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  • Author or Editor: Peter Semeniuk x
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Here we report the first evidence of resistance of roses to the blackspot disease, Diplocarpon rosae Wolf. Black-spot is a major foliar disease of roses that causes severe losses to commercial and home gardeners. It spreads rapidly on susceptible cultivars, results in premature defoliation, and severely reduces yield and quality of this popular plant. Growers must make frequent applications of fungicides which are costly in labor and materials and environmentally undesirable. Stewart and Semeniuk (3) reported on the problems and techniques in transferring resistance to blackspot from the diploid species to garden roses (1, 2). The breeding lines Spotless Gold, Spotless Yellow, and Spotless Pink will be released for use as resistant parents in breeding programs. This germplasm should be valuable to breeders for its resistance to 7 isolates of D. rosae from Belts-ville, Maryland, Tifton, Georgia, Ames, Iowa, Ithaca, New York, Delaware, Ohio, University Park, Pennsylvania, and Tyler, Texas. These roses have been released by the U.S. Department of Agriculture, Science and Education Administration. The developmental work was done by the Florist and Nursery Crops Laboratory at the Agricultural Research Center, Beltsville, Maryland.

Open Access
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There are very few small flowered ornamental plants that are ideal for use either in containers or as bedding plants. In 1973, a breeding program was initiated in the Ornamentals Laboratory to develop clones of Browallia speciosa Hook, suitable for year-round production in small containers (10 cm pots) that would have mass-market appeal.

Open Access
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The present study was conducted to determine the effects of 3 day/night temp regimes on vegetative growth, flower development, and fruit set of Browallia speciosa Hook. ‘Blue Troll’ (a semi-dwarf type) under growth chamber conditions.

Open Access
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Abstract

There are very few small “blue”-flowered ornamental plants adapted to use as bedding or potted plants or for use in hanging baskets. A breeding program was initiated in the Ornamentals Laboratory to develop a clone of Browallia suitable for year-round production in small Containers (10 cm pots) that would have mass-market appeal.

Open Access

Abstract

Bud applications of 6-benzylamino purine (BA) suspended in lanolin at concentrations of 1, 5, 25, and 50 mg/ml effectively induced either the initiation of bud growth or the development of lateral branches in nonpinched, nonbranching ‘Ruff and Reddy’ poinsettia (Euphorbia pulcherrima Wild ex. Klotz). No lateral branches developed on nonpinched controls. Application of 25 and 50 mg/ml of BA promoted additional axillary bud activity in untreated axillary buds above treated ones. This loss of apical dominance in upper untreated buds indicates that BA was transported. Bud applications of 150 μg/ml t-cinnamic acid (tCA) alone or in combination with BA had no effect on promoting bud activity.

Open Access

Abstract

Recently Raulston (1) reported that photoperiod and nutrition were important in determining the earliness and no. of inflorescences in annual statice (Limonium sinuata L.). Our results, based on date of first visible flower stalk (flowering) (Table 1) are comparable to his findings. Plants under Long Day (LD = 16 hr) came into flower an average of 22 days earlier than under Short Day (SD = 8 hr) treatment. The time of appearance of the first visible flower stalk varied greatly depending upon the cultivar and the photoperiod. Under LD, ‘Iceberg’ and ‘Gold Coast’ flowered first (an average of 115 days) while ‘Blue Bonnet’ and ‘Midnight Blue’ flowered last (an average of 139-140 days). ‘Twilight Lavender’ and ‘American Beauty’ were intermediate (approx 126-128 days). The greatest influence of photoperiod, however, was on the % of plants flowering. An average of 98% of the plants flowered under LD while only 52% flowered under SD. Flowering in ‘Gold Coast’ and ‘Iceberg’ under SD was reduced by ca. 20% while ‘Blue Bonnet’ failed to flower (Table 1).

Open Access

Abstract

Groups of poinsettia plants (Euphorbia pulcherrima willd. ex Klutzsch) were exposed at different seasons to enhanced levels of ultraviolet (280-320 nm) radiation, 01-13 weighted m W m−2 (UV-B), for 4 weeks in both vegetative and flowering growth stages. None of the cultivars showed any response in height, number of nodes, fresh weight, or dry weight. Some distorted leaves and bracts developed during the seasons of low light intensity but not during seasons of high light intensity, suggesting photorepair during the latter periods. The anthocyanin pigmentation produced in the bracts of flowering plants was partially destryoed by enhanced UV-B, whereas in vegetative plants the pigmentation in petioles was increased. Bracts from many of the treated plants showed increased absorbance in the UV-A and UV-B regions. Cultivars differed widely in their response to enhanced UV-B.

Open Access

Abstract

Coleus cultivars differed in their response to enhanced levels of UV-B. With 80% or greater increase in biologically effective radiation, some distorted leaves developed, anthocyanin pigmentation was decreased, and absorbance at several peaks in the UV region increased. Coleus was less sensitive during seasons of high ambient photosynthetically active radiation (PAR) than during low PAR suggesting photorepair was a factor in the response. None showed a response in height, number of nodes, fresh weight, or dry weight.

Open Access

Abstract

Comparative SO2 sensitivity was determined for red, pink, marble, and white cultivars of poinsettia, Euphorbia pulcherrima Willd. ex Klotzsch, belonging to 4 groups of sports: ‘Paul Mikkelsen’, ‘Annette Hegg’, ‘Eckespoint C-l’, and ‘Oakleaf’. Based on injury to the bracts, sports of the ‘Eckspoint C-l’ group were the most insensitive, whereas sports from the ‘Annette Hegg’ and ‘Paul Mikkelsen’ groups were the most sensitive. However, based on the number of leaves showing SO2 injury, sports from the ‘Oakleaf’ group were the most insensitive and those of the ‘Paul Mikkelsen’ group were the most sensitive. True leaves were generally much more sensitive to SO2 exposure than were corresponding bracts. There was no consistent relationship between bract color and extent of SO2 injury.

Open Access

Abstract

The influence of 3 germination temperature (16/13°, 21/18°, and 27/24°C day/night) and 2 growing temp (24/16° and 26/24°C day/night) on flowering in 6 cultivars of annual statice (Limonium cv.) grown under long days was determined over a 24-week period. When grown at 24/16°C nearly all of the plants produced a visible flower stalk irrespective of the germination temp. Flowering percentages at 26/24°C varied greatly, depending upon the cultivar and the germination temp. When grown at a temp of 26/24°C, the percentage of ‘Blue Bonnet’ flowering was low regardless of the germination temp. However, the percentage of ‘Midnight Blue’, ‘Iceberg’, and ‘Twilight Lavender’ plants flowering at a growing temp of 26/24°C was higher following germ temp of 16/13° or 21/18°C. ‘Gold Coast’ flowered irrespective of temp treatment. Except for ‘Gold Coast’, plants grown at 24/16°C generally had the earliest and greatest number of mature flower stalks, and the highest flower stage. Thus, growing temp appears to be the chief determinant of flowering in annual statice.

Open Access