The Advantages and Inheritance of Brown Stem Rot Resistance in Soybeans and The Implications to Breeding for Resistance (Phialophora Gregata, Disease Resistance)

60 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1984.Brown stem rot (BSR) is a fungal disease of soybean {Glycine max (L.) Merr.} caused by Phialophora gregata Allington and Chamberlain (W. Gams). Field and greenhouse tests were performed to study the effect of BSR resistance on soybean yield, to study the heritability and genetics of BSR resistance, an to develop efficient methods of selecting for BSR resistance.Field studies indicated that BSR resistance prevents yield loss in fields where susceptible soybean genotypes show BSR leaf symptoms. Resistance was associated with a 12 to 16% yield advantage in such fields. Efficient selection for BSR resistance can be accomplished in the greenhouse and in the field based on the presence or absence of leaf symptoms.When F3 populations segregating for BSR resistance were screened under controlled greenhouse conditions, heritability estimates for BSR leaf symptoms were two to three times higher than heritability estimates for stem symptoms. Greenhouse selection based on leaf symptoms will be more effective than selection based on stem symptoms.An attempt was made to detect Mendelian segregation patterns for BSR resistance in the segregating populations. Cluster analysis based on leaf symptom mean, stem symptom mean, and leaf symptom variance was used as the basis for classifying F3 families. A single dominant gene, designated Rbs, can account for segregation in one population. Segregation in another population appears to be controlled by Rbs plus another gene which duplicates or modifies the effect of Rbs. Efficient selection for Rbs can be accomplished through greenhouse screening.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD