Spatial and temporal analysis of chitinase accumulation and pathogen colonization in soybeans with tolerance to Phytophthora sojae infection

Tolerance to Phytophthora root rot (PRR) in soybean is a highly-heritable, multi-genic trait. Tolerance is a desirable trait in soybean lines because it is not race-specific and cannot be overcome by a buildup of a specific Phytophthora sojae races, unlike race-specific, single gene resistance. The plant-pathogen interactions occurring in the tolerant reaction to disease have not been thoroughly characterized.; The objective of this research was to characterize components of the plant-pathogen interaction occurring in tolerant soybeans infected with P. sojae that may be involved in limiting pathogen colonization and disease development.; One important aspect of this interaction is the timing of localized and systemic defense responses. Using chitinase as a marker of defense response activation, I characterized spatial and temporal patterns of chitinase isoform expression. I found that unique chitinase isoforms accumulate in soybean roots infected with P. sojae. Some of these isoforms are expressed earlier in tolerant cultivars than in susceptible cultivars and some of these isoforms are expressed systemically in tolerant cultivars and only locally in susceptible cultivars. This has helped to elucidate differences in the plant defense response between tolerant and susceptible cultivars.; Another important component of this interaction is the events involved in pathogen colonization of the root. To analyze the timing and extent of P. sojae colonization of the soybean root system, I utilized real-time PCR to detect and quantify P. sojae within the soybean root system. My results suggest P. sojae colonizes tolerant cultivars more slowly and to a lesser degree than susceptible cultivars.