Inheritance and Selection for Resistance to Phialophora Gregata in Soybeans
Hanson, Peter Mitchell
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https://hdl.handle.net/2142/71637
Description
Title
Inheritance and Selection for Resistance to Phialophora Gregata in Soybeans
Author(s)
Hanson, Peter Mitchell
Issue Date
1987
Department of Study
Agronomy
Discipline
Agronomy
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Agriculture, Agronomy
Abstract
Brown stem rot (BSR) caused by Phialophora gregata (Allington and Chamberlain) W. Gams is an important disease of soybeans (Glycine max (L.) Merr.) especially in the North Central U.S. Field and greenhouse experiments were initiated to study the inheritance of BSR resistance in a soybean plant introduction (PI), to examine the relationship between BSR disease symptoms and BSR-caused seed yield loss, and to determine the usefulness of root-dip inoculation as a means to evaluate soybeans for BSR resistance in the field.
F$\sb{2}$ plants and F$\sb{2}$-derived families in the F$\sb{3}$ generation of crosses PI437833 x 'Century', and PI437833 x L78-4094 were evaluated in the greenhouse for BSR resistance. Plants were classified as resistant or susceptible based on the presence or absence of foliar necrosis 5 weeks after inoculation. Resistance in PI437833 to BSR is conditioned by a single dominant gene, designated Rbs $\sb{2}$.
Century and 'BSR 201' soybean strains were inoculated in the field with a Type I isolate of P. gregata, or with water. Measurements of BSR leaf and stem symptoms, and pod and seed dry weight were recorded at five growth stages. BSR reduced pod and seed weight of Century by an average of 20% at R7.0, but BSR 201 was not affected. The reduction of pod and seed dry weight was greatest between R6.5 to R7.0, and was highly correlated to foliar necrosis.
Soybean strains (28) were root-dip inoculated in the field and greenhouse with a Type I isolate of P. gregata. Plants were scored for BSR resistance on the number of nodes showing necrotic foliage. In the first year, BSR leaf symptoms appeared 7 weeks after inoculation in the field, and were similar to greenhouse results. Leaf symptoms did not develop on susceptible plants in the field in the second year.
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