Evaluation of Bacterial Black Rot Disease (Xanthomonas Campestris PV. Campestris) Tolerance in Cabbage Carieties (Brassica Oleracea Var,. Capita)

Abstract

Bacterial black rot disease of Brassicas caused by bacterium Xanthomonas campestris pv. campestris has increasingly become the major constraint to sustained production of cabbage worldwide. Black rot problem is aggravated by continuous cropping due to cultivation of susceptible varieties and lack of suitable disease management strategies. Other challenges faced by smallholder farmers in the management of black rot include problems in seed quality. Field studies were conducted at Africa University farm situated in Mutare to evaluate black rot tolerance in cabbage varieties: Potomac, Star 3301, and Star 3311and Star 3316 from mid February to early May 2012. Cabbage seedlings were raised in the greenhouse and transplanted into the field plots on the 18th of February 2012. The experiment set up was laid out in a randomized block design with three replications and four varieties in each block (RCBD). Compound D was applied as a basal fertilizer at the rate of 30 grams per plant station and Carbaryl was applied on day of transplanting to control cutworms (Agrotis spp.). Data on disease incidence and severity was collected as from the 8th week after transplanting for four consecutive weeks. A Bacterial Black Rot Disease Score on Brassicas was used for data recording and calculating disease incidence and disease severity. Raw data on disease severity was used to prepare graphs and to calculate area under disease progress curve (AUDPC). Results showed that the variety Potomac was highly susceptible with AUDPC of 54 cm2 for the 3 replications as compared to the other 3 varieties. Potomac had higher disease incidence for week 1 it was 8.3%, week 2 25%, week 3 37.5% and rose to 58.5% in the fourth week. Data on disease severity was subjected to ANOVA in Minitab version 15 after transforming the data using the √(x+1) transformation. All varieties showed no significant difference in disease severity levels at P¿0.05 but in terms of disease incidence there were notable differences. This work established that the variety Star 3311 has high tolerance to bacterial black rot disease while variety Potomac was more susceptible. One would recommend farmers to choose among the Star varieties especially Star 3311 which is highly tolerant to black rot disease.