Electronic Thesis and Dissertation Repository


Master of Science




Dr. Mark Gijzen


The oomycete Phytophthora sojae causes stem and root rot of soybean plants. The interaction of pathogen avirulence (Avr) and host resistance (R)-genes determine the disease outcome. The Avr3a mRNA transcript level is variable among P. sojae strains and determines virulence towards the R-gene Rps3a. To study the inheritance of virulence, genetic crosses and self-fertilizations were performed. A cross between P. sojae strains ACR10 and P7076 causes transgenerational gene silencing of Avr3a allele, and this effect is meiotically stable up to the F5 generation. However, test-crosses of F1 (Avr3aACR10/Avr3aP7076) with strain P6497 result in expression of Avr3a in all progeny and release of silencing of the Avr3aP7076 allele. Progeny from P6497 X ACR10 crosses showed unusual inheritance for Avr3a expression. Overall, we conclude that Avr3a gene silencing is strain specific and could rely on epistatic factors. This study will lead to a better understanding of infection and virulence mechanisms that will help to better manage and safeguard soybean production.