Mubashir hussain PhD Scholar 13-arid-3282

Bio-based resistant inducers for sustainable plant protection against pathogens (Phytochemical pesticides)

Contents: Introduction Immune system in plant Resistance inducers 1. Chemical inducers 2. Microbial elicitors Bacterial elicitors Fungal elicitors 3. Plant extracts Algal extracts Extracts of higher plants 4. Composts 5. Biochar Conclusion Reference

Introduction In agriculture, plant varieties were domesticated and over time bred for yield and fruit quality. Plant disease resistance is often decreased compared to wild varieties Most plants including crops are susceptible to numerous diseases caused by different microorganisms (pathogens). Diseases decrease crop yield and quality and toxins released by microbes were usually present in the harvest.

Conti…. Formerly, diseases were responsible for severe economic and nutritional crises and are still responsible for a considerable loss in the worldwide crop production. To date, ensuring a satisfactory yield and the quality of the harvest requires an extensive use of numerous phytochemical pesticides. Pesticides harm crops, the environment, even the health of farmers and consumers and may lead to selection of resistant pathogen strains.

Alternative and sustainable disease management Alternatives include Organic and integrated farming practices Biological control Use of resistant hybrids or transgenic crops.

Limitations Some national legislative bodies do not allow genetic crop improvement by transgenesis and assisted crossing may also be prohibited for some crops, such as wine, protected by appellation seals.

Immune Systems in Plant Can be broadly classified as; Local defense system It is concerned with imparting immunity only at the site of infection. It is more common than proliferated one.  Proliferating defense system Can be Initiated sometimes due to local defense system Defense alert is amplified and transferred from the site of infection by a system of mobile signals into distal (systemic) plant parts.

IMMUNE SYSTEMS IN PLANT Proliferative defense system Systemic acquired resistance (SAR) Induced systemic resistance (ISR) Local defense system Hypersensitive response (HR) Effector-triggered immunity (ETI) MAMP/PAMP/pattern-triggered immunity (MTI/PTI).

Immune system in plants Step 1: Attack of non-self” signals Microbe/pathogen-associated molecular patterns (MAMPs/PAMPs) are conserved molecular structures essential for the overall fitness of microbes b) Host derived “danger” signals or damage-associated molecular patterns (DAMPs), such as pectin-derived oligogalacturonides, produced as a consequence of enzymatic microbial activities and toxins.

Conti..... Step 2: Recognition of foreign material MAMPs and DAMPs are recognized by plasma-membrane localized pattern recognition receptors (PRRs) and induce a broad variety of defense responses commonly referred to as MTI or PTI.

Conti..... Step 3: initial cascade of signaling events Tiggers ion fluxes leading to plasma membrane depolarization, production of reactive oxygen species (ROS), nitric oxide (NO) and activation of Mitogen-Activated and Calcium-Dependent Protein Kinases (MAPKs and CDPKs).

Conti..... Step 4: TF modulation activities   These signaling events modulate transcription factor (TF) activities Leading to massive transcriptional reprogramming related to defense.

Conti..... Step 5:Activation of defense gene 1. Pathogenesis-related (PR) proteins Hydrolytic enzymes β-1,3-glucanases and chitinases………………..degrade microbial cell walls Defensins…………………disrupting pathogen membrane Peroxidases, proteinase inhibitors or lipid-transfer proteins

Conti..... 2. Compounds with antimicrobial activity such as phytoalexins 3. Lignin and callose deposited to the cell wall assuring its strengthening 4. Production of ROS with a signaling role and direct antimicrobial effect 5. Stomatal closure

Conti.....  Which one is ultimately tunning and orchestring these responses???? Phytohormones such as Salicylic acid (SA), Jasmonic acid (JA), Ethylene (ET) Abscisic acid (ABA) Brassinosteroids (BR) Gibberellins

Resistance inducers 1. Chemical inducers Exogenously applied SA provided a broadspectrum disease resistance in tobacco leaves (White, 1979). Acibenzolar-S-methyl (ASM), named also benzothiadiazole (BTH) is an efficient broad-spectrum resistance inducer against bacterial, fungal and viral diseases in different monocot and dicot crops (Walters et al., 2013). Its commercialized forms known as Bion or Actigard (Syngenta) are widely used in agriculture.

Conti..... Probenazole, applied to rice crop…… control rice blast, caused by a fungus Magnaporthe grisea and bacterial leaf blight, caused by Xanthomonas oryzae pv. oryzae.

2. Microbial elicitors 2.1. Bacterial elicitors Three major categories BDCs , Effector class of BDCs, plant-associated microorganisms (Beneficial bacteria) BDCs These are the molecules with conserved sequence (MAMPs) Released either from bacteria. Released accidentally from bacteria (DNA, transcription, translation factors).

Name Functional class Origin Pathogen Host Selected references Lipopolysaccharide (LPS) Cell wall (outer membrane) component; MAMP Gram-negative bacteria Avirulent bacteria; Brassica campestris; Arabidopsis Newman et al. (2002) Flagellin Flagellar Several Pseudomonas syringae pv. tomato; etc. Arabidopsis most higher plants) Zipfel et al. (2004) EF-Tu; elf18/26 Translation factor; MAMP (Poly)peptide Escherichia coli tomato (Brassicaceae only) Kunze et al. (2004) 2,4-Diacetylphloroglucinol Toxin (antibiotic); Pseudomonas fluorescent Peronospora parasitica Iavicoli et al. (2003)

2.2 Effector class of BDCs can readily reach the plant cytoplasm, via a conduit called type III secretion system (T3SS). The T3SS effectors are aimed to manipulate host metabolism.

2.3 Plant-associated microorganisms (Beneficial bacteria) Some BDCs appear more feasible for practical plant protection than others, because they are inclusively delivered along with PGPR and/or bacterial endophyte cells.

Name Functional class Origin Pathogen Host Selected references Dimethyl disulfide VOC Bacillus (PGPR) Botrytis cinerea Tobacco; corn Huang et al. (2012) Nod factors (lipochitooligosaccharide) Symbiotic signal Rhizobia Microsphaera Soybean Duzan et al. (2005)

2.2 Fungal elicitors The treatment with chitin reduced the susceptibility of rice to M. oryzae (Tanabe et al., 2006). Chitosan was able to induce the level of chitinase activity and new isoforms of chitinase, resulting in the reduction of early blight disease in tomato leaves. (Sathiyabama et al., 2014). Tomato plants grown in the soil amended with monosilicic acid and chitosan slowed down the development of bacterial wilt (Kiirika et al., 2013).

3. Plant extracts 3.1. Algal extracts Initial work was demonstrated on Rubus fruticosus L. in 1995 (Patier et al., 1995)…….algal polysaccharides ……induce resistance against a broad range of pathogens and this capability relies mostly on the level of their sulfatation.

Algal extract source Recent applications/research as plant protectors refrences Laminarins and sulfated laminarin (PS3) brown algae such as Laminaria digitata B. cinerea and Plasmopara viticola in a grapevine. (Aziz et al., 2003) and (Gauthier et al.,2014) Ulvans Ulva studies were completed both on resistance induction against pathogens and defense mechanisms. (Stadnik and de Freitas, 2014) Carrageenans red algae long-lasting protection against biotrophic as well as hemibiotrophic pathogens (Mercier et al., 2001; Vera et al., 2012). fucans brown algae as Ascophyllum nodosum, Fucus spp. and Ecklonia spp. data on their elicitation effect on plants are rather scarce. (Klarzynski et al. 2003)

Extracts of higher plants Traditionally plants have been a valuable source of biologically active compounds especially for medicinal purposes. Various herbal extracts were also previously used to protect plants from pests and diseases but on a smaller scale. Now they are making a comeback in the form of so-called botanical biopesticides. Their direct antimicrobial effect to plant pathogens has been demonstrated many times.

Most commercially successful species with protective activity Giant knotweed (Reynoutria sacchalinensis (F. Schmidt) Nakai). An ethanolic extract of this plant was registered in 1990s as Milsana® has been proven to protect cucumber from powdery mildew (Daayf et al., 1995) Widely used other plants include , Azadirachta indica and Hedera helix. Recently, plant essential oils is considered as an efficient source of resistance against pathogens. e.g. Essential oil from Gaultheria procumbens

4. Composts Composts are products of aerobic biodegradation of different types of organic waste, which are mostly used as peat substitutes and soil amendments. Their suppressive effect against pathogens has been ascribed primarily to microbial populations colonizing rhizosphere and their competitive activity and antibiosis against root pathogens. However, a number of studies indicate involvement of induced resistance mechanisms.

5.Biochar Biochar is a coproduct of pyrolized biomass utilized as a soil amendment. . The results indicate that biochar has a potential to alleviate plant diseases and provide plants to efficient defense resistance against leaf pathogens.

Conclusion Promotion of plant disease resistance by stimulation of crops using bio- based compounds represents an alternative to chemical pesticides. During the last years, a boom of studies extended our knowledge of the potential of this approach. A high number of resistance-inducing compounds of different origins and nature were reported and their efficiency was evaluated in various plant-pathogen systems. Bio-based resistance inducers can be combined with biopesticides, biological control agents, biostimulants and even chemical pesticides, which could result in reduced pesticide consumption.

Reference: Burketova, L., L. Trda , P. G. Ott and O. Valentova. 2015. Bio-based resistance inducers for sustainable plant protection against pathogens. Biotechnology Advances 33 :994–1004.