Present Status of Pomegranate Bacterial Blight Caused by Xanthomonas axonopodis pv. punicae and Its Management

Bacterial blight of pomegranate caused by Xanthomonas axonopodis pv. punicae, of late, has become a major constraint in important pomegranate producing states of Maharashtra, Karnataka and Andhra Pradesh of India. In view of enormous losses which may extend up to 60-80% in unmanaged orchards under epidemic conditions, the present investigations were undertaken with the objective to ascertain the actual damage due to disease, disease epidemiology and to develop an effective disease management schedule. Surveys of important pomegranate growing states conducted during 2006 to 2008 revealed disease prevalence in different districts of Maharashtra viz., Solapur, Sangli, Pune, Nashik, Osmanabad, Aurangabad, Latur and Jalna in mild to severe form. Ahmednagar district, which was free from blight until 2007, also revealed severe blight infections in a few orchards of Sangamner taluka during July 2008. Satara and Dhule districts of the state, however, were found free from bacterial blight. In Andhra Pradesh disease was prevalent in mild to severe form in most pomegranate growing areas of Ananthpur district, whereas in Karnataka disease was prevalent in mild to moderate form in Bijapur, Gadag, Koppal and Bagalkot districts. All pomegranate cultivars grown in the region viz., 'Bhagwa', 'Ganesh', 'Mridula' and 'Arakta' were susceptible to the blight pathogen. Studies on disease epidemiology at Solapur revealed that though disease existed throughout the year at a temperature range of 9.0-43.0 degrees C and varying humidities (30.0->80.0%), disease development was rapid during the summer rainy months from July to September due to free water and high humidity. The Mrig bahar crop regulated in June-July (summer rainy season) revealed more disease pressure due to higher infection rate (0.2/unit/day) as compared to the Hastha bahar crop regulated in September-October (autumn season) which had an infection rate of 0.08/unit/day, thereby, indicating the brisk spread of the disease in the rainy season. Studies on pathogen's survivability revealed that Xanthomonas axonopodis pv. punicae was able to survive in naturally infected leaves collected from the diseased orchard for one year under laboratory conditions (25.0-38.0 degrees C). A field trial for the management of bacterial blight was conducted in an orchard having six-year-old 'Bhagwa' during 2007-2008. Adoption of an integrated disease management schedule which included practices like orchard sanitation, avoidance of rainy season crop (Mrig bahar) and regulating the Hastha bahar crop, judicious sprays of antibiotic Streptocycline (500 ppm) in combination with fungicides like carbendazim (0.15%)/mancozeb (0.2%)/copper oxychloride (0.25%) at 15 days interval resulted in 82.2% disease control and gave yield of 16 t/ha. In separate trials antibiotic Bactronol (2-Bromo, 2-Nitropropane, 1-3 diol) at 750-1000 ppm concentrations was also found effective in managing bacterial blight.