M. G. Cromey

Changes in post-harvest levels of Gaeumannomyces graminis var. tritici inoculum in wheat fields

Gaeumannomyces graminis var. tritici (Ggt) soil DNA inoculum levels in wheat fields were studied in NewZealand as part of work to identify wheat fields with a low risk of take-all. Ggt DNAinoculum levels have been identified overseas as peaking near the harvest date of wheat then declining. Early sowing is also reported to increase take-all infection. The changes in Ggt inoculum levels that occur during the post-harvest period in New Zealand and the implications were for the risk of severe take-all were unknown. Ggt DNA inoculum levels were monitored over the pre- and post-harvest period from February to July in 12 commercial wheat fields. For 10 second wheat fields, mean post-harvest inoculum levels peaked in March at 378 pg Ggt DNA/g soil. Mean inoculum levels then declined at each subsequent sample to the final sample in July when levels were less than one-third (103 pg Ggt DNA/g soil) of those in March. Linear regression was used to quantify the level of decline- from 1 March to 1 July predicted Ggt DNA levels declined by 78%. In two second wheat fields, post-harvest Ggt inoculum levels were also evaluated using an infectivity bioassay method. The bioassay results supported the declining Ggt inoculum levels observed using the Ggt DNA method. An implication of the results was that early sown consecutive wheat will be challenged by higher Ggt inoculum levels than late sown consecutive wheat.

Biofuels: the need for disease risk management.

The risks associated with biofuel crop production, such as higher food prices, economic viability, potential loss of biodiversity and soil degradation, have been discussed extensively [101,102]. Mo...

Consecutive wheat sequences: effects of contrasting growing seasons on concentrations of Gaeumannomyces graminis var. tritici DNA in soil and take-all disease across different cropping sequences

The extent and severity of wheat take-all (caused by Gaeumannomyces graminis var. tritici ( Ggt )) can vary considerably between growing seasons. The current study aimed to identify climatic factors associated with differing concentrations of Ggt DNA in soil and take-all disease at different stages of a sequence of wheat crops. Pre-sowing soil Ggt DNA concentrations and subsequent take-all disease in consecutive wheat crop sequences were compared across six seasons in 90 commercial cropping fields in Canterbury and Southland, New Zealand, between 2003 and 2009. Disease progress was assessed in additional fields in 2004/05 and 2005/06. While a general pattern in inoculum and disease fluctuations was evident, there were exceptions among wheat crop sequences that commenced in different years, especially for first wheat crops. In three consecutive growing seasons, there was very low inoculum increase in the first wheat crop, while increases in first wheat crops during the following three seasons was much greater. Low spring–summer rainfall was associated with low build-up of inoculum in first wheat crops. The inoculum derived from the first wheat then determined the amount of primary inoculum for the subsequent second wheat, thereby influencing the severity of take-all in that crop. Differing combinations of weather conditions during one wheat crop in a sequence and the conditions experienced by the next crop provided explanations of the severity of take-all at grain fill and the resulting post-harvest soil Ggt DNA concentrations in second wheat crops. Examples of contrasting combinations were: (a) a moderate take-all epidemic and high post-harvest inoculum that followed high rainfall during grain fill, despite low pre-sowing soil Ggt DNA concentrations; (b) severe take-all and moderate to high inoculum build-up following high pre-sowing soil Ggt DNA concentrations and non-limiting rainfall; and (c) low spring and early summer rainfall slowing epidemic development in second wheat crops, even where there were high pre-sowing soil Ggt DNA concentrations. The importance of the environmental conditions experienced during a particular growing season was also illustrated by differences between growing seasons in take-all progress in fields in the same take-all risk categories based on pre-sowing soil Ggt DNA concentrations.