Caladium (Caladium ×hortulanum Birdsey) is an ornamental aroid grown as landscape and potted plants. They are valued for their colorful foliage that comes in various leaf shapes and coloration patterns containing shades of red, pink, white, and/or green. The most common foliar disease of caladium is bacterial blight (BB), also known as Xanthomonas leaf spot, caused by Xanthomonas axonopodis pv. dieffenbachiae (Xad) (formerly X. campestris pv. dieffenbachiae) (Chase, 1997).
Symptoms of BB begin as small, angular, water-soaked lesions visible on the lower leaf surface. The lesion can either expand in between major veins causing a large V-shaped necrotic area or veins can be infected and cause necrosis of the vein and adjacent leaf tissue. Severe tissue necrosis can lead to premature defoliation. Under humid conditions, a yellow exudate composed of Xad can be observed on the abaxial surface of lesions. The bacteria in this exudate can be splash-dispersed and infect adjacent leaves and plants.
In Florida, where more than 95% of the world's commercial caladium tubers are produced (Deng et al., 2008), BB is an annual problem because hot, humid, and rainy weather conditions in the summer are ideal for disease development and the spread of Xad. Leaf necrosis and defoliation during severe epidemics of BB, especially those occurring earlier in the production season, may decrease tuber sizes and yields in commercial tuber production. Even relatively mild BB symptoms decrease the marketability of potted plants produced in nurseries and greenhouses.
BB is also a major disease in other ornamental aroids such as anthurium (Anthurium Schott), dieffenbachia (Dieffenbachia Schott), philodendron (Philodendron Schott), aglaonema (Aglaonema Schott), colocasia (Colocasia Schott), and syngonium (Syngonium Schott). There has been considerable research on xanthomonads that cause the BB in these aroids (Chase et al., 1992; Khoodoo and Jaufeerally-Fakim, 2004; Norman et al., 1997, 1999; Robène-Soustrade et al., 2006), but very little has been conducted on xanthomonad diseases of caladium. The main objective of this study was to identify commercial cultivars resistant to BB for use both by growers as a tool for management of BB and in a breeding program as sources of resistance in the development of new cultivars.
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