First Report of Cassava Bacterial Blight Caused by Xanthomonas axonopodis pv. manihotis in Burkina Faso

Abstract

Xanthomonas axonopodis pv. manihotis is the causal agent of Cassava Bacterial Blight (CBB) which is a major disease of cassava in tropical and subtropical areas. CBB is a foliar and vascular disease characterized by angular leaf lesions, blight, wilting, stem exudates and stem cankers. Since cassava is propagated clonally from stem cuttings, CBB plays a major role in limiting productivity with losses between 12-100% affecting both yield and planting material. In August of 2011 and October of 2012, CBB symptoms were observed on tenmonths-old field cassava grown in Bonfeba and in Takeledougou, Burkina-Faso (Cascades region). Symptoms consisted of angular water-soaked leaf lesions, wilt and visible exudates on the stem. White Xanthomonas-like strains were isolated from leaf tissues on LPGA medium (yeast 5 g, peptone 5 g, glucose 5 g, bacto agar 15 g, distilled water 1,000 ml). A PCR assay developed for the identification of X.axonopodis pv. manihotis (1) was used to determine the identity of Xanthomonas-like strains. X.axonopodis pv. manihotis strain CFBP7661 was used as a positive control. The expected DNA fragment (898bp) was obtained from all the strains. No fragment was observed for negative controls (distilled water as the template). Three X. axoponodis pv. manihotis strains were further analyzed by sequence analysis using the gyrB and rpoD housekeeping genes. When comparing rpoD and gyrB sequences, strains were 99 to 100% identical to sixty five different strains of X. axonopodis pv. manihotis. Pathogenicity tests were performed on greenhouse-grown 4-week-old cassava plants cv. MCOL 1522. Cultures were grown overnight in LPGA medium and adjusted in sterile water to 1 × 10 8 CFU/ml and inoculated into cassava leaves and stems as previously described (2). Control plants were inoculated with sterile water. X.axonopodis pv. manihotis strain CFBP7661 was used as a positive control. After 7 days of incubation in the greenhouse at 28 ± 1°C with a 12h photoperiod, inoculated leaves developed water-soaked lesions. Wilted leaves and stem exudates were visible at 30 days after stem inoculation. Symptoms were identical to those seen in the field. Control plants remained symptomless. Koch's postulates were fulfilled after re-isolation of Xanthomonas-like white strains from leaf symptoms on inoculated cassava and confirmation as X. axonopodis pv. manihotis by PCR assay as described above. Three strains (CFBP7945, CFBP7946, CFBP7947) were deposited in the French Collection for Plant-associated Bacteria (CIRM-CFBP). Information on Xam strains as well as gyrB and rpoD sequences are available through CIRM-CFBP http://www6.inra.fr/cirm_eng/CFBP-Plant-Associated-Bacteria. To our knowledge, this is the first report of CBB in Burkina Faso. Since cassava is becoming a crop of importance for human consumption in Burkina-Faso, CBB may limit productivity. Further surveys will be necessary to evaluate the geographic distribution and prevalence of CBB in Burkina-Faso and neighboring countries.1.

Improvement of the specific detection of <i>Xanthomonas phaseoli</i> pv. <i>manihotis</i> based on the <i>pthB</i> gene

“…For the reactions using the primer pair XV / XK developed by Verdier et al (1988), there was no amplification of the samples used. Contrary to what was verified by Wonni et al (2015), the expected DNA fragment was obtained from all the Xpm strains. However, five nonpathogenic Xpm strains were tested with the primer pair from the assay and produced no amplification product (Verdier et al, 1998).…”

“…manihotis (Constantin et al 2016) is one of the most destructive diseases of cassava (Manihot esculenta Crantz) (Parkes, Fregene, Dixon, Boakye-Peprah, & Labuschange, 2013). CBB is a foliar and vascular disease characterized by angular leaf lesions, blight, wilting, stem exudates, stem cankers, water-soaked lesions, angular necrotic lesions on the leaf blade, and necrotic lesions on the petioles and stem with gummosis (gum exudation) (Lopez & Bernal, 2012;Wonni et al, 2015).…”

Identification of cassava bacterial blight-causing Xanthomonas axonopodis pv. Manihotis based on rpoD and gyrB genes

“…The rpoD and gyrB genes have been used as molecular markers for the rapid detection and characterisation of Xam in Burkina Faso [23] and in the Ivory Coast [13], suggesting that these genes can be used for the study of a variety of bacterial pathogens.…”

The role of type III effectors from Xanthomonas axonopodis pv. manihotis in virulence and suppression of plant immunity

“…This disease threatens food security in the tropics, where cassava constitutes a major staple food (CABI, ; FAO, ). Rapid dispersal of CBB in some cassava production regions (Joseph and Elango, ) and new disease reports in regions in which cassava is a staple crop (Kone et al ., ; Wonni et al ., ) underscore the importance of finding new ways to manage this plant disease (Lopez and Bernal, ). The management of this, as well as other, plant diseases would greatly benefit from a comprehensive knowledge of pathogen population dynamics and of the genetic bases for virulence in the pathogen and for resistance/susceptibility in the plant (Dangl et al ., ; Li Y et al ., ).…”