Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Science

Program

Biology

Supervisor

Bernards, Mark

Abstract

Ginseng is a perennial plant that is prone to replant disease (GRD), in which ginseng cannot be re-cultivated in a former ginseng garden, largely due to pathogens in the soil. The current mitigation strategy is soil fumigation, but fumigants are being phased out. I assessed the use of solarization as an alternative to fumigation in treating GRD. Two factors, i.e., the timing and duration of solarization, were evaluated, using temperature comparisons, stand counts and root disease as indicators. I found that solarization of raised beds resulted in higher soil temperatures compared with unsolarized beds. While the duration of solarization did not improve the stand count in the first growth year, there was a significant increase in yield of marketable roots, and significant reduction in Illyonectria mors panacis root rot. I conclude that solarization is a promising alternative to fumigation to reduce the persistence of GRD in former ginseng gardens.

Summary for Lay Audience

Ginseng is a crop that is grown for its roots and is primarily used in Traditional Chinese Medicine. One major issue is replant disease, a condition in which ginseng cannot be re- planted in the same fields where it was grown previously due to disease-causing organisms in the soil. The current treatment against replant disease involves the use of chemical fumigants, which are hazardous to the environment. Solarization is a safer alternative. This involves harnessing the sun’s heat to warm the soil by placing clear plastic tarps over it. The increased soil temperature under the tarp can kill off detrimental disease-causing organisms. To evaluate the effectiveness of solarization on preventing ginseng replant disease, I conducted experiments in a former commercial ginseng garden known to harbor a significant level of replant disease.

My experiment focused on two factors. First, I looked at when to conduct the solarization treatment. Ginseng is usually cultivated in raised bed gardens, which are formed prior to planting by ploughing the soil into mounds. Since solarization typically only affects the top 10-15 cm of soil, forming beds after solarization may introduce un-solarized soil to the surface of the raised beds during their formation. Consequently, for my project, the bed was raised prior to solarization so that seeds would eventually be planted into solarized soil. Second, I considered the duration of the solarization process. I compared the impact of four different durations of solarization: zero, two, four, and six weeks. In a parallel experiment in the same replant garden, some flat ground plots were also solarized (prior to raised bed formation) for comparison.

To evaluate the effectiveness of the solarization treatment, I measured plant survival during the first year of cultivation, and monitored the roots for signs of disease. Initially, plant survival was higher in raised bed treatments. A minimum of Four Weeks of solarization was beneficial to plant quantity. This also reduced signs of disease symptoms especially those that caused replant disease. Overall, I concluded that solarization of raised soil beds could make an effective alternative to fumigation to eliminate replant disease in ginseng gardens.

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