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  • Author or Editor: Brent K. Harbaugh x
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Trachelium caeruleum has been grown in the United States as a cut flower for about a decade. Only two cultivars, `White Umbrella' and `Purple Umbrella', were readily available for commercial use before 1997, but nine new cultivars became available in the last few years. Comparative performance trials have been lacking for these cultivars in the United States. This trial evaluated 11 cultivars of trachelium for cut flower production performance (vegetative and flowering characteristics) and postharvest longevity. The evaluation was in the spring of 1999 at Bradenton, Fla. (27.4 N, 82.5 W; AHS Heat Zone 10; USDA Cold Hardiness Zone 9b). Plant height for all cultivars except `White Umbrella' was above 30 inches (76 cm), a height required for acceptance as a high quality cut flower. `Summer Lake' had the smallest inflorescence diameter of 3.9 inches (10.0 cm) and `Lake Powell' the largest at 6.1 inches (15.4 cm). `White Umbrella' (160 days from seed to flower) was the earliest to flower and `Lake Powell' (169 days) the last to flower. Vase life was as short as 7 days for `Summer Lake' to as long as 11 days for `White Umbrella'. `Lake Powell' (white color group), `Summer Blue Wonder' (blue color group), and `Lake Superior' (purple color group) had the highest overall rankings.

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Caladium (Caladium ×hortulanum) leaves can be injured at air temperatures below 15.5 °C. This chilling sensitivity restricts the geographical use of caladiums in the landscape, and leads to higher fuel costs in greenhouse production of pot plants because warmer conditions have to be maintained. This study was conducted to develop procedures to evaluate differences among caladium cultivars for chilling sensitivity and to identify cultivars that might be resistant to chilling injury. The effects of two chilling temperatures (12.1 and 7.2 °C) and three durations (1, 3, and 5 days) on the severity of chilling injury were compared for three cultivars known to differ in their sensitivity to low temperatures. Exposure of detached mature leaves to 7.2 °C for 3 days allowed differentiation of cultivars' chilling sensitivity. Chilling injury appeared as dark necrotic patches at or near leaf tips and along margins, as early as 1 day after chilling. Chilling injury became more widespread over a 13-day period, and the best window for evaluating cultivar differences was 9 to 13 days after chilling. Significant differences in chilling sensitivity existed among 16 cultivars. Three cultivars, `Florida Red Ruffles', `Marie Moir', and `Miss Muffet', were resistant to chilling injury. These cultivars could serve as parents for caladium cold-tolerance breeding, and this breeding effort could result in reduced chilling injury in greenhouse production of potted plants, or in new cultivars for regions where chilling occurs during the growing season.

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The ornamental value of caladium (Caladium ×hortulanum Birdsey) depends primarily on leaf characteristics, including leaf shape and main vein color. Caladium leaf shapes are closely associated with plant growth habit, stress tolerance, and tuber yield; leaf main vein colors are often used for cultivar identification. Thirty-eight crosses were made among 10 cultivars and two breeding lines; their progeny were analyzed to understand the inheritance of leaf shape and main vein color and to determine if there is a genetic linkage between these two traits. Results showed that a single locus with three alleles determined the main vein color in caladium. The locus was designated as V, with alleles V r, V w, and V g for red, white, and green main veins, respectively. The white vein allele was dominant over the green vein allele, but it was recessive to the red vein allele, which was dominant over both white and green vein alleles; thus the dominance order of the alleles is V r > V w > V g. Segregation data indicated that four major red-veined cultivars were heterozygous with the genotype Vr V g, and that one white-veined cultivar was homozygous and one other white-veined cultivar and one breeding line were heterozygous. The observed segregation data confirmed that the three leaf shapes in caladium were controlled by two co-dominant alleles at one locus, designated as F and f, for fancy and strap leaves, respectively. The skewedness of leaf shape segregation in some of the crosses implied the existence of other factors that might contribute to the formation of leaf shape. Contingency chi-square tests for independence revealed that caladium leaf shape and main vein color were inherited independently. The chi-square tests for goodness-of-fit indicated that the five observed segregation patterns for leaf shape and main vein color fit well to the expected ratio assuming that two co-dominant and three dominant/recessive alleles control leaf shape and main vein color and they are inherited independently.

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Abstract

Distribution of the greenhouse whitefly and its wasp parasite, were measured on 12 cultivars of tomato, Lycopersicon esculentum Mill., by counting populations of parasitized and nonparasitized whitefly nymphs per leaflet. Parasitism percentages· were similar on all cultivars despite large differences in whitefly populations. Second generation parasite populations correlated significantly with whitefly numbers (r=0.71**). “Pocketing” behavior significantly influenced whitefly distribution with minimal cultivar preference. However, distribution gradients showed that ‘Floradel’ was the center of 2 large pockets, indicating preference for it.

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Abstract

Nicotine sulfate and resmethrin, applied at recommended rates, were less toxic to adults and larvae of Encarsia formosa than were endosulfan, malathion, or naled. Adult parasites were killed by contact with any of the 5 chemicals. Endosulfan and malathion left residues toxic to adult E. formosa for 2 to 3 weeks; malathion and naled killed many 10- to 15-day-old parasite larvae. The potential uses of nicotine sulfate and resmethrin were shown in theoretical models for integrated control of greenhouse whitefly.

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The ornamental value of caladium (Caladium ×hortulanum Birdsey) depends to a large extent on its foliar characteristics. Efficient genetic improvement of caladium foliar characteristics requires a good understanding of the inheritance of these traits, including leaf shape, color, and spots. This study was conducted to determine the inheritance of leaf spots in caladium and to understand their relationships with leaf shape and main vein color. Eighteen controlled crosses were made among eight commercial cultivars expressing red or no leaf spots, and progeny of these crosses were observed for segregation of leaf spots as well as leaf shape and vein color. A single locus with two alleles is shown to be responsible for the presence or absence of leaf spots in caladium, with the presence allele (S) dominant over the absence allele (s). The major spotted commercial cultivar Gingerland is heterozygous for this trait. Leaf spots are inherited independently from leaf shape, but they are closely linked with the color of the main leaf veins. The recombination frequencies between the leaf spot locus and the main vein color locus ranged from 0.0% to 8.9% with the crosses or the parental cultivars used, with an average of 4.4%. Leaf spots and vein colors represent the first linkage group of ornamental traits in caladium and possibly in other ornamental aroids. The knowledge gained in this study will be valuable when it comes to determine what crosses to make for development of new cultivars. It may be also useful to those interested in determining the inheritance of similar traits in other ornamental plants, including other ornamental aroids such as dieffenbachia (Dieffenbachia Schott).

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