PUMMELO CANKER A NEW DISEASE OF PUMMELO IN BANGLADESH
R. Islam and T. K. Dey. 2012. Pummelo canker: a new disease of pummelo in Bangladesh. Bangladesh J. Plant Pathol. 28(1&2): 69-70
Citrus canker caused by Xanthomonas axonopodis was first time recorded from pummelo (Citrus grandis) in Bangladesh. Initially the disease appeared as small, slightly raised, round and light green spots on young leaves, twigs, and fruits. The size of lesion increased gradually with the progress of time. At advanced stage, the lesions become grayish white. Leaf surface as well as fruit skins become ruptured forming corky appearance with brown and sunken centers. Similar symptoms also appeared on inoculated fruits.
Pummelo (Citrus grandis) is a common citrus fruit in Bangladesh. It is grown in backyard orchards as well as small holdings. A total of 56,000 metric tons of pummelo is produced in the country (Mondol et al. 2011). Canker caused by the phytopathogenic bacterium, Xanthomonas axonopodis pv. citri) is a common disease of pummelo and other citrus crops grown in Bangladesh. The disease is responsible for reducing yield, quality and market values of citrus fruits (Agrios 2006). Its occurrence was first noticed in Bangladesh in 2008. The incidence and severity of the disease was found to be increasing year after year.
In Bangladesh, the pathogen causes necrotic lesions on leaves, stems and fruits under natural conditions irrespective of citrus crops. Initially the lesions appear as small, slightly raised, round and light green spots on young leaves, twigs and fruits. Later, the lesions become grayish white. Leaf surface as well as fruit skins become ruptured forming corky appearance with brown and sunken centers (Plate IA). The margins of the lesions on leaf are often surrounded by a yellowish helo.
Canker infected fruit samples were collected from Moulovibazer and Sylhet districts and the pathogen was isolated following tissue planting method (Schaad and Stall 1988). For isolation, small sections of infected fruit skin were cut with a sterile scalpel and surface sterilized with 1.0% chlorox solution. About 0.5 ml sterilized distilled water was placed in a sterilized watch glass. Few pieces of surface sterilized infected tissues were placed
in the water and pressed with the handle of the scalpel to crush the samples and kept for 30 minutes to release the bacteria into the water. One loopful of the bacterial suspension was streaked on yeast peptone sucrose agar (YPSA) plates. The plates were incubated at 28C for 72 hours (Schaad and Stall 1988). Bacterial colonies developed on the plate were further sub-cultured on same medium. Singe cell bacterial colonies were isolated and transferred to sterile distilled water in test tube. The water culture of the bacterium in test tubes was preserved at room temperature. The pathogenicity test of the pathogen was performed by inoculating healthy pummelo fruit. Apparently healthy fruits were surface sterilized with 1.0% chlorox. Hole (5mm diameter and 4 mm depth) was made on the surface of a fruit with a flame sterilized cork borer. One loopful of pure bacterial suspension preserved in test tube poured into the hole. Inoculated fruits were kept in a moist blotter on a tray, covered with a polythene bag to maintain high humidity and incubated at room temperature (30±2C). After seven days of incubation, characteristic symptoms of canker developed on inoculated fruit skins (Plate IB), which were almost similar to the symptoms appeared on fruits under natural conditions (Plate IA and B). Based on pathogenicity test the disease was confirmed as canker and the causal bacterium as Xanthomonas axonopodis. Available literature indicates that citrus canker of pummelo may be considered as the first report of the disease from the country.
Agrios, G. N. 2006. Plant Pathology. 5th Eds. New Delhi. India. p. 667.
Mondol, R. I., Islam, S., Bhuiya, A. J., Rahman, M., Alam, M. S. and Rahman, H. H. 2011. Krishi Projukti Hatboi (Handbook on Agro-technology). Fifth edition. Bangladesh Agicultural Research Institute, Gazipur-1701. pp 91-98.
Schaad, N.W. and Stall, R.E. 1988. Xanthomonas. In. Laboratory guide for identification of plant pathogenic bacteria, 2nd ed. (ed. N. W. Schaad). APS Press, St. Paul, Minnesota. 81-84 p