The suppression subtractive hybridization was employed to elucidate the resistance mechanism in Brassica oleracea var. capitata upon infection with Xanthomonas campestris pv. campestris. A cDNA library was constructed enriched in differentially expressed transcripts in the resistant cultivar Pusa mukta. A total of 150 unigenes were classified into five functional categories. The present study indicates that the defense-related unigenes accounted for the 35 % of the total unigenes studied. Confirmation of defense-specific representation genes through semiquantitative RT-PCR revealed their increased expression in the resistant cultivar which was validated by qPCR. The resistant cultivar elicited a strong hypersensitive response upon attack by black rot pathogen. The study is first of its kind where the resistant cultivar Pusa mukta in India has been assessed for its resistance to the bacterial pathogen.

Cabbage (Brassica oleracea var. capitata) is an important vegetable crop among crucifers. It is affected by a bacterial disease known as black rot. Black rot is caused by Xanthomonas campestris pv. campestris a disease of worldwide importance. The present study highlights the effect of biotic inducer—Pseudomonas fluorescens—and an abiotic inducer—2,6‐dichloro‐isonicotinic acid—in combating black rot, followed by their effect on the seed treatment and disease incidence, role of antioxidant enzymes followed by validation of the defence‐related genes by quantitative real‐time PCR. The resistant (Pusa mukta) and the highly susceptible (NBH boss) cabbage cultivars were analysed for defence‐related enzymes such as peroxidase and superoxide dismutase. An increase in total peroxidase and superoxide dismutase activity was observed upon inoculation with X. campestris pv. campestris. The activity was greater in resistant cultivar when compared to susceptible ones. Both enzyme activity assays and qPCR analyses for the expression of the defence genes in susceptible and resistant cultivars demonstrated that the peroxidase gene was up‐regulated in resistant cultivar compared to susceptible cultivar. The present study proved that P. fluorescens‐induced resistance against X. campestris pv. campestris in cabbage seedlings is more efficient as compared to the use of INA—abiotic inducer.