Gas Composition

While fungi involved in biodeterioration of grain are considered to be obligate aerobes, many are actually microaerophilic, being able to survive and grow in niches where other species cannot grow and, thus dominate specialized grain ecosystems. In many cases, decreasing O2 to < 0.14% is required before growth can be substantially reduced. Increasing CO2 to > 50% is required for inhibition of growth (Magan and Lacey 1984a). Some species, e.g., P. roqueforti, are able to grow and infect grain at > 80% CO2 provided at least 4% O2 is available. The use of integrated postharvest systems for prevention of deterioration entails modifying O2 and CO2 simultaneously and the use of (O2 free) N2. The tolerance to low O2 and high CO2 is also influenced by interactions with grain water availability. The treatment is more effective if the grain is dry. Controlled atmosphere storage is used for both control of molds and insects in moist stored seed systems. Regimes sufficient for molds may not, however, be effective against some storage insects that can survive and grow over a wide ERH range.

In summary, from the whole range of factors that can affect the colonization of seeds by microorganisms, aw is the most important single factor limiting their activity. Each microorganism has a specific range over which they can develop. Fungi are the most important group of microorganisms with capacity to colonize seeds because specialized groups can grow at intermediate and low aw levels. Fungi contribute greatly to seed losses, either alone or together with insects. Because the environment and other factors can change during seed/grain filling, harvest, and storage the

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