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Alternaria pathogenicity and its strategic controls

Anuj Mamgain, Rajib Roychowdhury and Jagatpati Tah

The Deuteromycetes fungal genus Alternaria comprises of different saprophytic as well as endophytic species and is well known for its notoriously destructive plant pathogen members. It has been found to have a drastic effect on the members belonging to the plant families such as Cucurbitaceae, Brassicaceae, Solanaceae which are having nutritional as well as economical food value. Majority of the members of Alternaria lack sexuality altogether, although few species have been found to have sexual stage in their life cycles. Several types of genes ranging from protein encoding genes to those involved in signal transduction cascades are found to be responsible for the pathogenesis. Production of host-specific toxins (HSTs) is found to be an affirming factor of pathogenesis. Most fungal host-specific toxins are metabolites although toxic substances including despipeptides and fucicoccin-like compounds. Genes encoding the biosynthesis of these HSTs are often contained on mostly conditionally dispensable chromosomes. The necrotrophic nature of Alternaria species typically leads to extensive damage of the plant and harvest product, with seedlings seldom surviving an attack. Apart from the role of toxins in Alternaria pathogenesis, few genes and /or gene products have been found to have a propounding effect as a pre-requisite for pathogenicity. For controlling the diseases, numbers of new chemicals are evaluated along with various biological control agents including bacteria, actinomycetes and fungi. Some plants and plant products are also found to be useful in controlling Alternaria infection.