Lecturer II, Federal University Dutsin-Ma
Effectiveness of biological control agent (Trichoderma harzianum) in managing pathogenic organisms
Studies were carried out on biological control using dual culture method to assess the potential of Trichoderma harzianum against Fusarium oxysporum, the causal agent of tuber dry rot disease of white yam in vitro. The rot-causing fungal organism was isolated from rotted yam tubers collected from different storage barns in Zaki-Biam, Benue State of Nigeria. The biological agent (T. harzianum) was introduced at three different times (same time with the pathogen, 2days before the inoculation of the pathogen and 2days after the inoculation of the pathogen). The experiment was conducted in the Advanced Plant Pathology Laboratory, Federal University of Agriculture, Makurdi, Nigeria. The plates were incubated for 192 hours and measurements of mycelial radial growths were done at 24 hours intervals beginning from 72 hour. The result of the in vitro interactions showed that the highest percentage growth inhibition of mycelia of the pathogen (77.99%) was recorded when T. harzianum was introduced two days before the inoculation of F. oxysporum, followed by introduction of T. harzianum same time with F. oxysporum (45.69%) and the least percentage growth inhibition (13.72%) was recorded when the antagonist was introduced two days after inoculation of the pathogen. In all the treatments, T. harzianum was able to significantly (P ≤ 0.05) inhibits the growth of F. oxysporum throughout the period of incubation. T. harzianum was observed to be effective in reducing the mycelial growth of F. oxysporum in culture in all the treatments and therefore showed the potential for biological control of the pathogen. Minimum inhibition concentration recorded showed that the effectiveness levels of T. harzianum were slightly effective to effective across treatments. It is therefore concluded that the antagonistic potentials of T. harzianum could be used as a good biological control agent of yam tuber rot caused by F. oxysporum in vitro this can also be applied on yam tubers both in the field and in storage to reduce rot causing organisms because the antagonist has proved effective in the in vitro control of pathogenic fungal organism.
Abstract: The biocontrol agent Trichoderma (T. harzianum, T. viride, T. virens, T. hamantum, T. koningii, T. pseudokoningii and Trichoderma species) inhibited variably (15.32 - 88.12%) the in vitro growth of Rhizoctonia solani causing root rot in cotton. The T. koningii MTCC 796 evidenced highest (88.12%) growth inhibition of test pathogen followed by T. viride NBAII Tv23 (85.34%). Scanning electron microscopic study confirmed mycoparasitism for MTCC 796 and Tv23 which were capable of completely overgrowing on R. solani by degrading mycelia, coiling around the hyphae with hook-like structures. The antagonists T. harzianum NBAII Th1 and, T. virens NBAII Tvs12 exhibited strong antibiosis and formed 2-4 mm zone of inhibition for 70.28% and 46.62%, respectively growth inhibition of test pathogen. Mycoparasitism is a strong mode of action for biocontrol activity compared with antibiosis. The antagonists Trichoderma strains were performed for start codon targeted (SCoT) polymorphism to acquire biocontrol genes from potent antagonist. The six unique SCoT fragments amplified by genomic DNA of best mycoparasitic antagonist MTCC 796 strain are subjected to DNA sequencing resulted to confirm two functional sequences for activity related to biocontrol genes. The phylogenetic and molecular evolution of functional 824 bp of SCoT-3(920) and 776 bp of SCoT-6(806) fragments signify sequence homology with biocontrol genes endochitinase (partial cds of 203 amino acids) and novel hmgR genes (partial cds of 239 amino acids), respectively and the same were annotated and deposited in NCBI GenBank database. The hmgR gene is liable to be express hmg - CoA reductase which is a key enzyme for regulation of terpene biosynthesis and mycoparasitic strains produced triterpenes during antagonism to inhibit growth of fungal pathogen as evidenced with GC-MS profile. The biocontrol genes are found in best antagonist T. koningii MTCC 796 for mycoparasitic activity to restrain the growth of test pathogen R. solani.
Pub.: 11 Oct '16, Pinned: 28 Sep '17
Abstract: Twelve isolates of Trichoderma (six of T. harzianum, five of T. viride, one of T. virens), which reduced variably the incidence of collar rot disease caused in peanut by Aspergillus niger Van Tieghem, were evaluated for their potential to produce lytic enzymes during in vitro antagonism. T. viride 60 inhibited highest (86.2%) growth of test fungus followed by T. harzianum 2J (80.4%) at 6 days after inoculation (DAI) on PDA media. The specific activities of chitinase, β-1,3-glucanase and protease were 11, 3.46 and 9 folds higher in T6 antagonist (T. viride 60 and A. niger interactions) followed by 8.72, 2.85 and 9 folds in T8antagonist (T. harzianum 2J and A. niger interactions), respectively, compared to the activity produced by control petri plate T13 (A. niger alone) at 6 DAI. Activity of these lytic enzymes induced in antagonists' plates comprises the growth of Trichoderma isolates. However, cellulase and poly galacturonase were found least amount in these antagonists treatment. A significant positive correlation (p=0.01) between percentage growth inhibition of test fungus and lytic enzymes - (chitinase, β-1,3-glucanase and protease) in the culture medium of antagonist treatment established a relationship to inhibit growth of fungal pathogen by increasing the levels of these enzymes. Among the Trichoderma isolates, T. viride 60 was found best strain to be used in biological control of plant pathogen A. niger.
Pub.: 01 Jan '12, Pinned: 28 Sep '17
Abstract: Trichoderma is one of the most exploited biocontrol agent for the management of plant diseases. Twenty strains of Trichoderma (six of T. harzianum, four of T. viride, three of T. virens, three of T. koningii, each one of T. hamatum, T. reesei, T. parceramosum and Trichoderma spp.) subjected to in vitro antagonism up to 12days after inoculation against Sclerotium rolfsii Sacc. causing stem rot in groundnut. A new concept was developed to determine inhibition coefficient representing pathogen biology and biocontrol related biophysical variables. Results explained differential inhibition coefficient of test pathogen by Trichoderma antagonists. The inhibition coefficient of test pathogen was examined highest (91.13%) by T. virens NBAII Tvs12 followed by T. virens MTCC 794 (89.33%) and T. koningii MTCC 796 (62.39%). Microscopic study confirmed biocontrol mechanism as mycoparasitism for Tvs12 and antibiosis for T. koningii MTCC 796. The sclerotial biogenesis of test pathogen was elevated during weak antagonism and diminished in interactions with strong antagonists. The inhibition coefficient of S. rolfsii was significantly negatively correlated with sclerotia formation and lipid peroxidation during the antagonism. Trichoderma strains were screened for fungicides (carbendazim and tebuconazole, thiram and mancozeb) and abiotic stress (drought and salt) tolerance. Results indicated that T. koningii MTCC 796 efficiently grew better than the other strains with maximum radial growth under adverse conditions. The genetic variability among the Trichoderma was determined using 34 gene specific markers which amplified 146 alleles. The SSR similarities explained substantial diversity (15 to 87%) across Trichoderma strains and pathogen S. rolfsii. Principal coordinates analysis (PCA) were comparable to the cluster analysis and first three most informative PC components explained 64.45% of the total variation. In PCA, potent antagonists appear to be distinct from other strains. Five SSR markers T1F/T1R(311), TvCTT56f/TvCTT56r(387), TvGAT18f/TvGAT18r(364), TvCA39f/TvCA39r(196) and TvAG29f/TvAG29r(418) found to be unique to distinguish best antagonist strain Tvs12. However, MTCC 796 was examined most stress tolerant strain with better inhibition coefficient which might be useful to control the disease under adverse conditions or as a part of integrated pest management.
Pub.: 03 Sep '17, Pinned: 28 Sep '17