*2.1.4 Sanitation*

Field sanitation is another important measure through cultural practices for preventing spread of plant disease and their management. Plant and plant parts are some of the best reservoirs of disease organisms. The inoculum present on few plants in the field may multiply on the plant and in due course of time may appear to cause epidemic in next season.

### *2.1.5 Eradication of alternate and collateral hosts*

Plant pathogens usually have a wide host range and they used weeds, wild host plants or self-sown host plants as means of their active survival during absence of main crop. Therefore, keeping the field free from additional host of pathogen is a major sanitary cultural practice. Their timely removal helps to control blast disease.

### *2.1.6 Fertilizer management*

A properly nourished plant is able to withstand or tolerate the attack of pathogens much better than a plant that has either nutrient deficiencies or excesses. A nutrientdeficient plant will be stressed and therefore more prone to disease attack. Excessive fertilizer applications can also cause plants to be more susceptible to disease. Nutrient can affect the relationship between crop and pathogen in many ways. Regulating the amount of nitrogenous fertilizer reduces incidence of blast and other diseases.

#### **2.2 Host plant resistance**

Exploiting host resistance to control disease is not only economical but also a practical necessity in a low value crop like millets where there is a limitation for any additional cash inputs such as fungicides, etc. Development of resistance varieties is the best way of combating the disease, which is primarily grown by resource-poor and marginal farmers. Disease resistant varieties identified and released for the different millets growing areas of India are tabulated in **Table 2**.

#### **2.3 Biological control**

Biological control is an alternative to synthetic chemical pesticides and having several benefits to human beings and ecosystem; they can ensure the protection of plants against biotic and abiotic stresses, production of good quality grains, improve soil fertility, sustainable and safety of environment. The demand for development and application of indigenous bioinoculant products has increased among researchers because of their role in plant growth promotion and crop protection in sustainable farming systems and also for their economic value. Bio-control agents especially strains of *Trichoderma* and *Pseudomonas* are useful for seed and soil borne diseases of millets.

In finger millet seed treatment with *P. fluorescens* @ 6 g/Kg seed and spray *P. fluorescens* formulations at 2 g/lit of water. First spray immediately after noticing the symptom. Second and Third sprays at flowering stage at 15 days interval was found effective for blast disease management.

### **2.4 Chemical control**

Chemicals are not normally used for disease management in millet, because of involvement of high cost of chemical and labor. However, sometimes its use in combination with resistant cultivar becomes necessary. Fungicides are mostly used either as seed treatment or foliar spray. However, combination of them gives better management.


#### **Table 2.**

*Blast disease resistant varieties identified and released for the different growing areas of India (2000–2018).*

Seed treatment with carbendazim @ 1 gm/Kg of seed. Spray any one of the fungicides *viz*., Carbendazim (0.2%) or Iprobenphos (IBP) (0.1%) or premixture fungicide (Carbendazim+Mancozeb) (0.1%), Ediphenphos (0.1%) or propiconazole (0.1%) or Tricyclazole (0.1%). First spray immediately after noticing the symptoms. Need-based second and third sprays at flowering stage at 15 days interval to control neck and finger infection in finger millet. Similarly in rice several fungicides like Tricyclazole have been extensively tested and recommended [57], Probenazole [58], Isoprothiolane [59], Azoxystrobin, *etc.,* are recommend to control blast disease. Many fungicides are used against blast disease, including benomyl, iprobenfos, pyroquilon, felimzone, diclocymet, carpropamid and metominostrobin [60].

#### **3. Future perspectives**

With the everyday increasing population of world demands not only the food security but also the nutritional security which combined to form agricultural sustainability. Updated reports show that the agricultural production needs to be increased 50% by 2050 to meet the growing food and nutritional demand [61]. Nutritional security is as much important as food security for better quality of life which can be fulfilled by the cultivation of millets on large scale. Erstwhile commercial crops like rice, wheat, sugarcane, maize, etc., have been given more importance owing to their wide distribution and acceptance as daily food. In recent times, millets especially small millets gaining huge attention with growing health concerns which are fulfilling by their nutraceutical properties. This results in increasing area of cultivation, and further pathogen gets better opportunity for survival and spread; changes in virulence spectrum; emergence of new pathotypes/races, *etc.,* which intern results in breakdown of resistance as well as expansion of host rage, *etc.,* may lead to drastic reduction in production and productivity.

Therefore, systemic research in small millets on many aspects like breeding of new varieties, sequencing of genome, etc., are still underway has to be initiated on priority. With the advent of advanced genomic approaches like next generation sequencing (NGS), genome editing techniques, etc., made identification, cloning and transfer of resistant (R) genes easy. Using of such approaches in millets aid in better understanding of the crops and pave way for possible manipulation of crop genome to generate disease resistant crops which is an eco-friendly perspective. This will make the millets possibly the eco-friendly alternative for nutraceutical supplement, cost effective due to no use of pesticides and farmer friendly. Also, surveillance of the established diseases and regular monitoring of new diseases aid in achieving the food and nutritional security.

#### **4. Novel/alternative strategies for enhancing blast disease resistances in millets**

Millets are known to show exceptional tolerance to both biotic and abiotic stress in comparison with the popularly grown cereals. The stress resilience is due to various morpho physiological, biochemical and molecular mechanisms. Yet, in the recent era of drastic climate change, there is an increasing report of occurrence of blast disease in millets. The scenario of changing disease severity emphasizes the need to explore into novel, alternative strategies for disease management (**Figure 3**).

*Blast Disease of Millets: Present Status and Future Perspectives DOI: http://dx.doi.org/10.5772/intechopen.111392*

**Figure 3.**

*Novel/alternative strategies for enhancing blast disease resistances in millets.*

#### **4.1 Exploitation of germplasm collection**

Germplasm collections aid in the preservation of genetic resources for use in agricultural research and crop improvement programs around the world. Various millet germplasm has been preserved in various national and international gene banks. International Crop Research Institute for Semi-Arid Tropics (ICRISAT), Patancheru, in collaboration with different national and international organizations has enormous collections of accessions of millets with various traits of interest from across the world. India holds largest collection of millets at ICAR-National Bureau of Plant Genetic Resources, New Delhi, followed by All India Coordinated Small Millets Improvement Project (AICSMIP) at Bangalore and IIMR, Hyderabad. Germplasm could be a fantastic low-cost resource for allele mining and genotypic variant identification for blast disease resistance and other essential agronomic features. Mapping with genetic markers, identifying trait-specific germplasm and identifying candidate genes have a wide range of applications in millet improvement programmes. Lack of genetic resources hampers improvement of millets. Identifying and use new genes for host plant resistance in order to generate cultivars resistant to biotic stresses is critical.

#### **4.2 Genomic assisted/physiological traits-based resistance breeding approaches**

How plants adapt to external conditions determines plants functional trait (morphological, phenological, physiological and nutritional). Variation in these features results in one genotype being superior to others. Automation, imaging and software solutions have opened the way for many high-throughput phenotyping research in recent years. To conduct genetic studies or marker-aided breeding in any crop, DNA-based molecular markers, genetic linkage maps and sequence information are required genomic resources. Early diversity studies utilizing first generation molecular markers (RAPD, RFLP and ISSR) revealed limited sequence diversity in most millet

populations [62], limiting their use in analyzing genetic variations in millet populations. Germplasm collections are used to select ideal mating parents for hybrid breeding, study population structure and analyze QTLs. On the other hand, adaptation of millets to diverse climate makes it impossible to rule out the possibility of the existence of considerable genetic diversity among the millets germplasms. The creation of relevant SNPs, as well as the mapping and tagging of QTLs related with blast resistance, would aid in the cloning of important disease resistance genes and the generation of resistant cultivars through a marker-assisted breeding programme [63].

#### **4.3 Application of PGPR/microbe-mediated mitigation**

Plant growth promoting bacteria (PGPB) promote growth and regulate plant development via cell proliferation and elongation, and development of lateral and adventitious roots by IAA production and ACC deamination. The various PGPB studies in millets include *Pseudomonas* sp.*, Florescent pseudomonads, Enterobacter* sp*. PR14, Sphingomonas faenimutants, Acinetobacter calcoaceticus* and *Bacillus amyloliquefaciens* EPP90. These bacteria help in mitigating the effects of various abiotic stresses by an increased phosphate solubilization and antioxidant activity of enzymes and accumulation of osmo-protectants and a decreased lipid peroxidation [64]. Isolation and identification of such PGPR/ microbes with antimicrobial properties against blast disease would be the breakthrough in eco-friendly management of the blast disease in millets.

#### **4.4 Application of biotic stress mitigants (chemical/biological)**

Rice blast disease, caused by *Magnaporthe oryzae*, is one of the most devastating diseases worldwide. Many excellent chemicals for this particular disease viz., blasticidin S, kasugamycin, iprobenphos (IBP), edifenphos (EDDP), isoprothiolane, ferimzone and metominostrobin have been developed. Present reports of resistance towards fungicides prioritize now as the high time to focus our interest in non-fungicidal disease controlling agents since they are supposedly specific to target organisms along with least resistance development problems. Actually, two groups of non-fungicidal rice blast chemicals are currently on the market; melanin biosynthesis inhibitors (e.g., fthalide, tricyclazole, pyroquilon, carpropamid, diclocymet and fenoxanil) and the so-called priming effectors or plant defense activators (probenazole, acibenzolar-S-methyl and tiadinil) which induce host resistance against the pathogen's attack [65]. Helvolic acid, a terpenoid molecule extracted from the yeast *Pichia guilliermondii.* Isolated from the medicinal plant *Paris polyphylla*, was found to strongly inhibit *M. oryzae* spore germination. Cryptocin, isolated from the fungal endophyte *Cryptosporiopsis quercina*, which colonizes the inner stem bark tissue of *Tripterygium wilfordii*, similarly affects *M. oryzae* [66]. In comparison with the synthetic fungicides now in use, these plant extracts are non-hazardous, ecologically safer, locally available, renewable and easily accessible when used to manage rice blast disease.

#### **4.5 Application of genome editing tools to improve disease resistance in millets**

Of late development of cultivars employing genetic engineering technologies is gaining importance in plant biology and stress physiology. Understanding the mechanisms that regulate gene expression and the ability to transfer essential genes from other organisms into plants will broaden the ways in which plants can be utilized. In the near future, the employment of innovative approaches combining physiological,

biochemical, molecular and genetic techniques could yield great results. Considering the geographical area of cultivation, available resources and the expertise of native researchers, millet genome editing is expected to progress at a slow pace. Due to limited expertise and infrastructure among millet research labs in developing countries the reach of modern tools like genome editing is delayed. Among the available genome editing tools, the CRISPR/Cas system may play a key role for genome editing in millets due to it user friendly and cost-effective construct design [67].

#### **4.6 Multi-omics approaches**

Most of the present information regarding the genome of millets is obtained through comparative genomics application with rice. With the availability of *Eleusine coracana*'s high-quality genome sequence, it will be possible to locate new selection targets and utilize genomic selection and prediction approaches. This will expedite the breeding process and will allow simultaneous selection for yield, quality and disease resistance. Up to date only draft genome sequences are released for finger millet [68], pearl millet [69] and proso millet [70]. Fully annotated genome sequences are not yet available for these millets. Not even a draft genome sequence is reported for other millets (little millet, barnyard millet and kodo millet) up to now. The cross genera transferability of the reported DNA markers demonstrates their usability in understanding phylogenetics. However, molecular breeding efforts utilizing omics tools and translational research are lagging in most of the millet crops [71]. Using transgenic technology or molecular-assisted breeding, the possible candidate genes found through various transcriptome and proteomic investigations could be used to generate cultivars with better adaptability to endure harsh climatic conditions.

#### **4.7 Monitoring evolving races of the pathogen**

In several Indian states, host-directed evolution of pathogenic variation has resulted in severe disease. As a result, understanding pathogen diversity, mode of action and genetics of host plant resistance is critical for developing successful crop improvement methods against biotic stressors. Despite significant progress in managing various fungal diseases in millet, there is still much room for improvement in developing disease management strategies, with a primary focus on virulence monitoring, identification and characterization of newer isolates and development of resistant hybrids/cultivars for commercial cultivation [72].

It is summarized that the blast disease poses a significant challenge to the millets production, now and in the future as evidenced by increase in disease incidence on pearl millet, finger millet and foxtail millet as well as the blast incidence is also observed on other millets viz., barnyard millet and brown top millet at few locations in moderate to severe form. In this chapter, attempts have been made to briefly summarize the key aspects of blast disease caused by *Magnaporthe* spp. and novel strategies for enhancing Blast disease resistances in millets. This chapter serves as a reference point for pathologists and breeders accompanied in field study in nonexhaustive manner to comprehend the complexity of diseases and to contemplate them in a more holistic manner.
