Fitt, Bruce

Huang, Yongju

Karandeni Dewage, Chinthani Shanika

Qi, Aiming

Stotz, Henrik

English

University of Hertfordshire Research Archive

Management of Diseases and Pests of Oilseed Rape Jellis & Fitt (Eds) 2021 Agrifood Charities Partnership & University of Hertfordshire 35  Disease management in oilseed rape: insights into the Brassica napus-Pyrenopeziza brassicae pathosystem  By CHINTHANI KARANDENI DEWAGE, AIMING QI, HENRIK U STOTZ, YONG-JU HUANG and BRUCE D L FITT Centre for Agriculture, Food and Environmental Management, School of Life and Medical Sciences, University of Hertfordshire, Hatfield, Herts. AL10 9AB, UK Corresponding Author Email: c.s.karandeni-dewage@herts.ac.uk  Introduction   Light leaf spot, caused by the fungal pathogen 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 (www.cropmonitor.co.uk) 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 (Gilles et al. 2001). Splash-dispersed conidia produced on diseased leaves are the main component of the secondary inoculum (Evans et al., 2003). Currently, the management of light leaf spot relies on fungicide applications, recommendations for resistant cultivars and cultural practices (AHDB, 2021). However, considering the frequent occurrence of light leaf spot epidemics in recent years, it appears that current control strategies are not sufficient to achieve successful control of light leaf spot. Even though the occurrence of severe epidemics of light leaf spot has been reported in the UK since 1970s, the knowledge about this pathosystem, especially in relation to the operation of host resistance, is very limited compared to that for other important pathosystems of oilseed rape such as phoma stem canker (Leptosphaeria maculans) (Boys et al., 2007; Karandeni Dewage et al., 2018). Therefore, this study focused on investigating interactions between P. brassicae and B. napus using single-spore isolates to provide better understanding of the different sources of resistance against P. brassicae.   Materials and methods   Single-spore isolates of P. brassicae were obtained from diseased leaf samples collected from oilseed rape crops and sub-cultured onto malt extract agar (MEA) plates. Pathogen inoculum was prepared from conidia produced by sub-cultured isolates using sterilised distilled water. The inoculum concentration was adjusted to 105 spores/ml and it was stored at -20ºC until needed. Oilseed rape genotypes that included commercial cultivars and breeding lines were selected, based on resistance ratings from the AHDB Recommended List (RL) trials and to represent diverse genetic backgrounds. Selected genotypes were grown under glasshouse conditions until they reached growth stage 1,4-1,5 (four-five leaves unfolded) and spray-inoculated with conidial suspensions prepared from single-spore isolates of P. brassicae. After inoculation, regular observations were made to identify the timing and appearance of different resistant/susceptible phenotypes. Final disease assessment was made at 29 days post inoculation (dpi) on plants that were destructively harvested at the stem base at 24 dpi and Management of Diseases and Pests of Oilseed Rape Jellis & Fitt (Eds) 2021 Agrifood Charities Partnership & University of Hertfordshire 36  incubated at 4ºC for five days in polyethylene bags. Light leaf spot severity was measured as % leaf area covered with P. brassicae sporulation and compared between different treatments to identify resistant/susceptible interactions.  Results and Discussion   Infected plants showed different resistant/susceptible phenotypes associated with P. brassicae. This included leaf deformations, necrosis and different numbers of acervuli (asexual sporulating structures of P. brassicae) with or without the presence of visible lesions. Leaf deformations appeared at c.7 dpi, indicating possible association with early stages of P. brassicae colonisation. Symptoms included leaf curling, leaf distortions and petiole elongations and could be seen to some extent in all the cultivars/lines tested in the experiments. Some of the cultivars/lines appeared to have necrotic responses to P. brassicae infection. Of these cultivars/lines, the majority had reduced numbers of P. brassicae acervuli, suggesting an association between these two phenotypes. Considering the light leaf spot severity measured as % leaf area with P. brassicae sporulation, there were significant differences (P ≤ 0.05) between cultivars/lines and between isolates and there were significant cultivar/line-isolate interactions. Some of the pre-breeding lines showed resistance against most of the isolates tested. These lines may provide sources of resistance for oilseed rape breeding programmes. There has been little work on specific host-pathogen interactions regarding light leaf spot disease, and identification of different types of resistance available in commercial oilseed rape cultivars is important for effective deployment of cultivar resistance. This study shows the potential for studying specific cultivar-by-isolate interactions in the B. napus – P. brassicae pathosystem using single-spore isolates of P. brassicae. It is anticipated that this type of experimentation will help to identify different sources of resistance that can be exploited in oilseed rape breeding programmes.  Acknowledgments We thank AHDB Cereals and Oilseeds, the Biotechnology and Biological Sciences Research Council, the UK Department for the Environment, Food and Rural Affairs (OREGIN), the Gen Foundation and the University of Hertfordshire for funding this work. We thank the charity and industry partners, Felix Cobbold Agricultural Trust, Elsoms Seeds UK Ltd and Limagrain UK Ltd, for their in-kind contributions.   References AHDB Cereals & Oilseeds. 2021. How to manage light leaf spot in oilseed rape. Agriculture and Horticulture Development Board. Available at: https://ahdb.org.uk/knowledge-library/how-to-manage-light-leaf-spot-in-oilseed-rape  (accessed 30 May 2021). Boys EF, Roques SE, Ashby AM, et al. 2007. Resistance to infection by stealth: Brassica napus (winter oilseed rape) and Pyrenopeziza brassicae (light leaf spot). European Journal of Plant Pathology 118:307-21. Evans N, Baierl A, Brain P, Welham SJ, Fitt BDL, 2003. Spatial aspects of light leaf spot (Pyrenopeziza brassicae) epidemic development on winter oilseed rape (Brassica napus) in the United Kingdom. Phytopathology 93:657-65. Management of Diseases and Pests of Oilseed Rape Jellis & Fitt (Eds) 2021 Agrifood Charities Partnership & University of Hertfordshire 37  Gilles T, Fitt BDL, McCartney HA, Papastamati K, Steed JM. 2001. The roles of ascospores and conidia of Pyrenopeziza brassicae in light leaf spot epidemics on winter oilseed rape (Brassica napus) in the UK. Annals of Applied Biology 138:141-52. Karandeni Dewage CS, Klöppel CA, Stotz HU, Fitt BDL. 2018. Host–pathogen interactions in relation to management of light leaf spot disease (caused by Pyrenopeziza brassicae) on Brassica species. Crop and Pasture Science 69:9-19.   

Disease management in oilseed rape: insights into the Brassica napus-Pyrenopeziza brassicae pathosystem

http://uhra.herts.ac.uk/bitstream/2299/25326/1/Disease_management_in_oilseed_rape_insights_into_the_Brassica_napus_Pyrenopeziza_brassicae_pathosystem_KarandeniDewage_et_al_2021.pdf

Disease management in oilseed rape: insights into the Brassica napus-Pyrenopeziza brassicae pathosystem

Abstract

Similar works

Full text

Available Versions

University of Hertfordshire Research Archive