  The mean populations of B.  tabaci nymphs, T. urticae (adults and eggs) on all treatments in 2022 and 2023 seasons.

Means followed by the same letters are not significantly different; small letters represent differences between data in rows based on least significant difference tests at the 5% level (LSD 5%).

Table 4: Chlorophyll (mg/g) of common bean plants as affected with all treatments during the 2022 and 2023 seasons.

Means followed by the same letters are not significantly different; small letters represent differences between data in rows based on least significant difference tests at the 5% level (LSD 5%).

b. Common bean seed yield and yield attributes

        Table 5 shows that all treatments had a significant impact on plant height, number of leaves, number of branches, length of the pod (cm), mean weight of pod (g), number of pods/plant, yield (g/plant), and yield (ton/fad.) in the 2022 and 2023 seasons. In both seasons plant height increased significantly compared to the monoculture treatment. In the first season, plant height was 49.3, 44.03, 51.3, 48.23 and 35.93 cm found in the second season it was 53.23, 45.9, 53.7, 49.2 and 37.8 cm.

The number of leaves were 21.87, 13.53, 21.47, 19.8, and 11.13 in the first season, and 23.6, 14.3, 23.9, 21.1, and 9.33 in the second season for intercropped basil, intercropped geranium, basil oil, geranium oil and monoculture, respectively. The number of branches planted was 4.2, 4.3, 4.3, 4.2 and 3.33 in the first season, but second season was 5.4, 4.9, 5.2, 4.9 and 3.17 for intercropped basil, intercropped geranium, basil oil, geranium oil and monoculture, respectively.

The data showed that length of pod was 17.07, 15.17, 12.77, 11.83, and 10.6 in the first season, but second season was 15.4, 14.0, 10.67, 9.93, and 8.93. Mean weight of pod was 4.63, 3.83, 3.6, 3.3 and 2.87 in the first season, but second season was 5.83, 5.07, 5.13, 4.57, and 3.67 pods. The number of pods/plants was 25.77, 17.83, 18.47, 17.3 and 13.67 in the first season, but second season was 23.3, 15.97, 16.13, 15.57 and 11.3 pods for intercropped basil, intercropped geranium, basil oil, geranium oil and monoculture, respectively.

In the first season, yield (g/plant) was 79.27, 68.63, 66.67, 59.97, and 42.4 g, but in second season, 87.47, 71.13, 70.17, 62.2, and 45.9g.  Yield (t /fad.) was 5.35, 5.18, 4.7, 3.96 and 2.95t in the first season, but second season was 6.37, 5.47, 5.53, 5.6 and 4.3t for intercropped basil, intercropped geranium, basil oil, geranium oil and monoculture, respectively.

Table 5: The impact of intercropping basil and geranium with their essential oils on common bean yield and growth characteristics in the 2022 and 2023 growing seasons.

Means followed by the same letters are not significantly different; small letters represent differences between data in rows based on least significant difference tests at the 5% level (LSD 5%).