Submitted to: American Society of Sugarbeet Technologists
Publication Type: Proceedings
Publication Acceptance Date: 6/5/2006
Publication Date: 2/26/2007
Citation: McGrath, J.M., Nagendran, S. 2007. Discovery of resistance to seedling disease caused by Rhizoctonia solani AG2-2, description of the host-pathogen interaction, and development of a seedling disease screening nursery. Proceedings of American Society of Sugar Beet Technologists 2007 Biennial Meeting. 44:151.
Technical Abstract: Sugarbeet seedling mortality caused by the damping-off pathogen Rhizoctonia solani AG2-2 is perhaps the most serious biotic cause of stand failure in the Michigan growing regions, and is likely important worldwide. Resistance to the seedling disease has not been available. Resistance would be beneficial in establishing uniform stands of beets, and the resulting improved harvest quality of similarly sized beets delivered to the factory. An initial set of experiments to examine disease progression in susceptible hosts was conducted with high and low virulence isolates in order to identify targets of opportunity for biotechnology manipulation, and during this work, the crown-and-root-rot (CRR) resistant release EL51 was demonstrated to survive early challenge by the highly virulent isolate R1. Subsequently, the host-pathogen interaction was examined in detail using light and fluorescence microscopy. The resistance reaction was characterized by the failure of the pathogen to ramify the water-conducting stele tissues of the young hypocotyl, with an apparent barrier at the narrow endodermis. Field experiments were initiated to determine if resistance was expressed under agronomic conditions by a simple modification of traditional CRR screening to that of inoculating 3-week-old seedlings. Full stands of EL51 were present at the end of the season, and stands of the susceptible hybrid USH20 were decimated. In 2006, the entire East Lansing CRR nursery was inoculated at the seedling stage, and clear germplasm differences in disease reaction were seen. The disease continued to develop throughout the growing season, suggesting both seedling and CRR resistance can be selected simultaneously with a simple modification in the timing of inoculation.