Dual confrontation
Statistical analysis revealed a highly significant effect (P<0.05), a remarkable difference in mycelial growth of Foa isolates with
Trichoderma harzianum (TH), compared to the control (Table 2), with formation of zone inhibition (Z), (Fig 1). We found that the mycelial growth in the control is always greater that obtained with the direct (dual) confrontations (Foa + TH), (Table 3).
The averages of mycelial growth of Foaisolates were consistently lower (between 2.04 and 2.53 mm / day), than the control (between 3.15 and 5.42 mm / day), (Table 3). This reduction is followed by a complete stop of the growth.
The inhibition rate (%) of mycelial growth (RI), of Foa under the direct effect of
T. harzianum varies between 28.42 and 59.12% (Fig 2), according to the isolate. 12 isolates (S1, S3, S9, S10, S11, S12, S15, S16, S17, S18, S19, S20), showed a very high inhibition rate that exceeded 50%. Also, we observed that all four isolates of Ghardaia region showed IR more than 50% (S17, S18, S19 and S20), (Table 3; Fig 2).
Indirect confrontation
Also, a significant effect (P<0.05) was observed by appearance of a difference on mycelial growth of Foa isolates in the effect of volatile substances indirectly confronted against
Trichoderma harzianum compared to the control (Table 4).
We observed that the average of the mycelial growth of Foa isolates by the effect of
T. harzianum (Table 3), is always lower (between 2.04 and 2.53 mm/day), than the control (between 2.13 and 4.88 mm/day).
The inhibition rate (IR%) of the mycelial growth of Foa under the effect of
T. harzianumvaries between 3.3 and 52.9% (Fig 2).
In comparison between the two tests of confrontation effects, we observed that the dual confrontation presented IR values very important with global average very close to 50% (49.80%), than IR values of indirect confrontation with global average under 50% (35.9%).
The potential of microoganisms as biological control agents against plant diseases has been identified for several years (
Howell, 2003). The antagonism action of microorganisms has been studied for many plant diseases
(Wells et al., 1972; Schirmbock et al., 1994; Elad and Kapat,1999;
Yedidia et al., 1999; Yedidia et al., 2001; Harman, 2000;
Sharon et al., 2001; Ozbay and Newman, 2004;
Hibar et al., 2007; El-Hassni et al., 2007; Kuçuk et al., 2007;
Dawidziuk et al., 2016; Benzohra et al., 2020).
The direct and indirect confrontation between the fungal antagonist
Trichoderma harzianum and the pathogen
Fusarium oxysporum f. sp
. albedinis (Foa) showed significant reductions in mycelial growth compared with the controlin all the isolates used. This reduction was represented by the inhibition rate (IR%) of mycelial growth. In dual confrontation, this rate varies between 28.42 and 59.12% and the indirect confrontation showed an inhibition rate varies between 3.3 and 56%, by the effect of
T. harzianum.
Hibar et al., (2007) reported that
T. harzianum was able to show a growth inhibition rate of 70 to 76% of
Fusarium oxysporum f. sp.
radici-lycopersici, tomato vascular wilt agent (
Lycopersicum esculentum L.). While
Boughedid and Filali (2015) reported aninhibition rate of mycelial growth by
T. harzianum varies between 50 and 57% on
Fusarium graminearum, Fusarium wilt agent of barley (
Hordum vulgare L.). Concerning a bayoud disease,
Sidaoui et al., (2018) reported that
Trichoderma longibrachiatum had a 63% inhibition rate on mycelial growth. These last two results are very closer to those obtained in our tests.
This inhibition of mycelial growth is known in the bibliography as “antibiosis”. Antibiosis is one of antagonism mode actions carried out by antagonistic fungi by the secretion of secondairyvolatile substances such as glio-viridines and glio-toxins, substances that act as antibiotics, can inhibit the development of several phytopathogenic fungi (
Howell, 2003).
In direct confrontation, there is another mode of antagonism called “mycoparasitism”. An example of this mode of action is on the
T. atroviride strains, which showed a mycoparasitism action against
Fusarium oxysporum f. sp.
ciceris (Foc), a vascular wilt agent in chickpea (
Cicer arietinum L.), by its ability to invade Foc colonies and sporulate above (Mach
et al.,1999). A significantly positive correlation exists between the efficacy of
Trichoderma strains in reducing disease index and growth inhibition in indirect confrontation under the effect of volatile antifungal substances (
Howell, 2003;
Kala et al., 2016; Fitrianingsih et al., 2019). This finding suggests that the antagonistic activation of our Foo isolates may be due in part to these volatile antifungal substances
(Mach et al., 1999). Many researches showed the biological control activity of
T. atroviride, that was due in part to the production of endochitinases
(Kullnig et al., 2000), to the production of antibiotics (antifungals), including aromatic antibiotics such as pyrones
(Keszeler et al., 2000), peptides
(Oh et al., 2000) and induction of resistance mechanisms in plants
(Brunner et al., 2005).
T. atroviride has shown a good efficacy in the biological control of
Rhizoctonia solani on potato in the field
(Kullnig et al., 2000) and also good protection against
Fusarium graminearum, when applied by treatment wheat seed
(Roberti et al., 2000). Recently, the biological control capabilities of this species have been shown against
Cryphonectria parasitica (Murril) Barr., the agent of chestnut cankerin USA
(Dodd et al., 2003).
According to
Hervas et al., (1997), the contribution of
T. harzianum (marketed biofungicide) to soil significantly reduces the incidence of Fusarium wilt of chickpea, caused by
Fusarium oxysporum f. sp.
ciceris.
Dubey et al., (2007) reported a significant reduction in glasshouses by seed application of
T. harzianum isolates against Pythium root rot.
Wang et al., (2003) reported that the other species of the antagonistic fungus,
Trichoderma viride, influences the development and survival of
A. rabiei, agent of ascochyta blight on chickpea. Some authors have noted that the absence of Bayoud disease in the palm groves of some Moroccan regions such as Marrakesh, seems linked to the phenomenon of the presence of antagonistic microorganisms in the soil (
Sedra, 1993;
Sedra and Rouxel, 1989). This remark was observed also in Algeria in the oases of Mizab region
(Benzohra et al., 2017).
All these results confirmed the importance of application of this fungal species as a means of biological control and are promising for the future in the program of integrated control of the Bayoud date palm.