Panama disease caused by Fusarium oxysporum f. sp. cubense infection on banana is devastating banana plantations worldwide. Biological control has been proposed to suppress Panama disease, though the stability and survival of bio-control microorganisms in field setting is largely unknown. In order to develop a bio-control strategy for this disease, 16S rRNA gene sequencing was used to assess the microbial community of a disease-suppressive soil. Bacillus was identified as the dominant bacterial group in the suppressive soil. For this reason, B. amyloliquefaciens NJN-6 isolated from the suppressive soil was selected as a potential bio-control agent. A bioorganic fertilizer (BIO), formulated by combining this isolate with compost, was applied in nursery pots to assess the bio-control of Panama disease. Results showed that BIO significantly decreased disease incidence by 68.5%, resulting in a doubled yield. Moreover, bacterial community structure was significantly correlated to disease incidence and yield and Bacillus colonization was negatively correlated with pathogen abundance and disease incidence, but positively correlated to yield. In total, the application of BIO altered the rhizo-bacterial community by establishing beneficial strains that dominated the microbial community and decreased pathogen colonization in the banana rhizosphere, which plays an important role in the management of Panama disease.

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Manipulating the banana rhizosphere microbiome for biological control of Panama disease.

From crossbreeding to biotechnology-facilitated improvement of banana and plantain.

Early blight is a disease that greatly affects Solanaceae, mainly damaging tomato plants, and causing significant economic losses. Although there are methods of biological control, these are very expensive and often their mode of action is slow. Due to this, there is a need to use new techniques that allow a more efficient control of pathogens. Nanotechnology is a new alternative to solve these problems, allowing the creation of new tools for the treatment of diseases in plants, as well as the control of pathogens. The aim of the present investigation was to evaluate the foliar application of selenium and copper in the form of nanoparticles in a tomato crop infested by Alternaria solani. The severity of Alternaria solani, agronomic variables of the tomato crop, and the changes in the enzymatic and non-enzymatic antioxidant compounds were evaluated. The joint application of Se and Cu nanoparticles decreases the severity of this pathogen in tomato plants. Moreover, high doses generated an induction of the activity of the enzymes superoxide dismutase, ascorbate peroxidase, glutathione peroxidase (GPX) and phenylalanine ammonia lyase in the leaves, and the enzyme GPX in the fruit. Regarding non-enzymatic compounds in the leaves, chlorophyll a, b, and totals were increased, whereas vitamin C, glutathione, phenols, and flavonoids were increased in fruits. The application of nanoparticles generated beneficial effects by increasing the enzymatic and non-enzymatic compounds and decreasing the severity of Alternaria solani in tomato plants.

The Application of Selenium and Copper Nanoparticles Modifies the Biochemical Responses of Tomato Plants under Stress by Alternaria solani.

Plants interact with a huge variety of soil microbes, ranging from pathogenic to mutualistic. The Fusarium oxysporum (Fo) species complex consists of ubiquitous soil inhabiting fungi that can infect and cause disease in over 120 different plant species including tomato, banana, cotton, and Arabidopsis. However, in many cases Fo colonization remains symptomless or even has beneficial effects on plant growth and/or stress tolerance. Also in pathogenic interactions a lengthy asymptomatic phase usually precedes disease development. All this indicates a sophisticated and fine-tuned interaction between Fo and its host. The molecular mechanisms underlying this balance are poorly understood. Plant hormone signaling networks emerge as key regulators of plant-microbe interactions in general. In this review we summarize the effects of the major phytohormones on the interaction between Fo and its diverse hosts. Generally, Salicylic Acid (SA) signaling reduces plant susceptibility, whereas Jasmonic Acid (JA), Ethylene (ET), Abscisic Acid (ABA), and auxin have complex effects, and are potentially hijacked by Fo for host manipulation. Finally, we discuss how plant hormones and Fo effectors balance the interaction from beneficial to pathogenic and vice versa.

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How Phytohormones Shape Interactions between Plants and the Soil-Borne Fungus Fusarium oxysporum.

Fusarium oxysporum is a devastating pathogen causing extensive yield losses in a variety of crops and development of sustainable, environmentally friendly methods to improve crop resistance is crucial We have used Host-Derived RNA interference (HD-RNAi) technology to partially silence three different genes (FOW2, FRP1 and OPR) in the hemi-biotrophic fungus Fusarium oxysporum f sp conglutinans Expression of double stranded RNA molecules targeting fungal pathogen genes was achieved in a number of transgenic Arabidopsis lines F oxysporum infecting the transgenic lines displayed substantially reduced mRNA levels on all three targeted genes, with an average of 75%, 83% and 72% reduction for FOW2, FRP1 and OPR respectively The silencing of pathogen genes had a clear positive effect on the ability of the transgenic lines to fight infection All transgenic lines displayed enhanced resistance to F oxysporum with delayed disease symptom development, especially FRP1 and OPR lines Survival rates after fungal infection were higher in the transgenic lines compared to control wild type plants which consistently showed survival rates of 10%, with FOW2 lines showing 25% survival; FRP1 lines 30-50% survival and FOW2 between 45-70% survival The down-regulation effect was specific for the targeted genes without unintended effects in related genes In addition to producing resistant crops, HD-RNAi can provide a useful tool to rapidly screen candidate fungal pathogenicity genes without the need to produce fungal knockout mutants

https://espace.library.uq.edu.au/view/UQ:490801/UQ490801_OA.pdf

Down-regulation of Fusarium oxysporum endogenous genes by Host-Delivered RNA interference enhances disease resistance

Soil-borne fungal pathogen, Fusarium oxysporum causes major economic losses by inducing necrosis and wilting symptoms in many crop plants. Management of fusarium wilt is achieved mainly by the use of chemical fungicides which affect the soil health and their efficiency is often limited by pathogenic variability. Hence understanding the nature of interaction between pathogen and host may help to select and improve better cultivars. Current research evidences highlight the role of oxidative burst and antioxidant enzymes indicating that ROS act as an important signaling molecule in banana defense response against Fusarium oxysporum f.sp. cubense. The role of jasmonic acid signaling in plant defense against necrotrophic pathogens is well recognized. But recent studies show that the role of salicylic acid is complex and ambiguous against necrotrophic pathogens like Fusarium oxysporum, leading to many intriguing questions about its relationship between other signaling compounds. In case of banana, a major challenge is to identify specific receptors for effector proteins like SIX proteins and also the components of various signal transduction pathways. Significant progress has been made to uncover the role of defense genes but is limited to only model plants such as Arabidopsis and tomato. Keeping this in view, we review the host response, pathogen diversity, current understanding of biochemical and molecular changes that occur during host and pathogen interaction. Developing resistant cultivars through mutation, breeding, transgenic and cisgenic approaches have been discussed. This would help us to understand host defenses against Fusarium oxysporum and to formulate strategies to develop tolerant cultivars.

https://link.springer.com/content/pdf/10.1007%2Fs00425-013-2024-8.pdf

Plant defense response against Fusarium oxysporum and strategies to develop tolerant genotypes in banana

Characterization of tolerance to Fusarium oxysporum f.sp., cubense infection in banana using suppression subtractive hybridization and gene expression analysis

Physiological and biochemical changes during moisture stress in banana.

Plant’s life cycle involves interaction with various microorganisms in their environment. Studies are being focused to uncover the molecular components involved in plant–microbe interaction to understand the mechanism of pathogen infection or symbiosis. Recently, research studies in this area focus mainly on environmental issues to provide sustainable agriculture and to increase productivity. In this context, researchers use various high-throughput ‘omics’ approaches which include genomics, to study the structural and functional aspects of genes and also compare the degree of gene expression in contrasting genotypes, transcriptomics that quantifies mRNA transcripts, proteomics that analyse the protein composition and metabolomics which identifies and quantifies cellular metabolites. In this chapter, we discuss the advancement of ‘omics’ platforms, in exploring the complex metabolic networks and regulatory mechanisms during plant–microbe relationship. This has significantly improved our understanding about carbohydrate metabolism between legume plants and rhizobacteria. ‘Omics’ platforms are being used largely in understanding and selecting efficient endophytic or beneficial strains with various improved traits like nutrient uptake, imparting abiotic and biotic stress tolerance during their interaction with host. Comparative studies by large-scale genome analysis of host and pathogen have helped in identification of various effector genes and the nature of pathogenicity induced by pathogen and also the difference in defence mechanisms amongst hosts. Climatic changes that affect the agriculture production and the ever increasing population worldwide are the two challenging factors that need to be balanced currently. In order to attain sustainable agriculture production and productivity, ‘omics’ is a promising tool to understand the plant–microbe interaction that aid in sustainable agriculture.

V. Swarupa

Papers

Plant defense response against Fusarium oxysporum and strategies to develop tolerant genotypes in banana

Characterization of tolerance to Fusarium oxysporum f.sp., cubense infection in banana using suppression subtractive hybridization and gene expression analysis

Physiological and biochemical changes during moisture stress in banana.

Omics-Driven Approaches in Plant–Microbe Interaction

Gene expression analysis in roots of musa acuminate ssp. burmannicoides 'calcutta-4', a banana genotype tolerant to fusarium wilt