Bio-control of deoxynivalenol and ochratoxins production in stored wheat and barley grains

Abstract

Stored cereals are prone to fungal infections and subsequent mycotoxins production which lead to great loss in quality of these cereals, in addition to economic losses. Nine different fungal species were isolated from stored wheat and barley grains collected from Tabuk-KSA stores on PDA medium. Two mycotoxigenic isolates namely; Aspergillus ochraceus and Fusarium graminearum were isolated from infected grains, their production capabilities of Ochratoxin A and Deoxynivalenol mycotoxins on infested corn grains, respectively, were confirmed using HPLC. Four isolates; Talaromyces purpurogenus, Emericella nidulans, Aspergillus fumigatus and Alternaria sp. were selected as they caused significant in vitro inhibition of the radial growth of both mycopathogens using dual culture and poisoned food techniques on PDA media, in percentages about 76-86; 69-85%, respectively. Identification of both toxigenic and selected isolates were confirmed by amplification of their 18srDNA through PCR and their accession numbers were assigned. Non- volatile metabolites of these selected isolates decreased the fungal dry wt. of both pathogens, in addition, the light microscope demonstrated their capabilities to distort, vacuolate and disintegrate the fungal hyphae of A. ochraceus and F. graminearum. These antifungal potential were attributed to the production of antifungal metabolites (antibiosis), competition for nutrients, space and their abilities to produce extracellular lytic enzymes. In addition they showed potent in vivo antimycotoxin potency, as they decreased the levels of OTA and DON in corn grains co-inoculated with both pathogens separately, and with the selected bio-agents to 12-20 µg\g; 16-25 µg\g, respectively, compared with control corn grains infested with the toxigenic isolates alone (26; 32 µg\g corn grains). All selected isolates decomposed the OTA and DON mycotoxins in corn grains previously contaminated with both toxins, however, the detoxification activities of T. purpurogenus and E. nidulans were more significant 82, 74%; 88, 79%, respectively. These decontamination activities were attributed to the production of extracellular hydrolyzing enzymes, metabolizing the toxins as nutrients (N sources) and decomposing them into non- toxic products. This is the first report of using T. purpurogenus and E. nidulans to inhibit the growth of toxigenic A. ochraceus, F. graminearum; in vivo decrease the OTA and DON levels (antimycotoxin potential) and degrade both mycotoxins. Both T. purpurogenus and E. nidulans could be formulated in the future to be used in cereal stores as efficient, ecofriendly biopreservatives, hence discarding the use of deleterious chemical fungicides.