Crown rot variety resistance ratings have for many years been a useful guide for choosing wheat varieties, especially where threat of the disease is considered moderate to high.
However, various research studies have noted that varieties within a given crown rot resistance rating group can vary considerably in yield loss when crown rot risk is high.
Crown rot is caused by the fungus Fusarium pseudograminearum; a stubble borne pathogen.
Particularly when dry springs occur, especially as sub-soil moisture levels dry out, crown rot can potentially reduce wheat yield, and also barley, by over 50 per cent.
While sub-soil moisture levels are currently generally excellent, significant yield losses could occur this year and in the following years when soil disease levels are significant.
Douglas Lush, and Dr Meiqin Lu, Australian Grain Technologies (AGT) northern variety support manager (and previously a DAFQ researcher) and wheat breeder, respectively, have analysed wheat grain yield data from five years of research trials conducted at Sunville, Narrabri.
Following research by various bodies, including NSW DPI, comparing variety yield in high versus low crown rot situations, the AGT analysis focuses on evaluating germplasm for yield performance in crown rot inoculated trials, comparing results to know variety responses.
Amongst AGT varieties Suncentral and Sunmaster have stood out in the analysis.
Based on several years of data, there was substantial variety variation in tolerance within resistance classes.
Suntop is used as the comparator, a MSS (moderately susceptible to susceptible) variety, as it has traditionally demonstrated crown rot tolerance similar or better than more resistant varieties with a moderately susceptible (MS) resistance rating.
In these trials, Suncentral yielded 9pc better than Suntop in high crown rot situations.
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Suncentral is a 2020 release with APH quality, quick to mid-maturity, good tolerance to root lesion nematode (P. thornei), overall good rust resistance rating, plus high yield. Sunmaster, also a 2020 release, was only slightly behind Suncentral in crown rot tolerance and yielded 8pc better than Suntop in high crown rot conditions.
Sunmaster, also APH quality, is a mid-season maturity type, shorter and overall higher yielding than Suntop.
Part of the difficulty with developing varieties with improved crown rot resistance is that multiple genes are involved. Dr Phil Davies, previously Sydney University crown rot research pathologist and now working with AGT, has been involved with research at Narrabri for many years.
His success with finding better tolerance to crown rot is that he has been able to link more of these genes together in a single line. These include genes from many overseas lines.
Plant breeders then incorporate these into their breeding programs.
The rate of yield loss from crown rot is only partially explained by the extent of typical symptoms such as stem browning and white heads with shrivelled or no grain.
Hence the importance of yield testing in high disease versus low disease situations.
Control of crown rot not only involves developing varieties with improved resistance but also via various cropping practices.
Rotations are very important, spacing barley and wheat crops with crops resistant to crown rot. For example faba beans, canola and chickpeas.
Recent research notes cotton and maize as effective at reducing crown rot inoculum loads.
Sorghum and mungbean effectiveness is more variable, but both generally reduced or only moderately increased inoculum levels.
Avoiding crown rot inoculum in the field by inter-row sowing is also a valuable control option.
Stubble management and stubble height in stubble retention cropping are also important control options.
A good spring will likely mask to a large degree crown rot issues but will not reduce the future risk of major crop losses.
And also impacting on future variety choices are other disease risks like yellow leaf spot, Septoria, the three rusts, as well as nematodes.
Tough variety decisions commonly need to be made, especially not neglecting the importance of crown rot.
Next week: Sunflowers, an option for a quick summer crop.
- Bob Freebairn is an agricultural consultant based at Coonabarabran. Email robert.freebairn@bigpond.com or contact (0428) 752 149.
