Current Status of *Fusarium* and Their Management Strategies

*Amar Bahadur*

## **Abstract**

*Fusarium* spp. is one of the most economically important plant pathogens causing a wide range of plant diseases with significant crop losses globally. *Fusarium* wilt is a major problem all over the world. *Fusarium oxysporum*, *Fusarium solani*, *Fusarium fujikuroi* are economic importance species in worldwide. *Fusarium solani* causing disease in many agriculturally crops and favored by high temperatures and warm moist soils. The fungus produces three types of asexual spores; microconidia, macroconidia and chlamydospores serve as propagules in infecting host plants and found endophytes and saprophytes. The color of the colony, length and shape of the macroconidia, the number shape of microconidia and the presence or absence of chlamydospores are key features for the differentiation of *Fusarium* species. Pathogens, forms over 100 *formae speciales* cause disease in dicot and monocot plant species and infecting a variety of hosts. Vegetative compatibility Groups (VCG) is used to differentiate their races. Resistant cultivars and bio-control agents (*Trichoderma* spp., and *Psedomonas* spp.) have been used to manage the disease.

**Keywords:** *Fusarium* spp., *formae speciales*, symptoms, disease cycle, management

### **1. Introduction**

Soil-borne pathogens caused infection in soil *via* the roots. *Fusarium* is a complex genus and worldwide distribution, causing diseases in plants, animals, and humans as well as the presence of non-pathogenic *Fusarium* in the natural ecosystem [1]. Fusarium wilt pathogen is one of the most destructive soil-borne pathogens around the world occurring in both saprophytic and pathogenic [2, 3]. Non-pathogenic and pathogenic *F. oxysporum* strains are in the soil, but the pathogenic strain causes severe vascular wilt disease in more than 150 agricultural crop species are banana, tomato, melon, watermelon, and cotton to be infected by vascular wilt [4]. Cereals and other food grains can be contaminated by Fusarium toxins and causes many diseases syndromes in mammals, moldy sweet potato toxicity, and poisoning in bean hulls [5]. *Fusarium* is one of the most important fungal genera that can produce mycotoxins. *Fusarium* mycotoxins are fumonisins, zearalenone, deoxynivalenol, and additional trichothecenes, cosmopolitan genus and numerous species are plant pathogens [6]. Cob rots in maize, caused mainly by *F. graminearum* and *F. verticillioides*, and both species produce mycotoxins which contaminate the grain and some strains of Fusarium solani cause collar rot of legume seedlings such as peas and bean. *Fusarium* species have their ability to grow on a wide range of substrates and their efficient mechanism for dispersal [7]. Many species are saprophytes which occur commonly in soil, colonize diseased roots, stems and grow quickly

on isolation media. It is important to test Fusarium isolates from diseased roots for pathogenicity to the plant. Diversity of host specificity within a single species into the 'forma specialis' each forma specialis exhibited a high level of virulence on a particular host species [8]. *Fusarium oxysporum* and their *formae speciales* that cause vascular wilt diseases, more than 100 Fusarium vascular wilt diseases worldwide and root rots cause with saprophytic strains as colonizing roots after the pathogen, forma specialis usually causes vascular wilt in only a single host specie. *F. oxysporum* mainly causes vascular wilt diseases, while *F. solani* mainly causes collar and root rots. Some strains of *F. oxysporum* can cause rots of melons and potato tubers. *Fusarium oxysporum* is an economically harmful species is a soil-borne phylogenetic diversified fungus with a wide host range including horticultural and grain crops that cause diseases such as wilt, rot, and damping-off [9, 10]. The pathogen has ranked fifth among the top 10 plant pathogenic fungi [11]. *Fusarium* wilt is one of the major diseases caused by *Fusarium oxysporum* strains and a major threat to agriculture [12]. Besides wilt disease, some strains can also cause foot- or root-rot resulting in serious yield losses in affected crops [13].

In the Cucurbitaceae family various *formae speciales* have been identified; among them, *F. oxysporum* f. sp. *cucumerium*, *F. oxysporum* f. sp. *niveum* and *F. oxysporum* f. sp. *melonis* are enormously important, whereas *F. oxysporum* f. sp. *niveum* is the most destructive pathogen of watermelon around the world [14]. Based on the host cultivar's resistance classified into four physiological races (0–3) [15]. The pathogen is responsible for yield losses of around 30–80% or even more [16, 17].

*Fusarium* is one of the most important groups of plant-pathogen causing diseases on crops. Plant-pathogenic fungi *Fusarium graminearum*, causes head blight of wheat and *Fusarium oxysporum*, which causes wilt and stem rot diseases [11]. *Fusarium* species produce a range of mycotoxins, most trichothecenes and fumonisins, which harm animal and human health [18]. *Fusarium* has a taxonomy with generic and species that diagnosing of diseases, identifying fungi, and developing management strategies. The generic concept of *Fusarium* was first diagnosed with the primary character of the banana-shaped conidia [19]. In *Die Fusarien*, which have a thousand species into 65 species, 55 varieties, and 22 forms in 16 sections and continued to use before 1960 [20]. In Russia, recognized and documented *Fusarium* [21, 22]. The Commonwealth Mycological Institute in the United Kingdom published The Genus *Fusarium* in understanding variability in *Fusarium* recognized 44 species and highlighted morphological characters, especially microconidia and the sexual reproductive structures, which used to differentiate species to identification [23]. A pictorial atlas to *Fusarium* that recognized more than 90 species [24]. A manual that recognized 41 species, and further 16 species were published [25]. *Fusarium* species use three predominant species concepts *viz*., morphological, biological, and phylogenetic to differentiate *Fusarium* species. Species concepts in *Fusarium* have been discussed [26]. Many "new" species of *Fusarium* discovered and described [27] and host species [28–30] are explored, grown in new areas [31–34]. Currently, there are more than 300 phylogenetically distinct species [35].
