Ophiobolins (Ophs) are a group of tricarbocyclic sesterterpenoids whose structures contain a tricyclic 5-8-5 carbotricyclic skeleton. Thus far, 49 natural Ophs have been reported and assigned into A-W subgroups in order of discovery. While these sesterterpenoids were first characterized as highly effective phytotoxins, later investigations demonstrated that they display a broad spectrum of biological and pharmacological characteristics such as phytotoxic, antimicrobial, nematocidal, cytotoxic, anti-influenza and inflammation-promoting activities. These bioactive molecules are promising drug candidates due to the developments of their anti-proliferative activities against a vast number of cancer cell lines, multidrug resistance (MDR) cells and cancer stem cells (CSCs). Despite numerous studies on the biological functions of Ophs, their pharmacological mechanism still requires further research. This review summarizes the chemical structures, sources, and biological activities of the oph family and discusses its mechanisms and structure-activity relationship to lay the foundation for the future developments and applications of these promising molecules.

The Biological Activities of Sesterterpenoid-Type Ophiobolins.

Plants possess a plethora of defense mechanisms that respond to both biotic and abiotic stresses. The response of a plant to various pathogens and pests can vary dependent on factors such as host variety, strain, as well as environmental factors. How quickly a plant responds to these stresses will determine the level of resistance of a plant species. The SAR and ISR mechanisms in plants work together to provide the host with protection against pathogen and pest attacks. Unlike SAR, ISR is induced by nonpathogenic allies from belowground in the form of plant growth-promoting bacteria. ISR is induced in the root and in foliar tissue and is able to provide the host plant with systemically induced resistance against a broad spectrum of microorganisms. Selected strains of plant growth-promoting rhizobacteria suppress diseases and pest infestation by inhibition of pathogens/pests as well as resulting in the induction of systemic resistance in planta. In rice these organisms have been known to activate the JA/ETH and auxin pathways. Due to the higher levels of endogenous SA in rice, the SA-independent pathways are a preferred way of inducing resistance within the rice host. There are various types of determinants that have been implicated to play a role in ISR. These determinants can either work individually or in combination to induce ISR in plants. From in vitro, greenhouse and field studies on rice, several strains of bacteria such as Pseudomonas spp., Bacillus spp., Serratia spp., and Azospirillum spp. have been listed as organisms with potential to function as biofertilizers and biopesticides in rice.

Induced Systemic Resistance in Rice

Biocontrol mechanism to suppress fungal and bacterial pathogens of rice cropby Pseudomonas sp . generally involves the production of antibiotics, siderophores, volatile compounds, hydrocyanic acid (HCN), enzymes and phytohormones. Rice is the staple food of over half of the world population. Diseases are the most important factors that affect rice production causing annual yield losses. Biological control is an eco-friendly, cost effective and sustainable alternative method in disease management.

http://www.isca.in/AGRI_FORESTRY/Archive/v1/i9/4.ISCA-RJAFS-2013-059.pdf

Pseudomonads: Potential Biocontrol agents of Rice Diseases

The objective of the study was to evaluate the effects of nine plant growth-promoting rhizobacteria (PGPR) alone or in combination on maize seed germination and seedling growth under laboratory and greenhouse conditions. The germination and growth tests were carried out in square petri dishes and pots. Maize seeds were inoculated with suspension of 108 CFU/ml of rhizobacteria. The experimental device was a random block of 16 treatments with four repetitions. Germination test results showed that seeds inoculated with PGPR including the control induced good germination in the range of 93.75% to 100%. The vigor index and root length of the seeds treated with Bacillus panthothenicus were significantly improved by 76.64% and 58.86%, respectively, while the maximal lengths of the seedlings were obtained with Pseudomonas cichorii with an increase of 118.95%. In greenhouse experience, data demonstrated that Serratia marcescens better improved the leaf area, height and underground biomass, respectively by 58.83%, 108.43%, and 59.16% as compared to the control. The highest fresh aerial biomass and air dry matter was obtained with plants treated only with Pseudomonas putida. These results show the potential to use such rhizobacteria as biofertilizers to improve maize productivity in Benin.

/pdf/influence-of-isolated-pgpr-rhizobacteria-in-central-and-fgzcx6eyjv.pdf

Influence of Isolated PGPR Rhizobacteria in Central and Northern Benin on Maize Germination and Greenhouse Growth

Rice blast caused by the fungal pathogen,Magnaporthegrisea (anamorph: Pyriculariagrisea) limits rice yield in all major rice-growing regions of the world.Conventional breeding for disease resistance is tedious, time consuming and mostly dependent on environment as compare to molecular breeding particularly marker assisted selection, which is easier, highly efficient and precise. Of the different types of molecular markers,microsatellites have been utilized most extensively, because they can be readily amplifiedby PCR and the large amount of allelic variation at each locus. Microsatellites are alsoknown as simple sequence repeats (SSR),These markers are abundant, distributed throughout the genome and are highlypolymorphic compared with other genetic markers.Recent advances in rice genomics have now made it possible to identify and map a number of genes through linkage to existing DNA markers. Among the more noteworthy examples of genes that have been tightly linked to molecular markers in rice are those that confer resistance or tolerance to blast. Therefore, in combination with conventional breeding approaches, marker- assisted selection (MAS) can be used to monitor the presence or lack of these genes in breeding populations.For example, marker-assistedbackcross breedinghas been used to integrate important genes with significant biological effects into a numberof commonly grown rice varieties. The use of cost-effective,finely mapped microsatellitemarkers and MAS strategies should provide opportunities for breeders to develophigh-yield, blast resistance rice cultivars.This update information willbe helpful guidance for rice breeders to develop durableblast resistant rice variety.

Blast resistance in rice: a review of breeding and biotechnology.

Sheath blight of rice is an economically significant disease worldwide. Use of plant growth-promoting rhizobacteria (PGPR), one type of microbial inoculants, for sheath blight management and yield enhancement of rice is gaining popularity in modern agriculture due to increasing concerns with the use of chemical fungicides. Among different microbial inoculants, PGPR are used for their growth-promoting activities and managing sheath blight in rice. However, the efficacy of experimental PGPR strains is typically not consistent under field conditions due to limited knowledge of their formulations, shelf life, delivery systems, compatibility with chemicals and agronomic practices, and the mode of action. In this chapter, a general review on scope and commercial potential of various PGPR for rice sheath blight management and yield enhancement is provided. Efficacy results obtained from tests with Integral®, a current commercial product, which contains the strain Bacillus subtilis MBI600, are presented as an example of the potential for PGPR in management strategies for sheath blight.

/pdf/commercial-potential-of-microbial-inoculants-for-sheath-2j0crqi3zw.pdf

Commercial Potential of Microbial Inoculants for Sheath Blight Management and Yield Enhancement of Rice

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Commercial Potential of Microbial Inoculants for Sheath Blight Management and Yield Enhancement of Rice