POMEGRANATE BACTERIAL BLIGHT: SYMPTOMATOLOGY AND RAPID INOCULATION TECHNIQUE FOR XANTHOMONAS AXONOPODIS pv. PUNICAE

Abstract

Complete range of symptoms of bacterial blight caused by Xanthomonas axonopodis pv. punicae on various pomegranate plant parts including fruit are described and illustrated. Some of the symptoms are reported for the first time. The pathogen caused blight symptoms on all plant parts except roots and flower. Among nine different inoculation methods evaluated for X. axonopodis pv. punicae on pomegranate, the spray method convincingly proved that spraying of inoculum yielded highly reproducible symptoms within 21 days under optimal temperature and humidity conditions and up to 39 days under less favourable conditions. Spray method was found to show blight symptoms on leaves with incidence of 71.0% and severity of 55.5%. Besides, the lesions which appeared on plants mimicked the natural symptoms observed in orchards. The incubation period for blight development ranged from 4 to 19 days depending on temperature and humidity conditions. The most favorable condition for onset of blight as well as completion of disease cycle was when temperature ranged between 25-35°C for at least 16 h and relative humidity >30% for 24 h. The spray method of inoculation is, therefore, recommended as a rapid, reproducible screening technique for pomegranate genotypes in resistance breeding programmes. The study indicated that X. axonopodis pv. punicae infects plant tissues through both natural opening as well as by injuries. The culture and PCR based detection assay further confirmed that the bacterial blight pathogen displayed no translaminar systemic movement and caused only localized lesions.