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  • Author or Editor: Brent K. Harbaugh x
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Cultivated caladiums (Caladium ×hortulanum Birdsey) are valued as important pot and landscape plants because of their bright, colorful leaves. Improving leaf characteristics or generating new combinations of these characteristics has been one of the most important breeding objectives in caladium. A major leaf characteristic in caladium is leaf blotching, the presence of numerous irregularly shaped color areas between major veins on leaf blades. This pattern of coloration in combination with bright colors has resulted in the popularity of a number of caladium cultivars. In this study, controlled crosses were made among three blotched and six nonblotched caladium cultivars. Their progeny were analyzed to understand the mode of inheritance of leaf blotching and its genetic relationship with the color of main leaf veins. Progeny of selfing nonblotched or crossing nonblotched cultivars were all nonblotched; selfing blotched cultivars (Carolyn Whorton, White Christmas, and Florida Blizzard) or crossing ‘Florida Blizzard’ and ‘Carolyn Whorton’ resulted in a 3:1 ratio (blotched:nonblotched); and progeny from crosses between blotched and nonblotched cultivars segregated in a 1:1 ratio (blotched:nonblotched). These results indicate that leaf blotching is controlled by a single nuclear locus with two alleles (B and b). χ2 analysis of the joint segregation between leaf blotching and vein color (V) in five crosses showed that the blotching allele B is linked to the green vein allele V g. ‘Carolyn Whorton’, ‘White Christmas’, and ‘Florida Blizzard’ are heterozygous for leaf blotching, and their genotype for leaf blotching and vein color (V r, V w, and V g for red, white, and green veins, respectively) are V r b//V g B, V g b//V g B, and V w b//V g B, respectively. This information will be valuable for planning crosses and breeding populations to develop new blotched caladium cultivars. The information gained in this study may be helpful for understanding the inheritance of similar traits in other aroids.

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The sporadic nature of inflorescence production and flower protogyny in caladium (Caladium ×hortulanum Birdsey) makes it desirable to store pollen and to rapidly assess its viability for cross-pollinations in breeding programs. This study was conducted to develop a procedure to determine caladium pollen viability and to use that procedure to evaluate the effect of short-term storage conditions on pollen viability. The sucrose level in the culture medium was found to have a significant impact on the in vitro germination of caladium pollen; a concentration of 6.8% was determined to be optimal for pollen germination. Caladium pollen lost viability within 1 day under room (24 °C) or freezing (-20 °C) temperatures, but could be stored at 4 °C for 2 to 4 days. Pollen stored at 4 °C produced successful pollinations. Data obtained from large-scale greenhouse pollinations supported use of this in vitro germination assay as a convenient way to evaluate caladium pollen viability (and fertility).

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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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