During February 2004, diseased double impatiens (Impatiens walleriana) plants were received from a commercial grower in southern California. The upper surfaces of symptomatic leaves were pale yellow with no distinct lesions. Diseased leaves later wilted, and severely affected leaves abscised from the stem. At the nursery, only double impatiens plants in the Fiesta series were infected, and some cultivars were more heavily infected than others. Disease incidence in cv. Sparkler Hot pink was nearly 100%. The interior of infected leaves was colonized by coenocytic mycelium. A conspicuous white growth was observed only on the underside of leaves. Sporangiophores were hyaline, thin walled, emergent from stomata, and had slightly swollen bases. Sporangiophore branching was distinctly monopodial. Smaller sporangiophore branches were arranged at right angles to the supporting branches, and tips of branches measured 8 to 14 μm long. Sporangia were ovoid and hyaline with a single pore on the distal ends. Distal ends of sporangia were predominantly flat but occasionally had a slight papilla. Short pedicels were present on the attached ends. Sporangia measured 19.4 to 22.2 (-25.0) μm × 13.9 to 16.7 (-19.4) μm. Oospores were not observed in leaf tissue. On the basis of symptoms and morphology of the organism, the pathogen was identified as Plasmopara obducens J. Schröt. Pathogenicity tests were done on double type cvs. Fiesta, Tioga Red, and Tioga Cherry Red and on single type cvs. Cajun Watermelon and Accent Lilac. Plants were spray inoculated with sporangiospore suspensions (1 × 104 sporangiospores per milliliter), incubated for 24 h in a dew chamber (18 to 20°C), and then maintained in a greenhouse (22 to 24°C). Symptoms and signs of downy mildew developed after 12 days only on inoculated cv. Fiesta plants, and the pathogen morphology matched that of the originally observed pathogen. Nontreated control plants did not develop downy mildew. To our knowledge, this is the first report of downy mildew on impatiens in California. P. obducens is one of two causal agents of downy mildew of impatiens (2,4). The other pathogen, Bremiella sphaerosperma, has dichotomous sporangiophore branching and causes lesions with well-defined margins (2,4). In the United States, the disease has been recorded in the eastern and northeastern states and in Indiana, Minnesota, Mississippi, Montana, and Wisconsin (3). In Canada, the disease has been recorded in Manitoba and Quebec (1). References: (1) I. L. Conners. An Annotated Index of Plant Diseases in Canada and Fungi Recorded on Plants in Alaska, Canada, and Greenland. Research Branch, Canada Department of Agriculture, Publication 1251, 1967. (2) O. Constantinescu. Mycologia 83:473, 1991. (3) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society, 1989. (4) G. W. Wilson. Bull. Torrey Bot. Club 34:387, 1907.

Lisianthus (Eustoma grandiflorum) is a high-value cut flower. However, major yield losses often result from gray mold caused by Botrytis cinerea. Various techniques were used to evaluate 12 lisianthus cultivars for resistance B. cinerea. Disease evaluations from detached leaf, leaf disc, cut stem, and in vivo growth chamber stem (GC) assays were correlated with those from an in vivo greenhouse stem (GH) assay, in which commercial greenhouse production of lisianthus was simulated. In all assays, stems or leaves were wounded before inoculation with spores or mycelia of B. cinerea. There was a significant (P ≤ 0.03) positive correlation between stem lesion length in the GH assay and disease incidence in the same assay (R = 0.74), stem lesion length from spore spray inoculation in the GC assay (R = 0.62), and percent necrosis from spore spray inoculation of detached leaves (R = 0.71). Correlations between stem lesion length in the GH assay and disease evaluations from spore drop and mycelial inoculation of detached leaves, leaf discs, and cut stems were not significant at P = 0.05. Considering only screening methods with significant correlations, ‘Magic Champagne’ was the most resistant cultivar (mean rank [mr] = 2 of 12). ‘Echo White’ and ‘Echo Lavender’ were the least resistant cultivars (mr = 11). The other cultivars were ‘Magic White’ (mr = 4); ‘Avila Ivory’, ‘Balboa Yellow’, ‘Echo Pink’, and ‘Magic Rose’ (mr = 5); ‘Balboa Blue’ (mr = 6); ‘Avila Blue Rim’ (mr = 8); and ‘Avila Purple’ and ‘Catalina Purple’ (mr = 9). The results from this study indicate that in vivo disease incidence, in vivo stem assays, and detached leaf assays, all initiated with wounding followed by spore spray inoculation, may be more reliable in evaluating lisianthus cultivars for resistance to B. cinerea than spore drop and mycelial inoculation of detached leaves, leaf discs, and cut stems. The results also indicate that lisianthus cultivars with moderate resistance to B. cinerea are commercially available. These cultivars have potential for use as germplasm in breeding lisianthus for resistance to the pathogen.

In the deserts of Southern California, globe artichokes (Cynara scolymus L.) are grown as annuals. Greenhouse-grown seedlings (5 to 6 weeks old) are commonly transplanted into minimum-tilled, drip-irrigated beds in late summer (August to September) and harvested in winter and spring (December to April). By mid-October of 1997 and 1999, up to 30% of the plants in some commercial fields were either stunted or dead. There was no further progression of the disease over the remainder of the production season. Primary and secondary roots of symptomatic plants submitted for diagnosis in October of 1997 and 1999 exhibited extensive root rot. The organism consistently isolated from rotted roots that were plated onto water agar grew optimally at 37°C, produced inflated sporangia, intercalary antheridia, and oospores characteristic of Pythium aphanidermatum Edson (Fitzp.). Soil temperatures at the 10 cm depth during late summer range from 25 to 34°C. These high soil temperatures are known to be favorable to the pathogenic activity of P. aphanidermatum. To confirm Koch's postulates, 6-week-old artichoke seedlings were transplanted into potting soil that was artificially infested with the pathogen (20 oospores per g of soil). Oospores were obtained from 2-week-old V8 agar cultures of the fungus. Inoculated and noninoculated control plants were incubated at 28°C and the experiment was repeated once. All inoculated plants died within 2 weeks and P. aphanidermatum was recovered only from the rotted roots of inoculated plants. This is the first report of P. aphanidermatum causing root rot on artichoke.

California has an extensive strawberry (Fragaria ×ananassa L.) industry that has built its reputation on the production of large volumes of fruit that are evenly and fully developed. While some fruit deformity occurs every year, in various counties during the 1997-2000 seasons there were higher than usual numbers of uneven or “catfaced” strawberry fruit. It was thought that the presence of the fungus Cladosporium cladosporioides (Fresen.) G.A. De Vries on flower anthers may have interfered with pollination and increased cull rates. We collected and incubated flower anthers to determine the fungal populations on such tissue and found that C. cladosporioides accounted for the majority of the culturable fungal colonies present. However, while 100% of a flower's anthers were colonized with C. cladosporioides after spray inoculations, the incidence and severity of malformed fruit were not significantly different from untreated flowers. Physically removing all anthers shortly after anthesis likewise did not result in significant differences in fruit quality when compared to untreated control flowers. We conclude that C. cladosporioides colonization of flower anthers has a minimal impact on fruit quality under most field conditions.

Powdery mildew caused by Erysiphe aquilegiae var. ranunculi is one of the major diseases affecting field-grown delphiniums (Delphinium spp.). Two lath house and two field experiments were conducted in 2003 and 2004 to evaluate nine delphinium cultivars for resistance to the disease. ‘Blue Bird’, ‘King Arthur’, ‘Cameliard’, and ‘Galahad’ were consistently more resistant [0–1.1 disease severity (ds) on a 0–5 scale] than ‘Casa Blanca’, ‘Blue Shadow’, ‘Belladona’, and ‘Bellamosum’ (2.9–5.0 ds). ‘Oriental Blue’ was moderately resistant (0–3.3 ds). Spearman's coefficients of rank correlation were significant for all pairs of experiments (0.70 ≤ rs ≤ 0.98; P ≤ 0.0354) except for the 2003–04 field experiments (rs = 0.66; P = 0.0525). Pearson correlation coefficients between experiments (0.86 ≤ r ≤ 0.99) were highly significant (P ≤ 0.0027). Disease severity values from lath house evaluations were almost identical to those from field evaluations.