Virulence patterns of oat crown rust in Australia - season 2022

Abstract

Puccinia coronataf. sp.avenae(Pca) is an important foliar pathogen of oat which causes crown rust disease. The virulence profile of 48Pcaisolates derived from different locations in Australia was characterised using a collection of oat lines often utilised in rust surveys in the USA and Australia. This analysis indicates thatPcapopulations in Eastern Australia are broadly virulent, in contrast to the population in Western Australia (WA). Several oat linesPcgenes are effective against all rust samples collected from WA, suggesting they may provide useful resistance in this region if deployed in combination. We identified 19 lines from the US oat differential set that display disease resistance toPcain WA, some in agreement with previous rust survey reports. We adopted the 10-letter nomenclature system to define oat crown rust races in Australia and compare the frequency of those virulence traits to published data from the USA. Based on this nomenclature, 42 unique races were detected among the 48 isolates, reflecting the high diversity of virulence phenotypes forPcain Australia. Nevertheless, thePcapopulation in the USA is substantially more broadly virulent than that of Australia. Close examination of resistance profiles for the oat differential set lines after infection with Pca supports hypotheses of allelism or redundancy amongPcgenes or the presence of severalRgenes in some oat differential lines. These findings illustrate the need to deconvolute the oat differential set using molecular tools.

Genotypic and resistance profile analysis of two oat crown rust differential sets urge coordination and standardisation

“…As reported earlier (Henningsen et al 2023), a higher virulence frequency was observed in the Pca isolates from Eastern Australia (QLD, NSW, VIC, and SA) than in those from…”

“…As reported earlier (Henningsen et al 2023), the Pca subpopulation from Eastern Australia (QLD, NSW, VIC, and SA) exhibited a higher frequency of virulence phenotypes compared to the Pca isolates from Western Australia (WA) towards oat differential lines from both the USA ( p = 0.00059) and Australian ( p = 0.00088) sets ( Figure S1 ). Oat cultivars Barcoo, Saia, and the differential line Pc63 exhibited resistance to all 25 Pca isolates, whereas certain oat lines, such as Swan, Ukraine, Marvelous, Santa Fe, Trispernia, Landhafer, Bondvic, Pc45, Pc54, and Pc67 displayed susceptibility to the majority or all isolates.…”

“…A set of 25 Pca isolates from major Australian oat-grown regions in 2022 was used ( Table S2, Henningsen et al 2023). Infection methods were adapted from Miller et al (2020), except that rust spores were mixed with talc powder instead of suspended in oil.…”

“…Infection scores were recorded at 10 dpi using a disease rating scale from Murphy (1935) and Nazareno et al (2018). The scores were subsequently converted to a 0-9 numeric scale for visualisation in heatmaps as described by Miller et al (2018Miller et al ( , 2020 and Henningsen et al (2023), using ComplexHeatmap (v2.14.0) in R (4.2.2) (Gu, 2022) and comparison of virulent impact using violin plots (ggplot2 package) and Wilcoxon rank sum tests in R v4.2.2.…”

“…This suggests the need for care to be taken in pathogen surveillance and postulation of R genes in breeding lines based on comparisons to the differential sets. Given that Pc91 remains effective in providing crown rust resistance in Western Australia (Henningsen et al 2023), we also tested the aforementioned Pc91 molecular markers (Gnanesh et al 2013; Klos et al 2017) on a collection of oat cultivars and identified putative carriers of Pc91 as a resource for breeding programs seeking to pursue marker-assisted selection to deliver durable resistance to crown rust.…”