Identification and Cultivar Reaction to Three New Races of the Spinach Downy Mildew Pathogen from the United States and Europe

Abstract

Since 1996, commercial spinach cultivars with resistance to four previously described races of Peronospora farinosa f. sp. spinaciae (races 1, 2, 3, and 4) were observed with high incidences of downy mildew both in California and Europe. Isolates of P. farinosa f. sp. spinaciae collected in California between 1997 and 2001, Arizona in 1999, and a single isolate collected in the Netherlands in 1996 were examined for their disease reaction on differential spinach cultivars and a set of commercial spinach cultivars. Disease reactions on the differential cultivars indicated the occurrence of three new races of P. farinosa f. sp. spinaciae. Two newly identified races, designated race 5 (isolate CA1) and race 6 (isolate SP1), were detected in the United States. The isolate from the Netherlands also was distinct and designated race 7 (isolate JVN7). Some cultivars with resistance to races 1, 2, 3, and 4 were susceptible to race 5, whereas others were resistant, indicating that resistance to a given race may be governed by different genes (or alleles) depending on the source of resistance. A survey of races in California indicated that races 5 and 6 predominated. Although the majority of the cultivars examined were susceptible to race 6 based on the traditional qualitative cotyledon inoculation assay, significant quantitative differences in resistance to race 6 were observed using a true-leaf greenhouse screening procedure. Although more work is needed to confirm the results of the true-leaf assays, the quantitative resistance observed using this procedure appears to be race specific.

Spinach: better management of downy mildew and white rust through genomics

“…Although inheritance studies were not conducted, seed from the two accessions was increased and distributed to breeders in the private sector. The rapid emergence of races 5, 6,7,8,9,10,11, and two additional deviating strains UA12, and UA13 (Correll et al 1990;Correll 1998;Handke et al 2000;Irish 2004;Irish et al 2003;2007) ignited efforts to broaden host resistance and develop a more thorough understanding of the genetics of resistance to Pfs.…”

Multiplex real-time PCR assays for detection of four seedborne spinach pathogens

“…Eleven new races and additional novel strains of P. farinosa f. sp. spinaciae have been identified in the past two decades (Correll et al 1990;Irish et al 2003Irish et al , 2007Feng et al 2014), and the global distribution of some races is consistent with seedborne transmission (Feng et al 2014). Verticillium dahliae, a seedborne pathogen of spinach that causes a vascular wilt, has been reported in commercial production fields in the USA, Canada and the Netherlands (Snyder and Wilhelm 1962;Van der Spek 1972, 1973Sackston and Sedun 1982).…”

“…; Irish et al . , ; Feng et al . ), and the global distribution of some races is consistent with seedborne transmission (Feng et al .…”

Construction of a Spinach Bacterial Artificial Chromosome (BAC) Library as a Resource for Gene Identification and Marker Development

“…spinaciae (Pfs), is the most economically important disease of spinach (Correll et al 2007; Morelock and Correll 2008;Correll et al 2011). As of 2014, 15 distinct races of Pfs have been described (Irish et al 2003;Irish et al 2007;Feng et al 2014). The most effective way to manage downy mildew is through host resistance.…”