Disease management in oilseed rape Bruce Fitt, Professor of Plant Pathology University of Hertfordshire

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1 Disease management in oilseed rape Bruce Fitt, Professor of Plant Pathology University of Hertfordshire 2

2 Winter oilseed rape disease losses (England) Defra-funded winter oilseed rape pest and disease survey (CropMonitor) Disease forecasting to guide fungicide timing 2010/2011 winter oilseed rape growing season Forecast dates (10% plants with phoma leaf spot) Sep Sep Sep Oct Oct Oct Oct Oct Oct Oct 27 Oct Evans et al. (2008) J Roy Soc Interface 5, Stonard et al. (2010) Eur J Plant Path 126,

3 Light leaf spot attacks leaves, stems and pods UK losses more than 100M per season Severity of light leaf spot has increased in England Light leaf spot (Pyrenopeziza brassicae) is a polycyclic disease

4 Changes in cv. Apex resistance against P. brassicae Market share (%) % leaf area with LLS NIAB data (Jane Thomas) Boys et al. (2007) Eur J Pl Path 118, Resistance gene against Pyrenopeziza brassicae Stops asexual sporulation There is cell death after 8-10 days Boys et al. (2012) Plant Pathology 61,

5 Resistance gene against Pyrenopeziza brassicae Susceptible (Cv Apex) Sub-cuticular hyphal growth on leaf veins (V) and lamina (L) Asexual sporulation Resistant (Cv Imola) Hyphal growth Collapsed epidermal cells on leaf vein (V) Boys et al. (2012) Plant Pathology 61, Resistance does not stop sexual reproduction (apothecia & ascospores) of P. brassicae in senescent tissues Apothecia are produced on leaf veins (V) of susceptible and resistant lines Boys et al. (2012) Plant Pathology 61,

6 Light leaf spot conclusions Light leaf spot severity has increased in England Oilseed rape cultivars differ in resistance against Pyrenopeziza brassicae Work is needed to identify UK races of P. brassicae Work is needed to identify sources of resistance against P. brassicae Phoma stem canker of oilseed rape Canker worldwide crop losses > 1000M annually, despite crop protection

7 Phoma stem canker (Leptosphaeria spp.); two co-existing pathogens Co-existence of L. maculans (Lm) and L. biglobosa (Lb) Fitt et al. (2006) Ann. Rev. Phytopath. 44,

8 Lm releases ascospores before Lb (autumn 2006, UK) Stonard (2008) PhD thesis, Nottingham Univ Huang et al. (2011) Plant Pathology 60, Understanding resistance to decrease risk of severe phoma stem canker on oilseed rape HGCA RD ; LINK SA 578, LK09138 BBSRC BB/I017585/

9 Leptosphaeria spp. ascospore release differed between regions and seasons Late release of ascospores caused upper stem lesions (L. biglobosa), 2011/2012

10 Late release of ascospores caused upper stem lesions, 2011/2012 Upper stem & stem base lesions both caused by L. biglobosa Phoma stem canker (L. biglobosa) conclusions L. biglobosa coexists with L. maculans on UK oilseed rape crops L. biglobosa can cause severe, damaging epidemics L. biglobosa is less sensitive to some fungicides than L. maculans There are interactions between cultivar resistance and L. biglobosa/ L. maculans Work is needed on resistance against L. biglobosa

11 Two types of resistance against L. maculans Time of HGCA RL resistance rating Resistance against L. maculans prevents substantial yield loss from phoma stem canker Losses in Australia (Mediterranean climate) Photo from Dr Steve Marcroft

12 R gene resistance; traditional cotyledon tests for determining L. maculans races Differential set with matching Avr genes Rlm1-3 Columbus Rlm2 Bristol Rlm Rlm4 Jet Neuf Rlm Rlm6 Darmor-MX Rlm Rlm No R Westar But population fixed (avr, virulent) at Avrlm2, Avrlm3, Avrlm9 loci Current L. maculans race distribution 11 UK sites, 4 outside UK Sample current populations 98 isolates from leaf spots on Drakkar (no R genes) Spore samples with 4 Burkard samplers

13 Frequency of L. maculans Avr alleles, population sampled from Drakkar in 2011/2012 Regional L. maculans race distribution (England) Percentages of avirulent and virulent alleles > 2010/ /12 At all 9 sites, population c. 100% Avirulent - Avrlm5 i.e. Rlm5 - Avrlm6 i.e. Rlm6 - Avrlm7 i.e. Rlm7? c. 100% Virulent - avrlm2 i.e. Rlm2 - avrlm3 i.e. Rlm3 - avrlm9 i.e. Rlm9 STILL EFFECTIVE INEFFECTIVE Rlm5 Rlm6 Rlm7 STILL EFFECTIVE

14 Regional L. maculans race distribution (England) Percentages of avirulent and virulent alleles > 2010/ /12 For some Avr genes, populations differ between sites Advantages of air sampling and PCR to determine L. maculans races Van de Wouw et al. (2010) Pl Path 59, Samples larger population, quicker, cheaper, less laborious than cotyledon assays

15 Breakdown of Rlm7? Phoma leaf spots on Excel (Rlm7) (also on Roxet (Rlm7)) Small spots, L. biglobosa or L. maculans? 9 Dec 2010 at Rothamsted Large spots, L. biglobosa or L. maculans? Phoma leaf spotting on Rlm7 cvs Roxet Roxet Excel

16 Phoma stem canker on Roxet (Rlm7) Harpenden, July 2012 Harpenden, July 2013 Management of resistance against L. maculans in Australia Similar schemes are operating in France and Canada

17 Management of resistance (Australia) (Part of step 3) Phoma stem canker (L. maculans) conclusions New opportunities to determine L. maculans races more quickly (air sampling & PCR) Work needed to regularly monitor regional distribution of L. maculans races (cf. France, Germany, Canada, Australia) Work needed to develop a strategy for regional deployment of different sources of resistance

18 Take-home messages Diseases cause large losses in UK oilseed rape crops Disease spectrum and pathogen populations are always changing There is a need for good resistance against these pathogens There are opportunities to exploit new genetic information to improve resistance against the pathogens There is a need for new strategies to manage oilseed rape diseases Thank you University of Hertfordshire Dr Yong-Ju Huang Georgia Mitrousia Dahlia Sidique Martin Malcolm-Brown Dr Emily Boys (HGCA) Dr Neal Evans (WIN) Dr Peter Gladders (ADAS) Dr Jenna Watts (HGCA) Prof Jon West (Rothamsted)