Aphanomyces Cochlioides - Root Rot of Sugarbeet

Krista Lueth Jeff Corliss

Justin Bickel

Importance of Sugar beets to Humanity

– Sugar beets were first discovered during the Crusades– Sugar beets were identified as a source of sugar

around 1750 – Approximately 30% of the world’s supply of sugar is

currently derived from sugar beets– Annual production of sugar beets is now about 260

million tons– Annual consumption of beet sugar is now about 120

million tons

Area Cultivated and Production of Sugar Beets in the Main Producing Countries and Regions

FAO/EBRD cooperation. 1999 Sugar Beets/White Sugar. FAO/EBRD Agribusiness Handbooks 4:35-43 1996 1998Country or region

Area(‘000 ha)

Production(‘000 tons)

% Area(’000 ha)

Production(‘000 tons)

%

ECC (total) 2,108 113,976 43 2,037 114,400 44France 460 31,211 12 413 31,407 12

Germany 515 26,604 10 503 26,940 10.5Italy 273 12,250 5 287 12,521 5UK 199 10,420 4 189 9,802 4

Spain 157 8,236 3 153 8,918 3.5Other European (total) 963 35,267 14 809 30,220 12

Poland 452 17,845 7 401 15,100 6Czech republic 104 4,315 1.5 79 3,722 1.5

Hungary 118 4,677 1.5 79 3,200 1.5USA 535 24,204 10 587 29,628 11.5Ukraine 1,260 23,008 9 1,000 16,000 6China 656 16,726 7 510 14,000 5.5Russian Federation 1,060 16,166 7 806 10,800 4Turkey 422 14,543 5 500 20,000 8Iran 149 3,686 2 191 4,754 2Others 498 7,491 3 514 19,060 7World Total 7,651 265,924 100 6,954 258,860 100

Aphanomyces cochlioidesA Water Mold

• Kingdom - Chromista• Phylum - Oomycota• Class - Oomycetes• Order - Saprolegniales• Family - Saprolegniaceae• Genus - Aphanomyces• Species - Aphanomyces cochlioides

About The Oomycetes• They are found all over the world in fresh and salt water habitats.

• Some of the terrestrial Oomycetes are among the most important plant pathogenic organisms

• They may be facultatively or obligately parasitic and aerobic.

• The cell walls of the group consist mostly of ß-1,3- and ß-1,6-glucans with a small amount of cellulose. A few members also have chitin deposits.

• They are diploid in the vegetative phase with meiosis occurring during gametogenesis

• The group is characterized by reproduction that includes interaction of male antheridia with female oogonia resulting in the production of oospores

Environmental Conditions Suitable For Growth and Germination of A. Cochlioides

• High water levels - 30 to 35 percent soil saturation is adequate for severe root rot

• Warm temperatures - 20 to 25 degrees Celsius is optimum for zoospore and oospore production

• Humidity - Incidence of this disease is greatest in the humid areas of the U.S.

Hosts of Aphanomyces cochlioides

– Over 30 species in several families can be artificially infected including the following

• Amaranthaceae,Carylophyllaceae, Aizoaceae, Hydrophyllaceae, Linaceae, Papaveraceae, Portulacaceae, Solanaceae, and Chenpodiaceae

– Cultures of Aphanomyces have also been isolated from naturally infected plants including the following

• Chenopodium album, Mollugo verticillata, Saponaria ocymoides, and Tetragonia tetragonioides

Differentiating Aphanomyces From Other Pathogens Involved In the Root Rot Complex

• Rhizoctonia solani - Foliar symptoms of Rhizoctonia root rot are characterized by sudden and permanent wilting. No yellowing is observed. Rhizoctonia tends to infect the roots from the outside in.

• Pythium ultimum - Causes poor emergence, uneven growth, dead seedlings, and reddish discoloration of aboveground plant parts. Infected plants develop abnormal, fleshy roots with constrictions and rotted areas of various shapes and sizes.

• Fusarium oxysporum - Older leaves of plants affected by Fusarium yellows show wilting and interveinal chlorosis. Leaves ultimately become dry and brittle. External root symptoms are not present. Vascular elements in taproots exhibit a reddish-brown necrosis when viewed in cross-section

• Viruses - Characteristic lesions on the leaves distinguish viral pathogens from Aphanomyces. Beet Soilborne Mosaic Virus and Beet Necrotic Yellow Vein Virusare representative of viral pathogens.

Permanent wilting of plant infected by Rhizoctonia solani leading to Rhizoctona root rot

Courtesy of Robert M. Harveson, Plant Pathologist, Nebraska Cooperative Extension

Fusarium YellowsCourtesy of Robert M. Harveson, Plant Pathologist, Nebraska Cooperative Extension

Life Cycle of Aphanomyces cochloiodes

• Aphanomyces is a water mold, and as such has the same general life cycle of other organisms in the family Saprolegniales

• The shape and size of the organs differ among these organisms, but the general idea is the same

• There are asexual zoosporangia that produce zoospores, and sexual oosporangia producing overwintering oospores that subsequently germinate to produce zoospores or hyphae

Asexual Reproduction of Saprolegnia

http://web1.manhattan.edu/fcardill/plants/protoc/sapro2.html

Asexual Reproduction and Secondary Inoculum in

OomycetesA Movie

Sexual Reproduction of Saprolegnia

http://web1.manhattan.edu/fcardill/plants/protoc/sapro3.html

Encysted primary zoospores form at apices of zoosporangia of A. cochlioides.

Windels, C. E. 2000. Aphanomyces root rot on sugar beet. Online. Plant Health Progress:10.1094/PHP-2000-0720-01-DG.

Here you can see several Oogonia. The light coloured structures inside the oogonia are unfertilized eggs called oospores.

http://www.uwinnipeg.ca/~simmons/saproleg.htm

Here you see a closeup slide of an Oogonia of Saprolegnia sp.

http://www.uwinnipeg.ca/~simmons/saprolg2.htm

Light microscopy of small feeder root. Circular, darkly stained structures are overwintering oospores.

Courtesy of Robert M. Harveson, Plant Pathologist, Nebraska Cooperative Extension

Acute Phase (black root)

• April to June• Above ground symptoms:

– A water soaked area extends up and down the hypocotyl from the point of entry of the pathogen then migrates to the petioles and cotyledons

• Below ground symptoms:– The invaded root or hypocotyl becomes brown and then

black as a result of the infection. • Entire fields of sugarbeet seedlings may be destroyed by black

root within 3 to 4 days if warm, moist conditions prevail

A brown, water-soaked rot occurs on the root and hypocotyl of young seedlings.

Windels, C. E. 2000. Aphanomyces root rot on sugar beet. Online. Plant Health Progress:10.1094/PHP-2000-0720-01-DG.

Black root (seedling) phase of sugar beet. Infected plant is on the left. Note the thin hypocotyl and lack of wilting in young leaves.

courtesy of C. M. Rush, Professor of Plant Pathology, Texas A&M University

Chronic Phase (root rot)

• June to August– plants that survived the first round of infection

• Above ground symptoms:– undersized plants– yellowing of the lower leaves– a 24 hour cycle of wilting and recovery

• Below ground symptoms:– lateral root infections and rotted root tips – taproot turns brown or black inside and out

Stunting and yellowing of lower leaves of sugar beet with Aphanomyces root rot (right) compared to healthy plant (left).

Windels, C. E. 2000. Aphanomyces root rot on sugar beet. Online. Plant Health Progress:10.1094/PHP-2000-0720-01-DG.

Foliage of plant infected with Aphanomyces cochlioides. Note the dull green of newer leaves and wilting and yellowing of older leaves.

Courtesy of Robert M. Harveson, Plant Pathologist, Nebraska Cooperative Extension

Young root infection showing yellowish-brown internal discoloration.

courtesy of C. M. Rush, Professor of Plant Pathology, Texas A&M University

Sugar beet roots with severe lateral root infections and rotted root tips.

Windels, C. E. 2000. Aphanomyces root rot on sugar beet. Online. Plant Health Progress:10.1094/PHP-2000-0720-01-DG.

Roots infected at the distal end, resulting in a tip rot.

Courtesy of Robert M. Harveson, Plant Pathologist, Nebraska Cooperative Extension

Roots showing internal discoloration at the tip of the taproot.

Courtesy of Robert M. Harveson, Plant Pathologist, Nebraska Cooperative Extension

Severe Black RootCourtesy of Robert M. Harveson, Plant Pathologist, Nebraska Cooperative Extension

Beets infected with A. cochlioides that have recovered. Latent infection is seen as the scabby, superficial lesions on roots.

Courtesy of Robert M. Harveson, Plant Pathologist, Nebraska Cooperative Extension

Mature roots that are malformed and scarred in appearance are indicative of Aphanomyces-infected seedlings and young plants that have recovered in dry weather

Courtesy of Robert M. Harveson, Plant Pathologist, Nebraska Cooperative Extension

Cultural Practices:

Some basic cultural practices are:• Plant early into cool soils.• Do not evaluate for moisture stress in the

afternoon.• If already infected, do not over water.• Control weed populations.• Produce a well-established crop early.

Chemical Control

• Chemical control is possible only as a seed treatment with the fungicide Tachigaren (active ingredient = hymexazol). This method can significantly reduce post emergent damping-off of seedlings and help to establish a vigorous stand; however, it is effective only with the black root seedling phase of the disease.

Chemical Controls

Fleishman, Dennis & Horny, Paul, July 1999, Sugarbeet Advancement: Tachigaren Trial, www.maes.msu.edu/ressta/saginawvalley/SBA1999/p37.PDF

Cultural ControlsBresnahan,G.A., Dexter,A.G., Windels,C.E., Brantner,J.R., and Luecke,J.L..2001. Influence

of Soil pH on Aphanomyces Cochloides in Sugar Beet.

Biological Controls

• Use of plant growth-promoting Rhizobacteria (PGPR)

• This leads to disease escape when the growth promotion results in shortening the time that a plant is in a susceptible state such as in the seedling stage when damping off is a problem

• Also the bacteria produce chemicals that are antagonistic to the pathogen

Resistant Varieties:

• There are several resistant varieties of Sugar beets available.

• There was a study conducted that tested many different species to determine resistance levels.

• Beta vulgaris maritima was found to be the most resistant variety to Aphanomyces cochlioides.

Results of a study showing the most resistant varieties of Beta species.

Luterbacher, M.C. et al. 2000. Disease Resistance in Collections of Beta Species. Journal of Sugar Beet Research. Vol. 37 No.3 pp.39-47

Beta Species Accessionstested

Aphanomyces BMYV Powderymildew

% % %B.v. maritima 97-100 26 14 8

B.v.v. FodderBeet

42 7 45 2

B.v.v. GardenBeet

67-71 9 44 3

B.v.v. Leaf Beet 106-111 6 22 5

Future Control Strategies

• IPM – Due to the lack of variety in pesticide control it is

important to practice a diverse management program focusing on targeting the pathogen while minimizing environmental damage

• Future Research– Research is necessary to gain more resistant

varieties of sugar beet and to find weaknesses in the pathogen that can be exploited

Summary

• Aphanomyces cochlioides continues to be one of the major pathogens associated with black root of sugar beets in the humid area of the United States. The most effective means of controlling the disease thus far has been by the use of resistant varieties together with a proper crop sequence, adequate fertilization and the use of seed treated with a fungicide