An Evaluation of Black Rot (Xanthomonas campestris pv. campestris) Disease Tolerance in Four Cabbage (Brassica oleracea var. capita ) Varieties

Abstract

Black rot (Xanthomonas campestris pv. campestris), is a major disease of the Brassica family throughout the world. In Zimbabwe the black rot problem is aggravated by cultivation of susceptible varieties by farmers and lack of technical expertise on disease management strategies. A field study was conducted at Africa University, Zimbabwe to evaluate tolerance of four cabbage (Brassica oleracea var. capitata) varieties that is Star 3301, Star 3311, Star 3316 and Star 3317, to black rot disease. The experiment was laid out in Randomized Complete Block Design (RCBD) with three replications and four varieties in each block. Each plot comprised 4 rows containing 8 plants in each row. Cabbage seedlings were transplanted on the 21st of January 2014. Compound D was applied as a basal dressing at the rate of 30g per plant station. At 21days after transplanting Ammonium Nitrate was applied at the rate of 2g per plant station. The seedlings were drenched using Carbaryl to control cutworms. Cultural practices such as sprinkler irrigation and weeding were carried out when necessary. Data on disease incidence and disease severity was collected from the 7th week after transplanting for four consecutive weeks. Bacterial Black Rot Disease Score Sheets on Brassicas were used for data recording as well as calculation of disease incidence and disease severity. Raw data on disease incidence was used to calculate Area Under Disease Progress Curve (AUDPC). Star 3311 had the least Area Under Disease Progress Curve (58cm²) while Star 3316 had the highest AUDPC (59.8cm²). Disease severity was low throughout the study period with a mean score of 3 for Star 3301, Star 3311, and Star 3316 while Star 3317 had a mean disease severity score of 4. Disease incidence was high throughout the study period reaching up to 100% in the 10th week after transplanting. Mean cabbage head weight was highest for Star 3311 and least for Star 3317. Area Under Disease Progress Curves and cabbage head weights were subjected to One-Way ANOVA Minitab Version. There was no significant difference among the four treatments at p ≤ 0.05, meaning that they had the same black rot disease tolerance levels. Yield difference was found to be insignificant among the four varieties. Farmers can still achieve higher yields if Star 3311 is selected as it showed slightly higher resistance level when compared to the other varieties.