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  • Author or Editor: James M. Warren x
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Abstract

(2-Chloroethyl)phosphonic acid (ethephon) plus 0.1% polyoxyethylene sorbitan (Tween 20) was applied as a fruit cluster dip at 2000, 4000, and 8000 ppm to highbush blueberries (Vaccinium corymbosum L. cv. Morrow) at different stages of berry development. Earliest ripening was obtained with 8000 ppm treatment made late in Stage II. Ripening date was not related to concentration when applied in Stage III. Harvest period was shortest, less than 1 week, when treatments were applied in Stage III, regardless of concentration. Berry weight decreased with increased concentration, but little difference was noted with respect to stage of development at time of application. Generally, pH decreased with increasing concentration of ethephon and with advancement in stage of development at time of treatment. An increase in ethephon concentration resulted in an increase in acidity, decrease in soluble solids (SS) and decrease in SS/acid ratio at each time of application until Stage III of fruit development. Stage III treatments showed no concentration effect with the exception of the acidity response to the 8000 ppm treatment. Optimum time of application was near the end of Stage II and the beginning of Stage III.

Open Access

Infection process of Puccinia hemerocallidis, the causal agent of daylily rust, and resistance responses in eight daylily cultivars, were studied macroscopically and microscopically. After germination of urediniospores, appressoria were formed at the tip of germ tubes and penetrated through stomatal openings. Intercellular hyphae aggregated and formed uredia under the infection sites, and released urediniospores after rupturing the epidermis. In highly resistant cultivars `Prairie Blue Eyes' and `Bertie Ferris', intercellular hyphal growth was restricted and uredia were not formed. No macroscopic symptoms of the disease were present on the leaf surface, although a few collapsed cells were observed microscopically. Both resistant and moderately resistant reactions were characterized by necrotic lesions with many collapsed cells under infection sites. The difference between these two reactions was that uredia and urediniospores were observed on the moderately resistant cultivar `Chicago Apache', but not on resistant cultivars, `Buttered Popcorn' and `Stella De Oro'. Sporulation was observed on both moderately susceptible and susceptible cultivars, but latent periods were delayed and the amount of urediniospore production was reduced on moderately susceptible cultivars, `Mary Todd' and `Chorus Line', compared to the susceptible cultivar `Pardon Me'. The results indicate that the hypersensitive cell death is one of the resistance responses to daylily rust, but necrotic lesions on leaf surfaces are associated with the amount of collapsed host cells. The delayed latent periods and reduced sporulation that resulted from restricted intercellular hyphal growth could represent another resistance mechanism in the daylily rust pathosystem.

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