How to conduct the ‘perfect · 2019. 2. 4. · – Phytoplasmas – MLOs • Viruses ... Early Blight of Tomato/Potato ... mites, nematodes, fungi and human activity Problematic

How to conduct the ‘perfect’ disease trial…

…when Mother Nature holds all the cards.

NAICC Efficacy Research Workshop - January 15th, 2019Dr. Gary E. Vallad, Associate Professor of Plant PathologyUniversity of Florida, IFAS, Gulf Coast Research and Education Center, Wimauma, FL, [email protected] 813-419-6577

mailto:[email protected]

What is the ‘perfect’ disease trial?

What is the key to a ‘perfect’ disease trial?

Know your target pathogen… Fungal vs. bacterial vs. viral

Life style – saprophyte, biotroph?

Soilborne vs. Airborne

Inoculum source

Know your host… Susceptibility

Crop development

Production system

Infection court

Know your environment… Trial design – Small plot vs. Demo

trial

Randomization, replication and blocking

Supplement environmental requirements

Know your treatment(s)… Modes of action

Compatibility

Use of adjuvant

Know your limitations… Logistics

Bias & error

Statistics

What is the objective? What is the patho-system?

Disease Triangle

Disease

Environment

Disease Triangle

Disease

Environment

Water is critical for most diseases:

• Germination• Infection -

penetration• Spread/Movement• Completion of

lifecycle

Disease Progress Parameters:

1. Initial inoculum2.Pathogen

generation time3. Time crop is

produced

Typical progress curve for polycyclic diseases

Disease ManagementDisease

Environment

Increase initial inoculum

Reduce initial inoculum

We can control when and how much inoculum is introduced in the system.


Environment

Increase initial inoculum

Reduce initial inoculum

Non-Favorable Environment


Environment

We can control when and how much inoculum is introduced in the system.

Often limited by environmental conditions.

Polycyclic and MoncyclicDiseases:• Reduce initial inoculum• Reduce infection rate• Reduce duration of epidemic

Relative contribution of each to the disease epidemic (polycyclic vs. monocyclic) will depend on the pathogen.Monocyclic Model

Polycyclic Model

xo and Q = initial inoculumR and r = rate of infection

t = time


Environment

http://www.apsnet.org/edcenter/advanced/topics/EpidemiologyTemporal/Pages/ModellingProgress.aspx#monocyclic

http://www.apsnet.org/edcenter/advanced/topics/EpidemiologyTemporal/Pages/ModellingProgress.aspx#polycyclic


Environment

physics.weber.edu/carroll/archimedes/crown.htm

How to improve disease:• Increase inoculum level• How inoculum is applied• Use a susceptible variety• Compromise the plant• Modify the environment• Planting date



Soilborne, airborne, vectored?

Inoculum source


Crop development

Production system

Infection court


trial




Compatibility

Use of adjuvant


Bias & error

Statistics






Inoculum source


Crop development

Infection court

Production system


trial




Compatibility

Use of adjuvant


Bias & error

Statistics






Inoculum source


Crop development

Infection court

Production system

Know your environment… Environmental requirements

(moisture, temp., soil pH)

Trial design – Small plot vs. Demo trial



Compatibility

Use of adjuvant


Bias & error

Statistics






Inoculum source


Crop development

Infection court

Production system






Compatibility

Use of adjuvants


Bias & error

Statistics



Know your target pathogens…• Fungi

– Ascomyetes– Basidiomycetes– Myxomycetes & Oomycetes**

• Bacteria– Phytoplasmas– MLOs

• Viruses– Includes viroids

• Nematodes

FUNGICause ~85% of all plant diseasesMulti-celled microorganismsSometimes visible without a

microscope; hand lensMany produce spores & spore-

bearing structures; others only mycelia (sterile)

Survive without hostMove plant-to-plant by wind, rain,

seed, & human activityMay have complicated lifecyclesDon’t assume lab inoculum = natural

inoculum

Rhizoctonia spp.

Fusarium spp.

Alternaria spp.

Phytophthora spp.

Know your target pathogen…

Credit: cdm.ipmpipe.org

Credit: www.apsnet.org

Early Blight of Tomato/Potato –Alternaria linariae & A. solani

Alternaria linariae

Kemmitt, G. 2002. DOI: 10.1094/PHI-I-2002-0809-01

A. solani


Credit: www.apsnet.org

Early Blight of Tomato/Potato –Alternaria linariae & A. solani

Alternaria linariae

Kemmitt, G. 2002. DOI: 10.1094/PHI-I-2002-0809-01

A. solani

• Can be cultured in the lab…although some isolates can be tricky to get sporulation (~ log 5 spores/ml).

• Conidia typically form singly -airborne.

• Warm, humid (75-84°F) conditions are conducive to infection.

• Spores can germinate in 40 min in the presence of free moisture at 82-86°F.


Savory et al. Molecular Plant Pathology, 2011

Cucurbit Downy Mildew –Pseudoperonospora cubensis




OBLIGATE BIOTROPH – requires a living hostAll cucurbits are susceptible; although pathogen population can vary for virulence towards specific cucurbit species.Favored by:• Temps 59-77oF• High relative humidity (> 90%)• Periods of extended leaf wetness

• Heavy morning dew• Foggy mornings• Rain

Spores are easily dispersed by wind and rain.




Natural progression of CDM

http://cdm.ipmpipe.org/Report early outbreaks to help inform local growers and forecast disease spread.

http://cdm.ipmpipe.org/



Natural progression of CDM

http://cdm.ipmpipe.org/Report early outbreaks to help inform local growers and forecast disease spread.

To facilitate diseases caused by obligate biotrophs:• collect leaves from diseased

areas – leaf washings• sentinel plots – susceptible

variety to get disease established early

• spreader rows/plots scattered in trial – plant early & stagger

http://cdm.ipmpipe.org/

Soilborne fungal pathogens -Fusarium wilt vs. Fusarium crown & root rot

F. oxysporum f.sp. radicis-lycopersici• Roots are typically showing symptoms of root rot. • Favored by soil temps of < 75°F and acidic soil pH

F. oxysporum f.sp. lycopersici• Roots typically remain intact. • Favored by soil temps of > 75°F and

acidic soil pH.

Available Host Resistance

Large and Beefsteak Disease Resistancez

Amelia R to F-R (1, 2, 3), N, S, TSW, and V (1) BHN 602 R to F-R (1, 2, 3), TSW, and V (1)BHN 975 R to FCR, F-R (1, 2), and V (1)Charger R to ASC, F-R (1, 2, 3), and V (1) IR to S and TYLCCrista R to ASC, F-R (1, 2, 3), and V (1), N, S, and TYLCEverglade R to ASC, F-R (1,2,3), S, V (1), IR to TYLCVFlorida 47 R to F-R (1, 2), V (1), ASC, and SFlorida 91 R to F-R (1, 2), V (1), ASC, and SHM 1823 R to FCR, F-R (1, 2), and V (1) IR to S, and TYLCHM 8849 CR R to FCR, F-R (1, 2), S, and V (1)Raceway (STM9203) R to ASC, FCR, F-R (1, 2), and V (1) IR to SRed Morning R to F-R (1, 2), ToM IR to TSW and V (1)Ridge Runner R to FCR, F-R (1, 2), V (1), and TYLCSanibel R to ASC, F-R (1, 2), N, S, and V (1)Sebring R to FCR, F-R (1, 2, 3), S, and V (1)Skyway R to F-R (1, 2) IR to N, TSW, TYLC

Chapter 17. Tomato Production. 2017-18 Vegetable Production Handbook

HOST RESISTANCEBest option to limit impact of other diseases, especially those that are difficult to manage with protective pesticides or where protective pesticides would interfere with the target pathogen.

White mold of potato/tomato –Sclerotinia sclerotiorum

https://www.canr.msu.edu/news/white_mold_or_sclerotinia_stem_rot_in_potatoes

Credit: Jeff Rollins, UF/IFAS

• Apothecia development requires cool, near-saturated soil conditions (50 – 68°F).

• Leaf wetness of 16 to 48 hours with temperatures in the range of 54 to 75°F promote ascosporegermination and infection.

InfectionCourt

Fruit and foliar blight of Pomegranate-Colletotrichum spp.

Disease causes nearly complete loss of the crop!

Fungicide efficacy trials

Fungus can be recovered from flower buds & blooms

PathogenBACTERIA

Single-celled microorganismsNeed a light microscope to seeUsually require a host to surviveWounds and natural openingsMove plant-to-plant by water

(irrigation/rain), seed, human activity, & insects

PHYTOPLASMAS/MLOSBacteria that lack a cell wallRequire a living host to surviveInsect vectored

Tomato Bacterial Spot –Xanthomonas spp.

Image credits: Ying-Yu Liao

Caused by X. perforans, race T4 Favored by warm (>80ºF) and humid

conditions. Easily spread by wind-driven rains and

handling wet plant tissues Seedborne pathogen

Symptoms: Water-soaked lesions initially and turn

necrotic 5 to 21 days after infection Fruit infections rare with X. perforans Surfactants aid bacterial infection;

especially Silicone-based surfactants!

Tomato Bacterial Spot – in FloridaXanthomonas perforans

Bacterial pathogens require high humidity; rain or dew. Are splash dispersed by rain and easily spread if physically handled when foliage is wet. In general, Xanthomonads are favored by hot >80°F and Pseudomonads by cooler <85°F temps.

Bacterial Disease Trials

• Easier to keep a fungus out of a bacterial trial than vice versa…good fungicides and bacteria grow quicker.

• For fungal trials – clean plants, isolation & avoid rainy season.

Bacterial Disease Trials

Bacterial Streaming…sign of bacteria!!Quickly distinguish between lesions caused by bacteria and fungi.

Can often be difficult to differentiate bacterial lesion from an early fungal lesion.

VIRUSESRequire an electron microscope to

observeComposed of DNA or RNA

enveloped by a protein coatRequire a living host to reproduceMove plant-to-plant by insects,

mites, nematodes, fungi and human activity

Problematic in vegetativelypropagated material

VIROIDSComposed of small segments of

RNA with no coat protein.

Pathogen

http://www.apsnet.org/edcenter/intropp/lessons/viruses/pages/tomatospottedwilt.aspx

Tomato spotted wilt virus - tospovirus




Inoculum source


Crop development

Infection court

Production system






Compatibility

Use of adjuvant


Bias & error

Statistics






Inoculum source


Crop development

Infection court

Production system






Compatibility

Use of adjuvant


Bias & error

Statistics



Symptoms – Signs - Ratings

Target Spot

Early Blight

Gray Leaf Spot

Can you identify the perpetrator?

Many fungal diseases can look alike… Without the aid of a microscope, exact identification can be tricky…

Target Spot Early Blight

Bacterial Streaming…sign of bacteria!!Quickly distinguish between lesions caused by bacteria and fungi.

Can often be difficult to differentiate fungal lesion from a bacterial lesion.

David B. Langston, University of Georgia, Bugwood.org

Wilting, but plants remain green!

Bacterial wilt of tomato; bacterial streaming from stem.

Southern blight of tomato; sclerotia of Sclerotium rolfsiion stem.

Can you identify the perpetrator?

Disease severity vs. AUDPC

Disease severity/incidence• Individual time points or repeated

measures• Unit-based (% or proportion of whole)

– Scales (Horsfall-Barratt)• Quantitative - normally distributed???

Area Under Disease Progress Curve• Summarize disease severity over time• Unit-less• Quantitative• Normal distribution

Disease Severity (%): DiseasedTrt Treatment, Rate/100 gal (Week) 14-Nov 16-Dec 13-Jan AUDPC Fruit (%)1 Bravo Weatherstik, 2 pt (1-7);

Fontelis, 16 floz (3,5,7); Scala, 7 floz (4,6); Inspire Super, 20 floz (5) 5.2ab 60.4ab 73.4ab 754a 14.4b

2 Penncozeb, 2 lb (1-7); Fontelis, 16 floz (3,5,7); Scala, 7 floz (4); Inspire Super, 20 floz (5); 3.0b 42.6bc 55.0bc 532b 16.3b

3 Penncozeb, 2 lb (1-7); Fontelis, 16 floz (3,5,7); Scala, 7 floz (4,7); Inspire Super, 20 floz (5); Switch, 14 oz (6,7); 3.0b 31.4c 42.6cd 415bc 11.6bc

4 Actigard, 0.5 oz (1-7); Penncozeb, 2 lb (1-7);Fontelis, 16 floz (3,5,7); Scala, 7 floz (4); Switch, 14 oz (6,7); 3.0b 15.4d 55.0bc 346c 14.0bc

5 Actigard, 0.5 oz (1-7); Penncozeb, 2 lb (1-7); Folicur, 8 oz (2,4,6); Fontelis, 16 floz (3,5,7); Scala, 7 floz (4); Switch, 14 oz (6,7) 3.0b 12.9d 31.4d 241d 7.9c

6 Non-Treated Control, (1-7) 9.1a 76.3a 97.0a 999a 34.4aP = 0.0275 < 0.0001 < 0.0001 < 0.0001 0.0032

Integrated Fungicide Programs

Field design Replication & Blocking Block perpendicular to

the known variation in the field!

Try to minimize variation within the block.

Randomize Keep it unbiased Keep it simple Include proper checks

& controls

SFT Land 1 Land 2 FT

350 210 203 314 403 350325 208 206 305 407 325300 209 201 309 413 300275 212 204 306 412 275250 211 202 308 410 250225 214 205 304 402 225200 213 207 311 401 200175 107 114 301 408 175150 106 113 312 411 150125 105 112 307 404 125100 104 111 310 409 100

75 103 110 303 414 75

50 102 109 302 405 5025 101 108 313 406 25

N

Moi

stur

e

Wind & Sunlight

Field design

FUM15-3 FUM15-4

On-farm studies require consideration of the growers system and limitations.• No inoculum• No non-treated control• Grower standard

Replication & Blocking Block perpendicular to




& controls

Field design

On-farm studies require consideration of the growers system and limitations.• No inoculum• No non-treated control• Grower standard

Replication & Blocking Block perpendicular to




& controls

Questions?

Gary ValladAssociate Professor of Plant PathologyUniversity of Florida, Plant Pathology Department, Gulf Coast REC; [email protected] 813-419-6577

mailto:[email protected]

Documents

How to conduct the ‘perfect · 2019. 2. 4. · – Phytoplasmas – MLOs • Viruses ... Early Blight of Tomato/Potato ... mites, nematodes, fungi and human activity Problematic