**1.1 Rice blast disease**

One of the major constraints for rice production in the USA is rice blast. Blast disease of rice is caused by the filamentous fungus *Magnaporthe oryzae*

### **Figure 1.**

*Photographs showing symptoms of leaf and panicle blast and asexual spores of rice blast fungus. (A) Panicle damage caused by blast; (B) severe blast lesions on rice seedlings affecting rice seedling establishment; (C) blast lesions on a rice leaf after diseased leaf from a field was placed in a petri dish with a prewetted filter paper for 24 h; and (D) four asexual spores of the rice blast fungus [9]. The pictures were taken either with an iPhone, with a dissecting microscope, or with a Nikon eclipse microscope.*

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**Figure 2.**

*microscope.*

*A Toolbox for Managing Blast and Sheath Blight Diseases of Rice in the United States of America*

The soil-borne, necrotrophic *Rhizoctonia solani* species have a wide range of host plant species. The anastomosis group AG1-IA of *R. solani* infects rice and causes sheath blight disease. *R. solani* is a monocyclic fungus. The life cycle of *R. solani* begins with mycelia growth from sclerotia soon after attachment onto rice seedlings/plants. The mycelia then move upward along the sheaths and leaves of rice plants, ultimately resulting in damages on the sheaths, leaves, and grains. The life cycle ends with the formation of overwintering structures, sclerotia on the sheaths,

*Photographs showing sheath blight disease on the sheaths, leaves, and grains (A and B) and young mycelia sheath blight fungus with 45 and 90° angles (C). Pictures were taken with an iPhone or with a Nikon eclipse* 

(synonymous with *Pyricularia oryzae*) which belongs to the *M. grisea* species complex. The *M. grisea* species complex is known to infect a wide range of monocots causing numerous diseases. However, infection of *M. oryzae* is highly specific to its host—rice (*Oryza sativa*) [3]. The infection of a *M. oryzae* isolate to an alternative species was only demonstrated under greenhouse conditions [4]. *M. oryzae* is a polycyclic pathogen that can reproduce 3–5 generations during a single crop season depending on geographic regions [5]. *M. oryzae* can survive in debris and seeds from previous crop seasons, and the fungi carrying debris and seeds are the primary sources of inoculum for blast epidemics [6–8]. Infection of *M. oryzae* starts with asexual conidia. The conidia germinate within a few hours after attachment and penetrate the host cells. Visible symptoms on rice leaves can be seen as early as 5 days after initial contact. A single blast lesion can produce thousands of conidia within a week and these conidia can spread to another rice plant through air, dew/ water, and physical contact. Each conidium is capable of causing the loss of a single

*DOI: http://dx.doi.org/10.5772/intechopen.86901*

rice panicle (**Figure 1**).

**1.2 Sheath blight disease**

leaves, seeds, and in soils [10] (**Figure 2**).

*A Toolbox for Managing Blast and Sheath Blight Diseases of Rice in the United States of America DOI: http://dx.doi.org/10.5772/intechopen.86901*

(synonymous with *Pyricularia oryzae*) which belongs to the *M. grisea* species complex. The *M. grisea* species complex is known to infect a wide range of monocots causing numerous diseases. However, infection of *M. oryzae* is highly specific to its host—rice (*Oryza sativa*) [3]. The infection of a *M. oryzae* isolate to an alternative species was only demonstrated under greenhouse conditions [4]. *M. oryzae* is a polycyclic pathogen that can reproduce 3–5 generations during a single crop season depending on geographic regions [5]. *M. oryzae* can survive in debris and seeds from previous crop seasons, and the fungi carrying debris and seeds are the primary sources of inoculum for blast epidemics [6–8]. Infection of *M. oryzae* starts with asexual conidia. The conidia germinate within a few hours after attachment and penetrate the host cells. Visible symptoms on rice leaves can be seen as early as 5 days after initial contact. A single blast lesion can produce thousands of conidia within a week and these conidia can spread to another rice plant through air, dew/ water, and physical contact. Each conidium is capable of causing the loss of a single rice panicle (**Figure 1**).
