Spinach Diseases

Spinach (Spinacia oleracea) is an important vegetable crop grown on more than 16,000 ha in the United States and is valued at approximately $184 million annually. Major areas of production include California, Colorado, Texas, Arkansas, Oklahoma, and parts of the east coast. 

Downy mildew, or blue mold, caused by Peronospora farinosa (Fr.) Fr. f. sp.spinaciae Byford, is an economically important pathogen on spinach in most regions where the crop is grown. Prior to 1996, four races of the pathogen were known to occur in the United States 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.

Peronospora farinosa (Fr.) Fr. f. sp.spinaciae Byford spores	Downy mildew symptom	Downy mildew symptom

Molecular Markers for Spinach gene resistant to downy mildew race 6.

  Amplified Fragment Length Polymorphism (AFLP) technique was employed to screen markers associated with spinach resistance gene to downy mildew race 6 with bulked segregant analysis (BSA) strategy in a BC₃F₂ segregating population. An AFLP marker was found to be tightly linked to the resistance gene with 1.2cM distance.  Four sequence characterized amplified region (SCAR) markers were developed after cloning and sequencing the specific AFLP fragment associated with the resistance gene. 

AFLP marker associated with spinach resistance gene to downy mildew race 6.

SCAR markers associated with spinach resistance gene to downy mildew race 6.

 Verticillium wilt, caused by Verticillium dahliae, which was not reported before 2002, is another spinach disease that threats fresh spinach production and seed production. With the colaboration with Dr. Lindsey J du Toit, Washington State University, two vegetative compatibility groups (VCGs) have been characterized so far.   Also a resistance screening procedure has been developed and the screening of spinach germplasm is ongoing.