Susceptibility of melon cultivars to Meloidogyne incognita and suppression by biocontrol agentsAbstract:
Melon (Cucumis melo L.) is widely consumed and among the most exported fresh fruits of Brazil. Despite substantial production, this crop is limited by several factors, notably the root-knot nematode Meloidogyne incognita, for which few management tools are available. In our work, we assessed the host status of ten different melon genotypes, from which we selected ‘Asturia’ for subsequent biocontrol experiments. We then evaluated the efficacy of Bacillus amyloliquefaciens, Pochonia chlamydosporia (i.e., Rizotec®), and Purpureocillium lilacinum twice against M. incognita, and, finally, we conducted a dose–response experiment using Rizotec® to determine its performance across application rates. All genotypes were susceptible. Regarding biocontrol, P. lilacinum significantly reduced nematodes per gram of root when applied once, compared with two applications for P. chlamydosporia. Regarding dose-response, increasing doses presented a strong negative correlation with final population size, with the EC50 estimated at 0.84 plant-1. In addition to reducing the nematode population, dosages also increased fresh weight, fruit weight, and stem diameter at themiddle and top of the plant. However, they only did so in the inoculated plants.Pochonia chlamydosporia (i.e, Rizotec) represents a potential strategy for the management of M. incognita and should be integrated with additional management practices to enhance its efficiency.
Index terms
Biological control; Cucumis melo; Root-knot nematode; Pochonia chlamydosporia; Purpureocillium lilacinum; Bacillus amyloliquefaciens
Resumo:
Melão (Cucumis melo L.) é amplamente apreciado e configura entre os principais hortifrútis frescos do Brasil. Apesar da produção substancial, essa cultura é limitada por diversos fatores, notavelmente pelo nematoide-de-galhas Meloidogyne incognita, para o qual poucas ferramentas de manejo encontram-se disponíveis. Em nosso trabalho, nós inicialmente avaliamos dez genótipos diferentes de melão, em que selecionamos a cultivar Asturia para experimentos subsequentes. Foi então avaliado o efeito de Bacillus amyloliquefaciens, Pochonia chlamydosporia (Rizotec®) e Purpureocillium lilacinum contra M. incognita em dois ensaios e, finalmente, foi realizado ensaio doseresposta utilizando Rizotec®. Todos os genótipos foram suscetíveis. Com relação ao controle biológico, P. lilacinum reduziu o número de nematoides por grama de raiz em um ensaio, enquanto P. chlamydosporia reduziu em ambos. Em relação à dose-resposta, o aumento das doses apresentou correlação negativa com a população final, com a EC50 estimada em 0,84 plant-1. Adicionalmente à redução das populações do nematoide, as doses incrementaram a massa fresca, massa dos frutos, diâmetro do caule no meio e no ápice da planta. Entretanto, apenas em plantas inoculadas. Pochonia. chlamydosporia (Rizotec®) é uma estratégia potencial a ser utilizada no manejo de M. incognita e deve ser integrada a outras ferramentas de manejo para aumentar sua eficiência.
Termos para indexação
Controle biológico; Cucumis melo; nematoide de galhas; Pochonia chlamydosporia; Purpureocillium lilacinum; Bacillus amyloliquefaciens
Introduction
Melon (Cucumis melo L. var. inodorus, var.cantaloupensis and var. reticulatus) is a widely consumed fresh fruit worldwide. In Brazil, the production initially started in the South Region in the 60s, but nowadays the main areas are located in the Northeastern Region of the country, with Rio Grande do Norte and Ceará as the leading producing states (BELING, 2023; LANDAU et al., 2020).
Currently, melon is one of Brazil’s most exported fresh fruits, with 257 thousand tonnes exported in 2021, worth US$ 165 million (BELING, 2023). Tied to this, it is societally relevant as an important source of income in the semiarid region of the Northeastern states.
Despite the impressive numbers achieved by melon producers of Brazil, several factors decrease the productivity of this crop.
Frequently, root pathogens play an important role by both decreasing yield and the host tolerance to harsh environmental conditions, which becomes even more relevant in semi-arid regions and due to climate change (PANDEY et al., 2024; SÁNCHEZ-BERMÚDEZ; DEL POZO; PERNAS, 2022).
Among root pathogens, plant-parasitic nematodes (PPNs) are a major constraint worldwide to cucurbits (JONES et al., 2013; KHAN et al., 2023), with one species in particular coming into the spotlight: the root-knot nematode Meloidogyne incognita (PINHEIRO; AMARO, 2010). Meloidogyne incognita and other root-knot nematodes are among the most harmful PPNs to vegetable crops, including Cucumis melo (AYALA-DOÑAS et al., 2020; HALLMANN; MERESSA, 2018; MOURA; PEDROSA; GUIMARÃES, 2002). Heavily infested plants present a shorter root system with numerous galls, the main symptom of Meloidogyne disease (CALDERÓN-URREA et al., 2016). Melon plants are stunted, wilted and exhibit malnourishment-derived symptoms (MOURA; PEDROSA; GUIMARÃES, 2002; PINHEIRO; AMARO, 2010). Meloidogyne incognita is widespread in producing areas, with reported losses reaching 100% (MOURA; PEDROSA; GUIMARÃES, 2002; PINHEIRO; AMARO, 2010).
The management of plant-parasitic nematodes (PPNs) remains a significant challenge, primarily due to the lack of effective and affordable control tools for several crops (ABD-ELGAWAD, 2024). Among available strategies, the use of resistant cultivars or genotypes stands out as the most desirable and cost-efficient option, as it does not increase farmers’ expenses while offering high efficacy (MOLINARI, 2011; PATHANIA et al., 2021). However, only a limited number of melon cultivars have demonstrated resistance to M. incognita (DINIZ et al., 2016; ITO et al., 2014; MACEDO DA SILVA et al., 2022). Crop rotation is another widely adopted practice; however, its effectiveness is constrained by the wide host range of polyphagous species such as M. incognita (JONES et al., 2013). Lastly, chemical control remains limited to seed treatment due to high costs and phase-outs/restrictions on nematicides, although novel ones were recently registered for melon x M. incognita.
Amidst this scenario, the deployment of biological control agents arose in Brazil as an alternative and has gained traction in recent years, driven by sustainability and the aforementioned limitations of chemical management and crop rotation.
In simple terms, biological control consists of using an antagonist to suppress the PPN below the damage threshold. Bionematicides can suppress PPNs and other pathogens through multiple mechanisms, such as direct parasitism and/or antibiosis, but under certain circumstances they are also able to colonise plants endophytically, inducing resistance and/or promoting plant growth (CHAKRABORTI; MANDAL; TIRU, 2025; FANAI et al., 2024; FONTANA et al., 2021).
Bacillus spp., Pochonia chlamydosporia and Purpureocillium lilacinum (syn. Paecilomyces lilacinus), are among the most used bionematicides in agriculture.
Bacillus spp. are one of the most widely used microorganisms against PPNs worldwide.
These rhizobacteria suppress PPNs by releasing toxic compounds and by forming a biofilm around roots (MAZZUCHELLI; MAZZUCHELLI; ARAUJO, 2020; VLAMAKIS et al., 2013). Bacillus amyloliquefaciens is one of the most promising biocontrol bacteria, with several strains used as active ingredients in 14 bionematicides out of 25 pesticides in Brazil (AGROFIT, 2025).
Among fungi, P. chlamydosporia and P. lilacinum are notable facultative parasites of juveniles, sedentary females and eggs of PPNs. In addition to the direct effects of these agents, these fungi secrete toxic metabolites and volatile compounds with deleterious effects on PPNs (PACHECO et al., 2022; PHILADELPHI et al., 2024). Despite their phylogenetic differences, all three can promote plant growth when colonising plants endophytically (FANAI et al., 2024; FONTANA et al., 2021).
Although promising, many bionematicides were not tested for M. incognita on melon.
In our work, we initially assessed the host status of 10 different melon genotypes, from which we selected ‘Asturia’ - a susceptible piel-de-sapo melon - for subsequent experiments. We then evaluated the efficacy of Bacillus amyloliquefaciens, Pochonia chlamydosporia, and Purpureocillium lilacinum against M. incognita, and, finally, we conducted a dose–response experiment using Rizotec® to determine its performance across application rates.
Methodology
Inoculum extraction
The M. incognita inoculum was obtained from a mix of cotton (Gossypium hirsutum L.) and melon roots, previously infested and maintained in a greenhouse. The population used in our experiments was originally isolated from cotton samples collected in Campo Verde, Mato Grosso (Brazil) and identified using morphology and esterase analysis (PAES et al., 2024; SOUZA; INOMOTO, 2021).
Inoculum plants were removed from the pots, and roots were washed with tap water, cut into 1 cm pieces, and blended using a commercial sodium hypochlorite solution (0.5%). Afterwards, the suspension was carefully poured into a set of two sieves, 60 and 500 mesh (0.0250 cm and 0.0025 cm aperture, respectively).
The debris from the last sieve was collected and poured into a 250 mL beaker, and then submitted to the centrifugal flotation technique for the isolation and concentration of nematodes using a sucrose solution, as described by Coolen and D’Herde (1972). The inoculum consisted of a mix of eggs and second-stage juveniles (J2).
Host status experiment
We initially sought to select a susceptible melon genotype for our assays. Sakata Seed Sudamerica® provided all the melon seeds used in the present work. In total, ten melon hybrids [seven Canary melon type (var. inodorus), two piel-de-sapo type (var. inodorus) and one Smell melon type (var. reticulatus)] were used to evaluate their host status to M. incognita, which includes both commercial and experimental genotypes (Table 1).
For the host status experiment, the melon plants were obtained by sowing the seeds of each genotype in pots (2 L capacity), previously filled with autoclaved sieved soil (121°C for 40 minutes). The melon seedlings were thinned to two plants per pot after seven days. Cucumber ‘Caipira’ (Cucumis sativus L.) was included as a known-reaction host to check inoculum infectiveness (ITO et al., 2014).
Ten cultivars were tested, and each genotype had six replicates inoculated and placed in a completely randomised way, and the experimental unit consisted of one pot containing two plants. Plants were inoculated with 300 nematodes and evaluated 60 days after inoculation.
Extraction was performed as previously described, and density was obtained by counting two aliquots of 0.5 mL using Peters’ counting slide under a light microscope. Final population and nematode per gram of root (Nem/g) were estimated, and plants were ranked as susceptible if the R value (Final Population/ Initial population) > 1 and resistant if < 1.
Biocontrol experiments
Based on the results of the host status experiment (Table 2), the cultivar ‘Asturia’ was selected for further use due to its susceptibility to M. incognita, robust growth under our experimental conditions, and overall technical tractability. Two experiments were done to evaluate the biocontrol agents B. amyloliquefaciens, P. lilacinum and P. chlamydosporia - evaluated at 40 and 60 days after inoculation.
The first two microorganisms were isolated and characterised by Brandão (2018), and they were deposited in the microorganism collection at the Laboratório de Fisiologia e Bioquímica Fitopatológica (Departmento de Fitopatologia e Nematologia, ESALQ/ USP). Pochonia chlamydosporia ‘P11’ is the active ingredient of Rizotec®.
Bacillus amyloliquefacienswas incorporated into the soil by applying a bacterial suspension obtained from washing overnight plates with autoclaved water, aided by a Drigalski spatula. The optical density (OD) at 600nm was 0.05 and 0.337 for experiments 1 and 2, respectively, using volumes of 5 mL and 10 mL. Purpureocillium lilacinum was incorporated into the soil by mycelium spread across four holes (2 cm deep) made close to the plant stem (0.4 g plant-1 and 0.8 g for experiments 1 and 2, respectively).
The mycelium was obtained by growing P. lilacinum in potato-dextrose (PD) medium for 10 days, subsequently filtered using a Kitasato set coupled with a vacuum pump. Pochonia chlamydosporia was obtained by diluting Rizotec in sterile water (0.3 g plant-1and 0.5 g plant-1 for experiments 1 and 2, respectively), followed by homogenisation and application in soil, similarly to P. lilacinum.
Plants were grown by planting pre-germinated seeds in 2 L pots containing autoclaved sifted soil. The seeds were germinated by sowing them into Petri dishes with sterilised, soaked filter paper (Whatman filter n° 40) for 48 hours at 28°C. Melon plants were maintained in a greenhouse under daily irrigation, and treated and inoculated after the first true leaf growth (~ 14 days after transferring to soil).
Inoculation was done 24 hours after treatments.
For that, 1,000 nematodes (egg + J2) were inoculated by pouring the suspension into 2 holes (2 cm and 4 cm deep) partially filled with vermiculite. Holes were closed by adding it, and plants were kept in shade for 24 h and transferred to a greenhouse. Each treatment was composed of 5 replicates, and the experimental unit consisted of one plant per pot. In order to evaluate the impact of biological control agents on melon growth parameters, the fresh weight of aerial part (g), plant height (cm), fruit weight (g), shoot diameter (cm) at two parts of the plants (base and middle of plant), and chlorophyll content were analysed.
The latter was done using a SPAD (SPAD- 502 Konica Minolta®, in which the 5th leaf from top to bottom (‘young’ leaf) and bottom to top (‘older’ leaf) was measured five times, in an equidistant anticlockwise way.
This was done to cover the area of leave, and thus the average was used. Evaluation was carried out at Laboratório de Póscolheita (Departamento de Fitopatologia e Nematologia, ESALQ/USP).
After collecting all measurements, the roots were transported to the Laboratório de Nematologia (Departamento de Fitopatologia e Nematologia, ESALQ/USP) for nematode extraction. This process was carried out as previously described, and nematode reproductive parameters (final population and Nem/g) were estimated.
Dose-response experiment
Plants were treated using increasing doses of Rizotec®. A stock suspension (60 mL) was prepared using distilled sterile water for each dose. The suspension was manually homogenised before the treatment, and a 5 mL aliquot of the solution was applied to each plant by distributing it into four holes (2 cm deep) positioned around the base.
The doses were control (water), dose 1 (0.1 g of Rizotec® plant-1), dose 2 (0.25 plant-1), dose 3 (0.5 plant-1), dose 4 (1 g plant-1), and dose 5 (2 g plant-1). After adding the treatments, the holes were carefully closed using sterile soil and randomly placed in the greenhouse until inoculation. Inoculation was performed by pouring 1,000 eggs + J2 per plant (0.42 mL) using the same procedures described previously, but uninoculated treatments were also included for comparison purposes and to investigate any biostimulant effect. Evaluation was carried out 60 days after inoculation, and each treatment comprised 5 replicates.
Similar to the previous, the same growth and nematode reproductive parameters were evaluated.
Statistical analysis
Statistical analysis of the data was performed using R statistical software v. 4.2.1(R CORE TEAM, 2022), and normality of the data was checked using the Shapiro-Wilk normality test (p > 0.05). For the host-status experiment, Tukey’s honest significant difference test was carried out using the Laercio package v. 1.0-1, whereas in the biocontrol experiments, pairwise comparisons between treatments and the control were performed using Student’s t-test with the Rstatix package v. 0.7.3. Regarding the dose-response experiment, correlation and linear regression analyses were performed using the R stats package v.5.2 and sought to determine the effect of Rizotec® on the M. incognita population and nematodes per gram of root. The best-fitting trendline was selected based on the highest R2. The EC50 was estimated by using the drc v.3.0-1 package.
Results
All cultivars were susceptible to M. incognita, presenting values greater than 1 (Figure 1 and Table 1). No statistical differences were obtained for R values (values ranging from 5.7 to 19.5); however, differences were observed regarding Nem/g – influenced by the root size/weight of each cultivar (values ranging from 271 to 1,791 Nem/g).
All plants presented maximum Gall index, which was more than 100 galls (= 5 according to Taylor and Sasser (1978)), spread across the root system. Brownish to dark reddish egg masses were easily spotted. As previously stated, ‘Asturia’ was selected for further experiments.
Reproductive variables obtained for melon cultivars inoculated with Meloidogyne incognita. A) Ten melon cultivars tested against M. incognita. R values ranged from 5.7 to 19.5 (cv. AF9723 and AF11838, respectively). Final population: boxplots; R value: coloured dots/ dashed lines. Boxplots: Centre lines show the medians; box limits indicate the 25th and 75th percentiles as determined by R software; whiskers extend 1.5 times the interquartile range from the 25th and 75th percentiles; grey dots represent outliers. B) Nematodes per gram of root obtained for M. incognita. Bars with the different letters differ statistically (Anova post-hoc Tukey honest test < 0.05).
In both biocontrol experiments 1 and 2, the treatments did not significantly influence melon growth parameters. On nematode reproduction, P. lilacinum significantly decreased the number of Nem/g in experiment 1 (Anova post-hoc T-Test p = 0.01), whereas P. chlamydosporia reduced Nem/g in both experiment 1 and 2 (Anova post-hoc T-Test p = 0.016 and 0.04, respectively). These data are shown in Figure 2 and Table 2.
Effect of the biocontrol agents Bacillus amyloliquefaciens, Purpureocillium lilacinum and Pochonia chlamydosporia (Rizotec®) on the suppression of M.incognita on melon cv. Asturia. A) Nematodes per gram of root in the experiment at 40 days after the inoculation. ‘*’ Statistically significant according to Anova post hoc Student’s T-Test (p = 0.01 and 0.016 for P. lilacinum and P. chlamydosporia, respectively); B) Nematodes per gram of root in experiment 2 at 60 days after inoculation.‘*’ Statistically significant according to Anova post hoc Student’s T-Test (p = 0.046). Boxplots: Centre lines show the medians; box limits indicate the 25th and 75th percentiles as determined by R software; whiskers extend 1.5 times the interquartile range from the 25th and 75th percentiles.
Dosage-response
As P. chlamydosporia (i.e. Rizotec®) was effective in reducing the number of M. incognita per gram of root in two subsequent experiments, we sought to test it further to define a dose-response against M. incognita.
As this section addresses product dosage, we found it more appropriate to refer to it using the product’s name.
Rizotec® was effective in reducing M. incognita populations on melon roots (Figure 3 and Table 3). The linear regression model was statistically significant (p = 0.019), and dosage presented a strong negative correlation with the nematode final population (r = -0.88) and a slight negative association with nematode/g (r = -0.02). In terms of curve fitting, a polynomial trendline provided the best fit to our dataset (R2 = 0.92, intercept = 5323.4), surpassing the linear model (R2 = 0.78, intercept = 5906.1) (Figure 3 and Table 4).
Dose–response of Rizotec® in melon inoculated with Meloidogyne incognita. 3A–3C) Effect of Rizotec® doses on the final M. incognita population. 3A) and 3B) show the best-fit trend lines for the average values: a linear model (R2= 0.78) and a polynomial model (R2 = 0.92), respectively. 3C) presents the log-logistic model with the estimation of the EC50. 3D–3G) Influence of Rizotec® on melon growth parameters in inoculated and uninoculated plants. Pochonia chlamydosporia improved several growth traits, but only in the presence of M. incognita. Parameters include fresh weight (3D), fruit weight (3E), shoot diameter at the middle portion (3F), and shoot diameter at the top of the plant (3G). 3H) Chlorophyll content in older leaves. An analysis revealed a significant difference in Y-intercepts (p = 0.0128), indicating that uninoculated plants had higher baseline chlorophyll content than inoculated plants at dose 0.
The polynomial curve encompassed a decrease in nematode population between 0.5 g and 1 g, followed by a plateau from 1 g plant-1to 2 g plant-1 (Figure 3A and 3B).
By fitting a log-logistic model (LL.3), the ED50 of Rizotec® was estimated at 0.84g plant-1, higher than the label recommendation (Figure 3C and Table 4). Interestingly, increasing doses of Rizotec® led to increasing fresh weight of the aerial part, but only for inoculated plants (Linear regression model for (+N) p = 0.002 and (-N) p = 0.4).
It was also observed that increasing doses of Rizotec® had a different impact on fresh weight if plants were inoculated with M. incognita or not (noninoculated vs inoculated plants - Linear Regression model p = 0.03) (Figure 3D). Similar patterns were obtained for fruit weight (p = 0.015) and stem diameter (middle of the plant and top of the plant, p = 0.0012 and 0.013, respectively), which showed a significant increase in higher doses, but only in inoculated plants (Figure 3D – G, p > 0.05).
These are further supported by correlation analysis, which scored higher in inoculated plants than non-inoculated plants: dose x fresh weight: r = 0.43 (+N) and 0.15 (-N); dose x fruit weight: r = 0.38 (+N) and 0.011 (-N); stem diameter middle: r = 0.37(+N) and 0.009 (-N); stem diameter top: r = 0.32 (+N) and -0.0243 (-N). Rizotec® did not influence other growth parameters assessed; however, interesting data were obtained regarding chlorophyll content.
In young leaves, chlorophyll content was borderline not significant for inoculated plants (Linear regression model: 0.06), but a higher correlation was obtained when compared to uninoculated plants (r = 0.35 (+N) and 0.05 (-N)).
Regarding chlorophyll content in older leaves, analysis revealed a significant difference in Y‑intercepts (p = 0.0128), meaning that uninoculated plants had higher baseline chlorophyll content than inoculated plants at dose 0 (Figure 3H). This is likely an indication of the impact of nematode parasitism in the above-ground parts of the plant. Data is also summarised in Table 5.
Discussion
Although management using resistance plants is one of the most efficient methods to control PPNs, resistance sources are hard to come by, and introgression of resistance from wild related species can take years of research (LOPES et al., 2019).
Cucumis metuliferus is a promising source of resistance to control them; however, crossing it with C. melochanges the fruit characteristics (EXPÓSITO et al., 2018; PINHEIRO et al., 2019). Even its use as a rootstock can affect fruit quality, such as Brix and flesh firmness, although some accessions of C. metuliferus do not affect them significantly (EXPÓSITO et al., 2018). This necessarily entails substantial difficulties in crossing and obtaining resistant melon genotypes, and thus a new source of resistance is needed.
In the absence of resistance and chemical nematicides, the deployment of biological control organisms to control PPNs received much attention in recent years, especially in Brazil. On top of their biological effect, some microorganisms also display the ability to colonise plants and promote beneficial effects, such as induced resistance and/or growth promotion (FONTANA et al., 2021; GHAHREMANI et al., 2019).
Melon growth parameters evaluated in experiments 1 and 2 were not influenced by the application of biocontrol agents in our experimental setup.
Although there researchers are often hesitant to report null or “negative” results, it is necessary for the progress of the field . It is noteworthy, though, that in the dose-response assay, P. chlamydosporia improved several characteristics, but only in the presence of M. incognita (Figure 3D - 3G). These biostimulant effects of P. chlamydosporia in the presence of M. incognita observed here corroborate its biology: plant colonisation is improved when plants are infected by nematodes (GHAHREMANI et al., 2019; VIAENE; COYNE; DAVIES, 2024).
However, P. chlamydosporia was reported to enhance plant tolerance to drought on soybean without the presence of PPN (Rodrigues et al., 2024).
Concerning nematode control, doses 4 and 5 (1g plant-1 to 2g plant-1, respectively) performed similarly (Figure 3D - G). As previously stated, the ED50 of Rizotec® was estimated at 0.84g plant-1, higher than the label recommendation (Figure 3C). However, although the ED50 is within the experimental range, caution should be taken, as the CI95% was relatively high (CI 95% = 0.18 to 3.99), indicating that the dosage was not precisely estimated.
Despite this caveat, our results are in agreement with data obtained by Viggiano et al. (2014), which showed suppression of M. javanica on cucumber (Cucumis sativus L.) by Rizotec® at higher- than-label dosage (18 g L-1) (VIGGIANO et al., 2014). Conversely, a lower concentration suppressed M. incognita on carrot and tomato (2 and 3 Kg ha-1, respectively) (BONTEMPO et al., 2017; SILVA et al., 2017).
Altogether, cucurbits may require higher concentrations for Meloidogyne control.
Pochonia chlamydosporia relies on several mechanisms to suppress PPNs, including direct parasitism of eggs, females and cysts and release of volatile and other toxic compounds (PACHECO et al., 2022). It can also activate latent defence mechanisms within the plant, inducing resistance against PPNs (GOUVEIA et al., 2023). Nevertheless, higher concentrations may incur greater costs for farmers, as well as operational limitations due to the viscosity of the product.
Purpureocillium lilacinum is among the most widely used microorganisms for the control of PPNs, suppressing species of Meloidogyne, Heterodera, and even arthropods like the spider mite Tetranynchus urticae (PARAJULI et al., 2014; SILVA et al., 2022).
In our work, P. lilacinum was effective in reducing Nem/g, but not consistently across both experiments. A few reasons could explain this inconsistency. The most common way of introducing fungal bionematicides in a system is by applying spores or resting structures produced by them. In our work, mycelium was obtained as an experimental subproduct of culture filtrate production and further investigated to assess its viability in biocontrol. This could have affected its performance. However, P. lilacinum can present variable levels of control, also varying due to the plant host species and other environmental factors (VIAENE; COYNE; DAVIES, 2024). It can also vary with nematode density. Purpureocillium lilacinum was not able to control M. enterolobii on tomato and banana at higher densities, only on low densities (SILVA et al., 201742).
This was corroborated by Dahlin et al.(DAHLIN et al., 2019), which observed that although P. lilacinum increased yield, nematode populations at planting were crucial for its efficacy. Lastly, P. lilacinum is a facultative parasite of females and eggs, exhibiting saprophytic activity in the absence of nematodes. However, it is unclear how they transition (or “switch”) from this to the parasitic stage, which could affect suppressive performance. Regardless, this particular strain shows great potential for suppressing M. incognita and for producing suppressive metabolites that impaired reproduction of Aphelenchoides besseyi in Fusarium sp.(PHILADELPHI et al., 2024).
In our work, B. amyloliquefaciens did not suppress M. incognita on melon; however, substantial data are available showing that it does suppress both other Meloidogyne spp. and other sedentary species (DALVAN DO NASCIMENTO et al., 2022; DE PAULA et al., 2024; GATTONI; PARK; LAWRENCE, 2022; MOREIRA et al., 2025).
Moreira et al.(2025) reported that B. amyloliquefaciens antagonism relies on the production of volatile and non-volatile toxic metabolites, as well as the formation of a biofilm on the root surface. Therefore, it may require a longer period to establish itself in the rhizosphere before the nematode infection.
Considering the diversity within B. amyloliquefaciens, it is likely that different outcomes can be achieved by deploying different strains. It is noteworthy that P. chlamydosporia is the only commercial treatment tested, and its performance could have been optimised in some way.
In contrast, B. amyloliquefaciens and P. lilacinum could likewise be optimised.
Conclusion
In summary, all melon genotypes were susceptible to M. incognita (R value >1).
Pochonia chlamydosporia was effective in reducing Nem/g in two experiments (biocontrol experiments 1 and 2). Regarding Rizotec®, from a nematode control perspective, it reduced the final population, with the ED50 estimated at 0.84 plant-1.
Application of Rizotec® also improved several plant growth parameters (fresh weight, fruit weight, stem diameter at the middle and top of the plant), but only in the inoculated plants. Bacillus amyloliquefaciens did not reduce M. incognita populations on melon and did not significantly increase any assessed parameter, whereas P. lilacinum reduced Nem/g in one experiment.
Pochonia chlamydosporia (i.e, Rizotec®) represents a potential strategy for the management of M. incognita and should be integrated with additional management practices to enhance its efficiency.
Acknowledgements
The authors would like to thank Dr Vincent C.T. Hanlon for revising the manuscript. We would like to thank Stoller do Brasil for providing the Rizotec® for our experiments and Sakata Seed Sudamerica for providing melon seeds. Authors would also like to thank Dr Lilian B.J. Bibiano, Dr Luis Eduardo C. Aranha, and Dr Marina R. P. Lima for their support during the execution of the experiments. VHMS and SFP would like to thank both CAPES and CNPq for funding and fellowships. VHMS also would like to thank Mrs Allyne Souza for her unconditional support in life and, in particular, during the execution of these experiments.
DATA AVAILABILITY
The data that support the findings of this study are available from the corresponding author, Souza, V.H.M., upon reasonable request.
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Edited by
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Scientific Editor
Alexandre Pio Viana
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Associate Editor
Everaldo Antonio Lopes
