Downy mildew, caused by Peronospora farinosa f. sp. spinaciae, is an economically important disease in most areas where spinach is grown. This disease has become increasingly important in production fields for prepackaged salad mixes where plant densities typically are very high. In Florida, spinach production for these markets has reached approximately 200 ha. Currently, seven physiological races of the downy mildew pathogen have been described (1). Downy mildew was observed in several commercial spinach fields in the Everglades agricultural area of Palm Beach County, Florida in January 2003 on cvs. Unipak 151 and Merlo Nero. Symptoms appeared as chlorotic and necrotic leaf spots. Disease incidence reached approximately 25% in some field locations. Economic losses were significant, since entire plantings in several fields were not harvested as a result of diminished quality. The race of a field isolate recovered from the cv. Unipak 151 was determined following greenhouse inoculation procedures and using differentials outlined by Irish et al (1). Greenhouse inoculation tests were conducted twice. Disease reactions on a U.S. and international set of differentials indicated that the isolate was race 5. To our knowledge, this is the first report of race 5 occurring outside of the California/Arizona spinach production area in the United States. There are commercial spinach lines with resistance to race 5, as well as the other described races (1). References: (1) B. M. Irish et al. Plant Dis. 87:567, 2003.

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.

White rust, caused by Albugo occidentalis, is an economically important disease of spinach (Spinacia oleracea). Although cultural practices and partial host resistance are used for disease management, control strategies often rely on fungicides. An alternative approach, the use of ionic (cationic or anionic) and nonionic surfactants, was evaluated for its effect on white rust in greenhouse and field experiments. Surfactant treatments were compared with a water control and two commercial fungicides, azoxystrobin (Quadris) and 1,2,3-benzothiadiazole-7-carbothioic acid S-methyl ester (Actigard). Greenhouse plants were treated with a single surfactant application followed by inoculation with sporangia. Disease severity was rated on leaves 8 to 12 days after inoculation. Field tests were conducted in Arkansas and Texas and received three to five surfactant applications during the season. Disease severity was determined at the end of the growing season. In greenhouse and field tests, all surfactant treatments showed significant reductions in white rust severity compared with water controls. The surfactants Naiad and sodium dodecyl sulfate (SDS) were highly effective and comparable to fungicides in reducing white rust severity. In a laboratory assay, microscopic examination revealed that most of the surfactants at low concentrations caused rapid (<2 min) zoospore lysis.

Spinach, Spinacia oleracea L., produced for processing in the Arkansas River Valley of western Arkansas was sampled for live and diseased aphids from 1990 to 1993. The green peach aphid, Myzus persicae (Sulzer),was the only aphid detected and its occurrence was highly variable. No aphids were detected in 14 of the 24 sampled fields. Nine of the 10 fields in which aphids were detected had individuals infected with the fungus Erynia neoaphidis (Remaudiere & Hennebert). No other fungal pathogens were observed. Infected aphids were detected in each of the 3 spinach production seasons (fall, winter, and spring). In several fields, especially during the winter of 1992, aphid populations declined with increased E. neoaphidis incidence. However, in fields with relatively high numbers of aphids this population decline occurred at or after the normal spinach harvest period. Aphids killed by E. neoaphidis were tightly held to spinach foliage and, when epizootics occurred at harvest, the spinach was rejected by the processor due to difficulty in washing the aphid cadavers from the product.

Additional index words.Daucus carota L., vegetable breeding of 3187C and 21 individual plants of HCM (two other known restorers of fertility in Cornell cytoplasm) yielded 0% to 35% fertile plants in populations of <30 progeny from each individual plant.As two or more genes condition restoration of fertility in carrot (Thompson, 1961), these populations are too small to conclude that the same genes restore fertility in Wisconsin Wild and Cornell cytoplasms, but the range in incidence of fertility among populations in either cytoplasm suggests that the Wisconsin Wild cytoplasm is similar or identical to the Cornell source with regard to restoration of fertility.

Progeny from a near-isogenic cowpea line responded heterogeneously when infected with a cowpea stunt-derived isolate of blackeye cowpea mosaic potyvirus (BlCMV). One group of plants developed a delayed, mild reaction to BlCMV while sister plants rapidly exhibited strong systemic mosaic symptoms. Conversely, enzyme-linked immunosorbent assay (ELISA) results indicated that BlCMV generally accumulated to the same levels and at the same rates in these two plant groups. Similar results were obtained for two commercial varieties that expressed different BlCMV symptoms. Symptom analyses and ELISA were used to demonstrate that one of these commercial varieties was highly resistant to this virus isolate. All genotypes responded with similar, mild reactions when inoculated with cowpea stunt-derived cucumber mosaic cucumovirus (CMV). Both symptoms and ELISA-detectable levels of CMV decreased as plants aged. Mixed infections with BlCMV and CMV resulted in severe cowpea stunt disease symptoms and high concentrations of CMV coat protein 20 days after inoculation in all plants that did not express extreme resistance to BlCMV. Interestingly, at early time points after inoculation, differences in symptom severity between singly and dually infected plants were not consistently correlated with significant differences in relative CMV concentrations. The results indicate that (i) resistance to BlCMV, as determined through visual observation, is not adequate when evaluating germ plasm for cowpea stunt disease resistance, and (ii) rapid development of severe symptoms on dually infected plants may not be due solely to increased CMV concentrations.

Fiely, M. B., Correll, J. C., and Morelock, T. E. 1995. Vegetative compatibility, pathogenicity, and virulence diversity of Fusarium oxysporum recovered from spinach. Plant Dis. 79:990-993. Four hundred thirty-nine isolates of Fusarium oxysporum recovered from symptomatic spinach seedlings and mature plants from Arkansas, California, New York, Oklahoma, South Carolina, Tennessee, and Washington in the United States as well as from Canada, Japan, and Sweden were examined for vegetative compatibility. A total of 110 isolates also were tested for pathogenicity on spinach. A minimum of 23 vegetative compatibility groups (VCGs) were identified among the 439 isolates in the collection. However, 216 (49%) of the isolates belonged to one of three vegetative compatibility groups (VCGs 1, 2, or 3). Of these 216 isolates, 125 (58%) belonged to VCG 1, 58 (27%) to VCG 2, and 33 (15%) to VCG 3. Fifty-five geographically diverse isolates from VCGs 1, 2, and 3 and 55 isolates vegetatively incompatible with VCGs 1, 2, and 3 were tested for pathogenicity on the spinach cultivar Grandstand. Of the 55 isolates in VCGs 1, 2, and 3 tested, 53 were pathogenic on spinach seedlings, while the 55 remaining isolates were not pathogenic on spinach. Among the three VCGs of Fusarium oxysporum f. sp. spinaciae identified, two distinct virulence phenotypes were detected. Isolates in VCGs 1 and 3 were significantly more virulent on the cultivar Grandstand than isolates in VCG 2. The F. o. f. sp. spinaciae population was composed of three VCGs that have a worldwide distribution, including the United States, Canada, Japan, and Sweden.

Resistance of spinach to white rust (Albugo occidentalis) and races 3 and 4 of downy mildew (Peronospora farinosa f. sp. spinaciae) was quantified on several cultivars and breeding lines in separate field inoculation experiments. Several cultivars and breeding lines from the Arkansas breeding program had undergone repeated field selections for white rust resistance (Fall Green, Ozarka II, FA88-310, FA88-354, and FA86-70) while others had not (Grandstand, St. Helens, and Hybrid 424). Resistance to both diseases was quantified by measuring disease incidence and severity at regular intervals 7-32 days after inoculation. The latent periods and the area under the disease progress curve (AUDPC) also were compared [...]

We characterized 215 isolates of Colletotrichum dematium collected from spinach in Arkansas, California, New Jersey, Oklahoma, Texas, and Ontario, Canada, for vegetative compatibility (using nitrate-nonutilizing mutants) and lesion type (primary or secondary). Isolates recovered from spinach leaves not previously damaged were identified as primary anthracnose isolates, whereas those recovered from leaves with white rust lesions (caused by Albugo occidentalis) were identified as secondary anthracnose isolates. Conidial size and colony color on acidified lima bean agar were recorded

The entomopathogenic fungus, Pandora neoaphidis (Remaudiere and Hennebert) Humber (Entomophthorales: Entomophthoraceae), was identified as the causal agent of epizootics in the green peach aphid, Myzus persicae Sulzer (Homoptera: Aphididae), on spinach, Spinacea oleracea L., in Arkansas. During February and March of 1990 epizootics appeared to cause the collapse of M. persicae populations on overwintering spinach. Prevalence rates of P. neoaphidis were greater than 90% on 20 March 1990 in both adult and immature aphids on spinach at the Kibler Experiment Station, Crawford Co., Arkansas. The fungus was cultured in vitro on egg yolk agar. In vitro-produced conidia were infective to M. persicae on spinach in the laboratory in preliminary experiments.

A preliminary study has shown that the addition of 15% (v/v) coconut water (CW) to the culture medium significantly improved callus growth, shoot-regenerative capacity, and shoot growth in leaf disk cultures of spinach (Spinacia oleracea L.). Subsequently, the influence of a range of CW concentrations, 0%, 5%, 10%, 15%, or 20% (v/v), was examined. Callus weight obtained after 5 weeks showed direct relationship to the concentration of CW. This stimulator action was observed in both cultivars tested in this study, `High Pack' and `Baker'. On CW-containing medium, shoot regeneration was expedited to 4 to 5 weeks compared with 8 to 12 weeks on a CW-free medium. Callus of `Baker' induced on a CW-free medium exhibited a significant increase in shoot regeneration frequency when transferred to a regeneration medium enriched with CW, suggesting that the addition of CW to the regeneration medium only is sufficient to achieve improved regeneration.

Shoots regenerated from leaf-derived callus of spinach (Spinacia oleracea L. cultivar ‘High Pack’) were induced to flower by exposure to 14-h photoperiods (50 μmol m−2 s−1) and day/night temperatures of 20°C16°C. Leaves from male and female plants served as sources for explants. Shoots regenerated from callus were induced to flower on a hormone-free medium. The majority of regenerated plants exhibited sex corresponding to their respective explant donors; a proportion of regenerants of male origin, however, shifted to monoecious. These sex-modified plantlets developed viable seeds in vitro. This phenomenon can be useful in producing seeds from elite selected male plants.

Spinach germplasm (707 accessions) from collections from six countries were screened for resistance to race 4 of the downy mildew pathogen Peronospora farinosa f. sp. spinaciae; these collections contained germplasm that originated from 41 countries. The predominant species examined was Spinacia oleracea L., however, eight accessions of S. turkestanica Iljin and two accessions of S. tetrandra Stev. were also tested. About 40 seedlings of each accession were inoculated. The cultivar St. Helens was included as a susceptible control in each test. The majority of accessions tested (>98%) were susceptible to race 4. Nine accessions exhibited some resistance to race 4 (9% to 38% of the seedlings within an accession were resistant), and two accessions, CGNO 9546 and SPI 82/87, exhibited a high level of resistance (60% and 80% resistant, respectively). Resistance identified in several of the accessions in this study may be useful for breeding for race 4 resistance.

Callus, induced in the dark from leaf tissue of spinach (Spinacia oleracea L. cv. Fall Green) on Murashige and Skoog (MS) medium supplemented with (in mg·liter -1 ) 2 kinetin and 0.5 2,4-D regenerated shoots upon transfer to a medium containing 2 kinetin, 0.01 2,4-D, and 1 GA 3 . Complete plants were established by stimulating rooting of the shoots with 1 mg IBA/liter and transferring them to potting soil; survival was 60%. Chemical names used: N-(2-furanylmethyl)-1H-purin-6-amine (kinetin); 2;4-dichlorophenoxy acetic acid (2,4-D); gibberellic acid (GA 3 ); 1H-indole-3-butanoic acid (IBA).

Regenerated spinach (Spinacia oleracea L.) maintained under a 10-h photoperiod (65 uE m -2 s -1 ) after an incubation period on a GA-containing medium were induced to flower in vitro. The plantlets were regenerated from callus initiated on MS medium with 2.0 mg L -1 kinetin and 0.5 mg L -1 2,4-D and were subsequently transferred to a medium containing 2.0 mg L -1 kinetin, 1.0 mg L- 1 GA, and 0.01 mg L -1 2-4,D. While on the regeneration medium, the cultures were exposed to a long-day photoperiod. Regenerants were transferred to an IBA-containing medium for rooting, after which flowering was observed. In vitro flowering plantlets exhibited male and female flowers depending on the sex of the explant donor. Female plantlets developed seeds in the culture vessels. This method of seed production from regenerants can eliminate time-consuming steps in acclimation, transplanting to soil, and plant maintenance.

Spinach, Spinacia oleracea L. breeding lines and a commercial cultivar were evaluated for differences in green peach aphid, Myzus persicae (Sulzer), preference, developmental time, adult longevity and fecundity. Aphid preference varied significantly among the breeding lines and the commercial cultivar ‘Kent.’ Line F70 was the only line significantly non-preferred when compared with ‘Kent’. Significant differences in aphid developmental time, adult longevity and fecundity were detected. Aphids held on line F70 required a longer period to reach reproductive age and produced fewer young than aphids held on ‘Kent.’