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Classification of Fusarium
Fusarium species are common fungus that can cause various ranges of diseases on a wide range of host plant. It can be a soilborne, airborne, or carried in plant residue, and also can be recovered from deepest root to the highest flower from any part of plant (Summerell, Baharuddin and Leslie, 2003). Fusarium species are abundance in soil and frequent association with plant roots, as either parasites or saprophytes that make Fusarium species considred as soilborne fungi. There are the active and passive means of dispersal in the atmosphere and are common colonizers of aerial plant parts that can give result of diseases that considerable as economic importance. The widespread distribution of Fusarium species depends on the ability of these fungi grown at various range of substrates and their efficient mechanism for dispersal (Nelson, Dignani, and Annaisie, 1994).
The taxonomy of Fusarium was diagnosed by Link began (1809). The primary characteristic is used to describe this genus that being presence of the distinctive canoe or banana shaped conidia. This characteristic is well known to all that work with this genus. According to the diagnosis of Link, the early of the research on Fusarium focused on the diagnosis, identification and enumeration of taxa that cause plant diseases. The fungus is isolate from individual plant species represented individual fungal species that were host specific. There are many species and proposed character, and multiple culture media that combined to make strain identification and species diagnosis very complicated. Huge number of Fusarium were describe and attributed various types of diseases outbreaks within a short period of time. (Leslie and Summerell, 2006).
In the year 1930's, the species concept within the genus was reformulated by Wollenweber and Reinking. They provided guidelines for identification which were independent from the plant host and based on the mycological characters of the strains involved. They began with approximately thousand named species of Fusarium described for every host. They reduced them in the monograph to about 65 species, 55 varieties and 22 forms that were arranged in 16 sections with some subsection. All this classification show the most detailed and many of this section and species are still in common use. It is well recognized that species within a section may not be monophyletic. The 16 sections that recognize by Wollenweber and Reinking were Eupionnotes, Macroconia, Spicarioides, Submicrocera, Pseudomicrocera, Arachnites, Sporotrichiella, Roseum, Arthrosporiella, Gibbosum, Discolor, Lateritium, Liseola, Elegans, Martiella, and Ventricosum.
By using single spore cultures method, in 1940s and 1950s Snyder and Hansen reduced the number of species within the genus to nine species. Those nine species that recognize by Snyder and Hansen were Fusarium oxysporum, Fusarium solani, Fusarium moniliforme, Fusarium roseum, Fusarium lateritium, Fusarium tricinctum, Fusarium nivale, Fusarium rigidiuscula, Fusarium episphaeria. The species concepts that were introduced by Snyder and Hansen were familiar to diagnosticians. It is because the concept are easy to apply and virtually every isolate could be identified to species easily.
Booth had determined the further significant development in the taxonomy of Fusarium during the year 1960s and 1970s. It was published as monograph that is The Genus Fusarium (Booth, 1971). It was included keys to the sections and species of Fusarium in a taxonomic system that originally from Wollenweber and Reinking's approaches. The use of the morphology of the conidiogenous cells, especially those producing the microconidia was introduced by Booth as a species level diagnostic character. For distinguishing some of the species in sections Liseola and Sporotrichiella by using conidiogenous cell morphology is essential now ( Booth, 1971).
Fusarium oxysporum and F. solani is two species that established by Snyder and Hansen that still have been used. Anyway, there is little doubt that these taxa consist more than a single species as described with more current species concepts (Leslie and Summerell, 2006).
Snyder and Hansen define the term formae speciales as a group that can infect only certain host genus or species. Formae speciales are the most common intraspesific designation that currently used in Fusarium. In Fusarium, the definition of formae speciales always related in term plant pathogenicity towards a host or group of usually related hosts. Formae speciales designation not specific only to Fusarium but also used to other plant pathogenic fungi (Leslie and Summerell, 2006).
For some cases, formae speciales can be further subdivided into races towards a particular set of host lines, varieties or cultivars. The phylogenetic significance of formae speciales and races are influence by the origin of the pathogenicity determinants. The strains within the race or formae speciales need not be monophyletic in origin if the pathogenicity is not an ancestral character (Leslie and Summerell, 2006). Other than pathogenicity test, crossing tests are also can be use for identifying formae speciales and races where mating may be made. The differentiation of formae speciales and races depends on selective pathogenicities to their hosts since they are closely similar in respect to the morphology of the macroconidia, microconidia and Hypomyces stage (Matuo and Snyder).
Pathogenicity was considered as the ability of parasite to interfere with one or more of the essential function of the plant to cause the diseases (Agrios 1978). They are characterized by the ability of the pathogen to grow and multiply rapidly on diseased plants and also by its ability to spread from diseased to healthy plants and to cause new diseases. Each of parasitic can cause disease to one or many kind of plant. The variability of pathogenicity of the pathogens can cause the newly developed resistant variety against some pathogens suddenly becomes susceptible. Some groups of individuals within one species of a pathogen can show pathogenicity to a different genus or species of plants.
Characteristic of Fusarium solani
Distribution of Fusarium solani
Genus Fusarium is associated with plant roots and debris, rhizosphere soil and organic matter belonging to soil inhabitant throughout the world (Summerell et al. 1993, Sanglang et al. 1995a, b). These fungi are colonizing wide and complex ecological niches that influenced primarily the function, form, and structure of ecosystem (Stoner 1981). Decomposition and utilization of a wide range of organic substrates is may be one of the mechanisms for these fungi to survive (Burgess 1981, Marasas et al. 1988). Fusarium species retrieved from both natural and agricultural ecosystems that have distinct climatic preferences. The range of species observed can be limited by the climate and local variations in weather. Even if several are present, their relative frequency will be influenced.
Fusarium solani has a universal distribution. It may be found in various native soil (Burgess, and Summerell, 1992, Clark, Hyun, and Hoy, 1998, El Gindy, and. Saad, 1990, Ellanskaya, Volz, Nevo, Wasser, and Sokolova, 1998) and become one of the few species of Fusarium that can be found from soil in high frequency in rain forest habitats (Summerell, Rugg, and Burgess., 1993). F. solani is known as a pathogen on a vast and diverse range of host plants. However, the utility of many of these recorded is questionable that cause the taxonomic diversity likely contained within this species complex. Fusarium solani has been suggested as a possible biological control for leafy spurge (Caesar, Campobasso, and Terraglitti, 1998), morning glory (Abbas, and Boyette, 1996), striga (Kroschel, Hundt, Abbasher, and sauerborn, 1996), Texas gourd (Boyette, Templeton, and Oliver., 1984, Weidemann, and templeton, 1988,Weideman, and Wehner, 1993), and water hyacinth (Jamil,. Narasaiah, and Thyagarajan, 1983).
Formae Speciales of Fusarium solani
Fusarium solani in section Martiella of the genus Fusarium is a soil-inhabiting fungus that can easily found everywhere in the world. Which is comprises of phytopathogenic and saprophytic strains that the former can be further divided into groups where each with distinctive host range. About eleven of these formae speciales have been described in the species (Snyder and Hansen 1941, Sakurai and Matuo 1959, Matuo and Sakurai 1965, McClure 1951, Sakurai and Matuo 1961, Roy 1997), where seven of that is are heterothallic with the common ascomycetous sexual stage of Nectria haematococca Berk. Et Br. which is belongs to the Hypocreales. Producing perithecia occur only when mating of within members of the same formae specialis which indicate that each formae specialis represents a single mating population (Matuo and Snyder, 1973). The sexual stages of the other four formae speciales are not known.
The presence of mating population as well as the diversity of much other type of traits in species suggests that this species is a biological species complex (VanEtten and Kistler 1988), eventhough based on the morphology of conidial state F. solani was described as a speciales (Snyder and Hansen, 1941). In comparative studies in United States and Japan from 1967 to 1970, particularly attention was given to both morphologic characters and mating populations as well to the pathogenicities of numerous isolates of all the formae speciales and races of F. solani from both laboratories. In addition to pathogenicity tests, the ability to cross was tested as an aid for identification of formae speciales and races (Matuo and Snyder, 1973).
Pathogenicity of Fusarium solani
Fusarium solani (Mart.) Sacc. f. sp. cucurbitae W. C. Snyder & H. N. Hans. was first reported on squash (Cucurbitae pepo L.) in 1930 in South Africa and subsequently on different cucurbits in the United States, Spain, Italy, New Zealan and Japan. This pathogen can cause crown and root rot disease of cucurbit that severely damage watermelon. Fusarium solani f. sp. cucurbitae can be found everywhere watermelon has been grown in Tunisia and become a serious problem for its production. On the basis of pathogenicity test on watermelon seedlings and muskmelon fruits, the Fusarium solani isolates were identified as Fusarium solani f. sp. cucurbitae that collected from different Tunisian cropping areas. Fusarium solani f. sp. cucurbitae race 1 is widely distributed in watermelon production areas, while the race 2 has a lower incidence but is present in northen, central and southern Tunisia (Boughalleb, Armengol, and El Mahjoub, 2005).
Foot rot in courgette is caused by Fusarium solani f. sp. cucurbitae race 1. The both morphology and host range of the pathogen are distinguished from F. solani from sweet pepper. All nine cultivars of the six species of Cucurbitaceae tested were susceptible in inoculation test. Inoculation with a spore suspension by root dipping or adding the suspension to the soil around the stem base or spraying the whole plant with it caused the courgette green became diseased. The wounded and young plants died more quickly than unwounded and older plants. The plants were affected more slowly with low inoculums densities than high densities. The differences in susceptibility of Cucurbitaceae tested were more pronounced (Paternotte, 1987).
Hypomyces solani Rke. et Berth. Emend Snyder. Et Hansen. is the perfect stage of F. solani which causes root rot of several important crops. Hansen and Snyder showed that H. solani f. sp. cucurbitae Snyd. Et Hans to be an extremely variable fungus in the form parasitic squash. Numerous strains in culture and in nature was found which differ not only in pigmentation, rate and type of growth but also in their sexual and compatibility groups. Some strains are more pathogenic than others and also capable of attacking a number of cucurbits including melons and gourds (Prasad, 1949).
Plant disease cause by Fusarium solani
Fusarium species act as plant pathogen that can cause variety type of disease such as crown rot, head blight, and scab on cereal grains, and other diseases such as pokkah-boeng on sugarcane and bakanae disease of rice (Booth, 1971). Fusarium oxysporum Schlechtend.:Fr. f. sp. Niveum (E.ESm.) W. C. Snyder & H. N. Hans. can cause Fusarium wilt on watermelon. This disease also an economically important disease of this crop and well established throughout the watermelon growing regions of the world. While the foot rot on courgette (C. pepo) caused by Fusarium solani f. sp. cucurbitae race 1. After a few weeks of planting, the symptom appear that the plant become dark green and are retarded in their growth. The stem base is soft and many roots are affected and lesion may found higher on the stem but then existing wound acted as site of infection (S. J. Paternotte, 1987).
Fusarium solani may cause a variety of diseases with different host. There are several host that commonly infected by F. solani causing dry rot of potato (Hooker, 1991), root rot and fruit rot of pumpkin (Tousson and Snyder, 1961) and stem lesion and fruit rot of green pepper (Fletcher, 1994). For example, F. solani (Mart.) Sacc. f. sp. pisi W. C. Snyder & H. N. Hans is an economically important fungal disease on pea that causes Fusarium root rot. Fusarium solani f. sp. pisi also affect several host other than pea, that is mulberry, ginseng and chickpea (Matuo and Snyder 1972, Kraft 1969). While F. solani f. sp. phaseoli is considered as the major pathogen causing root rot on bean (Steadman et al., 1975).