Bacterial blight (BLB) caused by Xanthomonas axonopodis pv. punicae (Xap) has emerged as a potential threat in pomegranate cultivation in India. To know the present disease scenario and to identify the root cause for its epidemic, survey was conducted in five different localities of Tamil Nadu. Per cent disease severity (PDS) ranged from 1 to 36 per cent on leaves and zero to 40 per cent infection on fruits. Bacteriophage or bacteria killer specific to Xap-1 (Sennampatty) isolate was isolated from pond water after enrichment of water sample. Phage produced plaques of 2 mm, 1 mm and < 1mm size that coalesced after 18 h of plating which shows virulence and rapid phage multiplication. Disease severity on test plants were studied to know the degree of virulence and variability among the isolates with highest severity of 37.31 per cent documented in Xap-1 followed by Xap-3 (28.7%) and Xap-2 (24.3%). Physiological factors such as temperature, pH and their role in growth of Xap-1 were accessed. Maximum growth was observed at 28˚C (0.86 OD) followed by 30˚C (0.68 OD) and pH 7 (1.83 OD) and optimum at 7-8 pH for virulent (Xap-1) isolate. Molecular confirmation of Xap through 16S rRNA sequencing gave the amplicon of 1500 bp size and amplification through KKM5 and KKM6 further confirmed specific identity.
Key words : Pomegranate, Bacterial blight, Bacteriophage, Physiological and molecular characterization