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The Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko) is one of the most destructive insect pests of cereals world‐wide. Although resistant cultivars have been bred, the biochemical mechanism of resistance is unknown. The aim of this work was to gain information on the mechanism of resistance which could contribute to more directed breeding of resistant cultivars in the future. The effect of RWA infestation on the inter‐ and intracellular β‐1,3‐glucanase activities was studied in different resistant wheat (Triticum aestivum L.) cultivars containing the Dn‐1 gene for RWA resistance and corresponding near‐isogenic susceptible cultivars. The activity was determined spectrophotometrically by measuring the release of glucose from laminarin. Infestation differentially induced the intra‐ and intercellular activities to much higher levels in resistant than susceptible cultivars within 48 h. According to immunological studies induced enzyme activities were due to increased protein levels. The intracellular β‐1,3‐glucanase contained about 8% exo‐activity. The exo‐activity made an insignificant contribution to the intercellular activity. The genetic background into which the resistance gene was bred did affect the level of activity that corresponded to the resistance performance. Seven apoplastic isoforms of β‐1,3‐glucanase, varying from acidic to basic, were resolved by isoelectric focusing. All isoenzymes were equally induced and no specific one could be linked to resistance or susceptibility. The RWA induced β‐1,3‐glucanase activity in resistant cultivars closely resembles defence responses during pathogenesis and seems to be part of a general defence response like the hypersensitive reaction (HR), which confers resistance to the RWA. This knowledge might be helpful in future to identify genes for RWA resistance. The increased β‐1,3‐glucanase activity after RWA infestation might serve as an additional measure to biochemically trace resistance in crosses during breeding.

The production of gibberellic acid (GA3) by Fusarium moniliforme M-7121 in solid-state culture was evaluated in flask cultures as well as in 3-I horizontal rotary reactors. The highest production rate of GA3 was with 80% (w/v) maize flour mixed with wheat bran. The optimum initial moisture content was inversely dependent on the ambient relative humidity. The initial water activity range for optimal growth and GA3 accumulation was about 0.98 to 0.99, which is unusually high for a filamentous fungus. A low O2 concentration resulted in a much decreased GA3 yield and the appearance of a yellow to reddish pigmentation in the mycelium. The lag phase was short and rapid growth continued for up to 2 days in the rotary reactor, with a maximum specific growth rate of 0.12 h(-1). The maximum rate of GA3 production occurred during the subsequent 3 to 10 days of incubation and the final GA3 concentration reached was 18.7 mg to 19.3 mg/g dry culture. The point of maximum GA3 accumulation after 10 to 12 days of incubation was usually marked by a sharp increase in pH.

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