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Biological control emerged as a rational, extremely necessary and essential alternative to agriculture today. Manipulation of the environment and the introduction of antagonists, both in the soil and in plant propagation organs, can guarantee the biological control of soil-borne phytopathogens. Among the biocontrollers used against soil pathogens, wild and improved isolates of Trichoderma spp. This fungus is a necrotrophic mycoparasite effective in controlling numerous phytopathogenic fungi, especially those with resistance structures considered difficult to be attacked by microorganisms, such as spores, sclerotia, chlamydospores and microsclerotia. The mechanisms of action by which the Trichoderma can act are: antibiosis, hyperparasitism, competition and also in some cases through promoting plant growth. With this vision, it is essential to integrate biological control with other available methods, such as the use and increase of vegetation cover or straw, chemical control and varieties with partial resistance or tolerance to diseases.
Despite being considered a free-living soil fungus, universally present in this environment, in all climatic zones, some species can be cosmopolitan (example T. harzianum) or limited in their geographic distribution (example T. viride). Trichoderma stromaticum It has possibly the most restricted distribution among the species of the genus and is only found associated with cocoa plants or the pathogenic agent Crinipellis perniciosa, which causes witches' broom in cocoa. A strong influence on the distribution of species of Trichoderma is the temperature. Species from cold regions have a low optimum temperature, as is the case of Trichoderma viride e Trichoderma polysporum, which develop well at 7°C, and Trichoderma minutisporum. Trichoderma koningii e Trichoderma hamatum support until
Trichodermas are known for their high capacity to produce enzymes that degrade cellulose and chitin. In the Philippines, T. harzianum it is inoculated into compost piles to accelerate cellulose degradation. Trichoderma reesei was considered the best known species for the commercial production of cellulase. In addition to cellulose and chitin, Trichodermas spp. are capable of degrading hydrocarbons, chlorophenicol, polysaccharides and xenobiotic pesticides used in agriculture. Issues related to environmental problems and production costs are the main reasons for the current expansion of the biological control market in the country.
Trichoderma spp as decomposer in plant growth
Some species of Trichoderma They can promote plant growth, increase germination and seed emergence, and can also have indirect positive effects by increasing plant growth. This occurs in an apparently symbiotic and non-parasitic relationship between the fungus and the plant, where the fungus occupies the nutritional niche and the plant is protected from diseases. After developing in the spermosphere, Trichoderma spp. It can be used in seed inoculation, as it ends up following the development of the root of the new plant, contributing to the fungus' pioneering role in this structure. Species of Trichoderma they produce organic acids that reduce the pH of the soil and allow the solubilization of phosphate, micronutrients and minerals such as iron, manganese and magnesium, useful for the plant's metabolism. Increased root or shoot growth increases resistance to biotic or abiotic stresses and changes in status plant nutrition.
Trichoderma spp as a biocontrol agent
The use of Trichoderma spp. has already been documented for the control of Rhizoctonia solani, Sclerotium rolfsii, Sclerotinia sclerotiorum, Fusarium spp. And Pythium spp. Trichoderma virens is effective against damping-off, caused by S. sclerotiorum e pythium ultimum e Rhizoctonia solani Kuhn. In cotton, suppression activity has been reported against Rhizoctonia solani, Fusarium oxysporum f.sp. vasinfectum.
From a biocontrol point of view, T. harzianum e T. asperellum are the most studied species, in addition to other species such as T. koningii, T. viride, T. hamatum, and T. pseudokoningii. Biocontrol activity is reported for populations of Trichoderma 105 - 107 CFU/g grown in a controlled medium, such as fumigated soil and applied to the soil in portions of one liter/m2, with 108 spores/liter. The conidia and chlamydospores of Trichoderma They are formulated and used to treat soil, seeds, bulbs and runners, and are also sprayed on the aerial part of plants.
Mechanisms of action Trichoderma spp in biocontrol
Suppression of a disease mediated by biocontrol agents and controller success. Therefore, understanding the relationships between organisms is among the fundamental factors for maintaining the natural balance of populations and biological cycles. In hyperparasitism, species of this genus are able to detect and locate hyphae of susceptible fungi (Figure 2), perhaps in response to chemical stimuli produced by the host's hyphae, forming structures similar to appressoria and tightly coiling along the entire length of the hyphae to then penetrate and digest it. This mechanism has already been demonstrated by several researchers through the interaction between T. harzianum, Rhizoctonia solani, Pythium e Sclerotim rolfsii.
The antifungal arsenal of Trichoderma includes a wide variety of lytic enzymes (example: exoglucanase, endoglucanase, cellobioase, cellulases, chitinases, glucanases), most of which play an important role in biological control. This fungus is capable of parasitizing and destroying even the resistance structures of phytopathogens, such as sclerotia of Sclerotinia sclerotiorum.
The interaction of Trichoderma with other microorganismsanisms
Some isolates from Trichoderma spp. induce systemic resistance in plants by activating the synthesis of pathogenesis-related proteins (PRPs), even before the pathogen invades the host plant. In many cases, salicylic acid and jasmonic acid, together with ethylene or nitrous oxide, induce a cascade of events that trigger the production of a wide variety of metabolites and proteins with diverse functions in the plant, modifying the proteome and plant physiology. . Figure 1 elucidates the main mechanisms of action of Trichoderma in soil, seeds and plants.
Figure 1 - Action of Trichoderma in soil, roots, seeds, vegetative parts and plants
The degree of protection promoted by isolates of Trichodermthe spp. which induces systemic resistance in plants, can be as effective as that promoted by fungicides. For example, the degree of control promoted by Trichoderma hamatum – T 382 against Phytophthora capsici was as effective as that promoted by the fungicide metalaxyl.
The importance of evaluating commercial products based on Trichoderma
Trichoderma it can be formulated in solid medium (WP), water-dispersible granules (WG) or oil (E) or even concentrated suspension (SC). How the living organism (spores or conidia) is used is important to maintain its viability, whether by cold conservation or storage at low temperatures and in a suitable environment. This type of service has been carried out by the Mycology and Plant Protection Laboratory (Lamip), at the Federal University of Uberlândia (UFU) for seven years, with the routine provision of services to the agricultural community and companies in the Triângulo Mineiro and Alto region. Paranaíba in Minas Gerais and throughout Brazil. Checking for bacterial contamination is also important, as their presence reduces the product's useful life.
In the present assessment, commercial products based on Trichoderma spp were sent by their respective companies. Table 1 contains a description of the bioproducts evaluated.
Table 1 - Description of biological products, active ingredient, formulation, concentration declared on the label and manufacturing company. UFU, Uberlândia, 2014
| Active ingredient | Formulation | Concentration Declared | ||
| Trichoderma spp | PM | 1,0 x 10 8* | ||
| T. harzianum | WP | 5,0 x 10 10* | ||
| T. asperellum | WG | 1,0 x 10 10* | ||
| T. harzianum | SC | 2,0 x 10 9** |
Active ingredient
Formulation
Concentration
Declared
Trichoderma spp
PM
1,0 x 10 8*
T. harzianum
WP
5,0 x 10 10*
T. asperellum
WG
1,0 x 10 10*
T. harzianum
SC
2,0 x 10 9**
*mL spores-1 or spores g-1
**viable conidia ml-1
To analyze the viability and concentration of bioproducts, serial dilutions of the products were carried out in distilled and autoclaved water, which were plated in Petri dishes containing PDA (Potato-Dextrose-Agar) medium, being incubated for five days at 22°C ±
Bioproducts (T. asperellum) And (T. harzianum) did not differ statistically from each other, both showing 98% spore germination, followed by Trichoderma spp, with 90%, and T. harzianum, with 60% germination (Table 2). Regarding bacterial contamination of the bioproduct (T. harzianum) showed greater contamination, differing from the other treatments. It is worth noting that this analysis was carried out for a batch or sample, which can vary even for a batch or sample depending on how it was handled from production, transportation to commercialization, or even storage.
Table 2 - Percentage of germination and bacterial contamination of bioproducts. UFU, Uberlândia-MG, 2014
| Bioproducts | Percentage germination | Contamination by Bacteria | ||
| (Trichoderma spp) | 90 | b | 3,0 x 10 6 | a |
| (T. harzianum) | 60 | c | 6,0 x 10 6 | b |
| (T. asperellum) | 98 | a | 5,0 x 10 5 | a |
| (T. harzianum) | 98 | a | 1,0 x 10 6 | a |
| CV (%) | 2,53 | 36,87 | ||
Bioproducts
Percentage
germination
Contamination
by Bacteria
(Trichoderma spp)
90
b
3,0 x 10 6
a
(T. harzianum)
60
c
6,0 x 10 6
b
(T. asperellum)
98
a
5,0 x 10 5
a
(T. harzianum)
98
a
1,0 x 10 6
a
CV (%)
2,53
36,87
Means followed by the same letter in the column do not differ from each other using the Tukey test, at 5% probability.
In Table 3 it can be seen that the concentration obtained in the Neubauer chamber is higher than the concentration declared on the label, however, this value does not correspond to the actual concentration of the bioproduct, since all spores present are accounted for, i.e. the spores that will germinate and those that will not germinate, so it is important to measure the concentration on the plate, where it can be seen that only the bioproducts (T. asperellum) And (T. harzianum) presented concentrations higher than those declared.
Table 3 - Concentration and viability of bioproducts. Uberlândia-MG, 2014
| Bioproducts | Concentration Declared | Concentration on Neubauer Chamber | Concentration on the board | Difference between Declared Concentration | |
| Neubauer Chamber | License plate | ||||
| Trichoderma spp | 1,0 x 10 8 | 7,5 x 10 9 | 1,0 x 10 7 | + 7,4x10 9 | - X 9,0 10 7 |
| T. harzianum | 5,0 x 10 10 | 2,0 x 10 10 | 3,0 x 10 6 | - X 3,0 10 10 | - X 4,9 10 10 |
| T. asperellum | 1,0 x 10 10 | 9,0 x 10 10 | 5,0 x 10 10 | + 8,0x10 10 | + 4,0x10 10 |
| T. harzianum | 2,0 x 10 9 | 2,0 x 10 10 | 6,0 x 10 9 | + 1,8x10 10 | + 4,0x10 9 |
Bioproducts
Concentration
Declared
Concentration on
Neubauer Chamber
Concentration
on the board
Difference between Declared Concentration
Neubauer Chamber
License plate
Trichoderma spp
1,0 x 10 8
7,5 x 10 9
1,0 x 10 7
+ 7,4x10 9
- X 9,0 10 7
T. harzianum
5,0 x 10 10
2,0 x 10 10
3,0 x 10 6
- X 3,0 10 10
- X 4,9 10 10
T. asperellum
1,0 x 10 10
9,0 x 10 10
5,0 x 10 10
+ 8,0x10 10
+ 4,0x10 10
T. harzianum
2,0 x 10 9
2,0 x 10 10
6,0 x 10 9
+ 1,8x10 10
+ 4,0x10 9
In the market, there is Trichoderma sold in its cultivation substrate, which is ground and packaged. This formulation is more difficult to apply due to clogging of nozzles. It also does not allow for long viability of the fungus, in addition to allowing greater contamination by other fungi and bacteria, thus reducing its efficiency in the field. There are other formulations on the market, such as pure spores, mixed in oil, in concentrated suspension or even in water-dispersible granules (WG), which facilitate application. With the emergence of oily formulations, this formulation provides greater stability of the active ingredient when stored at room temperature (24ºC - 26ºC). Furthermore, it has advantages in terms of ease of application and protection in the field of UV radiation. It is extremely important to choose a quality product, combined with a formulation that guarantees efficiency in the application and control of white mold, caused by Sclerotinia sclerotiorum and other soil-borne pathogens, such as Fusarium, rhizoctonia, Macrophomina etc.
Verification of hyperparasitism of Trichoderma spp about S. sclerotiorum
Among the antagonist's mechanisms of action, hyperparasitism can occur both through strangulation and penetration of the hyphae. Trichoderma spp on the pathogen, which can be observed in the scanning electron microscopy (SEM) photos - Figure 2 -, where all the isolates analyzed colonize the pathogen, either penetrating or strangling its hyphae, the growth of parallel hyphae is also noted .
Figure 2 - Photo with scanning electron micrograph of the interactions between Trichoderma spp and S. sclerotiorum, showing the strangulation and penetration of the antagonist hyphae over the pathogen, respectively: a.1 and a.2) (Trichoderma spp); b.1 and b.2) (Trichoderma harzianum); c.1 and c.2) (Trichoderma asperellum); d.1 and d.2) (Trichoderma harzianum)
Enzyme secretion constitutes an essential step in the biocontrol of fungi.
The two types of interactions verified in this work, penetration and strangulation, can be interpreted as hyperparasitic action. For both species, Trichoderma asperellum e T. harzianum, regardless of the formulation and commercial product studied, paired with the pathogenic fungus S. sclerotiorum. This same action was observed in the pairing of Trichoderma e Fusarium oxysporum and com T. harzianum e Rhizoctonia solani.
Selectivity of fungicides to commercial products based on Trichoderma
Table 4 presents the selectivity vitro of the main fungicides available on the Brazilian market.
Table 4 - Selectivity of commercial fungicides in different concentrations to isolates of Trichoderma spp. Uberlândia-MG, 2014
| Fungicides | PPM | Trichoderma | T. harzianum | T. asperellum | T. harzianum | |
| Witness | 0,0 | + + + + | + + + + | + + + + | + + + + | |
| (thiophanate + Fluazinan) | 0,1 | + + + | + + + | + + + + | ++ | |
| 1,0 | ++ | ++ | ++ | ++ | ||
| 10 | + | + | + | + | ||
| 100 | + | - | + | + | ||
| 1000 | - | - | - | - | ||
| (fluaizinan) | 0,1 | ++ | + | ++ | ++ | |
| 1,0 | ++ | + | ++ | ++ | ||
| 10 | + | + | ++ | + | ||
| 100 | + | + | ++ | + | ||
| 1000 | + | + | + | + | ||
| (thiophanate) | 0,1 | + + + + | + + + + | + + + + | + + + + | |
| 1,0 | + + + + | + + + + | + + + + | + + + + | ||
| 10 | + | + | + | + | ||
| 100 | + | + | + | + | ||
| 1000 | - | - | - | - | ||
| (Thioaphanate + fipronil + pyraclostrobin) | 0,1 | + + + | + + + | + + + | + + + | |
| 1,0 | ++ | ++ | ++ | ++ | ||
| 10 | + | + | + | + | ||
| 100 | + | + | + | + | ||
| 1000 | - | - | - | + | ||
| (carbendazin) | 0,1 | + | + | + | + | |
| 1,0 | + | + | + | + | ||
| 10 | + | + | - | + | ||
| 100 | + | + | + | + | ||
| 1000 | - | + | - | + | ||
| fludioxonil + tiran) | 0,1 | ++ | + | + | + | |
| 1,0 | + | + | + | + | ||
| 10 | + | + | + | + | ||
| 100 | + | + | + | + | ||
| 1000 | + | + | + | + | ||
| (procymidone) | 0,1 | + + + + | + + + + | + + + | + + + + | |
| 1,0 | + + + | + + + | + + + + | + + + | ||
| 10 | + | + | + | ++ | ||
| 100 | + | + | ++ | ++ | ||
| 1000 | + | + | ++ | ++ |
Fungicides
PPM
Trichoderma
T. harzianum
T. asperellum
T. harzianum
Witness
0,0
+ + + +
+ + + +
+ + + +
+ + + +
(thiophanate + Fluazinan)
0,1
+ + +
+ + +
+ + + +
++
1,0
++
++
++
++
10
+
+
+
+
100
+
-
+
+
1000
-
-
-
-
(fluaizinan)
0,1
++
+
++
++
1,0
++
+
++
++
10
+
+
++
+
100
+
+
++
+
1000
+
+
+
+
(thiophanate)
0,1
+ + + +
+ + + +
+ + + +
+ + + +
1,0
+ + + +
+ + + +
+ + + +
+ + + +
10
+
+
+
+
100
+
+
+
+
1000
-
-
-
-
(Thioaphanate + fipronil + pyraclostrobin)
0,1
+ + +
+ + +
+ + +
+ + +
1,0
++
++
++
++
10
+
+
+
+
100
+
+
+
+
1000
-
-
-
+
(carbendazin)
0,1
+
+
+
+
1,0
+
+
+
+
10
+
+
-
+
100
+
+
+
+
1000
-
+
-
+
fludioxonil + tiran)
0,1
++
+
+
+
1,0
+
+
+
+
10
+
+
+
+
100
+
+
+
+
1000
+
+
+
+
(procymidone)
0,1
+ + + +
+ + + +
+ + +
+ + + +
1,0
+ + +
+ + +
+ + + +
+ + +
10
+
+
+
++
100
+
+
++
++
1000
+
+
++
++
Selectivity: (-) absence: 0%; (+) bad: 0-25%; (++) regular: 25-50%;
(+++) good: 50-75%; (++++) very good: 75-100%.
Emergence speed indices for different commercial products based on Trichoderma
According to Graph 1, seed treatment with Trichoderma does not affect the speed of emergence, treatment with the bioproduct (T. asperellum) was higher, presenting the highest averages of emergence speed, considering both with and without inoculation of the fungus Sclerotinia sclerotiorum.
For seeds inoculated with the fungus, the product (T. asperellum) presented the best averages for emergency speed, being the only one to differ from the control.
Graph 1 - Average emergence speed of seeds treated with Trichoderma spp, with and without inoculation of S. sclerotiorum. Uberlândia-MG, 2011
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