Assessment of intrapathovar variability of Xanthomonas axonopodis pv. commiphorae through phenotypic and molecular markers

Abstract

Gummosis of guggal (C ommiphora wightii ) caused by X anthomonas axonopodis pv. commiphorae (X ac ) is one of the major reasons for drastic reduction in guggal population under natural plant stand. The pathogen spreads mainly through human activities (tapping). We isolated 43 X ac strains from 14 locations representing four different regions spread over three districts of Gujarat state, India. A polyphasic approach was followed to characterize these strains and to measure phenotypic and genetic variations among them. All strains were identical in colony morphology and were virulent on guggal. Some of the strains showed differential reactions towards certain biochemical tests viz ., acid production from carbon sources. Whole cell protein profiles were apparently uniform for all strains with similarity coefficients ranging between 0.75 and 1.00. Clustering based on sodium dodecyl sulphate–polyacrylamide gel electrophoresis banding patterns showed heterogeneity among the isolates, but strains originating from same zone had similar protein profiles. Inter simple sequence repeats (ISSR )‐based and repetitive elements (rep)‐based PCR analyses revealed genetic heterogeneity among the strains. Both these methods were equally effective in deciphering variability among the strains and indicated similar types of variability with highly significant correlation (r = 0.91) on the similarity matrices. The variation matrix analysis on combined ISSR ‐ and rep‐PCR data suggested 66.1% variability among X ac strains. The present study established that X ac strains from different geographical locations had profound genetic heterogeneity.