Growth inhibition of Colletotrichum gloeosporioides and Phytophthora capsici by native Mexican Trichoderma strains

Suppression of Phytophthora capsici in Chile Pepper Using Brassica juncea and Hordeum vulgare Cover Crop Residues and Trichoderma harzianum as a Biocontrol Agent

Phytophthora blight, caused by Phytophthora capsici, is a serious disease of many vegetable crops worldwide. In New Mexico, U.S.A., the disease affects chile pepper (Capsicum annuum L.), a major crop in the state. There is no single tool that effectively controls the disease. Continuous research is needed in identifying combination of tools that can reduce the impact of Phytophthora blight. We explored the potential of combining cover crops and biocontrol agents to reduce soilborne diseases. This study aimed to evaluate the effects of Indian mustard (Brassica juncea L.) cover crop on the antagonistic ability of Trichoderma harzianum against P. capsici in vitro and to quantify the impacts of combining soil amendment with residues from B. juncea and barley (Hordeum vulgare L.) cover crops and plastic covering on infection of chile pepper seedlings by P. capsici under greenhouse conditions. Volatiles from macerated tissue of B. juncea significantly reduced P. capsici and T. harzianum growth in the absence of soil by 89.0 and 79.0%, respectively. When incorporated in soils, volatiles from macerated tissue of B. juncea significantly reduced P. capsici and T. harzianum by 33.4 and 7.8%, respectively. T. harzianum was more resilient to B. juncea biofumigation than P. capsici. Significant reduction in disease incidence was observed with B. juncea-fumigated soil, while no disease suppression was observed with soil incorporation of H. vulgare residues. Covering soil with plastic was necessary for increasing the efficacy of B. juncea biofumigation.

Cellulase and chitinase activities and antagonism against Fusarium oxysporum f.sp. cubense race 1 of six Trichoderma strains isolated from Mexican maize cropping

OBJECTIVE

To evaluate the enzymatic and biocontrol capacity of native Trichoderma strains isolated from corn crops in Irapuato (state of Guanajuato) and Napízaro (state of Michoacán), Mexico.

RESULTS

Six native strains from Irapuato and Napízaro were tested, with five of them identified as T. harzianum and one as T. tomentosum. The six strains qualitatively and quantitatively showed enzyme activity for cellulase and chitinase. The best results were obtained for strains IrV6SIC7 and MichV6S2C2 with 878 IU L^-1 of chitinase and 1323 IU L^-1 of cellulase, respectively. All Trichoderma strains acted antagonistically toward Fusarium oxysporum f.sp. cubense race 1 (FocR1), with percentages of inhibition that ranged from 9 to 54%. In addition, the microscopic analysis allowed visualizing the mechanisms of mycoparasitism and antibiosis by either IrV6SIC7 or MichV6S2C2. The latter effects indicate that the tested native Trichoderma strains isolated from corn crops possessed enzymatic mechanisms as a strategy for biocontrolling FocR1 strains.

CONCLUSION

The enzyme production by the Trichoderma strains represents a potential biotechnological utilization for either agricultural or industrial purposes.

DYNAMICS OF A MATHEMATICAL MODEL FOR INTERACTION PLANT–PARASITE–TRICHODERMA

In this work, the impact of a biological agent (Trichoderma spp.) on the dynamic of a plant–parasite model is analyzed. It is assumed that the plant–Trichoderma spp. relationship is mutualistic, the Trichoderma spp.–parasite relationship is that of predator–prey, and the parasite is specialist. Conditions for pest eradication and for species coexistence are shown.

Plant growth-promoting microorganisms as biocontrol agents of plant diseases: Mechanisms, challenges and future perspectives

Plant diseases and pests are risk factors that threaten global food security. Excessive chemical pesticide applications are commonly used to reduce the effects of plant diseases caused by bacterial and fungal pathogens. A major concern, as we strive toward more sustainable agriculture, is to increase crop yields for the increasing population. Microbial biological control agents (MBCAs) have proved their efficacy to be a green strategy to manage plant diseases, stimulate plant growth and performance, and increase yield. Besides their role in growth enhancement, plant growth-promoting rhizobacteria/fungi (PGPR/PGPF) could suppress plant diseases by producing inhibitory chemicals and inducing immune responses in plants against phytopathogens. As biofertilizers and biopesticides, PGPR and PGPF are considered as feasible, attractive economic approach for sustainable agriculture; thus, resulting in a "win-win" situation. Several PGPR and PGPF strains have been identified as effective BCAs under environmentally controlled conditions. In general, any MBCA must overcome certain challenges before it can be registered or widely utilized to control diseases/pests. Successful MBCAs offer a practical solution to improve greenhouse crop performance with reduced fertilizer inputs and chemical pesticide applications. This current review aims to fill the gap in the current knowledge of plant growth-promoting microorganisms (PGPM), provide attention about the scientific basis for policy development, and recommend further research related to the applications of PGPM used for commercial purposes.

Antagonistic activity and characterization of indigenous soil isolates of bacteria and fungi against onion wilt incited by Fusarium sp

Tuber rot disease due to phytopathogen Fusarium oxysporum f. sp. cepae (Foc) infection is one of the main factors causing the decreasing global onions production. This study aims to find bacteria and fungi candidates with Foc antagonistic activity through in vitro tests using dual culture techniques. A total of three bacterial isolates and three fungal isolates isolated from the rhizosphere of healthy onion plants showed the ability to inhibit Fusarium oxysporum growth. LC648364 isolate had an average inhibitory capability of 65.93%. At the same time, LC648367 and LC648368 fungal isolates can inhibit the growth of F. oxysporum by as much as 74.82% and 67.76%, respectively. Molecular analysis based on 16S rRNA markers showed three isolates belonging to the Bacillus. The LC648364 isolates are closely related to species Bacillus sp. strain LLB-17, LC648365 is closely related to B. subtilis strain S11 and LC648366 is closely related to B. cereus strain EM6. For the fungi, based on internal transcribed spacer (ITS) gene markers, there are three isolates. The LC648367 isolate is closely related to Aspergillus tubingensis, LC648368 is closely related to Trichoderma asperellum and LC648369 is closely related to Issatchenkia orientalis. This study can be used to develop indigenous microbial consortiums as biological control agents for phytopathogenic fungi Fusarium tuber rot on onion.

Characterisation and antifungal activity of extracellular chitinase from a biocontrol fungus, Trichoderma asperellum PQ34

Trichoderma species were known as biological control agents against phytopathogenic fungi because they produce a variety of chitinases. Chitinases are hydrolytic enzymes that break down glycosidic bonds in chitin, a major component of the cell walls of fungi. The present study shows that extracellular chitinase activity reached a maximum value of approximately 22 U/mL after 96 h of T. asperellum PQ34 strain culture. The optimal temperature and pH of enzyme are 40°C and 7, respectively, whereas the thermal and pH stability range from 25°C to 50°C and 4 to 10, respectively. Chitinase at 60 U/mL inhibited nearly completely in vitro growth of Colletotrichum sp. (about 95%) and Sclerotium rolfsii (about 97%). In peanut plants, 20 U/mL of chitinase significantly reduced the incidence of S. rolfsii infection compared to controls. The fungal infection incidence of seeds before germination and 30 days after germination was only 2.22% and 2.38%, while the control was 13.33% and 17.95%. Besides, chitinase from T. asperellum PQ34 can also prevent anthracnose that is caused by Colletotrichum sp. on both mango and chilli fruits up to 72 h after enzyme pre-treatment at 40 U/mL. In mango and chilli fruits infected with anthracnose, 40 U/mL dose of chitinase inhibited the growth of fungi after 96 h of treatment, the diameter of lesion was only 0.88 cm for mango and 1.45 cm for chilli, while the control was 1.67 cm and 2.85 cm, respectively.

Involvement of lytic enzymes and secondary metabolites produced by Trichoderma spp. in the biological control of Pythium myriotylum

This investigation was aimed to evaluate the antimicrobial activities and involvement of extracellular lytic enzymes produced by four strains of Trichoderma in the inhibition of Pythium myriotylum. Antagonistic effects were tested by dual culture. Activities of lytic enzymes were evaluated from the filtrate of each strain after cultivation in selected media. Organic extracts were obtained from liquid media subsequent to the cultivation of Trichoderma in potato dextrose broth (PDB). Non-volatile organic compounds such as polyphenols and flavonoids were evaluated spectrophotometrically while volatile organic compounds (VOCs) were analyzed by gas chromatography coupled with mass spectrometry (GC-MS). The antimicrobial activity of the organic extracts was determined using the poisoning method. Results have shown that all the strains were antagonists against P. myriotylum. T. erinaceum (IT-58), T. gamsii (IT-62), T. afroharzianum (P8), and T. harzianum (P11) that were found to produce cellulase, protease, and xylanase. Over 20 compounds were identified in each extract, including esters, lactones, and organic acids. The organic extracts also contained high amounts of polyphenolic compounds and flavonoids and significantly inhibited the mycelial growth of P. myriotylum. The minimal inhibition concentrations were 80 μg/μL, 40 μg/μL, 20 μg/μL, and 10 μg/μL, for extracts obtained from T. erinaceum (IT-58), T. gamsii (IT-62), T. afroharzianum (P8), and T. harzianum (P11), respectively. There was significant correlation between the production of total polyphenol and flavonoid content and the antagonistic effects of the tested strains.