Botryosphaeria dothidea causing stem spots on Hylocereus undatus in Mexico

The epiphytic plant Hylocereus undatus Haworth, locally known as pitahaya, is endemic to Mexico. Recently, small-scale farming of this plant has begun and the harvested fruit exported to distant markets. In 2001 and 2002, samples of H. undatus with stem spots were collected from Mecapalapa, Xochitlan and Dolores Hidalgo in the state of Puebla. Early symptoms were small, chlorotic specks, which enlarged as they matured to a maximum of 0.5 cm in diameter (Fig. 1).

A fast-growing, mouse-grey coloured fungus was consistently isolated from these diseased stems. After 8 days, under continuous fluorescent light at 22-25°C, pycnidal fruiting bodies (180 x 150 µm) formed on potato dextrose agar (PDA). The conidia observed in these bodies were one-celled, hyaline, ellipsoidal to fusoid with distintinctly truncate bases and measured 12.15-19.44 x 4.86-8.51 µm (av. 16.49 x 5.90 µm). The isolated fungus conformed to the anamorphic Fusicoccum state of Botryosphaeria dothidea (Moug.:Fr) Ces & De Not. The teleomorph was never observed in culture, but was seen on infected plants. Healthy, detached H. undatus stems were inoculated with the Fusicoccum isolate, while three control stems were inoculated with sterile PDA discs. After incubation for three days at 25-30°C, under high humidity and a 12 h day length, disease symptoms similar to those observed on naturally infected plants were observed. All inoculated stems were infected and turned brown, in contrast to the negative controls which remained unaffected. The anamorphic Fusicoccum state of B. dothidea was re-isolated from the inoculated plants, thus satisfying Koch's postulates. This fungus has been previously reported to cause panicle and shoot blight and canker diseases of pistachio, peach, apple (Brown & Britton, 1986; Michailides, 1991), forest trees, chaparral bushes (Brooks & Ferrin, 1994) and many other plant species (Smith, 1934). This is however, the first report of stem canker of Hylocereus undatus caused by B. dothidea.