Investigating the emerging threat to oilseed rape posed by the newly identified phoma stem canker pathogen subclade Leptosphaeria biglobosa ‘canadensis’

This is one of the funded projects for our 2025 Undergraduate vacation bursary, click here to return to the list of 15 projects.

This project is going to be…	Experimental (lab/field based)
Institute	The University of Hertfordshire
Project supervisor	Prof. Yongju Huang
Title of Project	Investigating the emerging threat to oilseed rape posed by the newly identified phoma stem canker pathogen subclade Leptosphaeria biglobosa ‘canadensis’
Date of Project Commencement	01 July 2025
Duration (weeks)	8
Brief Description of Project	Oilseed rape is the third most important arable crop in the UK. However, maintaining the production of this crop is very challenging due to the changing climate and extreme weather events, combined with pests and diseases. Phoma stem canker (PSC) is a damaging disease of oilseed rape (OSR) in the UK, causing annual yield losses worth £60-70M, despite the use of fungicides. With predicted global warming and extreme weather events, yield losses are likely to increase. The disease is caused by two closely related species, Leptosphaeria maculans (Lm) and L. biglobosa (Lb), which co-exist on their host [1]. Lm is generally considered more damaging than Lb, because Lm is often associated with damaging stem base cankers and Lb is often associated with less damaging upper stem lesions. However, recent studies show that Lb can also cause stem base canker and lead to substantial yield losses in areas where Lb is present as the predominant pathogen[2-4]. Although, both Lm and Lb are present in UK, disease management practices have been targeted only towards Lm with little work on control of Lb. Furthermore, Lb has seven subclades and only the Lb ‘brassicae’ (Lbb) subclade was identified in Europe[5]. However, this changed in 2022 when the Lb ‘canadensis’ (Lbc) subclade was identified at two sites in the UK) [6]. Previously, Lbc mainly occurred in Canada and Australia, but recently it was also detected in China, where Lbb was predominant, and caused severe damage to OSR and brassica vegetables.This project aims to investigate the threat posed by the newly identified Lbc subclade to OSR. Firstly, the pathogenicity of the new Lbc isolates will be compared with (1) that of Lbc isolates from Canada and Australia and (2) of the existing UK and European Lbb isolates on different OSR cultivars. Lm isolates will be included as controls. The pathogenicity tests will be done by cotyledon inoculation. Secondly, effects of temperature on disease severity caused by Lm, Lbb and Lbc isolates will be investigate. Previous results showed that temperature affected host resistance against Lm. However, there is no information about effects of temperature on resistance against Lb (Lbb, Lbc). Plants will be inoculated using existing methods. The severity of leaf lesions will be assessed using image-based methods and the growth of the pathogen in the leaves will be assessed by qPCR. In addition, the student will visit field experiments to learn how to recognize phoma stem canker symptoms and how to assess the severity of phoma stem canker and other oilseed rape diseases, such as light leaf spot.This bursary project will provide the student with skills (e.g. fungal culture, microscopy, quantitative disease assessment, DNA extraction, qPCR and data analysis) and knowledge (e.g. background of this project, experimental design, impact of the disease on crop yield in field conditions) about plant pathology, which will be beneficial for the student’s career development. Recommended reading for the project1. Fitt, B.D.L., et al., (2006). World-wide importance of phoma stem canker (Leptosphaeria maculans and L. biglobosa) on oilseed rape (Brassica napus). Eur J Plant Pathol 114, 3–15. 2. Cai, X., et al., (2018). Evaluation of oilseed rape seed yield losses caused by Leptosphaeria biglobosa in central China. Eur J Plant Pathol 150, 179–190.3. Jacques, N., et al., (2021). New specific quantitative real-time PCR assays shed light on the epidemiology of two species of the Leptosphaeria maculans–Leptosphaeria biglobosa species complex. Plant Pathol 70, 643–654. 4. Huang, Y.J., et al., (2024). Effective control of Leptosphaeria maculans increases importance of L. biglobosa as a cause of phoma stem canker epidemics on oilseed rape. Pest Manag Sci 80, 2405–2415.5. Zou, Z., et al., (2019). A New Subclade of Leptosphaeria biglobosa Identified from Brassica rapa. Int. J. Mol. Sci. 20, 1668; doi:10.3390/ijms20071668. 6. King, K.M. & West, J.S. (2022). Detection of the Phoma pathogens Plenodomus biglobosus subclades ‘brassicae’ and ‘canadensis’ on wasabi, and ‘canadensis’ in Europe. Eur J Plant Pathol 162, 751-756.