An in vitro method for examining infection of soybean roots by Macrophomina phaseolina

A general limitation when studying the early events in the infection process of a soil borne plant pathogen is the detection of the hypha arrival at the root surface. We describe a new method to infect plants with soil borne pathogens that may be applicable to examination of the prepenetration and the penetration phases of other soil borne fungi as well as the early responses of the host plant. Development of the in vitro method allowed us to obtain roots of soybean plants infected with Macrophomina phaseolina to characterize the infection process. Using two infection systems we provide evidence that M. phaseolina produces hyaline structures which are undetected by staining methods based on fungal chitin dyes and were identified exclusively by stained lipid vesicles produced by the pathogen within host tissues.