3. Mode of transferal

The pathogens of pokkah boeng disease are transmitted by the movement of spores through airflow. For spores to take off, it depends on the environmental situation that requires different strategies to disperse. Fungal species that dispersed by rain splash are based on the "puff" and "tap" mechanisms that will cause the dry spores to become airborne, and usually the spores are curved like Fusarium species.

The growth of sugarcane is the most important factor in the biological control and prevention and land and natural environmental factor. The processes for controlling are limited, and there is an increasing need for novel and environmental strategies to control diseases of sugarcane. There will be four sections in this chapter, including Fusarium species complex (FSC) and their distribution, comparative genomics of Fusarium species complex (FSC), FSC and nitrogen, and sugarcane resistance to FSC.

#### 3.1. Fusarium species complex (FSC) and their distribution

Fusarium is a genus of filamentous fungi that includes many toxin-producing plant pathogens of agricultural significance and opportunistic human pathogens. The Fusarium collectively represents the most important group of fungal plant pathogens, causing various diseases on nearly every economically important plant species. Besides their economic importance, species of fusarium also serve as key model organisms for biological and evolutionary research. It is the most common and significant pathogen which spread pokkah boeng disease all over the world. Pokkah boeng disease of sugarcane can drastically reduce crop yield and quality. Fusarium species produce a number of secondary metabolites that are dependent on different physiological responses in plants and animals. It also produces a variety of other compounds such as other mycotoxins, pigments, antibiotics, and phytotoxins.

Fusarium species are commonly identified based on their micro- and macroscopic features. But these features are mostly unstable and render the taxonomy of the group problematic. The presence of different taxonomic systems for the genus also contributes to this problem. A number of molecular tools have been used to circumvent these limitations and also to characterize Fusarium isolates in terms of their genetic diversity, population biology, and phylogeny. In the studies presented here, Fusarium strains isolated from agricultural soils and plant tissues were characterized using different DNA-based tools.

Fusarium fujikuroi (formerly Gibberella fujikuroi) species complex (FFSC) members cause important diseases in gramineous crops. The FFSC becomes compatible with the species concept of F. moniliforme as described by Snyder and Hansen or section Liseola as defined by Wollenweber and Reinking. Fusarium fujikuroi is known to produce a broad spectrum of secondary metabolites.

To recognize and define species in the FFSC, various operational species concepts have been applied. However, a variety of genetic, ecological, and biological traits and properties may be used for this purpose. Only morphological species recognition (MSR), biological species recognition (BSR), and phylogenetic species recognition (PSR) have contributed significantly to the classification of Fusarium species in the FFSC. Of these, the MSR was the most widely used and has dominated Fusarium taxonomy since its establishment in 1809. The MSR also takes into account physiological characters such as growth rates at different temperatures, host associations, and secondary metabolite production. The majority of the current GFC species definitions and descriptions are based on such polyphasic or integrative taxonomic approaches that incorporate various types of data. Till now, two species of FFSC have been identified to cause sugarcane pokkah boeng disease in China.
