Onions & Mycorrhizae Lindsey du Toit, Jenny Knerr, & Dipak Sharma-Poudyal, Washington State University; Tim Paulitz, USDA ARS Pacific Northwest Vegetable Association Annual Convention & Trade Show Kennewick, WA 12-13 November 2014

Mycorrhizae • Mutualistic plant root-fungal associations • Mycorrhizal fungi are ubiquitous in most soils

- except where practices eradicate these fungi

• Most plant species form mycorrhizae

- except Chenopodiaceae, Brassicaceae

• Ectomycorrhizae – tree species primarily • Endomycorrhizae – trees & herbaceous plants

- Arbuscular mycorrhizae: >80% plant species - Ericoid mycorrhizae: Ericales - Arbutoid & monotropoid mycorrhizae: Ericales - Ectendomycorrhizae: only conifers Pinus & Larix - Orchid mycorrhizae: only Orchidaceae

Mycorrhizae diagram by Mark Kelly, Heartspring.net © 2012

Arbuscule:

Chemical exchange of - sugars, photosynthates - water, mineral nutrients

http://archive.bio.ed.ac.uk/jdeacon/mrhizas/ecbmycor.htm

Pinus sylvestris and Suillus bovinus mycorrhiza (D.J. Read)

C.F. Scagel

Onions and mycorrhizae • Sparse rooting system • Minimal root hairs • Slow growth • Highly responsive to AMF for water & nutrient acquisition • Molberg (1884) • Model for mycorrhizal research

Mycorrhizal benefits to onion • Improved soil structure - soil-penetrating hyphae - ‘sticky’ material binds small soil particles Miller & Jastrow (1992) - larger aggregates - improved aeration - water filtration - root penetration - soil tilth

Mycorrhizal benefits to onion More rapid & effective rooting Improved transplant survival and growth Increased P uptake, also Cu, Zn, … Fertilizer use efficiency, reduced fertilizer inputs? Moisture use efficiency = less moisture stress Charron et al. 2001a: Inoculation of onion transplants with Glomus intraradices or G. versiforme

Bulb diameter (mm)

• • • • •

Weeks after transplanting

Mycorrhizal benefits to onion • Charron et al. 2001a: Onion transplants

preinoculated with AM, P fertilizer levels

- Greater onion biomass than non-inoculated plants - Reduced time to bulb maturity (2-3 weeks) - Same effect with G. intraradices & G. versiforme - Firmer bulbs from plants with G. intraradices - Onion P concentration greater with AM - Greatest AM root colonization at low soil P

• Charron et al. 2001b: N, AM, bulb firmness

- Bulb firmness decreased with increasing N - Bulb firmness greater on AM inoculated plants - Differences between G. intraradices vs. G. versiforme

Mycorrhizal benefits to onion • Galvan et al. 2009: Netherlands, AM in organic vs. conventional onion crops

10% increase in AM colonization = 3.8 ton/ha yield increase (even at high P)

Yield (tons/ha)

- All plants had AM in both farming systems - Onion yield correlated with AM colonization Conventional: r = 0.70 Organic: r = 0.47

Arbuscular colonization (%)

Mycorrhizal benefits to onion • Tolerance of environmental extremes - Moisture stress - Soil salinity Bob Linderman

AM No AM No AM AM No salinity High salinity No salinity High salinity

Mycorrhizal benefits to onion

• ~50 less WR in AM & Folicur plots, season-long • Negative correlation of WR incidence & AM colonization • 2 Cvs.: Hoopla was more susceptible & had less AM than Fortress

Incidence of white rot (%)

• Greater tolerance of soilborne diseases - White rot, pink root, others? • Jaime et al. 2008: AM & white rot on muck soils, Ontario, Canada 40 c

35 30

bc 25

b

20 15

a

a

a a

ab a

a

10 5 0 Site 1

Site 2

Nontreated control Folicur 3.6F MIKKRO-VAM MYCORISE 1000 MYCORISE 255

Mycorrhizal benefits to onion • Bob Linderman & Anne-Cressey McGraw (1977)

- AM and pink root (Phoma terrestris) - 18 onion fields in Treasure Valley - 3 ‘new’ (≤5 years cultivation), 15 ‘old’ (≥20 years) fields

Mycorrhizal benefits to onion • Bob Linderman & Anne-Cressey McGraw (1977) • Soil fertility - ‘new fields’ had less available P - AM levels lowest in fields with >25 ppm P - AM levels lowest in fields with >40 ppm nitrate - Pink root severe regardless of nitrate level • Soil pH - Soil pH higher in ‘new’ (8.0) vs. ‘old’ fields (7.5) - Glomus mossae = most prevalent AM species - AM more prevalent at higher soil pH • Soil fumigation - less AM in fumigated fields

Mycorrhizal benefits to onion • Mechanisms of disease suppression by AM? 1. Physiological host change – less root exudation 2. Change in soil microbial population -

3. 4. 5. 6.

Increased # and proportion bacteria Direct pathogen suppression: antibiosis, competition, parasitism?

Competition for root colonization sites Induced defense in host Morphological changes in root system Damage compensation by greater root growth

Effects of agricultural practices • Crop rotations, cover crops

- Canola, broccoli, radish, mustards = no AM, lower AM population - Legumes (pea, bean, vetch, …) = increase AM

• Fertilizers

- High P, inorganic = inhibitory to some AM - Slow release, organic fertilizers = favor AM

• Soil fumigation

- MeBr, chloropicrin, metam sodium = eradicate or reduce AM - Nematicidal fumigants (Telone) = little/no effect

• Fungicides

- Foliar fungicides = no effect - Drench fungicides = no effect or major reduction - Seed treatments? Apron + Thiram, FD300, FI500, …

• Cultivation

Percentage of root with AM / Onion growth (g/plant)

Effects of fungicide drench treatments on onions inoculated with AM

Bob Linderman

Onions & mycorrhizae in the Columbia Basin Widespread use of soil fumigation in conventional onion crops, & green manure/biofumigant crops in organic onion bulb crops: • Potential benefits from AM inoculations • Inoculum placed directly under or with seed - earliest, most predictable AM formation - Shock et al. (2003) – no effects when AM applied 2 months after planting, high soil P • Fertility – low P, organic/slow release • Potential reduced fertilizer/pesticide needs • Improved yields &/or bulb storage quality

Evaluation of AM in onion crops in the Columbia Basin 1. 2. 3. 4. 5.

Funded by PNVA members & WSU BIOAg

Prevalence/diversity of AM in organic & conventional crops Influence of soil fumigation on AM in onion crops Potential for AM inoculation to suppress soilborne diseases Effect of AM on onion growth & P use efficiency Influence of fungicide seed treatments & soil applications on AM Rhizoctonia stunting (Rhizoctonia solani)

Pink root

(Phoma terrestris)

2013 AM Survey of Onion Crops in the Columbia Basin Incidence of AMF infection per field (%) Percentage of plants colonized by AM

100

100

100

84

80

68

56

60 40 20 0

16

96

92 76 52

2014 AM Survey of Onion Fields in the Columbia Basin a

a

ab abc abc

a

AM colonization: • all fields • 42-90% of roots Soil P: • Relatively low • 14-68 mg/kg

bc c

d

Soil pH: • 6.3 to 8.1 • Higher in organic fields

AM Survey of Onion Fields in the Columbia Basin 1. Prevalence/diversity of AM in organic & conventional crops

• • • •

•

Baited AMF by growing onions in soil sampled from fields Extracted DNA from onion roots Amplified 18S region of rDNA (AMV4.5NF/AMDGR primers – Van Geel et al. 2014) Sequencing of preliminary samples: Glomeraceae Glomus mossae, G. lamellosum, G. luteum, Rhizophagus irregularis, Funneliformis irregularis, … Pyrosequencing: AM diversity in organic vs. conventional soils

2. Influence of soil fumigation on AM in onion crops

• •

Soil sampled in fall 2014 from 4 fields just prior to fumigation + 4 fields not fumigated in fall Soil & plant samples collected in spring 2015 from all 8 fields - Assess influence of fumigation on AM prevalence & diversity

Effect of AM on Rhizoctonia solani AG 8 Trial 1 Trial 2

Control

Rhizoctonia solani AG 8

Control

R. solani

R. solani + AM

Mycorrhizae (BioTerra)

Sharma-Poudyal et al. 2014. Plant R. solani + mycorrhizae Disease Management Reports 8:V305 Mycorrhizae (BioTerra Plus)

Effect of AM on Rhizoctonia solani AG 8 y a a b

yz

yz

z c **

Sharma-Poudyal et al. 2014. Plant Disease Management Reports 8:V305

Effect of AM on onion growth & P use efficiency

BTP

20 ppm P Myco

BTP

Soil

40 ppm P Myco

80 ppm P BTP

Soil

Myco Soil

Confounded effects of AMF & nutrients in products? Product

N

P

K

S

B

Zn

Mn

Fe

BioTerra

208

41

2,807

508

1.51

6.9

54.2

98

MycoApply

137

20

1,139

67

0.32

1.8

4.9

34

2014 Onion grower field trials with AM inoculants Plant Health LLC

Ultrafine Endo

Other AMF products?

Mycorrhizal Applications, Inc.

Myconate Mycorrhizal Stimulant, Sym-Agro, Inc. www.mycovitro.com = Glomygel products www.pthorticulture.com/en/products = Pro-Mix Pur products

2014 Onion grower field trials with AM inoculants

Grower A: MycoApply with seed in hopper (only ~1/8 lb/acre of seed) Grower B: BioTerraPlus & MycoApply in gandy boxes (bridging in boxes, wind blew product off soil surface, not placed in-furrow) Grower C: MycoApply on seed in hopper at as high rate as possible BioTerra Plus formulation didn’t work with most growers’ equipment?

2014 Onion grower trials with AM inoculants Grower A: Rhizoctonia stunting too variable to detect effects of MycoApply or Quadris Grower B: Pink root (30 bulbs/plot) Severity of pink root (0-100%)

Treatment

North Trial

South Trial

Control

65.8 a

36.4 a

BioTerra Plus

66.9 a

38.5 a

MycoApply

67.0 a

49.8 a

Grower C: Pink root (100 bulbs/plot) Treatment

Severity of pink root (0-100%)

Control

34.5 ± 11.0

MycoApply

22.1 ± 9.7

Mycorrhizae & Onions in the Columbia Basin • Complete studies in progress: • 2015 Grower-cooperator trials

- Products? Including Myconate - Formulations compatible with equipment - Rates of inoculation, placement of AM - # of fields, replicated plots - Monitor crop growth, AM colonization, yield, diseases - Funding

• Contact: Lindsey du Toit [email protected] or 360-848-6140

Play With Your Food