No abstract

SU MMARYWinter waterlogging is expected to become an increasingly serious problem due to climate change. It is therefore important to find whether differences in tolerance to waterlogging exist between wheat cultivars grown in the UK. Screening experiments were conducted outdoors and in a glasshouse to investigate the yield response to waterlogging and waterlogging tolerance at the seedling stage. The experiments suggested that differences in tolerance existed between cultivars, in the form of digression of some cultivars from their expected yield in the outdoor experiment and a significant interaction between cultivar and waterlogging for shoot and root dry weight in the seedling experiment. Cultivars that appeared to differ in their responses to waterlogging were further tested in a field experiment over two seasons and in a second glasshouse seedling experiment. However, there was no significant relationship between measurements taken at the seedling stage and grain yield at maturity ; also the field experiment did not provide compelling evidence of differences in tolerance. Cultivars with the largest yield suffered the largest decrease due to waterlogging, and the yield of the cultivar with the lowest yield potential was unaffected. All cultivars showed considerable ability to compensate for winter waterlogging damage by vigorous spring growth. All cultivars produced nodal roots in response to waterlogging, and these displayed evidence of aerenchyma tissue by penetrating below the water level, but no cultivar was any better in this respect than any other. The results of these experiments suggest that screening for waterlogging tolerance at the seedling stage is not representative of final yield. It is suggested that the lack of diversity for tolerance is a result of the inbred nature of UK wheat cultivars and that the overall good level of tolerance and ability to compensate has been selected for, either inadvertently, or as a result of selecting the best cultivars in UK conditions, where tolerance to waterlogging is a part of the general winter hardiness required.

Field experiments were conducted to identify the impact of post-anthesis rainfall on the concentration of deoxynivalenol (DON) and zearalenone (ZON) in harvested wheat grain. Winter wheat plots were inoculated with Fusarium graminearum at stem extension (GS31) and prothioconazole was applied at mid-anthesis (GS65) to split plots and plots were subsequently mist irrigated for 5 days. Plots were either covered by polytunnels, irrigated by sprinklers or left as non-irrigated uncovered control plots after medium-milk (GS75). Plots were harvested either when ripe (GS92; early harvest) or three weeks later (late harvest). Fusarium head blight (FHB) was assessed each week from inoculation. At harvest, yield and grain quality was measured and grains were analysed for DON and ZON. Differences in rainfall resulted in contrasting disease pressure in the two experiments, with low FHB in the first experiment and high FHB in the second. Difference in FHB resulted in large differences in grain yield, quality and mycotoxin content. DON concentration was significantly (P < 0.05) higher in irrigated compared to covered and control plots in the first experiment, whereas in the second experiment, DON was significantly (P < 0.05) higher in the covered plots compared to the control and irrigated plots. ZON concentration was significantly (P < 0.05) higher in irrigated plots in both experiments. Later harvesting resulted in an approximate fivefold increase in ZON in the first experiment, but was not significantly different in the second experiment. Prothioconazole significantly (P < 0.05) reduced DON in both experiments, but gave inconsistent reductions to ZON. This is the first report to show that the post-anthesis rainfall can significantly increase ZON in wheat, which can increase further with a delayed harvest but may be significantly reduced with the application of prothioconazole. Importantly, in the absence of moisture late season, ZON remains at very low concentrations even when wheat is severely affected by FHB.

Legislative limits for Fusarium mycotoxins decrease from unprocessed wheat to processed products. A previous observational study identified a seasonal difference in the distribution of DON but not ZON within mill fractions. Rainfall is known to influence the production of these mycotoxins in wheat, but the effects of rainfall on their distribution within mill fractions is not known. Laboratory and field experiments were conducted to determine the impact of different watering regimes on the distribution of DON and ZON in wheat mill fractions. Results indicated that repeated wetting and drying could cause movement of DON towards equilibrium across the mill fractions. Whereas, high levels of rainfall could cause a large reduction of DON in the grain, predominantly from the bran fraction, resulting in a proportional increase within white flour. ZON was detectable in fewer samples but results indicated it is less mobile within the grain. It is important for processors to be aware of the variation of mycotoxin distribution within mill fractions and the drivers of this variation to ensure limits set for grain intake result in mill products within mycotoxin legislative limits.

No abstract