Biology & Management of Biology & Management of Brown Root Rot of AlfalfaBrown Root Rot of Alfalfa

F.A. Gray, C.R. Hollingsworth, D.W. KochR.W. Groose and R.C. Larsen

Anamorphic (asexual) stage: Phoma sclerotioides

(syn. Plenodomus meliloti & Plenodomus sclerotioides)

Fungal Taxonomy

8-wk-old culture on PDA

Pycnidia (SEM, 110x) Hyaline, single-celled conidia (400x)

History

1933-1st reported on sweet clover in Canada

1984 – widespread on alfalfa in the Peace River Valley of Alberta

1996 – 1st reported on alfalfa in the U.S. in Wyoming

Host Range

Alfalfa

Alsike Clover

Bird’s-Foot Trefoil

Red Clover

Sainfoin

Sweet Clover

(J.G.N Davidson)

Survival & Spread

- Survival: in plant debris & in soil

- Spread: by wind & grazing animals

(J.G.N Davidson)

Diagnosis

Farson, Wyoming Spring of 1996

Severe Winterkill

Plants removed showing severe root rot

Close up of dead and dying plants

a. Plant Symptoms

Dead

Diseased

Diagnosis

b. Root isolation

c. PCR-based SCAR markers (R.C. Larsen, USDA-ARS, Prosser, WA)

Root isolation on PDA at 500 F. after 8 weeks

Note white mycelium, black pycnidia and yellow spore masses

Distribution

Currently known distribution in the U.S.

(Idaho, Montana, Wisconsin, Wyoming)

CANADAIndigenous Fungus

USA

Recommended Control Practices in Canada

1. Crop rotation – Grow annual crops such as oats or barley for 3 years between alfalfa crops. Avoid rotation with other forage legume crops especially sweet clover.

2. Harvesting/Grazing Management

- Avoid excessive cutting

- Avoid late fall cutting

- Avoid overgrazing & grazing in the fall before the ground is frozen.

3. Maintain proper soil fertility

4. Plant a resistant variety

- The variety Anik

(Medicago falcata) is

partially resistant.

- The variety Peace is the

least susceptible of the

M. sativa varieties

J.G.N Davidson.

AnikPeace

Farson, Wyoming

Recommended ControlPractices in the USA

1. Same as for Canada (items 1, 2, and 3)

2. Reaction of most U.S. varieties to BRR is currently unknown

3. The variety “Peace” performed well in the presence of BRR at Farson, Wyoming but may be susceptible to other major stand decline diseases in the U.S.

4. Other varieties performing well in the presence of BRR at Farson include: Ranger, Avalanche + Z and Spreador 3

Other available information on Brown Root Rot:

a. University of Wyoming Bulletin, B-1136, “Brown Root Rot of Alfalfa”

b. BRR Evaluation Protocol for, “Standard Tests to Characterize Alfalfa Cultivars” (pending final approval)

Fagray@uwyo.edu