Email: zhi.zheng@csiro.au

Fusarium crown rot (FCR), caused primarily by Fusarium pseudograminearum, is a growing threat to wheat production in semi-arid regions worldwide. Its prevalence has surged in conservation cropping systems in recent years due to frequent cereal rotations and stubble retention. While several loci conferring FCR resistance have been identified in wheat, previous studies suggested interference from factors like plant height and heading time.

To remove the effects of such characteristics and accurately assessing effects of these loci, near isogenic lines (NILs) have then been generated for several of them. Facilitated by transcriptome profiling, markers tightly linked several of these loci have been obtained by analysing NIL-derived populations. With the assistance of the diagnostic markers developed, these loci were pyramided, and the results showed gene pyramiding can be effective in enhancing resistance to this disease in wheat. However, only limited number of resistant loci have been identified and additional resistant sources of resistance are urgently needed.

Our current efforts focus on introducing Fhb7 gene into Australian wheat and combine it with other loci which are already in Australian breeding pipelines. This gene showed significant promise, with backcross lines in 2023 single-row field trials showing up to 11.4% higher grain yield under FCR pressure compared to lines lacking the gene. Similarly, disease severity differed significantly with the lines possessing Fhb7 showing less severe symptoms. Breeding lines with five loci (on chromosomes 2B, 2D, 3B, 5D and 7D (Fhb7), respectively) assessed in 2023 showed that the genotypes with Fhb7 and 3B locus had the highest grain yield in the presence of FCR followed by the lines with all five resistant loci, which are significantly higher than the lines without any of these loci.

In addition, our recent findings suggest a potential link between FCR resistance and drought tolerance. Analysis of RNA-seq from one NIL pair targeting the 2D locus in wheat that showed significant differences in FCR resistance and drought tolerance, revealed that similar regulatory frameworks were activated in response to both stresses.

Future use of drought tolerance genes in breeding program may potentially provide resistance to this disease in wheat. Furthermore, we at CSIRO successfully cloned the first gene conferring FCR resistance in barley. Investigating the potential of transferring this resistance to wheat through gene editing represents an exiting avenue for further improving FCR resistance. Taken together, the battle against FCR necessitates a multi-pronged approach.