Pathogenic ability of isolated wheat root rot causal organisms
The tested isolated two pathogens
R. solani and
F. graminearum proved their pathogenic ability to infect wheat seedlings causing root rot disease incidence. Data presented in Table (1) revealed that the recorded root rot incidence were 82.2 and 74.6% for wheat seedlings grown in infested soil with
R. solani and
F. graminearum, respectively. Meanwhile, un-infested control treatment showed no disease symptoms. In this concern, it was reported that wheat suffered mainly by
Rhizoctonia species causing root rot worldwide (
Demirci, 1998;
Hashem and Hamada, 2002;
Atef, 2008;
Tunali et al., 2008; Hamada et al., 2011; Guo et al., 2012). Furthermore, in all regions worldwide where cereal crops are cultivated, it was reported that seedling blight, root rot and head blight diseases caused by various soilborne pathogenic fungi,
Fusarium spp. and
R. solani (
Fernandez and Jefferson, 2004;
Nicholson et al., 2004; Asran and Eraky, 2011). Also,
Nourozian et al., (2006) stated that
F. graminearum and
F. culmorum are predominant and cause root rot, food rot, crown rot, stem rot and head blight in wheat.
Greenhouse experiment
Presented data in Table (2) and Fig (1) showed records for wheat seedlings root rot incidence and their reduction at each used biotic treatment and fungicide as well. Data in Table (1) revealed significant effect of all applied biotic and fungicide treatments against the incidence of root rot disease.
Rhizoctonia solani and
F. graminearum caused root rot infection ranged between 14.6-30.52% and 17.50-59.50% at applied biotic treatments, respectively. The fungicide treatment recorded 10.0 and 3.0% root rot incidence at treatment of
R. solani and
F. graminearum, compared with 92.0 and 83.17% at untreated control, respectively. On the other hand, illustrated data in Fig (1) showed that
B. subtilis, P. fluorescens and
A. brasilense have superior effect against disease incidence compared with
T. harzianum. They revealed announced reduction in disease incidence calculated as 93.6, 85.5, 84.5% and 33.1, 28.4, 35.3% as well as 66.6 and 43.7% for grown wheat seedling in infested soil with
R. solani and
F. graminearum, in relevant respective order. Meanwhile, moderate effect was observed at chitosan treatment whereas it could reduce disease incidence by 77.7 and 70.9% at soil infested with
R. solani and
F. graminearum, respectively. High reduction 86.3% of root rot was recorded for planta guard (the commercial bio-product containing 10
8 spore suspension of
T. harzianum) at infested soil with
R. solani and 78.9% at
F. graminearum infested soil. At fungicide treatment high reduction was observed in disease incidence in soil infested with
R. solani and
F. graminearum calculated as 89.1 and 96.3%, respectively. The stated results were found in a harmony with previous reports of several investigators. Several researchers recorded that biological control agents are sustainable and effective bio-inputs that could be used for plant diseases.
Trichoderma harzianum and
Pseudomonas fluorescensas gave maximum disease control of sunflower collar rot
(Gandhi et al., 2017). Also,
Bacillus subtilis,
P. fluorescens, Trichoderma and
Gliocladium were used beneficially against
Fusarium oxysporum f. sp.
Lycopersici of tomato wilt and
F. graminearum of wheat
(Moussa et al., 2013; Estefania and Ligia, 2018;
Fitrianingsih et al., 2019). Recognition of certain rhizobacteria can trigger a systemic resistance reaction that renders the host less susceptible to subsequent infection by virulent agents
(Bhutani et al., 2018; Herve et al., 2019; Firdous et al., 2019). Furthermore,
Trichoderma spp. are considered within the greatest recorded fungi for biological approach for controlling plant pathogens. These antagonists produce various enzymes such as chitin-lytic enzyme which implicated as an agent sharing in their ability as biocontrol action (
Cherif and Benhamou, 1990;
Lorito et al., 1993; Lima et al., 1997). Atef (2008) reported that application of either
T. harzianum or
B. subtilis individually or in combination was effective in control root rot of wheat caused by
R. solani under
in vitro and greenhouse trails. Moreover, it was reported that wheat grain dressing with antagonistic bacteria, including Pseudomonas and Bacillus, have essential effect for controlling
F. graminearum and
F. culmorum the causal agents of seedling blight disease
(Johansson et al., 2003; Khan et al., 2006). Also, reduction of anthracnose symptoms on strawberry plants previously inoculated with
A. brasilense was observed
(Tortora et al., 2011). In the present greenhouse study chitosan treatment found to have suppressing effect against the both pathogens causing root rot disease incidence. Chitosan as byproduct was reported to have inhibition efficacy against various plant pathogens either as direct effect against pathogenic microorganisms (
Allan and Hadwiger, 1979). Whereas the toxic effect as mode of action of Chitosan has generally suppress the growth of plant pathogenic fungi through its connection with the ultrastructural changes in the fungal hyphae
(Lafl-amme et al., 1999). Also, chitosan treatment has indirect effect through enhancing plant resistance to the all parts of plants,
e.g. seeds
(Benhamou et al., 1994), fruits (
Benhamou, 2004) and leaves
(Trotel-Aziz et al., 2006). Referring to the obtained results in present work, it is clearly to note that application of vital bioagents or commercial bio-products considered safe and promising for controlling such root rot diseases.
