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

Erland LiljerothPlant Protection Biology, SLU, Alnarp, Sweden

“Help to self-help” against potato late blight

Can induced resistance be used in practical plant protection – combined

with lower doses of fungicides?

Phosphite

Alkali salts of phosphite ionsHPO3

2- / H2PO3-

• Taken up by plants but not metabolized

• Oxidized to Phosphate, PO43- , by soil

bacteria. harmless?• Also direct effect against oomycetes• Salts have long history in plant

protection

Beta-amino butyric acid (BABA)

• Induce resistance in many plants• Normally not found in plants, few

cases in plant roots, in bacteria• No direct effect on Phytophthora

infestans

Liljeroth et al. 2010, Bengtsson et al. 2014 Burra et al. 2014, Liljeroth et al., 2016

3 hours 6 hours 11 hours

- Immune system process- Defense response- Response to abiotic stimulus- Phenylpropanoid metabolicprocess- Response to wounding

- Defense response - Response to jasmonic acid stimulus- Response to salicylic acid stimulus- Aromatic amino acid family biosynthetic process- Carbohydrate catabolic process

- Membrane lipid metabolic process - Cell wall organization or biogenesis- Phosphatidylinositol metabolicprocess- D-amino acid 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

- Cell wall organization or biogenesis - Cell wall polysaccharide metabolic process- Cellulose synthase activity - External encapsulating structure organization

Burra et al. 2014

Expression analysis of Phosphite treated potato

Field trials 2011-2013

2011: Proalexin, Shirlan, Combinations Bintje, Ovatio, Seresta, Merano2012: Proalexin, Ranman Top, Combinations Bintje, Ovatio, Seresta, Merano2013: Proalexin, Ranman Top, Combinations Bintje, Sava, Seresta, Merano2014: Proalexin, Fungicide strategy*, Combinations Bintje, Perlo* = Revus, Infinito, Ranman Top alternated

Effect of Proalexin (Potassium phosphite) alone and in combination with:Shirlan (Fluazinam)Ranman Top (Cyazofamid)

Measurements:Late blight developmentTuber rot after 3 months storageYield

Randomized block design, 4 blocksPlot size: 20 m2

Liljeroth et al., 2016

Yield vs. Late blight severity in table potato

Liljeroth et al., 2016

UntreatedFungicidePhosphiteCombination

Field trials2011-2014

Phosphite efficacy depend on cultivar resistance

“Degree of resistance”

Liljeroth et al., 2016

Open symbols:Starch cultivarsColoured symbols:Table cultivars

Phosphite had best effect in more resistant starch cultivars

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)

Residue levels

Analysis with ion chromatography

Year Cultivar Treatment Applied PO3 PO3 in tubers Percent of total appliedPO3 found as residue in tuberskg/ha mg/kg FW

2013 Sava Control 0 -Proalexin 12 times 7,5 L/ha 10,8 123 30

Merano Control 0 -Proalexin 12 times 7,5 L/ha 10,8 205 35

2014 Bintje Control 0 -Proalexin 12 times 5 L/ha 7,2 57 12Proalexin 12 times 2,5 L/ha combined with Ranman Top 0,25 L/ha 3,6 27 18

- Below detection limit <0,01 mg/kg

Maybe limited use possible in table potato?Starch potato?

Liljeroth et al., 2016

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 (T4, T5, T6), • Ranman Top (T2, T10, T11, T12)

Measurements: Late blight development, Yield, Tuber rot after 3 months storage

Randomized block design, 4 blocksPlot size: 20 m2

Trial 2015

Treatment Cultivar Fungicide dose (%) Phosphite dose (%) Interval (days)1 Untreated Kuras 0 0 72 Fungicide Kuras 100 73 Fungicide Kuras 50 74 Fungicide Kuras 25 75 Combination Kuras 50 50 146 Phosphite Kuras 100 77 Untreated Sarion 0 0 78 Fungicide Sarion 100 79 Fungicide Sarion 50 7

10 Fungicide Sarion 25 711 Combination Sarion 50 50 1412 Phosphite Sarion 100 7

Trial 2016

Treatment Fungicide dose (%) Phosphite dose (%) Interval (days)1 Untreated 0 02 Fungicide 100 73 Fungicide 50 74 Fungicide 25 75 Combination 50 50 76 Combination 25 75 77 Combination 25 50 78 Phosphite 100 79 Phosphite 50 7

10 Phosphite 25 711 Combination 50 100 1412 Combination 100 100 14

Cultivar: Kuras

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

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

Effects on starch content 2016

Late blight trials 2012-2016• 5 Trials• Cultivars: Seresta/Merano2012-13; Kuras2016

• Reduced dose fungicides: equal yield and starch yield compared to full dose, butsome 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

Treatment Interval Late blight (rAUDPC) Yield (ton/ha) StarchContent (%) Starch Yield (ton/ha)Untreated control 7 days 0.221a 45.2c 22.3b 10.0dFungicide 100% dose 7 days 0.090cd 49.8ab 23.1ab 11.5abcFungicide 50% dose 7 days 0.093cd 49.6ab 23.4a 11.6abPhosphite 100% dose 7 days 0.105c 49.4ab 22.4b 11,0bcPhosphite 50% dose 7 days 0.129b 47.8bc 22.8ab 10.8cCombination Fungicide50%/Phosphite50% 7 days 0.085d 49.9ab 22.8ab 11.3abcCombination Fungicide100%/Phosphite100% 14 days 0.084d 52.0a 22.8ab 11,8a

Alternaria infections in late blight trial 2016

Sept 6, 2016

• Despite that all plots weretreated 5 times with Signum

• Up to 25 % infection in beginning of september

• Earlier years only minor infections.

Alternaria infectionCombinations Late blight fungicides Phosphite

Significanlty lower Alternaria infection withPhosphite treatment compared to late blightFungicides (AVOVA: p<0.0014)

All plots treated with Signum 5 times

Analysis of PO3 residues

Tubers from field trial 2015 and 2016

MRL table potato: 30 mg/kg

Means±SD from 4 replicate plots (mg PO3/kg FW)

Treatment TubersKuras 2015 Kuras 2016

Untreated control 0 0.7±1.5Phosphite 2.5 L/ha (50%) 12 times (combined) - 44±6.6Phosphite 1.25 L/ha (50%) 12 times (combined) - 27±9.7Phosphite 5 L/ha (100%) 6 times (combined) - 55±9.7Phosphite 5 L/ha (100%) 12 times 118±11.4 111±11.2Detektionsgränsen var 1 mg/kg friskvikt

Analysis of processed products

Means from 4 replicate plots (mg PO3/kg FW)

Treatment Starch Pulp Fruit sapKuras Sarion Kuras Sarion Kuras Sarion

Untreated control 0 0 0 0 0 0Phosphite 2.5 L/ha (50%) 6 times 0 0 19±3.6 15±2.8 2,7±0.6 2,7±1.2Phosphite 5 L/ha (100%) 12 times 0 0 71±9.9 63±8.6 11±1.7 14±1.7Detection limit: 1 mg/kg FW

Processed samples from field trial 2015

Pooled samples (mg PO3/kg DW)

Treatment Fiber ProteinKuras Sarion Kuras Sarion

Untreated control 0 0 0 0Phosphite 2.5 L/ha (50%) 6 times 0 0 7,7 13Phosphite 5 L/ha (100%) 12 times 12,3 6,8 100 83,3Detection limit fiber: 1 mg/kg DWDetection limit protein: 7 mg/kg DW

Fiber and protein made from pulp and fruit sap, respectively

Most of phosphite end up in wash water –spread to fields – oxidised to PO4 – kinetics?

per DW !!

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 delayedsenescence?

• Phosphite alone gave lower starch content.– Delayed senescence?

• Reduced fungicide doses give same yield as full doses, but some yearsmore late blight.

• Can phosphite integrated in control strategies reduce the risk of fungicideresistance?

• Residue concerns in table potato, but maybe possible to handle in starchpotato?

• With limited use MRLs are not exceeded• Registration against potato late blight possible in EU?

Resistance Biology groupLed by Prof. Erik AndreassonPlant Protection Biology, SLU Alnarp

Thanks to…..

Financial support: • SLF• Partnership Alnarp• Lyckeby starch

Thanks to the Rural Economy and Agricultural Societies ”Hushållningssällskapet” for performingthe field trials