**6. Sustainable crop disease management by genetic engineering (GE)**

In addition to a plethora of published GE strategies, ongoing research, and the wide expansion of genetic resources, conceivable applications are gaining momentum [70] that invests prospective for future generations. The dynamics of the adaptation of pathogen toward the host can be invested by GE strategies due to its selective efficacy against a group or particular target pathogens. Such a targeted advantage minimizes health concerns at the consumers' end with no risk of nontarget biota in an agrarian ecosystem. Some of the processes that occur naturally have also been undertaken in GE processes (**Table 1**). Although the futuristic potential of GE strategies with controlled disease conditions in the subsequent host generations is questionable in the present day, it is demonstrated that GE strategies that were initiated as a proof of concept are now well-established and have been marketed as commercially viable varieties.

#### **6.1 Boosting plant recognition of infection**

Similar to a human system, plants also trigger defense molecules on recognizing particular molecules of invading pathogens generally referred to as pathogen-associated molecular patterns (PAMPs; [71–73]) that illicit a PAMP-triggered immunity. Although PAMP receptor molecules differ among plant species, genes that encode PAMP receptor can be transformed into other crops for triggering immunity [73]. Such a method of transformation does not introduce a novel defense mechanism but rather introduces a receptor that helps the transformed plant recognize infection making it independently counter the infection by its natural immune system [74–77].


#### **Table 1.**

*Genes and their contributions to the plant-pathogen interaction studies.*

**133**

*Antimicrobial Resistance with Special Emphasis on Pathogens in Agriculture*

An intracellular receptor protein (R-protein) is produced as a mechanism of effector-triggered susceptibility which is banked on by a model of disease resistance [72, 103]. This protein is specifically detected in the presence or when an activity of a pathogen effectors is triggered resulting in effector-triggered defense [103]. However, these effectors may modify or change the defense response in the host in response to a new effector produced by the pathogen. With this production of specific R genes with respect to the pathogen effector, pools of resistance genes evolved can be made useful in breeding crops for disease resistance by producing cisgenics [104]. Exceptional efforts by conventional introgression of cisgenes undertaken in crops such as apple, banana, grape, and potato have established it to be labor intensive and time consuming [73, 104]. GE strategies offer a major advantage not only by making it easier and faster but also evading linkage drag [50, 74]. Further introgression of R genes can be made feasible between unrelated plant species among monocots and dicots [77, 105–108]. The tendency of the pathogen to overcome the resistance rendered by R genes can be circumvented by mining R genes from unrelated species by integrating GE strategies and breeding [109, 110].

The activity of defense can be boosted by targeting molecules such as reactive oxygen species, pathogenesis-related genes involved in defense regulation, signaling, and associated processes activating acquired resistance. Such measures were profited to a great extent in enhancing resistance to diseases such as citrus greening and pathogens such as *Rhizoctonia solani* and *Magnaporthe oryzae* that utilizes the plant's own natural immune system without the introduction of new or novel

Some important genes that facilitate normal physiology in plants have been observed to be involved in facilitating pathogen colonization and infection. Changes induced in such susceptibility genes is an efficient strategy for disease resistance [113]. Disarming susceptibility genes may alter the pathosystems and many host factors that contribute to compatibility between the pathogen and host. Gaining a new function to replace the lost host factor is not a likely by the pathogen to overcome the activity of a disarmed susceptibility gene; therefore, this strategy

RNA interference is elicited in plants to silence genes that render pathogenicity by using genetic constructs with identical sequence of dsRNA. Such efforts directly trigger posttranscriptional gene silencing of the natural disease process. Such a process of silencing does not generate a biochemical pathway or produce a novel protein. Integrating the need of the hour with the potential of the strategy of RNA silencing proved profitable for the papaya industry in Hawaii [114, 115]. Such applications are observed in cases where severe strains of the virus can be reduced in case of an infection by a mild strain. Implementing a natural phenomenon for cross-protection as a means to manage disease conditions has practical drawbacks. These drawbacks were controlled by feeding insects with dsRNA constructs that

*DOI: http://dx.doi.org/10.5772/intechopen.88440*

**6.3 Upregulating defense pathways**

metabolic pathways [111, 112].

**6.4 Disarming host susceptibility genes**

does not leave any exogenous DNA [113].

**6.5 Silencing essential pathogen genes**

can trigger RNAi [116, 117].

**6.2 Mining R genes**

*Antimicrobial Resistance with Special Emphasis on Pathogens in Agriculture DOI: http://dx.doi.org/10.5772/intechopen.88440*

## **6.2 Mining R genes**

*Antimicrobial Resistance - A One Health Perspective*

*Agrobacterium tumefaciens*

*Agrobacterium tumefaciens*

*Meloidogyne incognita*

*Pseudomonas syringae*

*Alternaria brassicicola; Botrytis* 

*Golovinomyces orontii*

*Hyaloperonospora arabidopsidis*

*cinerea*

*Ralstonia solanacearum*

*Bipolaris maydis*/*Cochliobolus heterostrophus*

*Botrytis cinerea*, *Erwinia chrysanthemi*

**Disease Pathogen species Pathogen class Gene product Reference**

*Erysiphe orontii* Fungus Receptor-like

Biotrophic bacteria

Necrotropic fungus

Biotrophic fungus

Biotrophic oomycete

Biotrophic bacteria

Necrotrophic fungus

fungus

fungus

fungus

fungus

Blight rot *Burkholderia glumae* Bacteria MAP kinase [99]

fungus

Leaf blight *Xanthomonas oryzae* Bacteria Stearoyl-ACP

Aphid *Myzus persicae* Insects Fatty acid

*Blumeria graminis* Biotrophic

*Botrytis cinerea* Necrotrophic

*Leveillula taurica* Biotrophic

*Fusarium oxysporum* Hemibiotrophic

Rice blast *Magnaporthe oryzae* Hemibiotrophic

Bacteria Arabinogalactan protein

Bacteria Mannan synthase

protein

kinase

Lectin receptor kinase

Membraneattached protein

MAPkinase phosphatase

desaturase

Mitochondrial transmembrane protein

Long-chain aldehyde synthesis

oxidase

Membraneanchored protein

desaturase

Lipid transfer protein

Transcription factor WRKY

desaturase

Fungus, bacteria ABA aldehyde

Insects Fatty acid

*Xanthomonas oryzae* Bacteria MAPKKK [98]

Polygalacturonase and expansin

ADP ribosylation factor—GTPase activating factor

Expansin [85]

Nematode Kelch repeat

*Heterodera schachtii* Nematode Ethylene response [83, 84]

[78, 79]

[80, 81]

[82]

[22]

[86]

[87]

[88]

[89]

[90]

[91]

[92]

[93]

[94]

[97]

[95, 96]

[100, 101]

[102]

**Plant species**

Arabidopsis Crown gall

disease

Crown gall disease

Root-knot nematode

Powdery mildew

Root-cyst nematode

Bacterial speck

Powdery mildew

Downy Mildew

Bacterial wilt

corn leaf blight

Powdery mildew

mold/rot

Soft rot, gray mold/ rot

Powdery mildew

Fusarium wilt

blight

Rice Bacterial

Aphid *Macrosiphum* 

*Genes and their contributions to the plant-pathogen interaction studies.*

*euphorbiae*

Maize Southern

Tomato Gray

Gray mold/rot; leaf spot

**132**

**Table 1.**

An intracellular receptor protein (R-protein) is produced as a mechanism of effector-triggered susceptibility which is banked on by a model of disease resistance [72, 103]. This protein is specifically detected in the presence or when an activity of a pathogen effectors is triggered resulting in effector-triggered defense [103]. However, these effectors may modify or change the defense response in the host in response to a new effector produced by the pathogen. With this production of specific R genes with respect to the pathogen effector, pools of resistance genes evolved can be made useful in breeding crops for disease resistance by producing cisgenics [104]. Exceptional efforts by conventional introgression of cisgenes undertaken in crops such as apple, banana, grape, and potato have established it to be labor intensive and time consuming [73, 104]. GE strategies offer a major advantage not only by making it easier and faster but also evading linkage drag [50, 74]. Further introgression of R genes can be made feasible between unrelated plant species among monocots and dicots [77, 105–108]. The tendency of the pathogen to overcome the resistance rendered by R genes can be circumvented by mining R genes from unrelated species by integrating GE strategies and breeding [109, 110].

### **6.3 Upregulating defense pathways**

The activity of defense can be boosted by targeting molecules such as reactive oxygen species, pathogenesis-related genes involved in defense regulation, signaling, and associated processes activating acquired resistance. Such measures were profited to a great extent in enhancing resistance to diseases such as citrus greening and pathogens such as *Rhizoctonia solani* and *Magnaporthe oryzae* that utilizes the plant's own natural immune system without the introduction of new or novel metabolic pathways [111, 112].

#### **6.4 Disarming host susceptibility genes**

Some important genes that facilitate normal physiology in plants have been observed to be involved in facilitating pathogen colonization and infection. Changes induced in such susceptibility genes is an efficient strategy for disease resistance [113]. Disarming susceptibility genes may alter the pathosystems and many host factors that contribute to compatibility between the pathogen and host. Gaining a new function to replace the lost host factor is not a likely by the pathogen to overcome the activity of a disarmed susceptibility gene; therefore, this strategy does not leave any exogenous DNA [113].

#### **6.5 Silencing essential pathogen genes**

RNA interference is elicited in plants to silence genes that render pathogenicity by using genetic constructs with identical sequence of dsRNA. Such efforts directly trigger posttranscriptional gene silencing of the natural disease process. Such a process of silencing does not generate a biochemical pathway or produce a novel protein. Integrating the need of the hour with the potential of the strategy of RNA silencing proved profitable for the papaya industry in Hawaii [114, 115]. Such applications are observed in cases where severe strains of the virus can be reduced in case of an infection by a mild strain. Implementing a natural phenomenon for cross-protection as a means to manage disease conditions has practical drawbacks. These drawbacks were controlled by feeding insects with dsRNA constructs that can trigger RNAi [116, 117].
