Natural occurrence and pathogenicity of Xanthomonas bacteria on selected plants

Abstract

The bacterial genus Xanthomonas consists of several species of economic importance, among which Xanthomonas campestris pv.musacearum (Xcm), the cause of enset and banana wilt is the most important in tropical Africa. However, the natural occurrence and host range of this species is yet to be clarified. The objectives of this study were to verify the presence of Xanthomonas bacteria on plants growing in and around enset gardens in South and Southwest Ethiopia, and to elucidate the pathogenicity of Xcm strains to cultivated and wild plants. Several economical and ornamental plants were assessed for wilting in South and Southwest Ethiopia. Wilting was visible on Canna spp. with 9.8% incidence and 30% prevalence, while reddish streak symptoms (typical of Xanthomonas bacteria) were observed on the leaves of sugarcane, sorghum and wild sorghum with disease incidence ranging from 20 to 80%, and prevalence varying from 30 to 100%. The pathogenicity of three Xcm isolates to five plant species was tested in a factorial experiment arranged in CRD with five replications. All the tested Xcm isolates were found to be pathogenic to banana, cultivated and wild enset, Canna indica, Canna orchoides, maize, sorghum and finger millet. The analysis of variance for incubation period and disease incidence revealed significant differences (p<0.05) among test plants and isolates. Results suggest marked variations among test plants' ability to resist the bacterium. Variations were also evident in the aggressiveness of the bacterial isolates. On the other hand, enset and banana did not show any symptom after being inoculated with four Xanthomonas isolates from other crops.

Evaluation of banana genotype resistant to Xanthomonas wilts disease (Xanthomonas campestris pv. musacearum) in south east of Ethiopia

“…However, isolate I 1 was found to be a weaker pathogen as compared to other isolates. The result of the present study is in accordance with the finding of Alemayehu et al (2016), who reported that significance differences among isolates were recorded to induce initial wilting three to four weeks after inoculation under greenhouse condition. Similarly, Ibrahim (2013) reported that there was difference among Xcm isolates for inducing disease symptom on inoculated genotype.…”

“…Yellowish bacterial ooze was observed, when pseudostem and leaf petiole were cut. Such typical symptoms were described under field and experiment condition by Gizachew (2000), Dereje (1985) and Alemayehu et al (2016).…”

Risks Posed by Intercrops and Weeds as Alternative Hosts to Xanthomonas campestris pv. musacearum in Banana Fields

“…A more recent study by Chala et al (2016) using three Xcm isolates obtained from cultivated enset, wild enset and banana reported typical disease symptoms 2–3 weeks after the inoculations with incidences of 40–67% in maize, 25–50% in sorghum, 13% in wild sorghum and 1–17% in millet ( Eleusine coracana ). However, some of the above studies did not report re-isolation of Xcm from these alternative host plants while Koch’s postulates were not reported in all the studies.…”

“…A number of studies have been conducted to understand how other plant species (weeds and cultivated crops) in the environment of banana and enset interact with Xcm (e.g., Yirgou and Bradbury, 1974; Ashagari, 1985; Ssekiwoko et al, 2006a; Aritua et al, 2008; Karamura et al, 2015; Chala et al, 2016). Whereas studies consistently report Canna spp., a common weed, to develop XW characteristic symptoms similar to those in banana after inoculation with Xcm (Ssekiwoko et al, 2006a; Chala et al, 2016), they give a mixed and less clear picture regarding the interaction of Xcm with the cereals, especially with maize.…”

“…Whereas studies consistently report Canna spp., a common weed, to develop XW characteristic symptoms similar to those in banana after inoculation with Xcm (Ssekiwoko et al, 2006a; Chala et al, 2016), they give a mixed and less clear picture regarding the interaction of Xcm with the cereals, especially with maize.…”