2019 ASHS Annual Conference

Downy mildew, caused by the oomycete Peronospora effusa [=P. farinosa f. sp. spinaciae] is the most devastating disease in spinach. Utilizing host genetic resistance is the most effective disease management method particularly for organic production. Identification of new resistant sources and understanding the genetic basis of disease resistance mechanism is crucial to sustain the spinach industry in the United States. The Pfs shows race specificities to the resistant host and 17 races have been reported in spinach. Over 10 new Pfs races were identified in the last two decades and the new races overcome the resistance genes deployed in the released resistant cultivars. Rapid emergence of new races and subsequent breakdown of resistant genes demands search for new resistance sources, developing linked marker, and incorporating the resistant loci into elite cultivars. To identify the molecular markers linked to resistance against Pfs16, we investigate spinach F2 population generated from a cross of Whale x Lazio. Whale is resistant to Pfs16 while Lazio is susceptible. Seedling progenies were inoculated with Pfs16 in the growth-dew chamber facility and were scored for disease response. The downy mildew disease response fits a 3:1 segregation ratio (P = 0.7) implying dominant allele governing the resistance mechanism. DNA from parents and all progeny were submitted for genotyping by sequencing (GBS). Single nucleotide polymorphism (SNP) markers identified from GBS will be used to construct a genetic map and map the resistance locus. Tightly linked SNP markers and the flanking sequences identified following the mapping effort will be used to screen for candidate genes involved in disease resistance. The newly identified markers linked to the resistant allele can be used in marker-assisted selection and pyramiding of multiple resistance genes.