The Development of Simple Methods for the Maintenance and Quantification of Polymyxa graminis

Polymyxa graminis, a root endoparasite of several cereal species, is considered to be non-pathogenic but serves as a vector of various plant viruses belonging to the genera Bymovirus, Furovirus, and Pecluvirus. Specifically, it reduces barley productivity by transmitting the Barley Yellow Mosaic Virus (BaYMV). To date, due to its obligate biotrophic property, no artificial culturing of P. graminis was reported and its quantification was also technically challenging. Here, we developed a novel and simple method to infect P. graminis within sterile barley roots in contamination free by preparing nearly pure zoospore inoculum. Such artificial maintenance of P. graminis was verified based on the presence of various developmental stages in infected barley roots under microscope. In addition, the population of resting spores in host tissue was determined by establishing standard curve between manually counted number of spores and C_t values of 18S rDNA amplification using quantitative real-time PCR. Furthermore, it was validated that standard curve generated was also applicable to estimate the abundance of P. graminis in soil environments. In conclusion, the present study would help to generate a system to investigate the etiological causes as well as management of plant diseases caused by P. graminis and BaYMV in tissue and soil.