Biological Control of Anthracnose (Colletotrichum Species) of Sorghum (Sorghum Bicolor L.) Using Trichoderma Isolates Under in Vitro Conditions
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Date
2019-10-10
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Addis Ababa University
Abstract
Biological control with microbial antagonists is considered an alternative approach for controlling
plant diseases. Trichoderma species are one of the potential fungal biocontrol agents in suppression
of soil-borne and foliar pathogens. The present study aimed to evaluate, test and characterize
potential biocontrol agents of Trichoderma isolates against two pathogenic isolates of
Colletotrichum species under in vitro condition. Infected sorghum leaf, sheath, stalk and soil
samples were collected from different ecological habitat of Welkait district for the isolation of
Colletotrichum isolates. The study examined the effect of pH and temperature on the mycelia
growth and spore yield of Trichoderma isolates in broth culture. In this study, the in vitro potential
of 7 Trichoderma isolates were evaluated against two pathogenic Colletotrichum isolates in dual
culture techniques and through production of volatile and non-volatile inhibitors. Pathogenicity test
was confirmed Colletotrichum isolates as one of the fungal organisms responsible for sorghum
anthracnose disease. It was observed that the optimum pH and temperature for maximum mycelial
growth and spore yield produced by Trichoderma isolates in broth cultures was pH 7.5 and 25OC,
respectively. In vitro screening results showed that the proportion of isolates with antagonistic
activities was the highest for the AUC-1 isolate followed by AUC-2 isolate. In vitro confrontation
analysis revealed that all Trichoderma isolates were highly antagonistic against AUC-1 whereas
AUT-97, AUT-131, AUT-11 and AUT-12 isolates displayed over 75% inhibition of mycelial
growth of AUC-2 isolate (P<0.05). The isolates AUT-11 and AUT-12 showed consistent results in
volatile and non-volatile activity under in vitro condition against any of the two pathogen isolates
tested. Under in-vitro dual culture test, all isolates of Trichoderma were able to inhibit the growth
of both Colletotrichum isolates at rates ranging from 58.92% to 90.29% after 8 days of incubation.
The highest mean inhibitory effect on the growth of the test pathogens were achieved by AUT-11
isolate (90.29%) against AUC-1 and AUT-97 isolate (81.1%) against AUC-2 while AUT-32 isolate
showed the lowest mean inhibitory effect restricting it almost completely in plates as compared to
the control consisting of any of the two test pathogens growing alone. In dual culture, volatile and
nonvolatile tests, all the Trichoderma isolates significantly inhibited the radial growth of the two
Colletotrichum isolates at (P<0.05) compared with control. Thus, the use of novel isolates of
Trichoderma with efficient antagonistic capacity against Colletotrichum isolates is a promising
alternative strategy to pesticides for sorghum anthracnose disease management.
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Keywords
Antagonism, Colletotrichum, Dual Culture, Inhibition, Trichoderma