Black Rot (Xanthomonas campestris pv. campestris) Control in Field Grown Cabbage (Brassica oleracea var. Sugar Loaf) with Moringa oleifera Extracts

Aims: To evaluate if the antibacterial compounds present in Moringa were significant enough to effect suppressive effect on Xanthomonas campestris pv campestris (black rot) in field grown cabbages (Brassica oleracea), in an open field experiment.

Study Design: The experimental design was a 3 x 3 factorial laid out in a split plot in two blocks with three replicates.

Place and Duration of Study: Field experiments were carried out for 6 months during the October 2015 to April 2016 season at Victory Farm in Beatrice, Zimbabwe

Methodology: Three aqueous Moringa extracts (leaf, bark, and seed) at 3 concentration levels of 60, 100 and 140% were sprayed as foliar applications weekly from 5 weeks after crop emergence in cabbages for the duration of the study. The antibacterial activity for each of the different Moringa plant extracts was evaluated by recording number of totally defoliated plants once every week.

Results: The results indicated high significance in antibacterial activity of all the three Moringa extracts as they were able to achieve control of Xanthomonas campestris pv campestris black rot disease at varying levels in the cabbage plants (P < 0.05). The highest inhibition of black rot disease progression was recorded during 8th week after crop emergence with the seed extract recording the least mean leaf defoliation of 2.965 followed by the bark extract (3.312) and lastly leaf extract (3.486). Moringa seed extract had the highest antibacterial activity against the black rot disease in cabbages in this study.

Conclusion: Bacterial black rot disease caused by Xanthomonas campestris pv campestris in cabbage can be effectively managed by using either seed, bark, or leaf aqua-based Moringa extract sprays. The 100 and 140% concentration levels were most effective, compared to the 60% concentration level. Further studies need to be carried out to assess if the utilization of the Moringa seed extract as a seed dressing would not increase its antibacterial effects against the test pathogen since it is an important seed borne disease of brassicas and crucifers.