Evaluation of varietal resistance in cabbage against the black rot pathogen, Xanthomonas campestris pv. campestris in Tanzania

Abstract

The management of black rot of cabbage, caused by Xanthomonas campestris pv. campestris (Xcc), has increasingly become very difficult for smallholder growers in Tanzania due to cultivation of susceptible varieties. Thirty-one local and introduced cabbage varieties were screened for resistance to black rot under field conditions with varying rainfall pattern in Tanzania. Differences in resistance among varieties were observed in the field for both foliar and internal stem/head symptoms. Generally, varieties with good foliar resistance also showed less black rot in stems and heads. Open pollinated varieties were highly susceptible to black rot. Partially resistant F1 varieties included: Amigo F1, Maja F1, Rotan F1, Ducati F1, Adelita F1, Bravo F1, Blue Thunder F1, Fortress F1, JK-1 F1, Gianty F1, T-689 F1, N-9690 F1, N 66 F1 and Riana F1. However, some of these varieties had undesirable characteristics (head splitting, poor taste, loose or flat heads) for adoption by farmers in Tanzania. In another field trial, the reaction of five selected cabbage varieties to inoculation with four Xcc strains through the roots or foliage was investigated. Results did not reveal any apparent differential variety reactions to inoculation methods or Xcc strains. The extent of black rot development in the varieties was similar when Xcc strains were applied through the roots as compared to the leaf hydathode route, implying that improper crop debris disposal may aggravate black rot in cabbage in smallholder farmers’ fields. One aberrant strain of Xcc caused less severe black rot compared to the rest of the strains.