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Fungal colonization of stored grain bulks is a major threat for mycotoxin contamination and reduction in viability of grain when stored under unsafe conditions, e.g. under high r.h. and insect presence. An investigation was carried out to identify the trends of the changes in the fungal species communities during storage of wheat grain under these unsafe storage conditions. The distribution change of fungi genera was monitored on small grain samples of three wheat varieties with different kernel size and hardness (soft, medium-hard and hard), during 160 d storage at constant temperature of 22-23°C, at two r.h. levels, and with or without an infestation by the rice weevil S. oryzae. According to their behavioral differences related to grain water activity affinity, fungi genera were classified in three groups: i/ The hydrophilic group of field fungi (Fusarium, Geniculifera, Sepedonium, and Chrysogenum); ii/ The intermediate semi-xerophilic fungi (Alternaria, Mucor, Ulocladium, Epicoccum, and Arthrobotrys); iii/ The storage xerophilic fungi (Penicillium and Aspergillus). Temporal abundance of these three groups with grain storage time and condition was observed in weak relation with wheat variety and insect presence. The multivariate comparison of the different experimental situations revealed a difference in the susceptibility of varieties to fungal species colonization in close relationship with the final equilibrium level between ambient r.h. and grain moisture content which was observed variety-dependent. This difference was not related to grain hardness but rather to a different r.h. affinity. For one variety (Apache), the germination rate was declining more rapidly than for the two others with storage time. Any significant relation between sound and infested grain condition and the contamination rate by storage fungi could be found. The susceptibility of the three wheat varieties to critical storage conditions and fungal colonization may lead in one variety to a hot-spot formation.

Pesticide residues are found in oilseeds (rapeseed and sunflower) and crude oils: they are mainly organophosphate insecticides (pirimiophos-methyl, malathion when authorized) used in empty storage facilities and for direct application to stored cereal grain. Even if some secondary pests are found in stored oilseeds, French regulations do not allow use of these insecticides on stored oilseeds. These residues arise from cross-contamination from storage bins and grain handling equipment of grain stores, and not from illegal use. This uptake of insecticide residues from their storage environment by oilseeds may lead to residue contents that exceed regulatory limits. A three-year investigation in grain storage companies allowed us to follow the course of sunflower batches and rapeseed batches during storage seasons 2006-2007, 2007-2008 and 2008-2009, from reception at the storage facility to outloading. Each of these batches was sampled at outloading, and was analyzed for insecticide residues. Traceability of oilseeds established by grain-store managers allowed us to identify cross-contamination sources. The insecticides that were most commonly detected were pirimiophos-methyl, malathion, and dichlorvos (in sunflower 2006-2007), plus chlorpyriphos-methyl and deltamethrin. Pirimiophos-methyl was the most commonly detected active substance, and caused the most cases of non-accordance with regulatory levels in rapeseed. Cross-contamination could have occurred when cereal grains were treated upon receipt, when rapeseed was also delivered, especially when treatments were done systematically to the cereal grains. For sunflower, the main cross-contamination hazard resulted from treatment of cereals at the period of receipt or at their outloading, just before sunflower seeds batches were outloaded. Another situation led to cross-contamination, but generally at a lower extent: oilseeds stored in bins that contained previously treated cereals, or loaded in empty bins with handling equipment treated before the receipt of oilseeds.

A multidimensional laboratory trial was carried out to identify how key overall quality traits of different common wheat varieties change during storage, to understand their interactions in the process of deterioration, and finally to reveal underlying trends of critical storage conditions that may endanger grain quality. A large set of qualitative criteria were followed on grain batches of three wheat varieties with various qualities for food processing, which were stored for 160 d at 22-23°C, under two different relative humidities (r.h.), and with or without infestation by the rice weevil Sitophilus oryzae. All variables involved in quality components assessment were recorded at 42-d periods. From the Pearson’s product moment correlation matrix, it was observed that the quality traits that correlated significantly to biotic variables (insect and fungal species dynamics) were: moisture content, hL mass, seed viability, and fat acidity of extracted flour. The interactions between biotic deteriorative factors and qualitative trait changes revealed through principal component analysis (PCA) were significant between four factors explaining the major part of qualitative criteria variance: storage duration; moisture content; hidden infestation density; fungal contamination level. The rate of increase of insect population was significantly different among varieties. PCA revealed that the significant difference in qualitative deterioration pattern among the three varieties was not related to their hardness, but to a different r.h. affinity. The germination rate was the qualitative criteria the more early declining during storage. The technological properties of extracted flour from each variety were significantly affected only when insect density exceeded 1000 insects per kg, a situation only observed in hot-spots. This work highlighted the trends of variation in quality traits of wheat varieties when stored under critical conditions. It can be used in IPM approaches to predict the susceptibility of a wheat variety to insect and fungi damage during storage.

Une expérience de stockage de paddy a été réalisée en conditions tropicales simulées d’un atelier climatisé, dans des enceintes élaborées en matériaux plastiques souples de 2 types différents. La conservation du grain dans ces enceintes d’une capacité unitaire de 50 la été conduite dans 4 conditions différentes : - témoin (stockage normal aéré); - stockage hermétique, seulement confiné; - purge complète avec un mélange CO2/air à 50% (v/v) avant fermeture complète; - purge avec CO2 pur. Les enceintes contenaient 20 kg de riz paddy semi-humide à 17% de teneur en eau, infesté par Sitophilus oryzae à tous ses stades. Pendant 3 mois de conservation avec des prélèvements hebdomadaires, les variations de l’équilibre de sorption gazeuse entre les atmosphères modifiées et le riz ont été observées. Les perturbations de l’étanchéité au moment des prélèvements sont rapidement compensées par la reprise de la respiration des microorganismes présents dans le grain semi-humide. Le maintien d’un très faible niveau d’oxygène résiduel dans les poches les plus étanches a pu être réalisé malgré le prélèvement de grain. L’adsorption de dioxyde de carbone sur le grain a été active pendant 3 semaines au début de la conservation ce qui a permis de préciser les règles d’utilisation des atmosphères modifiées par le CO2 pour la désinsectisation des céréales. Les volumes nécessaires pour le gazage en conditions pratiques sont précisées dans le cas de la conservation du riz paddy semi-humide en climat tropical., In simulated tropical climatic conditions, a trial on paddy storage was conducted in small hermetically-sealed bags (50-l capacity) made from 2 different types of plastic material. Four treatments were studied as follows : - control (aerated storage); - hermetic storage; - initial purge with gas mixture, 50% CO2 in air (v/v); - initial purge with pure CO2. Each bag contained 20 kg of damp paddy (17% moisture content) infested with all stages of S oryzae. Weekly sampling over a 3-month storage period permitted determination of the lethal effects on insects, CO2 production rate and variations in gas adsorption by the grain (figs 1-4). CO2 adsorption was active over the first 3 wk (fig 5). Disturbance of the air-tight seal during weekly sampling was rapidly compensated for by microfloral respiration which is the main source of CO2 production in grain at 17% water content (table I and fig 6). This led to oxygen consumption within a few days after each grain sample withdrawal, and in consequence a very low level of residual oxygen content was maintained in bags with the best level of airtightness (type "B", figs 1-2). The adsorption-desorption effect was quantitatively assessed. This permitted the fitting of an evolutionary theoretical model for prevision of the decrease in total gas volume inside the bags (fig 5). Guidelines for a practical utilization of modified or controlled atmospheres by CO2 enrichment are presented for damp paddy storage under tropical conditions.