Beauveria bassiana and Metarhizium anisopliae are two of the most important and widely used entomopathogenic fungi (EPFs) for pest control. Recent studies have shown that they can also promote plant growth after artificial inoculation. To more accurately evaluate the colonization and growth-promoting effects of Beauveria bassiana and Metarhizium anisopliae on agricultural crops, in this study, maize seedlings were treated with 13 Beauveria bassiana strains and 73 Metarhizium anisopliae strains, respectively, as rhizosphere fungi in a hydroponic system. Plant growth parameters, including plant height, root length, and fresh weight, were monitored and recorded for 35 consecutive days to confirm the growth-promoting effect of entomopathogenic fungal inoculation. The results of fungal recovery rate (FRR) assessment showed that both Beauveria bassiana and Metarhizium anisopliae are capable of endophytic colonization of maize tissues. On day 7, the detection rate of Beauveria bassiana was 100% in both stems and leaves, but by day 28, the detection rate in stems decreased to 11.1% and in leaves to 22.2%. However, *Beauveria bassiana* was not detected in the roots until day 28, with a detection rate of 33.3%. Throughout the observation period, *Metarhizium anisopliae* strains were isolated from the roots, stems, and leaves of the plant with a high detection rate. PCR amplification of fungal-specific DNA bands further confirmed the systematic colonization of *Beauveria bassiana* and *Metarhizium anisopliae* in various tissues; this method demonstrated a higher detection sensitivity and a 100% positive reaction. Compared with the initial values in the hydroponic solution, by day 21, the fungal density decreased to less than 1%. Thus, the two selected strains of entomopathogenic fungi successfully established endophytic colonization, rather than colonization, of the corn rhizosphere and significantly promoted its growth in a hydroponic system. Entomopathogenic fungi have enormous potential for use in organic farming, including as biopesticides and biofertilizers.
Entomopathogenic fungi (EPFs) have proven their importance as biological control agents (BCAs) for the management of various pests due to their broad host range, ease of production, stability, and high pathogenicity. 1,2,3 In China, *Beauveria bassiana* and *Metarhizium anisopliae* are commercially used for the sustainable control of major corn pests (such as corn borer and cotton bollworm) to avoid the overuse of chemical pesticides. 4 In pest management with fungi, the triangular relationship between plants, pests, and fungi is much more complex than the relationship between pests and fungal pathogens.
Many plants live in symbiosis with endophytic fungi 5 , which inhabit plant tissues without causing significant harm to them 6 . Endophytic fungi are organisms that form after establishing a mutualistic symbiotic relationship with their host 7 . They can directly or indirectly promote plant growth and enhance their adaptability to adverse conditions, including biotic and abiotic stresses 8, 9, 10 . Endophytic fungi possess important phylogenetic characteristics and lifestyle features, such as colonization, dispersal, host plant specificity, and colonization of various plant tissues 11 . The use of endophytic fungi as endophytic organisms has attracted widespread research attention and has demonstrated many unique advantages over traditional endophytic organisms.
Beauveria bassiana and Metarhizium anisopliae can infect a variety of plants, including but not limited to wheat, soybean, rice, legumes, onion, tomato, palm, grape, potato, and cotton. 12 Local or systemic infection mainly occurs in the roots, stems, leaves, and internal tissues of plants. 11 Artificial infection through seed treatment, foliar application, and soil irrigation can promote plant growth through endophytic infection by fungi. 13,14,15,16 Seed treatment of crops with Beauveria bassiana and Metarhizium anisopliae successfully induced endophytic infection in plant tissues and promoted plant growth by increasing stem height, root length, root fresh weight, and stem fresh weight. 17,18,19 Soil inoculation and foliar spraying of Beauveria bassiana are also the most commonly used application methods, which can significantly promote the growth of maize seedlings.20
The aim of this study was to evaluate the growth promoting effects and colonization characteristics of maize seedlings by Beauveria bassiana and Metarhizium anisopliae and their impact on plant growth in hydroponic systems.
In a 35-day experiment, treatment with the fungi Beauveria bassiana and Metarhizium anisopliae significantly promoted corn growth. As shown in Figure 1, the stimulating effect of the fungi on various corn organs depended on their growth stage.
Corn seedling growth under different treatments over time. From left to right, the differently colored lines represent corn seedlings in the control group, the Beauveria bassiana-treated group, and the Metarhizium anisopliae-treated group, respectively.
Colonization of maize tissues by *Beauveria bassiana* and *Metarhizium anisopliae* was further investigated using PCR amplification. Table 5 shows that *Beauveria bassiana* colonized 100% of all maize organ tissues at each sampling point (7–35 days). Similar results were observed for *Metarhizium anisopliae* in leaf tissues, but colonization by this fungus did not always remain at 100% in maize stems and leaves.
Inoculation methods are crucial for fungal colonization patterns. 28 Parsa et al. 29 found that *Beauveria bassiana* can colonize plants endophytically when sprayed or watered, whereas root colonization is only possible with watering. In sorghum, Tefera and Vidal reported that leaf inoculation increased the rate of *Beauveria bassiana* colonization in the stem, whereas seed inoculation increased the rate of colonization in both roots and stems. In this study, we inoculated roots with two fungi by adding a conidial suspension directly to the hydroponic system. This method may improve the efficiency of fungal dispersal, as running water can facilitate the movement of fungal conidia to corn roots. In addition to inoculation methods, other factors such as soil microorganisms, temperature, relative humidity, nutrient medium, plant age and species, inoculation density, and fungal species can influence the successful colonization of various plant tissues by fungi. 28
Furthermore, PCR amplification of fungal-specific DNA bands represents a new and sensitive method for detecting fungal endophytes. For example, after culturing plant tissues on selective fungal media, a low number of free detector receptor (FRR) was detected for *Beauveria bassiana*, but PCR analysis yielded 100% detection. Low population density of endophytic fungi in plant tissues or biotic inhibition of plant tissues may be the cause of unsuccessful fungal growth on selective media. PCR amplification can be reliably applied to the study of endophytic fungi.
Previous studies have shown that some endophytic insect pathogens can act as biofertilizers by promoting plant growth. Jaber et al. [ 16] reported that wheat seeds inoculated with Beauveria bassiana for 14 days had greater stem height, root length, fresh root weight, and stem weight than uninoculated plants. Russo et al. [30] reported that foliar spraying of maize with Beauveria bassiana increased plant height, leaf number, and first ear node number.
In our study, two selected entomopathogenic fungi, Beauveria bassiana and Metarhizium anisopliae, also significantly promoted maize growth in a hydroponic plant growing system and established systematic colonization of various tissues of maize seedlings, which is expected to promote growth in the long term.
In contrast, Moloignane et al. found that even 4 weeks after soil irrigation, there were no significant differences in plant height, root count, leaf count, fresh weight, and dry weight between grapevines treated and untreated with *Beauveria bassiana*. This is not surprising, as the endophytic capacity of specific fungal strains can be closely related to the host plant species, plant cultivar, nutritional conditions, and environmental influences. Tull and Meying investigated the effect of *Beauveria bassiana* seed treatment (GHA) on maize growth. They found that *Beauveria bassiana* acted as a growth promoter in maize only under nutrient-sufficient conditions, and no stimulatory effect was observed under nutrient-deficient conditions. Thus, the mechanism of plant response to the endophytic effects of fungi is far from clear and requires further investigation.
We investigated the effects of the entomopathogenic fungi *Beauveria bassiana* and *Metarhizium anisopliae* as growth promoters in maize. However, whether the primary mechanism is rhizosphere or endophytic remains unclear. We monitored the population dynamics of *Beauveria bassiana* and *Metarhizium anisopliae* in hydroponic solutions and plant tissues to elucidate their mechanisms of action. Using colony-forming units (CFU) as an indicator, we found that the abundance of *Beauveria bassiana* and *Metarhizium anisopliae* in the hydroponic solution rapidly decreased. After one week, the residual concentration of *Metarhizium anisopliae* was less than 10%, and *Beauveria bassiana* was less than 1%. In the hydroponic maize solution, both fungi virtually disappeared by day 28. Control experiments showed that conidia of both fungi retained high viability in the hydroponic system after one week. Thus, endophytic fungi, influenced by conidial adhesion, host recognition, and endogenous pathways , are the primary cause of the sharp decline in fungal abundance in the hydroponic system. Furthermore, the growth-promoting function of fungi is primarily due to their endophytic function, not rhizosphere function.
Biological functions are generally associated with population density. Only by quantifying the number of endophytic fungi in plant tissues can we establish a relationship between plant growth stimulation and endophytic fungal population density. The mechanisms by which plant growth is stimulated in entomopathogenic fungal-plant interactions require further investigation. Entomopathogenic fungi not only possess significant potential for biological pest control but also play an important role in stimulating plant growth, opening new perspectives on the ecological interactions between plants, pests, and entomopathogenic fungi.
Ninety uniformly growing and healthy corn seedlings were randomly selected from each experimental group. The growing medium around the roots of each seedling was carefully rinsed with distilled water to avoid damaging the root system. The treated corn seedlings, which had uniform growth in both above- and below-ground parts, were then transplanted into a hydroponic corn growing system.
All experimental data were analyzed using one-way analysis of variance (ANOVA) in IBM SPSS Statistics (version 20.0), and the significance of differences between treatments was determined using Tukey’s HSD test (P ≤ 0.05).
Since the plant material was purchased from a local certified distributor, no license was required. The use of plants or plant material in this study complies with relevant international, national, and/or institutional guidelines.
In conclusion, two entomopathogenic fungi, *Beauveria bassiana* and *Metarhizium anisopliae*, played a positive role in promoting maize seedling growth after rhizosphere inoculation with a hydroponic system. These two fungi were able to establish systematic colonization of all maize organs and tissues through the root system within one week. Fungal population dynamics in the hydroponic solution and fungal colonization of maize tissues revealed that, in addition to rhizosphere function, the endophytic function of the fungi made a more significant contribution to the observed plant growth promotion. The endophytic behavior of the fungi demonstrated some species-specific characteristics. The amplification of fungal-specific DNA bands using PCR proved to be more sensitive than colony detection methods using fungal-selective media. This method can be used to more accurately track fungal colonization and their spatial distribution in plant tissues. Further research is needed to elucidate the mechanisms by which plants and plant pests respond to the endophytic effects of fungi (additional information).
The datasets generated during this study are available from the corresponding author upon reasonable request.
Post time: Jan-20-2026