Globodera pallida suppression and glucosinolate depletion in soil cultivated with brassicas under glasshouse conditions

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1 Globodera pallida suppression and glucosinolate depletion in soil cultivated with brassicas under glasshouse conditions Bruno M. Ngala, Simon R. Woods & Matthew A. Back

2 Background I PCN - Destructive pests of potatoes ( 25.9 million per annum AHDB) Pesticides are under threat Montreal Protocol - Substances that Deplete the Ozone Layer Authorisation directive 91/414/EEC replaced by EC 1107/2009

3 Background II

4 Background III Partial biofumigation (theory): 1. Glucosinolates have been recoded in the leachates from brassica roots (McCully et al., 2008) 2. Myrosinase has not been recoded in root leachates 3. Several soil-borne microbes produce myrosinase E.g. Aspergillus spp. (Sakorn et al.,1999)

5 Hypothesis: Partial biofumigation is responsible for reduced population densities of potato cyst nematodes (Globodera pallida) during the cultivation of brassica cover crops Testing the hypothesis: Determine the viability of PCN (G. pallida) before and after brassica incorporation Measure glucosinolate (sinigrin) degradation AND total microbial activity before, during and after biofumigants

6 Treatments Oilseed radish cv. Bento (Raphanus sativus) Indian mustard cv. Caliente (ISCI) 99 (Brassica juncea) Untreated +/- soil sterilization

7 Experiment design CRBD: 6 treatments/5 Reps (repeated twice) Nylon sachets containing 50 cysts of G. pallida Buried at 10 cm depth

8 Materials & Methods: Incorporation

9 Materials & Methods: PCN viability assessment (I)

10 Materials & Methods: PCN viability assessment (II) 10

11 Materials & Methods: Measurement of total microbial enzyme activity and glucosinolates Measurement of total microbial enzyme activity Fluorescein diacetate assay (FDA) (Solaiman, 2007) FDA is converted into fluorescein by microbial enzymes creating a more intense colour Colour intensity measured at 490 nm Measurement of sinigrin degradation 50g soil samples spiked with sinigrin (2-propenyl GSL) Sinigrin extracted using 70% methanol 96h later Analysed using HPLC analysis (Ngala et al., 2014) 11

12 Results: Glucosinolate (sinigrin) degradation (expt 1) Pre-sowing biofumigants Before incorporation After incorporation

13 Sinigrin conc. (mm) Sinigrin conc. (mm) Sinigrin conc. (mm) Results: Glucosinolate (sinigrin) degradation (expt 2) a ab ab ab ab b Pre-sowing biofumigants 4 0 Untreated-S Untreated B. juncea R. sativus B. juncea-s R. sativus-s Treatments 3 2 Before incorporation Untreated-S Untreated B. juncea R. sativus B. juncea-s R. sativus-s Treatments 3 2 b a After incorporation 1 0 c c c c Untreated-S Untreated B. juncea R. sativus B. juncea-s R. sativus-s Treatments

14 Results: Total microbial enzyme activity (expt 2) Pre-sowing biofumigants Before incorporation After incorporation

15 Results: PCN egg viability pre-incorporation G. pallida mortality cyst -1 (%) ab b ab ab ab 20 a Untreated-S Untreated B. juncea R. sativus B. juncea-s R. sativus-s

16 Sinigrin conc. (mm) Results: The relationship between sinigrin concentration and total microbial enzyme activity y = x R² = Total microbial activity (µg fluorescein g -1 dry soil) preincorporation

17 G. pallida mortality cyst -1 (%) Results: The relationship between total microbial enzyme activity and the mortality of G. pallida y = x R² = Total microbial enzyme activity (µg fluorescein g -1 dry soil) preincorporation

18 Conclusions Raphanus sativus significantly suppressed PCN pre-incorporation (partial biofumigation) Enhanced degradation of sinigrin was observed in pots where B. juncea and R. sativus was grown both pre and post incorporation Significant differences in total microbial enzyme activity were seen between the treatments pre-sowing, pre-incorporation and post incorporation of biofumigants Untreated/sterilised soil had the lowest total microbial enzyme activity The highest total microbial enzyme activity (pre and post incorporation) was observed in pots where B. juncea and R. sativus were grown in unsterilised soil

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20 Acknowledgements CERC Staff PML staff Local growers: Mark Davies and Neil Furniss Sponsorship from: - 16/10/2015