I choose this microbe because one of my friends, who happens to work at his family's green house, absolutely detests what it does to their ornamental plants. As you can tell, S. rolfii isn’t a microbe that is helpful; rather, it destroys crop and ornamental plants. This soil fungus is directly associated with Southern Blight, also known as crown rot and white mold.
The common symptoms and signs of infection are yellow wilting of the plants lower leaves, dieing back from the tips to the stem. Dark brown lesions may also be seen on stems along with cottony white, thread-like material called mycelium. The most distinguishing feature is its sclerotia, a small, round, brown to tan colored structure resembling a mustard seed in the soil around the plant on even on it. This feature allows for survival in wintry conditions when under cover of snow or mulch. S. rolfii may be confused with Sclerotina sclerotiorum which also produces mycelia, both of which have a wide range of hosts.
S. rolfii is known to infect around 200 different genera of ornamental plants and field crops within a variety of regions that provide warm or hot weather with high moisture. Initial infections commonly occur in late spring, when air temperatures rise above 75°F; several days of drought followed by high soil moisture appears to be conducive to high levels of sclerotia germination. Optimal conditions for disease development are air temperatures of 85° to 95°F. A few plants species that are susceptible to infection are: beans, carrots, corn, cucurbits, crucifers, eggplant, onions, peppers, radish, taro, tomatoes, yams, daylily, astilbe, hostas, peony, phlox, ajuga, delphinium, potato, bentgrasses, bluegrass, fescues, and ryegrasses. Once the plant and soil have been infected, you may want to replace them with plant species not susceptible to the disease such as Abutilon, Hyacinth, Alyssum, Bells of Ireland, lavender, Cleome, Mertensia, cockscomb, Portulaca, four o’clock, primrose, English daisy, statice, Fritillaria, tansy, globe amaranth, Freesia, Gypsophila, and Geranium (wild geranium). Replacing infected soil with the previously mentioned species and avoiding further spread through infected plant parts and soil are the best ways to deal with this threat other than prevention and licensed chemicals. The spores can survive several years so extended crop rotation may be necessary in soils that have previously been infected.
References:
http://www.ctahr.hawaii.edu/adap2/information/pubs/2000-17.pdf
http://www.extension.umn.edu/projects/yardandgarden/ygbriefs/p152southernblight.html
http://www.ppdl.org/dd/id/southern_blight-hosta.html
http://aggie-horticulture.tamu.edu/tomatoproblemsolver/roots/23.html
http://www.ipm.ucdavis.edu/PMG/r785100911.html
http://www.caf.wvu.edu/kearneysville/disease_descriptions/southernblight.html
*Disclaimer - This report was written by a student participaring in a microbiology course at the Missouri University of Science and Technology. The accuracy of the contents of this report is not guaranteed and it is recommended that you seek additional sources of information to verify the contents.
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