3.1.1. Fusarium verticillioides

damaged top, and stalk may occur in highly susceptible varieties. The base of affected leaves is often narrower than that of normal leaves. Ladder-like lesion on the spindle leaves pronounced yellowing, wrinkling of the spindle, twisting or tangling appearance of the spindle, marketing red stripes, and shortening of the leaves accompanied the malformation or distortion of the young leaves. The most advanced and serious stage of pokkah boeng is a top rot phase. Leaf infection sometimes continued to downward and penetrates in the stalk by way of a growing point. The young spindles are killed and the entire top dies. Leaf sheaths may also

The reddish tissue form ladder-like lesions, often with dark edges. These lesions sometimes break through the surface of the rind. Occasionally, the pathogen also attacks the spindle, and from there it moves down the terminal portion of the stalk causing top rot. The pathogen makes its entry into the host tissues through any sort of injury made by insects or borers or natural growth cracks, etc. The severity of symptoms varies with the susceptibility of a variety and with the congenial environmental conditions and governs the development of the causal organism. During fungal penetration and growth inside the plant, Fusarium proteases and mycotoxins act in a kind of strategic cooperation during spike and core colonization by featuring complementary roles during the host defense suppression and the intracellular colonization of spikelet.

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

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

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

become chlorotic and develop asymmetrical necrotic areas of reddish color.

142 Fusarium - Plant Diseases, Pathogen Diversity, Genetic Diversity, Resistance and Molecular Markers

3. Mode of transferal

are curved like Fusarium species.

sugarcane resistance to FSC.

3.1. Fusarium species complex (FSC) and their distribution

Fusarium verticilloides is the most commonly reported fungal species infecting sugarcane. F. verticillioides is the accepted species, which was also known as Fusarium moniliforme. It can able to produce the chemical agent fusaric. Among the Fusarium species, F. verticillioides is the most prominent Fusarium species in China. It is regulated by the fumonisin biosynthetic gene cluster (FUM), responsible for transport proteins. In our previous study, a total of 101 isolates were recovered from the sugarcane plants affected by pokkah boeng, which were collected from the major sugarcane-producing areas (Guangxi, Yunnan, Guangdong, Fujian, Hainan) in China throughout 2012 and 2013. More than 90% of the isolates (94 isolates) belonged to F. verticillioides, which was closely related to F. sacchari, using the morphological observation and the phylogenetic tree of rDNA-ITS region sequence amplified using fungus-conserved ITS1 and ITS4 primers.

Fusarium verticillioides causes seedling decay, stalk rot, and mycotoxin contamination in sugarcane. This destructive disease occurs virtually everywhere that sugarcane is grown worldwide. Airborne spores (conidia) arising from fungal growth on plant debris or current growth on silks or leaves may cause infection. F. verticillioides (teleomorph Gibberella moniliformis) is a filamentous fungus that produces two types of conidia—macroconidia and microconidia. The fungal colony of the F. verticillioides isolate (CNO-1) appeared to be pale in color but became

orange at the top as it aged, while it was initially white at the bottom which later changed into a yellow color. The fungus is distributed throughout the world but predominant in humid tropical and subtropical regions and also present in the temperate regions.

plant host in which it causes disease. From a traditional taxonomic point of view, F. oxysporum isolates are differentiated from each other based on the pathogenicity as formae speciales, but this has been shown to be an unreliable approach. Vegetative compatibility groups (VCG) have been useful in the FOSC to characterize strains with similar pathogenic properties, and their genetic basis is an active area of research on the toxigenic species and mycotoxins in FOSC.

*Fusarium* Species Complex Causing Pokkah Boeng in China

http://dx.doi.org/10.5772/intechopen.73133

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Fusarium oxysporum can spread short distances by irrigation water and contaminated agricultural machinery and via air or long distances by infected seeds and planting material. This prevents transport of water and nutrients to the rest of the host, causing wilting, discoloration, and ultimately death of the plant. Some strains of Fusarium oxysporum are pathogenic to different plant species; they penetrate into the roots and provoke the vascular system, causing

Fungal growth initiated with white mycelium which subsequently turned pale violet. Ten isolates were recovered from the single-spore cultivation. The mycelia were floccose, sparse, or abundant. The microconidia were oval, elliptical, or kidney shaped and with 0 septate, while the macroconidia usually had three septa. The apical cell was tapered and basal cell was foot shaped. The morphological features and sporulation pattern were consistent with the description of Fusarium oxysporum (Leslie et al., 2006). The pairwise alignment and phylogenetic tree based on three genes (rDNA-ITS, GenBank Accession No. KU863663; pgx4, KU863663; tef, KU933831) and other reference sequences from GenBank also showed that our

Comparative genomics allows investigating many questions of evolutionary and functional significance of sequence features. By associating the species-specific genes with the unique characteristic of that species, researchers can find the potential relationship between genotype and phenotype. Various forward and reverse genetic methods have been developed to explore the repertoire of Fusarium genes contributing to disease formation, mycotoxin production, and sporulation. Phylogenetic tree is another application of comparative genomics to infer evolu-

The whole genome of three fungal isolates (CNO1, YN41, and BS2–BS6) from the Fusarium species complex (FSC) that caused pokkah boeng disease of sugarcane was sequenced by Illumina and PacBio platforms. The genome coverages ranged from 100 to 200. The newly sequenced genomes, along with five previously sequenced isolates (F. fujikuroi IMI58289, F. verticillioides 7600, F. mangiferae, F. circinatum FSP34, and F. oxysporum 4287), were selected based on their incidence in geographical locations, taxonomy/species, host isolation, toxin production, and pathology. Overall, the eight sequenced genomes were comparable in size and structure. The sizes of the eight sequenced genomes ranged from 41.9 to 61.4 Mb with approximately 48.0 of GC content (from 47.3 to 48.3). The CDS (protein-coding genes) ranged

The development of genomics is allowing the incorporation of new tools and resources to address the important new challenges for agriculture. The commercial sugarcane cultivars used today resulted from crosses of S. officinarum and S. spontaneum. However, the reproductive

tionary relationship and to estimate diverge time based on the sequence similarity.

from 10,522 to 17,753. The gene density ranged from 284 to 356 per Mb.

severe damage on many plant species of economic importance.

isolate gx3 belonged to Fusarium oxysporum, close related to FFSC.

3.2. Comparative genomics of Fusarium species complex (FSC)

## 3.1.2. Fusarium proliferatum

Fusarium proliferatum is grouped in FFSC and can be found on a wide host range as well as pathogenic on various agricultural crops. F. proliferatum is a common pathogen infecting numerous crop plants and occurring in various climatic zones. It occurs worldwide as a moderately aggressive pathogen of multiple plant species. F. proliferatum is well documented as a fumonisinproducing species, and some strains can produce large quantities of fumonisins, a group of polyketide-derived mycotoxins. F. proliferatum causes diseases on a remarkably wide range of plant species, including asparagus, banana, date palm, fig, mango, pine, and sorghum. F. proliferatum causing sugarcane pokkah boeng disease was firstly detected in 2012 in China. F. proliferatum in sugarcane is important for resistance, for estimating the evolutionary risk of the pathogen, and for planning the agricultural management practices.

During winter or in dry periods, F. proliferatum survives in the soil and on plant debris. It also produces other mycotoxins, including beauvericin, enniatins, fusaric acid, fusarin, fusaproliferin, and moniliformin. F. proliferatum can be distinguished from other species of the FFSC by analysis of molecular markers. Most recent assessments of fungal pathogens have used multilocus markers to detect populations. The ability of strains and species from geographically separated locations to recombine poses the danger of introducing virulence or toxigenic genes into local pathogen populations. The most commonly observed in human infections are F. proliferatum. However, members of FFSC are increasingly identified in especially invasive and disseminated infections in hemato-oncological patients. Many environmental Fusarium species and the human infections they cause have a worldwide distribution. The knowledge of the genetic structure of the F. proliferatum populations might be useful in order to establish effective strategies for controlling the disease.

#### 3.1.3. The other members of Fusarium fujikuroi species complex (FFSC)

Other FFSC, viz., F. sacchari, F. verticillioides, F. proliferatum, and F. subglutinans, have been isolated from sugarcane. The fungus F. sacchari grows on decaying plant material and produces a large number of conidia that are spread by wind and rain. The stem borer D. saccharalis was shown to carry the fungus from plant to plant in different locations and provide access of conidia in the wind and rain to the inner stem, through their damage made to the stalk. Sugarcane infestation by the stem borer E. saccharina is a major problem in the sugar industry. The lepidopteran's infestation of sugarcane by boring the stalk rind permits Fusarium species access to the stem tissue. As a result, E. saccharina infestation is usually associated with Fusarium infection, which can cause stem rot in sugarcane.

#### 3.1.4. Fusarium oxysporum species complex (FOSC)

Fusarium oxysporum is one of the most economically important pathogens in the genus, but members of this species complex are generally considered to be non-toxigenic. F. oxysporum comprises over 120 known strains or "special forms," each of which is specific to a unique plant host in which it causes disease. From a traditional taxonomic point of view, F. oxysporum isolates are differentiated from each other based on the pathogenicity as formae speciales, but this has been shown to be an unreliable approach. Vegetative compatibility groups (VCG) have been useful in the FOSC to characterize strains with similar pathogenic properties, and their genetic basis is an active area of research on the toxigenic species and mycotoxins in FOSC.

Fusarium oxysporum can spread short distances by irrigation water and contaminated agricultural machinery and via air or long distances by infected seeds and planting material. This prevents transport of water and nutrients to the rest of the host, causing wilting, discoloration, and ultimately death of the plant. Some strains of Fusarium oxysporum are pathogenic to different plant species; they penetrate into the roots and provoke the vascular system, causing severe damage on many plant species of economic importance.

Fungal growth initiated with white mycelium which subsequently turned pale violet. Ten isolates were recovered from the single-spore cultivation. The mycelia were floccose, sparse, or abundant. The microconidia were oval, elliptical, or kidney shaped and with 0 septate, while the macroconidia usually had three septa. The apical cell was tapered and basal cell was foot shaped. The morphological features and sporulation pattern were consistent with the description of Fusarium oxysporum (Leslie et al., 2006). The pairwise alignment and phylogenetic tree based on three genes (rDNA-ITS, GenBank Accession No. KU863663; pgx4, KU863663; tef, KU933831) and other reference sequences from GenBank also showed that our isolate gx3 belonged to Fusarium oxysporum, close related to FFSC.
