Interaction between Phytophthora megasperma f. sp. glycinea and Glycine max

The Glycine max (soybean): Phytophthora megasperma f. sp. glycinea (Pmg) pathosystem has served as a model for elucidating the mechansim of incompatibility in gene-for-gene interactions. This interaction was accurately and precisely investigated on the taproots of aeroponically-grown soybeans. An aeroponics system, developed for this investigation, provided facile access to the roots for direct application of inoculum, observations and measurements. Taproots were inoculated by submerging the root tip in a zoospore suspension.Disease symptoms first appeared as brown necrotic flecks (lesions) at the site of infection. Lesion development was influenced by the presence or absence of an effective Rps gene, the effective Rps gene present, the cultivar, temperature, time, age of plant at inoculation, inoculum concentration, and aggressiveness of the Pmg isolate. Soybean cultivars with and without effective Rps genes formed incompatible interactions. In the presence of an effective Rps gene, the interaction between soybean and Pmg was always incompatible, although there was variation in the magnitude of the interaction. In the absence of an effective Rps gene, the interaction between soybean and Pmg formed a continuum from an incompatible interaction characterized by a small necrotic fleck, to a compatible interaction characterized by an expanding lesion that extended from the root tip to the cotyledons.Linear spline models consisting of two intersecting straight lines with slopes B1 and B2 were used to describe lesion expansion over time on the taproots of seven soybean cultivars following a compatible interaction. Estimates of B1 among the cultivars did not differ significantly. Estimates of B2 did differ significantly and provided an accurate description of host resistance. Estimates of B1 did differ significantly among isolates of Pmg and provided an accurate description of pathogen aggressiveness.U of I OnlyETDs are only available to UIUC Users without author permissio