Epidemiology of blackleg pathogen Leptosphaeria maculans

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1 Epidemiology of blackleg pathogen Leptosphaeria maculans Bonny Vogelzang,PhD candidate Supervisors: Eileen Scott (UA) Jenny Davidson (SARDI) Kathy Ophel-Keller (SARDI) Moin Salam (DAFWA)

2 Spore trapping + PCR based diagnostics Develop as tool for Biosecurity surveillance Epidemiology Fast Reliable Sensitive? Specific?

3 Methods/Results Three endemic pathogens as models Mycosphaerella pinodes (peas) Leptosphaeria maculans (canola) Ascochyta rabiei (chickpeas) Real-time PCR tests available for each Confirmation by microscopy, trap plants Optimise DNA extraction from spores on tapes Specificity of PCR tests Sensitivity Conidia (6 spores) Ascospores variable DNA yield 10µm 10µm 10µm

4 Leptosphaeria maculans Epidemiological questions 1.Verification of epidemiological models 2.Interruption to ascospore production 3.Spore dispersal

5 Life cycle of Leptosphaeria maculans on Brassica napus. (Howlett et al., 2001).

6 Blackleg Sporacle/ SporacleEzy Predicts 1.Onset of pseudothecial maturity and 2.Onset of ascospore showers On basis of daily mean temperature and daily mean rainfall (Salam et al 2007; Salam et al 2003)

7 1. Verification of Blackleg Sporacle/SporacleEzy Ho: That the model correctly predicts days on which spores are released (a)yes or no? (b) How many spores?

8 Verification of model Spore trapping 2008 Model predictions for blackleg Struan/Kingsford % spores released Nov 31-Dec 29-Feb 29-Apr 28-Jun 27-Aug 26-Oct 2008

9 Verification of Model Spore trapping 2009 Model predicts proportion of spores released by date How does this relate to amount of disease? Quantify disease based on prior knowledge of relative disease severity for that region Two sets of spore traps / trap plants with different inoculum loads High Medium low

10 2. Effect of interruption to ascospore production Background: NSW 2006 season started wet, then drought April 2007 starting inoculum levels high Why?

11 Wagga Wagga, New South Wales Canola blackleg: predicted seasonal pattern of daily ascospore release from infected residues of crop grown in Daily ascospore release (fraction of total) J-07 F-07 M-07 A-07 M-07 J-07 J-07 A-07 S-07 O-07 N-07 D-07 J-08 F-08 M-08 A-08 M-08 J-08 J-08 A-08 S-08 O-08 N-08 D-08 Month Slide courtesy M. Salam 2006 growing season (May to October) rain: 120 mm

12 Wagga Wagga, New South Wales Canola blackleg: predicted seasonal pattern of daily ascospore release from infected residues of crop grown in Daily ascospore release (fraction of total) J-06 F-06 M-06 A-06 M-06 J-06 J-06 A-06 S-06 O-06 N-06 D-06 J-07 F-07 M-07 A-07 M-07 J-07 J-07 A-07 Month Slide courtesy M. Salam 2006 growing season (May to October) rain: 120 mm

13 2. Effect of interruption to ascospore production Research question: Does ascospore release immediately resume following prolonged drought or do pseudothecia dry out and die?

14 2. Effect of interruption to ascospore production Methods: 2008 stubble collected Struan Feb 09 Precondition stubble (16 o C, 95% RH) => pseudothecial maturation Stubble then placed in field but sheltered from rain Monthly sampling up to 12 months Ascospores released immediately on wetting? Viability of ascospores? Density of pseudothecia on stubble

15 Background: 3. Spore dispersal study Sub-model on ascospore dispersal based on pea pathogen (Mycosphaerella pinodes) L.maculans spores are larger than M. pinodes likely to drop out earlier Research question: What is the impact of ascospore size on distance of dispersal by wind?

16 3. Spore dispersal study Methods: Canola stubble infected with L.maculans Pea stubble infected with M. pinodes Rotorod air samplers at distances 0, 250, 500, 750, 1500m downwind from stubble Stubble wetted 5 minutes per hour Air sampling for 3-4 hours PCR-based tests, microscopy, trap plants

17 Expected Outcomes Epidemiological models tested using 2008 and 2009 spore trap data for Kingsford, SA Model predictions of proportion of spores released related to disease severity under two inoculum load scenarios Pseudothecial survival under drought conditions determined Data on L. maculans ascospore dispersal collected for incorporation into dispersal submodel

18 Questions?

19 References Howlett BJ, Idnurm A, Pedras MC (2001) Leptosphaeria maculans, the causal agent of blackleg disease of brassicas [Review]. Fungal Genetics & Biology 33, Salam M, Khangura RK, Diggle A, Barbetti MJ (2003) Blackleg Sporacle: A model for predicting onset of pseudothecia maturity and seasonal ascospore showers in relation to blackleg of canola. Phytopathology 93, Salam MU, Fitt BDL, et al. (2007) Two weather-based models for predicting the onset of seasonal release of ascospores of Leptosphaeria maculans or L. biglobosa. Plant Pathology

20 Experimental system Cereal/pulse/oilseed cropping system Three model pathogens; Varying concentrations of ascospores Morphologically distinct Mycosphaerella pinodes (peas) Leptosphaeria maculans (canola) Ascochyta rabiei (chickpeas)