In recent years, some researchers have noticed that there are organic biofertilizers with the potential to be used to reduce the population of M. exigua in coffee plantations. These biofertilizers come from the fermentation process of sugarcane molasses and promote improvements in the soil microbiota, inducing resistance and stimulating the development and photosynthetic potential of the plant.
Coffee (Coffea arabica L.) has considerable economic importance for Brazil. However, even with the benefits that it provides for the world agricultural sector, the crop presents some phytosanitary problems, including phytonematodes. Among the more than 90 species included in the genus Meloidogyne, in arabica coffee M. exigua Goeldi deserves to be highlighted.
One of the management methods most used to reduce the population of Meloidogyne spp. is the application of chemical nematicides. However, researchers around the world have been looking for management measures that are less aggressive to the environment, including the concomitant application of low toxicity chemicals, such as Fluensulfone, with agents of biological control such as Bacillus spp. and the fungus Trichoderma and/or biofertilizers. These antagonists can occur naturally, by manipulating the environment or by introducing one or more antagonistic organisms into crop areas.
Nematode Distribution in Soil and Roots
Table 1 lists the treatments, with their respective doses and application times.
| Treatments | dose L/ha |
|---|---|
| 1 – Bio1 | 10 |
| 2 – Bio1 + Bio1 | 10 + 10 |
| 3 – Bio1 + Bio2 | 10 + 20 |
| 4 – Bio3 | 300 g |
| 5 – Bio4 | 1.5 |
| 6 – Flu5 | 1.5 |
| 7 – Flu + Bio1 | 1.5 + 10 |
| 8 – Control | – |
Means followed by the same letter do not differ from each other by the Scott-Knott Teste at a 5% probability level.
Figure 1 shows the average numbers of nematodes present in the soil and roots of plants submitted to the different treatments.
The lower numerical value of M. exigua individuals found in the soil in relation to coffee roots can be explained by the biological characteristics of Meloidogyne spp. For nematodes of this genus, J2 are attracted by root exudates from roots, migrate through the root cortex and establish their feeding sites near the pericycle. At this point, the J2 go through four ecdyses, become sedentary adult females, and usually lay their eggs within the root itself. From these eggs, new J2 will hatch. Thus, it is common to find higher numbers of J2 and eggs inside the root than in the soil.
Population Growth Potential of Phytonematodes
As time passes the population increase of phytonematodes in the field is expected, since these pathogens multiply in their host on a logarithmic scale. Thus, given that a female of Meloidogyne spp. produces around 500 eggs, and considering that approximately 5% of these eggs survive to complete their cycle, there will be at the end four generations respectively: 25, 625, 15,625 and 390,625 adults.
Effect of Trichoderma harzianum-Based Product
The biological product based on Trichoderma harzianum provided a decrease in the average population of M. exigua, which can be explained by the antagonistic fungus’ capacity to colonize the egg masses produced by Meloidogyne exigua and the consequent impairment of the nematode’s life cycle.
In addition to the direct effects on phytonematodes, Trichoderma harzianum also stimulates the root development of the plant, releasing metabolites that act as phytohormones and resistance inducers, in addition to promoting the decomposition of organic matter and, consequently, the release of nutrients to the plants, making them more resistant to phytonematodes.
This antagonist presents sophisticated strategies for capturing and infecting nematodes, being able to act as a predator, parasite of eggs and sedentary females, in addition to the synthesis of toxic metabolites and competition with pathogens. In fact, this antagonist can exert direct parasitism on eggs and juveniles by increasing the activity of chitinases and proteases, which is indicative of the ability to infect eggs and the induction of host plant defense mechanisms.
Thus, Trichoderma sp. is a viable option for the management of M. exigua due to the results obtained in our research and the characteristics that make it a good biological control agent, acting in the preventive protection of plants, in the restoration of the microbial community and in the recovery of soil structure weakened by intensive agricultural practice.
Effect of Bacillus subtilis and Bacillus licheniformis-Based Product
Bacillus subtilis and Bacillus licheniformis, had a positive effect on the reduction of M. exigua population. These bacteria, when present in the rhizosphere, are able to prey on and compete with nematodes, in addition to stimulating plant growth and inducing plant resistance to the attack of these phytopathogens. It is also important to highlight that these bacteria have a high ability to compete in the soil and colonize the root system, feeding on root exudates and forming a protective biofilm around the root.
During bacterial development, secondary metabolites are secreted with a nematicidal and/or nematostatic effect that limits the reproduction of nematodes. This proves that this product has potential for the management of M. exigua due to its mechanisms of antibiosis, parasitism and competition.
In addition, one of the main characteristics that make Bacillus subtilis and Bacillus licheniformis good biological control agents is the production of toxic compounds that, in contact with nematodes, interfere with their reproductive cycle, mainly in the oviposition and hatching of juveniles, in addition to aiding plant growth.
Effect of Fluensulfone
The positive effect of Fluensulfone in the population reduction of M. exigua both in the soil and in the roots was expected. Fluensulfone has shown considerable nematicidal activity, especially against Meloidogyne spp. In addition to its low toxicity to non-target organisms, Fluensulfone has some characteristics that make it a good chemical control agent for phytonematodes, such as nematicidal activity rather than nematostatic effect and systemic nematicidal activity. Although it acts differently from organophosphates and carbamates, the mode of action of Fluensulfone on Meloidogyne spp. is still not well understood.
Fluensulfone in high concentrations affected the stylet movement of second-stage juveniles (J2) of Globodera pallida. However, at lower concentrations and in contact with the nematode for longer periods, the nematicide led to impaired metabolism and tissue degeneration of the pathogen.
In the area where it was used in association with Fluensulfone, there was a reduction in the number of nematodes in the soil and roots. Some chemical nematicides can cause nematode paralysis by exposing them to antagonists or reducing the nematode population to levels where these antagonists can act more effectively. The bacterium Pasteuria penetrans, for example, is not affected by aldicarb, carbofuran, mirol, forate and oxamyl, which makes it possible to use the bacterium with these pesticides.
Relative Efficiency of Treatments
The Relative Efficiency (RE) (%) of the treatments is shown in Fig. 2.
The RE ranged from 34.77% at T1 (Organic biofertilizer containing strains of Bacillus subtilis, B. licheniformis and Lactobacillus sp.) to 45.04% at T3 (Organic biofertilizer containing strains of Bacillus subtilis, B. licheniformis and Lactobacillus sp. + Humic and fulvic acids), and, except for T1 and T2, all treatments presented RE greater than 40% (Fig. 3). Higher ER was observed for T3, T5, T6 and T4, respectively, which clearly demonstrates that biofertilizers used in combination (T3) and the Trichoderma harzianum-based biopesticide (T5) have a higher RE than that observed in plants treated with nematicide alone (T6) .
Temporal Effects of Treatments on Nematode Population
As there was no significant interaction of the products in the application periods (DAA), the effect of the treatments at each collection time after application of the treatments will be shown in Fig. 3.
In the evaluation carried out at 180 DAA, there was reduction in the population of the nematode in the roots, in contrast to previous evaluations (Fig. 3).
However, in subsequent evaluations at intervals of 240 DAA and 360 DAA, there was an increase in the population of M. exigua (Fig. 3).
This population increase of the nematode at 240 and 360 DAA can be explained by the climatic conditions that prevailed during the experimental period. Between January and April 2020 the maximum temperature fluctuated between 28 ℃ and 30 ℃ and the minimum between 26.0 ℃ and 16.5 ℃, and the average precipitation reached 330 mm in January. This made the environment very favorable to the increase in the population of M. exigua in the evaluations at 240 and 360 DAA, although the plants had received the treatments.
Nematodes of the genus Meloidogyne can complete their cycle under optimal temperature conditions in 28 days. However, night and day temperature variations can change the time of consummation of this cycle, reaching 60-70 days in the winter period.
When the soil temperature is around 29 ℃, there is a significant increase in the reproduction of Meloidogyne spp. and in the formation of galls compared to plants kept at temperatures varying between 23 ℃ and 25 ℃ due to the greater penetration of juveniles in the roots of these plants. The authors also observed that the hatching of J2 of M. incognita was higher when using 29 ℃ compared to the temperature oscillating between 23 ℃ and 25 ℃. The percentage of J2 of hatched M. chitwoodi and M. hapla was significantly lower at 15 ℃ than at 20 ℃ and 25 ℃, with greater nematode hatching occurring at 25 ℃.
Despite the increase in the population of the nematode in the assessment carried out at 240 DAA and 360 DAA, there was a reduction in the population of M. exigua in the last assessment carried out at 420 DAA (Fig. 2). In this case, there was less precipitation and a lower temperature in the period that preceded this evaluation (Fig. 3), which did not favor the significant increase in the nematode population and allowed the treatments to have their effects in reducing the pathogen population.
There is a clear relationship between the population increase of the nematode and the ideal soil and climate conditions for coffee growing conditions. The adaptation and reproduction of M. exigua is enhanced in places with hot and humid climates, the same conditions that are ideal for the development of arabica coffee.
Effects on Coffee Yield
The average of coffee yields in bags/ha for the years 2019 and 2020 are shown in Fig. 4.
The highest yields in 2019 were observed in plants treated with T1-Organic biofertilizer containing strains of Bacillus subtilis, B. licheniformis and Lactobacillus sp. (53 sc/ha) and T5-Bio4 (52.75 sc/ha), whereas in 2020 it was in plants that received T3 – Organic biofertilizer containing strains of Bacillus subtilis, B. licheniformis and Lactobacillus sp. + Humic and fulvic acids (54.5 sc/ha) and T6-Fluensulfone (58.25 sc/ha) and T7-Fluensulfone + Organic biofertilizer containing strains of Bacillus subtilis, B. licheniformis and Lactobacillus sp. (62.12 sc/ha) (Fig. 4).
In general, productivity in both 2019 and 2020 was lower in untreated plants compared to those that received treatments (Fig. 4). This is explained by the higher populations of M. exigua observed in the control (Fig. 1).
These damages to coffee productivity are explained by the parasitism of nematodes on plants, which results in the creation of permanent feeding sites in root tissues, consisting of giant cells in the cortex, endoderm, pericycle and parenchyma.
The formation of root galls on coffee plants is the most characteristic symptom produced by M. exigua. These galls appear mainly on the thinnest roots and are the result of hypertrophy and hyperplasia of cells in the vascular parenchyma of the root. These cells are multinucleated and function as true food supply stores for sedentary nematodes. All these physiological and mechanical damages lead to reduced productivity, as observed in untreated plants in our study.
The arabica coffee bush attacked by M. exigua can have its production reduced by between 30 and 45%. In contrast, although young plants are more harmed, depending on some factors, such as soil type, adult plants can suffer serious defoliation, impairing the production of photoassimilates. This can lead to reduced productivity, as observed in the two years of harvest in plants that did not receive any treatment (control) in our research.
Yield Losses and Profitability
Table 2 shows all the information that was used to calculate the yield losses that the coffee grower had in his cultivation area in 2019 and 2020 due to the parasitism of M. exigua on the coffee plants, as well as its profitability due to the application of treatments.
| Treatments | Total cost of treatment application/ha(Product + application) | bags harvested/ha | Productivity sales value/ha | Net profitability from the sale of productivity /ha | |||
|---|---|---|---|---|---|---|---|
| 2019 and 2020 | 2019 | 2020 | 2019 | 2020 | 2019 | 2020 | |
| T1 -Bio1 | 390.00 | 53.00 | 44.87 | 24,099.10 | 23,781.10 | 23,709.10 | 23,391.10 |
| T2 -Bio1 + Bio1 | 630.00 | 46.25 | 45.37 | 21,029.87 | 24,046.10 | 20,399.87 | 23,416.10 |
| T3 -Bio1 + Bio2 | 670.00 | 46.62 | 46.62 | 21,198.11 | 24,708.60 | 20,528.11 | 24,038.60 |
| T4 -Bio3 | 570.00 | 45.65 | 45.50 | 200757.05 | 24,115.00 | 20,187.05 | 23,545.00 |
| T5 – Bio4 | 400.00 | 52.75 | 42.77 | 23,985.42 | 22,668.10 | 23,585.42 | 22,268.10 |
| T6 – Flu5 | 1,800.00 | 42.25 | 58.25 | 19,211.07 | 30,872.50 | 17,411.07 | 29,072.50 |
| T7 – Flu + Bio1 | 2,040.00 | 49.52 | 62.12 | 22,516.74 | 32,923.60 | 20,476.74 | 30,883.60 |
| T8 – Control | 0 | 41.77 | 44.37 | 18,992.81 | 23,516.10 | 18,992.81 | 23,516.10 |
| 1Organic biofertilizer containing strains of Bacillus subtilis, B. licheniformis and Lactobacillus sp.; 2Fluid biofertilizer 100% organic and rich in organic matter (humic and fulvic acids; 3Biopesticide based on B. subtilis lineage FMCH002 (DSM32155) and B. licheniformis lineage FMCH001 (DSM32154); 4 Biopesticide based on Trichoderma harzianum strain ESALQ-1306; 5 Fluensulfone (5-chloro-2-(3,4,4-trifluorobut-3-f enylsulfonyl)-1,3-thiazole). | |||||||
Analyzing the results obtained in 2019, it is clear that, in the short term, T1 and T5 present satisfactory results in the reduction of the nematode population (Fig. 1) and, consequently, in the increase in productivity (Fig. 4) and profitability (Table 2). Because they are cheaper and environmentally friendly products they can be considered a useful tool for the management of M. exigua parasitizing arabica coffee.
In the year 2020, they were no longer the most promising, probably because there were extremely favorable environmental conditions for the population increase of M. exigua, which led to a reduction in productivity. Thus, in cases of high favorability to the nematode population increase, biological products applied alone may not be enough to reduce the number of nematodes in the soil and roots and consequently generate profit for the coffee grower.
This is very evident in the 2020 harvest, in which it is observed that, despite the considerable increase in the population of M. exigua due to the heat and humidity favorable to its reproduction, the application of the chemical nematicide alone or in combination with the biological ensures profit for the producer. This was precisely because this chemical nematicide has a more drastic and faster effect on the nematode population compared to bionematicides and biofertilizers.
Conclusion
Biofertilizers, biopesticides and Fluensulfone are useful tools for the management of M. exigua parasitizing arabica coffee, as they reduce damage and yield losses and guarantee increased productivity and profitability for the coffee grower by means of reducing the pathogen population. However, when climatic conditions are extremely favorable to nematodes, biofertilizers and biopesticides alone are not enough to reduce the nematode population satisfactorily.
The ideal is to resort to the application of chemical nematicide alone or in combination with biofertilizers (Fluensulfone + organic biofertilizer containing strains of Bacillus subtilis, B. licheniformis and Lactobacillus sp), which ensures greater profitability for the producer, explained by the fact that the chemical nematicide has a more drastic and faster effect in reducing the nematode population compared to biofertilizers and bionematicides.
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