A Consortium of Pseudomonas aeruginosa and Trichoderma harzianum for Improving Growth and Induced Biochemical Changes in Fusarium Wilt Infected Bananas

Plant growth-promoting bacteria potentiate antifungal and plant-beneficial responses of Trichoderma atroviride by upregulating its effector functions

Trichoderma uses different molecules to establish communication during its interactions with other organisms, such as effector proteins. Effectors modulate plant physiology to colonize plant roots or improve Trichoderma's mycoparasitic capacity. In the soil, these fungi can establish relationships with plant growth-promoting bacteria (PGPBs), thus affecting their overall benefits on the plant or its fungal prey, and possibly, the role of effector proteins. The aim of this study was to determine the induction of Trichoderma atroviride gene expression coding for effector proteins during the interaction with different PGPBs, Arabidopsis or the phytopathogen Fusarium brachygibbosum, and to determine whether PGPBs potentiates the beneficial effects of T. atroviride. During the interaction with F. brachygibbosum and PGPBs, the effector coding genes epl1, tatrx2 and tacfem1 increased their expression, especially during the consortia with the bacteria. During the interaction of T. atroviride with the plant and PGPBs, the expression of epl1 and tatrx2 increased, mainly with the consortium formed with Pseudomonas fluorescens UM270, Bacillus velezensis AF12, or B. halotolerans AF23. Additionally, the consortium formed by T. atroviride and R. badensis SER3 stimulated A. thaliana PR1:GUS and LOX2:GUS for SA- and JA-mediated defence responses. Finally, the consortium of T. atroviride with SER3 was better at inhibiting pathogen growth, but the consortium of T. atroviride with UM270 was better at promoting Arabidopsis growth. These results showed that the biocontrol capacity and plant growth-promoting traits of Trichoderma spp. can be potentiated by PGPBs by stimulating its effector functions.

Growth Enhancement and Resistance of Banana Plants to Fusarium Wilt Disease as Affected by Silicate Compounds and Application Frequency

The amendment of soils with silicate (Si) compounds is essential to promote growth performance and control Fusarium wilt disease in bananas. Two successive greenhouse trials were conducted at the experimental farm of the University of Putra Malaysia. The treatments were arranged in split plots using a randomized complete block design (RCBD) with four replicates to investigate the effects of Si compounds and application frequency on controlling FOC. Si compounds were used at a constant concentration of 0.1%: T0 (control), T1 (13% SiO2:20% K2O), T2 (26.6% SiO2:13.4% K2O) and T3 (36.2% SiO2:17% Na2O). There were three application frequencies by day intervals (DI): 0DI (without any application), 7DI (12× within 12 weeks after transplanting (WAT)), 15DI (6× within 12 WAT) and 30DI (3× within 12 WAT). From these findings, we observed that the photosynthesis rate started to increase from 10.6 to 19.4 µmol CO2 m-2s-1, when the total chlorophyll content started to increase from 3.85 to 7.61 mgcm-2. The transpiration rate started to increase from a value of 1.94 to 4.31 mmol H2O m-2s-1, when the stomata conductance started to increase from 0.237 to 0.958 mmol m-2s-1. The proline content started to increase from 22.89 to 55.07 µmg-1, when the relative water content started to increase from 42.92 to 83.57%.

Microbial consortium mediated acceleration of the defense response in potato against Alternaria solani through prodigious inflation in phenylpropanoid derivatives and redox homeostasis

The present study was carried out in a pot experiment to examine the bioefficacy of three biocontrol agents, viz., Trichoderma viride, Bacillus subtilis, and Pseudomonas fluorescens, either alone or in consortium, on plant growth promotion and activation of defense responses in potato against the early blight pathogen Alternaria solani. The results demonstrate significant enhancement in growth parameters in plants bioprimed with the triple-microbe consortium compared to other treatments. In potato, the disease incidence percentage was significantly reduced in plants treated with the triple-microbe consortium compared to untreated control plants challenged with A. solani. Potato tubers treated with the consortium and challenged with pathogen showed significant activation of defense-related enzymes such as peroxidase (PO) at 96 h after pathogen inoculation (hapi) while, both polyphenol oxidase (PPO), and phenylalanine ammonia-lyase (PAL) at 72 hapi, compared to the individual and dual microbial consortia-treated plants. The expression of antioxidant enzymes like superoxide dismutase (SOD) and catalase (CAT) and the accumulation of pathogenesis-related proteins such as chitinase and β-1,3-glucanase were observed to be highest at 72 hapi in the triple microbe consortium as compared to other treatments. HPLC analysis revealed significant induction in polyphenolic compounds in triple-consortium bioprimed plants compared to the control at 72 hapi. Histochemical analysis of hydrogen peroxide (H2O2) clearly showed maximum accumulation of H2O2 in pathogen-inoculated control plants, while the lowest was observed in triple-microbe consortium at 72 hapi. The findings of this study suggest that biopriming with a microbial consortium improved plant growth and triggered defense responses against A. solani through the induction of systemic resistance via modulation of the phenylpropanoid pathway and antioxidative network.

Age-Related Rhizosphere Analysis of Coffea arabica Plants

The analysis of large-scale sequence data has revealed that plants over time recruit certain microbes that are efficient colonizers of the rhizosphere. This enrichment phenomenon is especially seen in annual crops, but we suggest that there could have been some type of enrichment in perennial crops such as coffee plants. To verify this hypothesis, we performed a metagenomic and chemical analysis in rhizosphere with three different plant ages (young, mature, and old) and cultivated on the same farm. We verified that from mature to old plants, there was a decrease in diversity, particularly Fusarium and Plenodomus, while there was an increase in Aspergillus, Cladosporium, Metarhizium, and Pseudomonas. We also detected that the abundance of anti-microbials and ACC-deaminase grows as plants age, although denitrification and carbon fixation had reduced abundances. In summary, we detected an enrichment in the microbial community, especially in the great increase in the participation of Pseudomonas, passing from 50% of the relative abundance as the plants get older. Such enrichment can occur through the dynamics of nutrients such as magnesium and boron.

Biostimulant Activity of Silicate Compounds and Antagonistic Bacteria on Physiological Growth Enhancement and Resistance of Banana to Fusarium Wilt Disease

Biostimulants such as silicate (SiO₃^2-) compounds and antagonistic bacteria can alter soil microbial communities and enhance plant resistance to the pathogens and Fusarium oxysporum f. sp. cubense (FOC), the causal agent of Fusarium wilt disease in bananas. A study was conducted to investigate the biostimulating effects of SiO₃^2- compounds and antagonistic bacteria on plant growth and resistance of the banana to Fusarium wilt disease. Two separate experiments with a similar experimental setup were conducted at the University of Putra Malaysia (UPM), Selangor. Both experiments were arranged in a split-plot randomized complete block design (RCBD) with four replicates. SiO₃^2- compounds were prepared at a constant concentration of 1%. Potassium silicate (K₂SiO₃) was applied on soil uninoculated with FOC, and sodium silicate (Na₂SiO₃) was applied to FOC-contaminated soil before integrating with antagonistic bacteria; without Bacillus spp. ((0B)-control), Bacillus subtilis (BS), and Bacillus thuringiensis (BT). Four levels of application volume of SiO₃^2- compounds [0, 20, 40, 60 mL) were used. Results showed that the integration of SiO₃^2- compounds with BS (10⁸ CFU mL^-1) enhanced the physiological growth performance of bananas. Soil application of 28.86 mL of K₂SiO₃ with BS enhanced the height of the pseudo-stem by 27.91 cm. Application of Na₂SiO₃ and BS significantly reduced the Fusarium wilt incidence in bananas by 56.25%. However, it was recommended that infected roots of bananas should be treated with 17.36 mL of Na₂SiO₃ with BS to stimulate better growth performance.

Effectiveness of Endophytic and Rhizospheric Bacteria from Moringa spp. in Controlling Pythium aphanidermatum Damping-Off of Cabbage

In this study, endophytic and rhizospheric bacteria were isolated from Moringa olifera and M. perigreina from Oman, and their in vitro antagonistic activity against Pythium aphanidermatum was tested using a dual culture assay. The promising strains were tested further for their compatibility and potential for plant growth promotion, biofilm formation, antifungal volatile organic compound (VOC) production, and the biological control of P. aphanidermatum damping-off of cabbage (Brassica oleracea L.) under greenhouse conditions. A total of 12 endophytic and 27 rhizospheric bacteria were isolated from Moringa spp. Among them, Bacillus pumilus MPE1 showed the maximum antagonistic activity against P. aphanidermatum in the dual culture assay, followed by Paenibacillus glucanolyticus MPE3 and Pseudomonas indica MOR3 and MOR8. These bacterial isolates induced abundant morphological abnormalities in the hyphae of P. aphanidermatum, as observed via scanning electron microscopy. The in vitro cross-streak assay showed that these bacterial isolates were compatible among themselves, except for P. indica MOR8 × P. glucanolyticus MPE3. These antagonists released VOCs that restricted the growth of P. aphanidermatum in an in vitro assay. These antagonistic bacteria released 2,4-dimethylheptane and 4-methyloctane as the predominant volatile compounds. Of the four antagonistic bacterial strains, P. indica MOR8 was capable of forming biofilm, which is considered a trait that improves the efficacy of rhizosphere inoculants. The results of the greenhouse experiments showed that the soil treatment with B. pumilus MPE1 showed the highest reduction (59%) in the incidence of P. aphanidermatum damping-off in cabbage, evidencing its potential as a biological control agent for the management of this disease. Further research is needed to characterize the antifungal traits and activities of B. pumilus MPE1 and to assert its potential use against other soil-borne plant pathogens.

Synchronized Efficacy and Mechanism of Alkaline Fertilizer and Biocontrol Fungi for Fusariumoxysporum f. sp. cubense Tropical Race 4

The purpose of this study was to determine the effect and mechanism of alkaline fertilizer, bio-control fungi, and their synergistic application on control of Fusarium Tr4 incidence. Synchronized use of the alkaline fertilizer and biocontrol fungi eliminates rhizome browning and reduces the incidence rate of banana Fusarium wilt. The incidence of yellow leaves (ratio of yellow leaf to total leaf) and disease index in +Foc Tr4 CF treatment were the same (65%), while incidence of yellow leaves and disease index in +Foc Tr4 AFBCF were 31% and 33%, respectively. Under the stress of Foc Tr4 infection, the synergistic utilization of the alkaline fertilizer and biocontrol fungi would raise the activities of peroxidase, catalase and superoxide dismutase in banana roots. The root activity of banana was also increased. As a result, the banana height and stem diameter increments, shoot and root dry weight, accumulation of N, P and K in banana plants had been increased. The efficacy of the synergistic application of alkaline fertilizer and biocontrol fungi was not only reducing Foc Tr4 pathogen colonization and distribution in banana plants, but also preventing tylosis formation in vascular vessel effectively. Therefore, the normal transport of water and nutrients between underground and aboveground is ensured.

Synergistic effect of growth-promoting microorganisms on bio-control of Fusarium oxysporum f. sp. pisi, growth, yield, physiological and anatomical characteristics of pea plants

Fusarium root rot caused by Fusarium oxysporum is an aggressive disease-causing damping-off, root rot, and vascular wilt in all peas growing fields. The disease can cause 100% yield losses under favorable conditions. The present study aims to control Fusarium root rot using Trichoderma harzianum, Pseudomonas fluorescens, and arbuscular mycorrhizal fungi, singly or in combinations. The results showed that all treatments significantly enhanced not only the plant growth, total phenol, activities of antioxidant enzymes, but also, the yield and seed quality. Several changes in the anatomical, physiological, and characteristics of the treated plants were also recorded. Compared to the untreated control treatment, under greenhouse conditions, the maximum reduction of the disease severity (80%) was achieved by the synergistic triple treatment consists of arbuscular mycorrhizal fungi, Trichoderma harzianum, and Pseudomonas fluorescens, as they gave the best growth and yield parameters. The same combination showed the highest activity of the antioxidant enzyme peroxidase (57.1%), as well as the highest total phenol content (117.7%), over the control. The synergistic triple increased the contents of protein (64.6%), total soluble sugars (48.5%), and total carbohydrate (24.8%) in seeds of pea compared with the control. The synergistic triple treatment led to an increase in the thickness of the root section (25%), the thickness of the cortex (24.8%), the thickness of the vascular cylinder (31.5%), and the diameter of the xylem vessels (81.5%) of the root. Based on their efficiency and eco-safety, this synergistic triple might be very effective for controlling root rot disease of pea caused by F. oxysporum, as well as improve the growth, yield, and seed quality.