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Zhanao Deng and Brent K. Harbaugh

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Zhanao Deng and Brent K. Harbaugh

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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Brent K. Harbaugh and Robert J. McGovern

Fusarium crown and stem rot, caused by Fusarium avenaceum, is a serious disease of lisianthus, Eustoma grandiflorum Raf. (Shinn.). While more than 80 new cultivars of lisianthus have been released for sale in the United States in the past decade, there is a lack of information on their susceptibility to this pathogen. Forty-six cultivars of lisianthus were evaluated for resistance to F. avenaceum. Cultivars were grouped according to blue/purple, pink, or white colors and evaluated within their color class. Although all cultivars evaluated were susceptible to F. avenaceum, partial resistance was observed as indicated by differences in the length of time to symptom expression and in the frequency of diseased plants. `Ventura Deep Blue' and `Hallelujah Purple' (25%) in the blue group, `Bridal Pink' (23%) in the pink group, and `Heidi Pure White' (53%) in the white group had the lowest frequency of diseased plants at 55 days after inoculation. In 21 of the 46 cultivars, 80% to 100% of the plants expressed symptoms at 55 days after inoculation. Screening cultivars for resistance to F. avenaceum is the first step to breeding and developing resistant cultivars. These results also can be useful to growers who could select cultivars that express some level of resistance as an aid in management of this disease until more resistant cultivars are released.

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Brent K. Harbaugh and John W. Scott

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Brent K. Harbaugh and Michael R. Evans

Nonplanted Caladium × hortukmum Birdsey `Candidum' tubers were exposed to 26 (control), 38,43, or 48C for 1,2, or 3 days. Then tubers were planted and forced in a glasshouse for 4 weeks at 18 to 33C (air). Leaf emergence from tubers exposed to 48C for 1 or 2 days required 3-12 days longer than leaf emergence from control tubers. No leaves emerged from tubers treated at 48C for 3 days. Exposing tubers to 38C for 3 days or 43C for 1 day did not affect subsequent plant growth. Exposing tubers to 43C for 2 or 3 days or 48C for 1 or 2 days resulted in plants with reduced shoot fresh weights and fewer leaves ≥ 15 cm. In a second experiment, planted tubers were forced for 10 days at 26C so that roots had developed to the edge of the pot and shoots had emerged to the soil surface. These planted (sprouting) tubers were exposed to 43C for 0,4,8,12,16,20, or 24 hours/day for 1,3, or 5 days and then forced for 7 weeks in a glasshouse. With 3- or 5-day treatments, days to leaf emergence increased as the hours of exposure to 43C increased. Only 33% of planted tubers exposed to 43C for 24 hours/day for 5 days sprouted. Tubers exposed to 43C for≤ 12 hours/day for 3 days produced plants of similar or greater height, numbers of leaves □≥15 cm wide, and shoot fresh weights, but additional hours of daily exposure decreased these plant characteristics. At 5 days, plant height, number of ≥ 15-cm-wide leaves, and shoot fresh weight decreased linearly with increased hours of exposure of tubers to high temperature.

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Brent K. Harbaugh and R. J. McGovern

Fusarium crown and stem rot, caused by Fusarium avenaceum (Fr.: Fr.) Sacc., is a serious disease of lisianthus [Eustoma grandiflorum Raf. (Shinn.)]. While more than 80 new cultivars of lisianthus have been released for sale in the United States in the last decade, there is a lack of information on their susceptibility to this pathogen. Forty-six cultivars of lisianthus were evaluated for their response to infection by F. avenaceum. Cultivars were grouped according to blue/purple, pink, or white flower colors and evaluated within their color class. Although some plants of all cultivars were susceptible to F. avenaceum, partial resistance was observed as indicated by differences in the length of time to symptom expression and in the frequency of diseased plants within each color group. In 21 of the 46 cultivars, 80 to 100% of the plants expressed symptoms within 55 days after inoculation. The lowest frequencies of diseased plants 55 days after inoculation were found in `Ventura Deep Blue' and `Hallelujah Purple' (25%), `Bridal Pink' (23%), and `Heidi Pure White' (53%) for the blue/purple, pink, and white flower color groups, respectively. Screening cultivars for resistance to F. avenaceum is the first step in breeding resistant cultivars. The methods we developed for these studies should be useful in screening for resistance. These results also may help growers select cultivars that are less susceptible to F. avenaceum, which should aid in the management of this disease.

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Michael R. Evans and Brent K. Harbaugh

Before being forced as potted plants, tubers of two Caladium ×hortulanum Birdsey cultivars were subjected to different methods of de-eyeing (terminal bud removal), either before or after 6 weeks of curing and storage. The cultivar Frieda Hemple (`FH'), a type with numerous buds that does not require de-eyeing, was less affected by deeyeing than `Fannie Munson' ('FM'), which has a single dominant bud and requires deeyeing. De-eyeing had little effect on `FH' development. For `FM', regardless of the time of de-eyeing, all treatments reduced height, increased the number of leaves, increased total leaf area, and reduced mean leaf area when compared to intact tubers. However, as the size of the tuber piece removed during de-eyeing increased, the variability within each treatment increased. Based on the results of this research, the best method of de-eyeing would be to destroy or remove the dominant terminal bud while removing as little of the surrounding tissue as possible. The time of de-eyeing can depend on producer preference, since the time of de-eyeing did not affect development significantly.