Purpose
Phytophthora stem and root rot (Phytophthora sojae) is a major soybean disease throughout the Midwest. Two general types of disease resistance exist in soybean.
- Race-specific resistance to the over 30 races of P. sojae is conditioned by soybean Rps (resistance to P. sojae) genes that occur at eight (8) known genetic loci. While these individual genes offer strong resistance, due to its simple genetic basis, such resistance can be readily defeated by the development of new races of the pathogen.
- General resistance to P. sojae (also called partial resistance) involves several genes and is thus genetically more complex. Although it does not provide as strong a resistance, it is a highly attractive alternative to race-specific resistance, because it is thought to be more stable or durable. It may also provide resistance to all races of P. sojae. However, the genes conferring this resistance have not been as thoroughly characterized in soybean.
In both resistance types, most aspects of plant defense are induced only after pathogen attack. Such induced defense responses include local, near-systemic and truly systemic forms of resistance. Depending on the type of resistance, the host, the host tissue and the pathogen, a wide range of cellular and molecular defense mechanisms can be involved.
The inter-relationships of the actual defense responses are not well understood. The Graham lab has demonstrated that in soybean, race-specific resistance involves the race-specific regulation of many of the same defenses induced in general resistance. The purpose of this study is to identify the genetic components of most importance to both race specific and general resistance and how they are related to one another. The evidence from the project should lead to new genetic and chemical strategies for control of Phytophthora.
Procedure
This study will employ a new technique called "gene silencing" to provide rigorous and direct genetic evidence for those defense genes that are most critical to resistance to this devastating pathogen. In other words, the Graham and Yu research team have developed a gene silencing protocol for soybean roots that allows them to selectively knock-out the expression of individual genes putatively related to defense and thus rigorously evaluate their true contribution to disease resistance.
In the study, they will individually silence genes belonging to two general classes thought to be most important to soybean root and hypocotyls resistance to P. sojae.
Impact
This project will address the profitability of soybeans at the production level through basic research that will lead to identification of genetically defined processes and traits that can be modified for enhanced disease resistance.
The work should lead to the identification of some of the key defense genes underlying general and race-specific resistance in both soybean roots and stems. This information will be valuable for both genetic and chemical strategies for disease control. The identification of key genes will provide markers and assist breeders in developing the most highly and broadly resistant lines.
The researchers also look forward to the possibility of the development of natural or chemically based elicitors tailor made to enhance natural soybean resistance through the selective control of key genes.
