Aphanomyces Cochlioides - Root Rot of Sugarbeet

1. Aphanomyces Cochlioides - Root Rot of Sugarbeet Krista Lueth Jeff Corliss Justin Bickel

2. 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

3. Area Cultivated and Production of Sugar Beets in the Main Producing Countries and RegionsFAO/EBRD cooperation. 1999 Sugar Beets/White Sugar. FAO/EBRD Agribusiness Handbooks 4:35-43

4. Aphanomyces cochlioidesA Water Mold • Kingdom - Chromista • Phylum - Oomycota • Class - Oomycetes • Order - Saprolegniales • Family - Saprolegniaceae • Genus - Aphanomyces • Species - Aphanomyces cochlioides

5. 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

6. 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.

7. 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

8. 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.

9. Permanent wilting of plant infected by Rhizoctonia solani leading to Rhizoctona root rotCourtesy of Robert M. Harveson, Plant Pathologist, Nebraska Cooperative Extension

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

12. 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

13. Asexual Reproduction of Saprolegniahttp://web1.manhattan.edu/fcardill/plants/protoc/sapro2.html

14. Asexual Reproduction and Secondary Inoculum in Oomycetes A Movie

15. Sexual Reproduction of Saprolegniahttp://web1.manhattan.edu/fcardill/plants/protoc/sapro3.html

16. 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.

17. 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

18. Here you see a closeup slide of an Oogonia of Saprolegnia sp.http://www.uwinnipeg.ca/~simmons/saprolg2.htm

19. Light microscopy of small feeder root. Circular, darkly stained structures are overwintering oospores.Courtesy of Robert M. Harveson, Plant Pathologist, Nebraska Cooperative Extension

20. 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

21. 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.

22. 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

23. 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

24. 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.

25. 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

26. Young root infection showing yellowish-brown internal discoloration.courtesy of C. M. Rush, Professor of Plant Pathology, Texas A&M University

27. 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.

28. Roots infected at the distal end, resulting in a tip rot.Courtesy of Robert M. Harveson, Plant Pathologist, Nebraska Cooperative Extension

29. Roots showing internal discoloration at the tip of the taproot. Courtesy of Robert M. Harveson, Plant Pathologist, Nebraska Cooperative Extension

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

31. 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

32. 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

33. 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.

34. 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.

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

36. 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.

37. 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

38. Resistant Varieties: • There are several resistant varieties of Sugar beetsavailable. • 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.

39. Results of a study showing themost 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

40. 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

41. 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