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Title:Analyses of Interactions Between Soybean and Phialophora Gregata
Author(s):Willmot, David Brett
Doctoral Committee Chair(s):Nickell, Cecil,
Department / Program:Agronomy
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Agriculture, Agronomy
Abstract:Resistance to the fungal pathogen, Phialophora gregata (Allington and Chamberlain) W. Gams, the cause of brown stem rot (BSR) in soybean (Glycine max (L.) Merr.), is critical to prevent yield losses in the northern USA. The objective of the first phase of this study was to determine the effect of P. gregata source on aggressiveness and physiologic specialization. Isolates were derived after two cycles of infection from four host cultivars in ten sites. Out of twenty-seven isolates, two were virulent on PI 437833. BSR 201 was resistant to all isolates. Isolates derived from BSR 201 had lower aggressiveness. The data showed a high level of variability for aggressiveness and the first report of physiologic specialization in P. gregata.
The second research phase objectives were to determine the pattern of inheritance of BSR resistance in PI 437970, study allelic relationships with $Rbs\sb1$ and $Rbs\sb2$ and gain similar preliminary information for PI 437685D, PI 86150 and PI 423930A inoculated in the field and greenhouse. Resistance is conditioned by single dominant genes in all four cultivars. The gene in PI 438970 demonstrated duplicate dominant epistasis with $Rbs\sb1$ and $Rbs\sb2$ indicating a third distinct gene designated $Rbs\sb3$.
The third research phase objectives were to develop an efficient evaluation method for BSR resistance and determine the influence of pathogen isolate on cultivar reactions from two in vitro assay methods. One in vitro method utilized P. gregata phytotoxins to differentiate excised cotyledon reactions in a callus inducing medium containing 50% crude fungal culture filtrate. Ratings on degree of green color retained and level of callus initiation were compared to uninoculated broth control treatments. In the second in vitro method, callus pieces were placed on growth media with 17% culture filtrate. Among the ten cultivars by three isolate treatments--80, 100 and 90% of the BSR reaction classifications according to the cotyledon method corresponded to the greenhouse assay classifications. The callus piece method had a 73% average correspondence. Physiologic specialization was demonstrated in parallel in vitro assays.
Issue Date:1988
Description:99 p.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1988.
Other Identifier(s):(UMI)AAI8823291
Date Available in IDEALS:2014-12-16
Date Deposited:1988

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