Symptoms of bacterial blight appear first on leaves as small, irregularly shaped, water-soaked spots. They vary from 2 to 5 mm in diameter and have necrotic centers. The water-soaked spots, when viewed against light, look translucent. They turn light brown gradually and then dark brown and are surrounded by prominent water-soaked margins. Severely affected leaves become yellow and are easily shed. Bacterial ooze is sometimes found in the centers of the spots.
Dr. V. I. BenagiProfessor and Head, Department of Plant Pathology, UAS, Dharwad – 580 005, Karnataka, India
Host: Pomegranate (Punica granatum L.)Disease name: Bacterial blight of pomegranatePathogen name: Xanthomonas axonopodis pv. punicae
Bacterial blight of pomegranate was first reported in India from Delhi in 1952 and was of minor economic importance until 1998. Presently, the disease occurs widely and outbreaks have been recorded in all major pomegranate-growing states including Maharashtra, Karnataka, and Andhra Pradesh. Losses caused by bacterial blight were recorded in Hanumangarh district of Rajasthan in 2009. Until recently, the disease was prevalent only in India, but it was also reported from South Africa in 2010. Bacterial blight of pomegranate affects leaves, twigs, and fruits. Infected fruit and twigs are potential sources of primary inoculum. The secondary spread of bacterium is mainly through rain and spray splashes, irrigation water, pruning tools, humans, and insect vectors. Entry is through wounds and natural openings. The first water-soaked lesions develop within 2–3 days and appear as dark red spots. Disease buildup is rapid from July to September. Severity increases during June and July and reaches a maximum in September and October and then declines. Bacterial cells are capable of surviving in soil for >120 days and also survive in fallen leaves during the off-season. High temperatures and low humidity or both favor disease development. Optimal temperature for growth of bacterium is 30°C; thermal death point is about 52°C.
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