Detached Leaf Assay: A Rapid Screening Technique to Study Foliar Diseases of Soybean

A detached leaf screening technique was developed to evaluate soybean for resistance to powdery mildew (Microsphaera diffusa) at ISU and rust (Phakopsora pachyrhizi) at GXAAS. In powdery mildew, first fully opened trifoliate leaves were collected excising at the base of petiole from three varieties, placed two leaves per 14-cm dia × 2-cm ht sterile Petridish containing a layer of wet wahtman#1 filter paper and sponge (10-cm L × 5-cm W × 1-cm H). Leaves placed in Petri dishes for detached leaf assay (DLA) and the seedlings grown in plastic cups for whole plant assay (WPA) were spray inoculated separately with 1 × 10(^3) and 1 × 10(^4), and 1 × 10(^5) conidia ml(^–1) and distilled water spray maintained as control. Inoculated leaves and seedlings were incubated at 24°C in fluorescent light (radiation of 5.48 J/second × m(^2) area) with 16h photoperiod for two weeks and were evaluated for disease reaction. Of the three varieties tested, Pioneer 93M42 showed higher severities compared with Latham 2485 and Pioneer 92M40RR and of the three concentrations, 1 × 10(^5) showed higher severities compared with other two. The DLA and WPA were tested for soybean rust pathogen using 10 cultivars and six isolates collected from three locations in China. Of the ten genotypes tested Ye-Qing × Bu-Lei-Mei showed S-S reaction across all the isolates and reactions of other genotypes against the isolates tested are presented in this paper. Also, we discuss results of the techniques tested against P. pachyrhizi, and M. diffusa. Main advantage of the DLA method is to facilitate assaying soybean response to multiple fungal pathogens in a short period. Disciplines Plant Pathology Comments This poster was presented at the 2007 North Central Division Meeting, June 19–21, 2007, Lafayette, IN. This article is available at Iowa State University Digital Repository: http://lib.dr.iastate.edu/plantpath_conf/2