Ian Small & Mathews Paret

June 2nd, 2017

Perennial peanut pathology: recognizing diseases

Diseases are not a major concern –let’s keep it that way!

Pathogen

Host

Environment

Goal: identify these three diseases by the end of the session

Peanut stunt virus (PSV)Symptoms:

- Stunted plants

- Chlorosis

- Mottling

- Malformed leaves

- Reduced foliage yield

Florigraze shows symptoms more readily than other varieties but many are infected

• Widespread in forage legumes especially white clover (Trifolium repens L)

• Seed-transmitted in annual peanuts (A. hypogaea L.)

• Virus vectored by aphids (Brunt et al. 1966)

• Known aphid vectors include • Aphis craccivora (cowpea aphid)

• A. spiraecola (spirea aphid)

• Myzus persicae (green peach aphid)

Baker, Blount and Quesenberry 1999. Plant Pathology Circular No. 395

Peanut stunt virus (PSV)

• Unknown what role perennial peanut plays as reservoir for PSV for other susceptible crops including annual peanut

• Little known on production loss and stand longevity for perennial peanut• Florigraze can be impacted

Peanut stunt virus (PSV)

Leaf spots

Example: Pepper spot and leaf scorch

Caused by a fungal pathogen

(Leptosphaerulina crassiasca)

Symptoms:

- Small dark brown or black lesions, typically less than 1 mm in diameter

- Lesions irregular to circular in shape

Survives between seasons on plant residue

2011 Pepper spot disease severity as indicated by the Area Under Disease Progress Curve (AUDPC). Different letters above the mean bars indicate statistical differences based on Student Newman Keuls Test (P=0.05)

2011 Pepper spot disease severity progression over a peak 2-month period.

Perennial peanut samples received and processed since 2012 at the NFREC diagnostic lab and the key pathogens identified are below

Disease and pathogen n = 33 Time period

Southern Blight (Sclerotium rolfsii) 4 May - Jul

Rhizoctonia root and stem rot (Rhizoctonia spp.) 4 May - Nov

Pythium root rot (Pythium spp.) 3 July - Aug

Fusarium root and stem rot (Fusarium spp.) 4 Jul

Anthracnose (Colletotrichum spp.) 2 May - Jun

Leaf spot (Sclerotinia homeocarpa) 4 May - Jul

Pepper spot and Leaf Scorch (Leptosphaerulina crassiasca) 1 Jun

Phomopsis leaf blight (Phomopsis spp.) 2 Jun - Jul

Rust 6 Jul - Nov

Unknowns 4

Perennial peanut rust

Caused by a fungal pathogen

(not yet officially reported)

Symptoms:

• Raised orange pustules on lower surface of leaves

• Pustules rupture to expose reddish brown spores

• As disease progresses pustules on upper surface of leaves

Perennial peanut rust

Perennial peanut rust

Severe rust on Ecoturf in November 2016

Extended season, favorable conditions for disease

Photo credit: David Wright

Perennial peanut rust

Diseases do not develop overnight

Scout your fields to assess disease and time cuts

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Day of epidemic

Breeding for resistant varieties

1. Continue the emphasis on breeding resistant varieties

2. Consider disease susceptibility when selecting varieties for new plantings

3. Do not delay cutting hay, or risk losing quality

Three tactics to minimize disease issues

• As acreage of perennial peanut increases the likelihood of disease issues will increase

• Populations of plant pathogens change, so be vigilant

Looking ahead

Challenges:

• Quantifying perennial peanut growth over time is labor intensive

• Assessing disease severity is subjective

Applications:

• Breeding new varieties

• Understanding field variability (low vs high yielding areas)

Using technology to accelerate breeding and improve productivity

Application of technology

Remote Sensing

Unmanned Aerial Vehicles (UAVs)

Visual, multispectral, thermal cameras

Geographic Information Systems (GIS)

PhotogrammetryJames Clohessy

DJI Matrice 100

DJI Zenmuse Z3

SlantRange 3p4 Spectra

410-950nm

Preliminary results

Resources:

EDIS SS-AGR-37 Blount et al. Peanut Stunt Virus Reported on Perennial Peanut in North Florida and Southern Georgia

Questions?

Understanding field variability