Host–pathogen interactions in relation to management of light leaf spot disease (caused by Pyrenopeziza brassicae) on Brassica species

Abstract

Abstract. Light leaf spot, caused by Pyrenopeziza brassicae, is the most damaging disease problem in oilseed rape (Brassica napus) in the United Kingdom. According to recent survey data, the severity of epidemics has increased progressively across the UK, with yield losses of up to £160M per annum in England and more severe epidemics in Scotland. Light leaf spot is a polycyclic disease, with primary inoculum consisting of airborne ascospores produced on diseased debris from the previous cropping season. Splash-dispersed conidia produced on diseased leaves are the main component of the secondary inoculum. Pyrenopeziza brassicae is also able to infect and cause considerable yield losses on vegetable brassicas, especially Brussels sprouts. There may be spread of light leaf spot among different Brassica species. Since they have a wide host range and frequent occurrence of sexual reproduction, P. brassicae populations are likely to have considerable genetic diversity, and evidence suggests population variations between different geographic regions, which need further study. Available disease-management tools are not sufficient to provide adequate control of the disease. There is a need to identify new sources of resistance, which can be integrated with fungicide applications to achieve sustainable management of light leaf spot. Several major resistance genes and quantitative trait loci have been identified in previous studies, but rapid improvements in the understanding of molecular mechanisms underpinning B. napus-P. brassicae interactions can be expected through exploitation of novel genetic and genomic information for brassicas and extracellular fungal pathogens.

Contrasting Responses of Rhizosphere Bacterial, Fungal, Protist, and Nematode Communities to Nitrogen Fertilization and Crop Genotype in Field Grown Oilseed Rape (Brassica napus)

“…Notably, nitrogen fertilization was associated with increases in relative abundance of a number of pathogens in the rhizosphere of OSR. This included Leptosphaeria maculans and L. biglobosa, which cause blackleg diseases which impact OSR yields globally (Fitt et al, 2006), Pyrenopeziza brassicae, responsible for light leaf spot, the predominant OSR disease in the UK (Dewage et al, 2018), Olpidium brassicae, which is associated with OSR yield decline (Hilton et al, 2013(Hilton et al, , 2021, and Mycosphaerella sp. which are common plant pathogens and includes several species which infect oilseed rape, such as M. brassicola (ringspot disease) and M. capsellae (white leaf spot disease).…”

Azole fungicide sensitivity and molecular mechanisms of reduced sensitivity in Irish Pyrenopeziza brassicae populations

“…11 The disease has recently overtaken phoma stem canker and become the primary disease of OSR in the UK, with severe epidemics causing annual yield losses up to £160 M per year. 12,13 The pathogen is capable of infecting the leaves, flowers, stems and pods during the cropping season, [14][15][16] and due to its mixed reproduction and its polycyclic life cycle, 17,18 the pathogen has a high evolutionary potential. 11 Although LLS has been present in Ireland for a long time [19][20][21] and Irish OSR growing conditions are favorable for its development, there is no detailed information on the impact of this disease on OSR in Ireland.…”

“…This is the case for light leaf spot (LLS), caused by Pyrenopeziza brassicae , one of the most important diseases of OSR in the UK and Northern Europe 10 and widespread globally, with records in various countries in Europe, Oceania and Northern America 11 . The disease has recently overtaken phoma stem canker and become the primary disease of OSR in the UK, with severe epidemics causing annual yield losses up to £160 M per year 12,13 . The pathogen is capable of infecting the leaves, flowers, stems and pods during the cropping season, 14–16 and due to its mixed reproduction and its polycyclic life cycle, 17,18 the pathogen has a high evolutionary potential 11 .…”

“…Current strategies to control LLS consist of a combination of crop management practices, host resistance and fungicide applications 13,22 . However, cultural practices alone cannot control epidemics sufficiently, 12 and cultivar resistance is often not enough to prevent the disease in conducive environments 10 . Therefore, LLS control often relies on the use of fungicides, 13 with the most widely used and effective class of fungicides being the demethylation inhibitors (azoles).…”