Fusarium spp. - Horticultural importance.  Detection of pathogenic species by molecular methods. 

Fusarium spp. It includes a very diverse group of filamentous fungi that colonize aerial and underground parts of plants, and waste and other organic substrates, so it can be found on earth (ground). They are able to infect a wide range of plant species, causing conditions that manifest as wilts and root rots. As a result, they cause significant economic losses in agriculture, processing industry and processing into food and the feed due to the decline in their quality. However, some species of Fusarium are beneficial in agriculture and have been used in biological control of certain diseases caused by pathogenic species, especially those belonging to the species Fusarium oxysporum. 

The genus Fusarium can produce various kinds of elements that allow it to spread in nature, microconidia, chlamydospores and microconidia which may all be present in some species, while they are not in others. The morphological characteristics of these elements have been taken into account to make the taxonomy of the different species, and plant species affected. 

Currently, methods of molecular biology have allowed some 150 describe morphological species and / or different phylogenetically characterized and accepted by taxonomists well. Testing genomic amplification to intergenic sequences encoding ribosomal RNA, or EF-1alpha (elongation factor alpha), that distinguish species level gene can be used.

As plant pathogen, Fusarium spp. It is capable of colonizing a variety of plant species as diverse as tomato, potato, eggplant, melon or watermelon, and pine, snuff or cereals, among others.  

Among the pathogenic species we can include: 

• It is affecting producing potato leaf chlorosis, stunting or leaf loss.
• Fusarium culmorum affecting rice, barley, maize, melon, beet and wheat. Penetrates very young plants germinated seeds or roots, destroying them . In adult plants it attacks the stem base causing premature wilts, browning and drying of the plant.

• Arthrosporioides Fusarium Fusarium oxysporium together to f. sp. Cubense affects the platanero and   It causes Panama disease causing wilting of the plant. 

Fusarium oxysporium is the most widely distributed species worldwide. It is a common soil pathogen considered saprophyte which thrives on decaying organic matter, which easily survives. This pathogen is dispersed by two main routes, irrigation water dispersion or through agricultural instruments and through transplanted plants or their seeds. Infects plants with mycelium or spores germinating penetrate the plant through the root, and from this, the mycelium advances until reaching the vascular network. Once the vessels produces microconidia spread through the sap to the top of the plant can block the flow of that. 

Microbiological identification of Fusarium species can be made from vascularized plant tissues cultured in selective media with antimicrobials to prevent the development of the concomitant bacteria in the sample, or directly through a soil sample, followed by identification of the / s species / s isolated according to their morphological characteristics or studying the genomic sequence.

However, molecular methods for detection and identification of species to obviate culture isolation and the time required for development in laboratory culture, can be applied directly to samples obtained from the affected plants. These molecular methods amplified by PCR (polymerase chain reaction) genes encoding ribosomal RNA or spacer sequences (ITS1, ITS2 or IGS) found between the genes of ribosomal RNA in both cases the advantage of which are repeated in the genome of the fungus with the sensitivity of the test is increased.