Evaluation of Natamycin Seed Treatments for Stemphylium...

Evaluation of Natamycin Seed Treatmentsfor Stemphylium botryosum & Other Necrotrophic Pathogens of Spinach

Lindsey du Toit, Mike Derie, & Barbara Holmes, Washington State UniversityPop Vriend Seeds, Andijk, The Netherlands

DSM Food Specialties B.V., Delft, The NetherlandsASTEC Global, Maarssen, The Netherlands

International Spinach Conference, 14-15 February 2018, Murcia, Spain

Seedborne Pathogens of Spinach

• >40 plant pathogens of spinach• fungal, bacterial, viral, phytoplasma, nematode

• a minority are seedborne & seed transmitted

• Important spinach pathogens that can be seedborne• Downy mildew - Peronospora farinosa f. sp. spinaciae

• Verticillium wilt – Verticillium dahliae

• Fusarium wilt – Fusarium oxysporum f. sp. spinaciae

• Cladosporium leaf spot – Cladosporium variabile

• Stemphylium leaf spot – Stemphylium botryosum

• Anthracnose – Colletotrichum dematium f. sp. spinaciae

• CMV – Cucumber mosaic virus

• Opportunistic/saprophytic, necrotrophic fungi on spinach seed:Acremonium, Alternaria, Ascochyta, Aspergillus, Bipolaris, Botrytis,

Doratomyces, Epicoccum, Melanospora, Penicillium, Phoma, Phomopsis,

Rhizopus, Ulocladium, …

Seed Treatments with Efficacy Against Some

Seedborne Pathogens of Spinach

• Downy mildew - Peronospora farinosa f. sp. spinaciae

mefenoxam, metalaxyl

• Verticillium wilt – Verticillium dahliae

hot water, thiabendazole, thiophanate methyl

• Fusarium wilt – Fusarium oxysporum f. sp. spinaciae

hot water, thiabendazole, thiophanate methyl

• Cladosporium leaf spot – Cladosporium variabile

hot water, chlorine, thiram, iprodione, fludioxonil, azoxystrobin, …

• Stemphylium leaf spot – Stemphylium botryosum

iprodione, azoxystrobin + fludioxonil, pyraclostrobin + boscalid

• Anthracnose – Colletotrichum dematium f. sp. spinaciae

hot water, thiabendazole, azoxystrobin + fludioxonil

Need for Organic Spinach Seed Treatments

1. Hot water, chlorine, other disinfectants insufficient for internal

infections &/or thermo-tolerant pathogens

2. No highly effective organic seed treatments

3. Natamycin:• Produced by Streptomyces natalensis, found in Pietermaritzburg, Natal,

South Africa by Prof. Johanna Westerdijk (Netherlands)

• Natamycin isolated in 1955 (Struyk 1957, Antibiotics Annual):

• Initially named pimaricin, changed to natamycin by WHO

• Effective against true fungi, not oomycetes

• Binds to ergosterol, inhibits amino acid & glucose transport across

plasma membrane

• Used in food industry: e.g., dairy products

• >150 countries

• No resistance risk evident

natamycinvgp.com

Materials & Methods

Two spinach seed treatment trials:1. Trial 1 (du Toit et al. 2018. Plant Dis. Mgt. Rep. 12:V050)

a. Rates of natamycin: 0, 0.5, 1.5, 4.5 g/kg seed

b. Priming duration: none, short, medium, long (proprietary)

2. Trial 2

a. Rates & formulations of natamycin

b. Priming vs. coating

For each trial, 4 reps of 100 seed/treatment:

1. AOSA blotter seed germination assay

2. Freeze-blotter seed health assay

Trial 1: Seed germination assay(du Toit et al. 2018. Plant Dis. Mgt. Rep. 12:V050)

Natamycin seed treatment

Seed

germ

ination a

t 7 d

ays (

%)

None Short priming Medium priming Long priming

ANOVA Pr < 0.0001 = highly significant differences


Seed

germ

ination a

t 21 d

ays (

%)


Trial 1: Seed germination assay(du Toit et al. 2018. Plant Dis. Mgt. Rep. 12:V050)

ANOVA Pr = 0.0008


Ste

mphyliu

m b

otr

yosum

(%)


Trial 1: Seed health assay(du Toit et al. 2018. Plant Dis. Mgt. Rep. 12:V050)

ANOVA Pr < 0.0001


Vert

icill

ium

spp.

(%)



ANOVA Pr < 0.0001


Altern

aria s

pp.

(%)



ANOVA Pr < 0.0001


Actin

om

yce

tes

(%)



ANOVA Pr < 0.0001

Trial 2: Seed germination assaySeed germination: No significant differences among treatments at 7, 14, or 21 days: P ≥ 0.2165

Similarly for % rotten seed, % abnormal germination, and % non-germinated seed

PrCt

Seed

germ

ination a

t 21 d

ays (

%)

Primed Ct

Pr

+

ctNone Pr Ct Pr Ct Pr Ct Pr PrCt

a

ab

b

c

cdcde

dedef

efghdefgh

fghi

ghi

hi hi hi i

defg

Ste

mphyliu

m b

otr

yosum

(%)


Trial 2: Seed health assayStemphylium botryosum: Highly significant differences among treatments (P < 0.0001)

aa

ab

bc

cd

cdecd cde

defdefgdefg

defghefgh

h gh fgh

cde


Vert

icill

ium

spp

.(%

)Trial 2: Seed health assay

Verticillium spp.: Highly significant differences among treatments (P < 0.0001)

b bc

a

bcd

cdbcd cdbcdcd

ddcd

d d d d

bcd


Fusari

um

spp.

(%)

Trial 2: Seed health assayFusarium spp.: Highly significant differences among treatments (P < 0.0001)

Summary

• Spinach seed treatment with natamycin at 0.5 to 1.5 g/kg

seed with a ‘short’ priming duration:

• Highly effective against all necrotrophic fungi detected

• No effect on potentially beneficial actinomycetes

• No phytotoxicity at these rates, potential phytotoxicity at

higher rates

• Not effective for downy mildew

• Additional research:

• Additional seed lots, field trials

• Pursue registration on spinach seed for conventional &

organic crops

Evaluation of Natamycin Seed Treatments for Stemphylium...

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