Can potassium phosphite be integrated in late blight control strategies in starch potato?

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1 Can potassium phosphite be integrated in late blight control strategies in starch potato? Erland Liljeroth Plant Protection Biology, SLU, Alnarp, Sweden

many plants Normally not found in plants, few cases in plant roots, in bacteria No direct effect on Phytophthora infestans Taken up by plants but not metabolized

2 Can induced resistance be used in practical plant protection combined with lower doses of fungicides? Help to self-help against potato late blight Beta-amino butyric acid (BABA) Phosphite Alkali salts of phosphite ions HPO 3 2- / H 2 PO 3 - Induce resistance in many plants Normally not found in plants, few cases in plant roots, in bacteria No direct effect on Phytophthora infestans Taken up by plants but not metabolized Oxidized to Phosphate, PO 4 3-, by soil bacteria. harmless? Also direct effect against oomycetes Salts have long history in plant protection Liljeroth et al. 2010, Bengtsson et al Burra et al. 2014, Liljeroth et al., 2016

Expression analysis of Phosphite treated potato - Immune system process - Defense response - Response to abiotic stimulus - Phenylpropanoid metabolic process - Response to wounding - Defense response

- Systemic acquired resistance, salicylic acid mediated signaling pathway - Jasmonic acid and ethylene-dependent systemic resistance, ethylene mediated signaling pathway 3 hours 6 hours 11 hours -

3 Expression analysis of Phosphite treated potato - Immune system process - Defense response - Response to abiotic stimulus - Phenylpropanoid metabolic process - Response to wounding - Defense response - Response to jasmonic acid stimulus - Response to salicylic acid stimulus - Aromatic amino acid family biosynthetic process - Carbohydrate catabolic process - Response to stimulus - Defense response - Systemic acquired resistance, salicylic acid mediated signaling pathway - Jasmonic acid and ethylene-dependent systemic resistance, ethylene mediated signaling pathway 3 hours 6 hours 11 hours - Membrane lipid metabolic process - Cell wall organization or biogenesis - Phosphatidylinositol metabolic process - D-amino acid catabolic process Burra et al Cell wall organization or biogenesis - Cell wall polysaccharide metabolic process - Cellulose synthase activity - External encapsulating structure organization

Field trials 2011-2013 Effect of Proalexin (Potassium phosphite) alone and in combination with: Shirlan (Fluazinam) Ranman Top (Cyazofamid) 2011: Proalexin, Shirlan, Combinations Bintje, Ovatio,

4 Field trials Effect of Proalexin (Potassium phosphite) alone and in combination with: Shirlan (Fluazinam) Ranman Top (Cyazofamid) 2011: Proalexin, Shirlan, Combinations Bintje, Ovatio, Seresta, Merano 2012: Proalexin, Ranman Top, Combinations Bintje, Ovatio, Seresta, Merano 2013: Proalexin, Ranman Top, Combinations Bintje, Sava, Seresta, Merano 2014: Proalexin, Fungicide strategy*, Combinations Bintje, Perlo * = Revus, Infinito, Ranman Top alternated Randomized block design, 4 blocks Plot size: 20 m 2 Measurements: Late blight development Tuber rot after 3 months storage Yield Liljeroth et al., 2016

5 Yield vs. Late blight severity in table potato Field trials Untreated Fungicide Phosphite Combination Liljeroth et al., 2016

6 Phosphite efficacy depend on cultivar resistance Open symbols: Starch cultivars Coloured symbols: Table cultivars Degree of resistance Liljeroth et al., 2016 Phosphite had best effect in more resistant starch cultivars

7 Concerns with phosphite Not registrated as control agent in potato in Europé Plants take up but does not metabolize PO3 > Residues EFSA Equated to Fosetyl-Al General very low toxicity risk to insectivorous birds data gap Effects on natural waters data gap Current MRL: 30 mg/kg potato (COMMISSION REGULATION (EU) No 991/2014)

8 Residue levels Analysis with ion chromatography Year Cultivar Treatment Applied PO3 PO3 in tubers Percent of total applied PO3 found as residue in kg/ha mg/kg FW tubers 2013 Sava Control 0 - Proalexin 12 times 7,5 L/ha 10, Merano Control 0 - Proalexin 12 times 7,5 L/ha 10, Bintje Control 0 - Proalexin 12 times 5 L/ha 7, Proalexin 12 times 2,5 L/ha combined with Ranman Top 0,25 L/ha 3, Below detection limit <0,01 mg/kg Liljeroth et al., 2016 Maybe limited use possible in table potato? Starch potato?

Field trials 2015-2016 with starch potato Effect of Proalexin (Potassium phosphite) alone and in combination with fungicide program: Revus (T1, T3, T7, T8, T9) Infinito

9 Field trials with starch potato Effect of Proalexin (Potassium phosphite) alone and in combination with fungicide program: Revus (T1, T3, T7, T8, T9) Infinito (T4, T5, T6), Ranman Top (T2, T10, T11, T12) Randomized block design, 4 blocks Plot size: 20 m 2 Measurements: Late blight development, Yield, Tuber rot after 3 months storage

10 Trial 2015 Treatment Cultivar Fungicide dose (%) Phosphite dose (%) Interval (days) 1 Untreated Kuras Fungicide Kuras Fungicide Kuras Fungicide Kuras Combination Kuras Phosphite Kuras Untreated Sarion Fungicide Sarion Fungicide Sarion Fungicide Sarion Combination Sarion Phosphite Sarion 100 7

11 Trial 2016 Cultivar: Kuras Treatment Fungicide dose (%) Phosphite dose (%) Interval (days) 1 Untreated Fungicide Fungicide Fungicide Combination Combination Combination Phosphite Phosphite Phosphite Combination Combination

12 Results 2015 Low dose of fungicides combined with phopshite: Less late blight infection, maintained yield Low dose fungicide only: More late blight infection, maintained yield

13 Results 2016 Low dose of fungicides combined with phopshite: Less late blight infection, maintained yield Low dose fungicide only: More late blight infection, maintained yield

14 Effects on starch content 2016

15 Late blight trials Trials Cultivars: Seresta/Merano ; Kuras2016 Treatment Interval Late blight (raudpc) Yield (ton/ha) StarchContent (%) Starch Yield (ton/ha) Untreated control 7 days 0.221a 45.2c 22.3b 10.0d Fungicide 100% dose 7 days 0.090cd 49.8ab 23.1ab 11.5abc Fungicide 50% dose 7 days 0.093cd 49.6ab 23.4a 11.6ab Phosphite 100% dose 7 days 0.105c 49.4ab 22.4b 11,0bc Phosphite 50% dose 7 days 0.129b 47.8bc 22.8ab 10.8c Combination Fungicide50%/Phosphite50% 7 days 0.085d 49.9ab 22.8ab 11.3abc Combination Fungicide100%/Phosphite100% 14 days 0.084d 52.0a 22.8ab 11,8a Reduced dose fungicides: equal yield and starch yield compared to full dose, but some years higher late blight severity. Phosphite alone: significant lower starch content compared to fungicides only (ANOVA: p<0.0008). Combinations: lowest late blight severity, highest yield and starch yield

16 Alternaria infections in late blight trial 2016 Sept 6, 2016 Despite that all plots were treated 5 times with Signum Up to 25 % infection in beginning of september Earlier years only minor infections.

17 Alternaria infection All plots treated with Signum 5 times Combinations Late blight fungicides Phosphite Significanlty lower Alternaria infection with Phosphite treatment compared to late blight Fungicides (AVOVA: p<0.0014)

18 Analysis of PO3 residues Tubers from field trial 2015 and 2016 Means±SD from 4 replicate plots (mg PO3/kg FW) Treatment Tubers Kuras 2015 Kuras 2016 Untreated control 0 0.7±1.5 Phosphite 2.5 L/ha (50%) 12 times (combined) - 44±6.6 Phosphite 1.25 L/ha (50%) 12 times (combined) - 27±9.7 Phosphite 5 L/ha (100%) 6 times (combined) - 55±9.7 Phosphite 5 L/ha (100%) 12 times 118± ±11.2 Detektionsgränsen var 1 mg/kg friskvikt MRL table potato: 30 mg/kg

Analysis of processed products Processed samples from field trial 2015 Means from 4 replicate plots (mg PO3/kg FW) Treatment Starch Pulp Fruit sap Kuras Sarion Kuras Sarion Kuras Sarion Untreated

19 Analysis of processed products Processed samples from field trial 2015 Means from 4 replicate plots (mg PO3/kg FW) Treatment Starch Pulp Fruit sap Kuras Sarion Kuras Sarion Kuras Sarion Untreated control Phosphite 2.5 L/ha (50%) 6 times ±3.6 15±2.8 2,7±0.6 2,7±1.2 Phosphite 5 L/ha (100%) 12 times ±9.9 63±8.6 11±1.7 14±1.7 Detection limit: 1 mg/kg FW Fiber and protein made from pulp and fruit sap, respectively Pooled samples (mg PO3/kg DW) Treatment Fiber Protein Kuras Sarion Kuras Sarion Untreated control Phosphite 2.5 L/ha (50%) 6 times 0 0 7,7 13 Phosphite 5 L/ha (100%) 12 times 12,3 6, ,3 Detection limit fiber: 1 mg/kg DW Detection limit protein: 7 mg/kg DW per DW!! Most of phosphite end up in wash water spread to fields oxidised to PO4 kinetics?

20 Conclusions Phosphite in combination with reduced fungicide doses provide good late blight protection and good yield also at long intervals. Phosphite reduced early blight severity. Effect of phosphite on Alternaria or K fertilizing or delayed senescence? Phosphite alone gave lower starch content. Delayed senescence? Reduced fungicide doses give same yield as full doses, but some years more late blight. Can phosphite integrated in control strategies reduce the risk of fungicide resistance? Residue concerns in table potato, but maybe possible to handle in starch potato? With limited use MRLs are not exceeded Registration against potato late blight possible in EU?

21 Thanks to.. Resistance Biology group Led by Prof. Erik Andreasson Plant Protection Biology, SLU Alnarp Financial support: SLF Partnership Alnarp Lyckeby starch Thanks to the Rural Economy and Agricultural Societies Hushållningssällskapet for performing the field trials

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