Black rot, caused by Xanthomonas campestris pv. campestris (Xcc) is a disease of crucifer crops. The objective of this study was to characterize races of Xcc, their distribution and genetic diversity in India. Two hundred and seventeen isolates of bacteria were obtained from 12 different black rot‐infected crucifer crops from 19 states of India; these were identified as Xcc based on morphology, hrpF gene and 16S rRNA gene based molecular markers and pathogenicity tests. Characterization of races was performed by using a set of seven differential crucifer hosts, comprising two cultivars of turnip (Brassica rapa var. rapa) and cultivars of Indian mustard (B. juncea), Ethiopian mustard (B. carinata), rapeseed mustard (B. napus), cauliflower (B. oleracea) and Savoy cabbage (B. oleracea var. sabauda). Races 1, 4 and 6 of Xcc were identified and, among these races, race 1 followed by race 4 dominated most of the states of India. Genetic diversity of the Indian isolates of Xcc was analysed using repetitive sequence‐based PCR (rep‐PCR) including primers for REP (repetitive extragenic palindromic), ERIC (enterobacterial repetitive intergenic consensus) and BOX (amplifying with BOX A1 R primer) repetitive elements. This method of fingerprinting grouped the isolates into 56 different DNA types (clusters) with a 75% similarity coefficient. Among these clusters, DNA types 22 and 53 contained two different races 1 and 4, whereas DNA type 12 contained races 1, 4 and 6. However, no clear relationship was observed between fingerprints and races, hosts or geographical origin.

Xanthomonas campestris pv. campestris (Pammel) Dowson (Xcc) is the causal agent of black rot disease of crucifers worldwide. Seventy five isolates of Xcc were collected from 12 agro-climatic regions of India to determine the distribution pattern of races and diversity of the population. Based on pathogenic reaction on seven standard differential crucifers, race 1, 4 & 6 were found to be prevalent. For assessing the pathogenic diversity, forty one cultivars of crucifers comprising seven Brassica and coeno species were inoculated artificially under field conditions. Brassica juncea cultivars (Pusa Bold, Varuna, Pusa Vijay, Pusa Mustard 21 and Pusa Mustard 25) showed resistance against all the strains of Xcc, whereas the Brassica olerecea cultivar Pusa Ageti was found to be resistant to races 1 and 4. Genetic characterization of these 75 strains of Xcc was carried out using rep-PCR (ERIC, REP and BOX-PCRs) followed by phylogenetic analysis. The strains of Xcc clustered into 6 groups at 50% similarity coefficient and among these groups, 28 strains of Xcc belonging to races 1, 4 & 6 were clustered together under Group 5. Sequences of the 16S rRNA, hrpF and efP genes of five strains representing the races 1, 4 and 6 were used for multilocus sequence analysis. Based on sequence analysis of 16S rRNA and hrpF genes, the Indian strains were found to be very closely related to the strain Xcc ATCC 33913 (race 3, UK), whereas based on efP sequences, they were found to be closely related to strains race 1 Xcc B100 (Italy) and race 9 Xcc 8004 (UK).

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Xanthomonas campestris pv. Campestris (Xcc) causing black rot disease of crucifer crops, is a serious worldwide problem resulting in >50% loss under environmental conditions favorable to the pathogen. For the characterization of Xanthomonas campestris pv. campestris races to standardize the Indian cultivars of Brassica spp. total of 184 representatives lines of the family crucifereae from of five economically important Brassica species, i.e. B. carinata, B. juncea, B. napus, B. oleracea, and B. rapa grown in India were inoculated by 75 strains of Xcc, belonging to three races 1, 4 and 6 in 2012-13 and 2013-14. Disease reaction of these cultivars was compared with the standard differential hosts of crucifer for disease incidence and diseases severity. Indian cultivars of B. juncea (Pusa Bold, Pusa Varuna, Pusa Vijay, Pusa Mustard-21, Pusa Mustard-25, Pusa Sag), B. olerecea var. botrytis (Pusa Sukti), B. olerecea var. capitata (KGMR) and B. rapa (Pusa Swarnima) were at par with the standard differentials of respective Brassica species and thus could be suitable to useas alternative differential hosts for characterization of Xcc races. 20 cultivars of Brassica spp. grown in India were further validated as differential crucifer host to characterize the races of Xcc on the molecular basis using four set of primers, viz. CAPS (ACS2) CAPS (BTPT) and CAPS (NDPK3) and among them, Br 019305 primer amplified at 906 bp in all cultivars, while primer CAPS (ACS2), CAPS (BTPT) and CAPS (NDPK3) primers were amplified multiple bands. Combined phylogenetic UPGMA study at 75% similarity coefficient, 19/20 accessions were divided into three groups and distinguished resistant and susceptible cultivars against black rot disease.