Abstract only

The composition of fungi afflicting rice during vegetation has be en studied well enough and it numbers over 300 species. Far less data are available in relation to fungal mycobiota contaminating rice grain during its storage. Lvova L. S. (1982) has established zonal loca- lization of micromycetes species per layers of piled- Up rice. Species Aspergillus f1avus prevailed in grain layers at a temperature of 30-40° C, while less abundant and therefore fewer observations were made for A. glaucus and A. candidus. In the upper and lower layers, other species of Aspergillus and Penicillium predominated. Rice grain is known to accumulate comparatively lower amounts of aflotoxins from mycotoxins against other crops under natural conditions. In the mid-50s, Japan was the scene of severe cases of toxicoses in man and animals afflicted with beriberi -yellow rice disease. It was found later that etiologic factor were fungi Penicillium citreo-viride, P. chrizogenum and Aspergillus terreus -producers of mycotoxin citreoviridin (CT). CT has strong neurotoxic action and is the cause of heavy alimentary mycotoxicoses in man and domestic animals. In the clinical presentation of acute and sub-acute poisoning by this mycotoxin there prevail symptoms of afflicting the CNS and cardiac vascular system as well. LD50 for mice in peroral administering makes up to 29 mg/kg, while in inter-abdominal as much as 7.5 mg/kg. The level of glycogen in brain tissue diminishes upon intoxication by CT. The inhibiting role of said toxin in relation to mitochondrial ATPase has been established. Mycotoxin plays a part in etiology of the cardiac form of beriberi, normally regarded as B- avitaminosys. Under natural conditions, CT is detected in rice, sugar, sausage, and fruit juices. The goal of this work is to expose, among fungi-contaminants of rice, possible producers of CT, conditions of toxin-making in pure crops and in association with others more frequently found species of mycomycetes. Rice is not cultivated in Armenia, but imported from various countries in big quantities Mycological examination was applied to 40 species of rice imported into Armenia from Pakistan, Thailand, Turkey and USA. 28 species of mycelial fungi from genera Rhizopus (2 species), Mucor (2), Aspegillus (8), Penicillium ( 12), Trichoderma ( I ), Trichotecium (1), Fusarium (1), Cladosporium(l) have been revealed and identified. The overwhelming majority of them referred to genera Aspergillus and Penicillium. The highest incidence was found in species A.-f1avus and A. niger from Pakistan. Endeavors to ascertain aflotoxin B 1 in 12 rice samples were not effective. The growth dynamics and toxin forming capacity in growing fungi -possible producers of CT, on sundry nutrient media and rice under artificial infection were studied. Toxicity was studied by biological and chromatographic methods. As a result of the investigation of 17 strains, highly toxic isolates belonging to species A. terreus, P. citreo-viride, P. citrinum have been revealed. From the crops used as a substrate promoting the CT syntheses, the moist rice f1our was found to be the most favorable medium. Maximal synthesis of toxin up to 5 mg/kg was observed upon the growth of fungus P. citreo-viride. The most favorable medium conducive to the production of CT is the modified Czapek's medium containing 10% of glucose and 5% of peptone. The maximum biosyntheses of toxin was revealed on the 20th day of incubation. pH 5.8- 6.2 is conducive to amassing of CT. The most pro- nounced toxicity exhibited strains P. chrizogenum C-95, 2/31, P. citreo-viride 1153, 1154, Q-11 0; A. terreus C-162, C-133, i.e. 7 from 17 strains (41 %). In mixed crops, the inhibiting action of A. f1avus and. A. niger on the growth of fungus and biosynthesis of mycotoxin CT by species P. citreo- was observed.

English

0409|AGRIS 0401|AL-Wheat Program

Juan Carlos Mendieta

CIMMYT Publications Collection