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Title:Effect of cover crops on suppressing soilborne diseases of soybean and the association of green stem disorder with anthracnose, charcoal rot, and soil moisture
Author(s):Wen, Liwei
Advisor(s):Hartman, Glen L.; Eastburn, Darin M.
Department / Program:Crop Sciences
Discipline:Crop Sciences
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):soybean soilborne diseases
cover crops
green stem disorder
charcoal rot
soil moisture
Abstract:Suppressive soil is one in which a pathogen does not become established or persist, or becomes established but causes little or no damage in comparison to what would develop in a conducive soil. Some cover crops can foster the development of suppressive soils. Cover crops are more commonly used in the management of soilborne diseases of high value crops like fruits and vegetables and there is less information on their effectiveness in agronomic crops like soybeans. In this study, field trials were conducted from 2010 to 2012 on four farms at four locations in Illinois to evaluate the effectiveness of four cover crops (cereal rye, brown mustard, winter canola, and winter rape) on maintaining soybean stands, decreasing the incidence and severity of soybean diseases, changing soil pathogen populations, changing soil microbial community structures, and increasing soybean yield. Data of cover crop biomass, soybean stand, foliar and root disease levels, and yield were taken over two seasons to evaluate the effectiveness of different cover crops. Soil samples were collected after cover crops to compare pathogen population levels and the soil microbial communities among various cover crop treatments. The cover crops were successfully established at all the four experiment trial locations every year. Cereal rye and rape had better performance than the other two cover crops, including that cereal rye generated significantly more biomass than the other cover crops (P < 0.05), and cereal rye and winter rape significantly improved soybean stands in plots infested with Rhizoctonia solani. In some cases, cereal rye increased soil supressiveness to R. solani and F. virguliforme, as measured in greenhouse bioassays with sampled field soils. Cereal rye and rape also significantly decreased the amount of soybean cyst nematode in the soil. Cereal rye significantly improved yield in soils where Rhizoctonia root rot was a problem. Soilborne pathogen populations were not significantly different over cover crop treatments, and none of the cover crops resulted in bacterial or fungal richness changes or obvious bacterial or fungal community structure shifts. Green stem disorder (GSD) of soybean [Glycine max (L.) Merr.] is an abnormal condition in which soybean stems stay moist and immature after pods and leaves have fully dried and matured. Delayed maturity of soybean stems has not been found to cause yield loss; however, it significantly increases the difficulty of harvesting the grain because the moist green stems of plants are more difficult to cut than plants without green stems. GSD is referred to as a disorder rather than disease since the cause of GSD is still unknown. The goal of my research was to investigate GSD and its occurrence within two soybean cultivars when inoculated or mock-inoculated with two soybean pathogens under different soil moisture conditions. The specific objectives were to determine the: (i) association of GSD with infection of each fungal pathogen alone; (ii) interaction between M. phaseolina and C. truncatum infection on GSD incidence; and (iii) interaction between soil moisture and M. phaseolina infection on GSD incidence. Two soybean genotypes differing in relative sensitivity towards GSD based on prior field results were used in all experiments. Stine 2463, a GSD sensitive cultivar, and Hughes 441, a GSD insensitive cultivar were used in five experiments. Soybean plants were mock-inoculated and inoculated with C. truncatum, M. phaseolina, or both. Overall the results of the five experiments indicated that GSD incidence was independent of soil moisture level (P > 0.05); there was a significant (P < 0.0001) negative relationship between M. phaseolina inoculation levels and GSD incidence for Stine 2463, R² = 0.6376, and Hughes 441R, R² = 0.6323, with incidence of GSD decreasing concomitantly with increases in M. phaseolina inoculum levels: and there was a significant negative association (P < 0.01) for lower GSD incidence with higher percent rate of C. truncatum infection.
Issue Date:2013-05-24
Rights Information:Copyright 2013 Liwei Wen
Date Available in IDEALS:2013-05-24
Date Deposited:2013-05

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