ARS | Publication request: Spinach downy mildew: overview of races and the development of molecular markers linked to major resistance genes.

Submitted to: Advances in Downy Mildew Research
Publication Type: Book/Chapter
Publication Acceptance Date: May 1, 2007
Publication Date: July 1, 2007
Citation: Correll, J. C., Feng, C., Irish, B. M., Koike, S. T., Morelock, T. E., Bentley, T. C., and Tomlinson, A. N. 2007. Spinach downy mildew: overview of races and the development of molecular markers linked to major resistance genes. In: Lebeda A. and Spencer, P., editors. Advances in Downy Mildew Research. Vol. 3 Proceedings of the 2nd International Downy Mildew Symposium. Palcky University in Olomouc and JOLA, v.o.s., Kostelec na Hane (Czech Republic). p.135-142.

Interpretive Summary: Spinach has become an important leafy vegetable crop as evidenced by recent increases in production and per capita consumption. Downy mildew is considered one of the most important spinach diseases and production constraints. To date, ten downy mildew races have been described on a set spinach differentials lines, which consist mostly of obsolete, difficult to obtain hybrid cultivars. In an effort to address the lack of accessibility to these differentials, an initial open pollinated, non-hybrid differential line was generated. This new differential line can be regenerated easily, assist in race identification, help to elucidate resistance genetics, as well as serve as a valuable resource for molecular marker development. Moreover, the outlined procedure will serve as a guideline for the future development of open pollinated differential lines with a common genetic background, yet differing in resistance.

Technical Abstract: Spinach (Spinacia aleracea) has become an increasingly popular leafy vegetable crop, particularly in the United States. Recent trends have shown a substantial increase in per capita fresh market spinach consumption with a corresponding increase in production. As a result, spinach production practices have changed significantly over the past decade. And these changes have impacted downy mildew, caused by Peronsopora farinosa f. sp. spinaciae. Ten races of the pathogen have been reported in the U. S. and 9 races in the European Union. Races of the downy mildew pathogen are currently identified by qualitative disease reactions on a genetically diverse set of spinach differentials. Maintaining the differential set of cultivars and reference isolates of the pathogen is problematic. The current differentials include genetically diverse spinach cultivars, some of which of which are hybrids that are no longer produced. Development of open pollinated near-isogenic lines (NILs), each containing a single disease resistance locus within an otherwise susceptible and uniform genetic background, would facilitate identification of races of the downy mildew pathogen, could greatly aid in understanding the genetics of resistance, can could be a valuable resource for developing molecular makers linked to major disease resistance genes. The objectives of this effort were to initiate the development of a set of peon pollinated NILs, using different sources of major genes for resistance and utilize these genetic resources to develop molecular markers linked to major disease resistance loci.