Extensive research in the 20 th century explored the potential for mitigation of drought by applying polymers (film antitranspirants) to leaves to reduce water loss. It was concluded that film antitranspirants are of limited usefulness, since the polymers reduced photosynthesis (in addition to transpiration) and this was assumed to be detrimental to growth and yield. We propose, however, that irrespective of reduced assimilate availability from photosynthesis, the most drought sensitive stage of yield formation in wheat may respond positively to antitranspirant application. Six field experiments involved applying the film antitranspirant di-1-p-menthene at five development stages and 10 soil moisture deficits (SMD) in total over three years. Yield was reduced when the film antitranspirant was applied at development stages less-sensitive to drought, from inflorescence emergence to anthesis, consistent with the conclusions from previous research. In contrast, yield was increased when the film antitranspirant was applied at flag leaf stage, just before the stage most sensitive to drought (boot stage). These results show that film antitranspirant has the potential to mitigate drought effects on yield of wheat.

Greenhouse experiments were conducted in order to determine the impact of seed-borne Microdochium nivale var. nivale and var. majus inoculum, and seed treatment with a carboxin+thiram mixture, on the development of seedling blight, and on subsequent stem colonisation and growth of winter wheat (cv. Cadenza). Experiments were conducted at temperatures favourable (3°C) and unfavourable (22°C) to M. nivale. Seed-borne inoculum resulted in seedling blight symptom development when plants were grown at 3°C, but not when plants were grown at 22°C. For seedlings grown at 3°C, plants arising from heavily blighted seedlings developed more severe symptoms of stem colonisation, when compared with those arising from seedlings from carboxin+thiram treated seeds. In addition, the vigour of such plants (assessed by determining the number of tillers and ears per plant, stem length, green leaf area, dry weight and yield) was also significantly lower than for plants arising from carboxin+thiram treated seeds. Microdochium nivale var. majus and var. nivale appeared to have little effect on plant vigour from seedlings grown at 22°C. This is the first recorded incidence of seedling blight affecting subsequent plant growth. Microdochium nivale var. majus and var. nivale stem colonisation increased from growth stage (GS) 40-49 to harvest in plants raised from seedlings grown at both temperatures. Microdochium nivale var. majus and var. nivale were isolated from the second node at GS 40-49 and the third node at harvest of plants from seedlings grown at 3°C. For plants from seedlings raised at 22°C, M. nivale var. majus and var. nivale were isolated from the first node at GS 40-49 and the second node at harvest. Carboxin+thiram seed treatment decreased the extent and severity of stem colonisation on plants from seedlings grown at 22°C.

Exposure to pre-emergent freezing temperatures significantly delayed the rate of seedling emergence (P < 0.05) from an infected and a non-infected winter wheat cv. Equinox seed lot, but significant effects for timing of freezing and duration of freezing on final emergence were only seen for the Microdochium-infested seed lot. Freezing temperatures of −5• C at post-emergence caused most disease on emerged seedlings. Duration of freezing (12 hours or 24 hours) had little effect on disease index but exposure to pre-emergent freezing for 24 hours significantly delayed rate of seedling emergence and reduced final emergence from the infected seed lot. In plate experiments, the calculated base temperature for growth of M. nivale and M. majus was −6.3• C and −2.2 • C, respectively. These are the first set of experiments to demonstrate the effects of pre-emergent and post-emergent freezing on the severity of Microdochium seedling blight.

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