Recent progress in the characterization of molecular determinants in the Xanthomonas axonopodis pv. manihotis–cassava interaction

Abstract

Cassava bacterial blight, caused by Xanthomonas axonopodis pv. manihotis (Xam), is a widespread disease that affects cassava (Manihot esculenta Crantz). Studies on the pathogen population structure, pathogen diagnosis, identification and expression of plant genes involved in resistance have been carried out. Different molecular techniques were developed to assess the genetic diversity among the Xampopulations. Characterization of Xam population dynamics over time had enable us to determine the different factors that are associated with resistance breakdown and those that influence the genetic structure or virulence phenotypes of the pathogen's population. Methods for detecting the pathogen in vegetative planting materials and true seeds were developed and contributed to reduce the impact of the disease. To better understand the genetics of resistance a quantitative trait loci (QTLs) approach was developed. Using a PCR-based strategy with degenerate primers we isolated two resistance gene candidates in cassava. We also characterized a region of a chromosome rich in R-gene like sequence. In this review we also report the main results obtained by transcript profiling methodologies, cDNA-AFLP and ESTs developed by the authors to characterize the genes involved in disease resistance. All together these techniques allowed the identification of molecular markers either associated to CBB resistance or that may represent putative genes involved in disease resistance. This article reviews current knowledge on the molecular cassava-Xam interactions.

Phenotypic and genotypic diversity of Xanthomonas axonopodis pv. manihotis causing bacterial blight disease of cassava in Kenya

“…Colony color varied from white to cream in all the isolates except one isolate (Xam12-W) that was yellow (Figure 3). These observations confirm reports by Verdier et al [23] who found that Xam colonies appear creamy and whitish in color and form distinct isolated colonies. In addition, Trujillo et al [24] reported that Xam cultured on selective media is distinguished by white and cream colonies.…”

“…Leaf tissues were macerated into small pieces of about 2 mm 2 ). The Petri dishes were incubated at 28 °C for 48 hours.…”

“…manihotis (Xam) is a major disease of cassava across sub-Saharan Africa and South America. It is a vascular disease that reduces the production of cassava up to 100% since it affects both planting material and yields [2,3]. Diverse symptoms are displayed by CBB infected cassava plants including wilting of leaves, blighting, formation of angular leaf lesions, stem cankers, stem and leaf exudates production and, dieback of stems.…”

Unlocking the potential of tropical root crop biotechnology in east Africa by establishing a genetic transformation platform for local farmer-preferred cassava cultivars

“…manihotis (Xam) . This disease is present in all regions where cassava is grown and production losses can reach up to 80 or 100% (Verdier et al, 2004; Ogunjobi and Dixon, 2006). While there are a few cassava cultivars that show relatively high levels of natural resistance to CBB (Restrepo et al, 2004), they are either not well adapted to particular agroecological regions where cassava is cultivated or do not exhibit the farmer- and/or consumer-preferred characteristics.…”

Cassava: An appraisal of its phytochemistry and its biotechnological prospects

“…manihotis is a world-wide problem causing bacterial blight on cassava Chellappan et al, 2004;Fregene et al, 2004;Gómez-Vásquez et al, 2004;Kemp et al, 2004Kemp et al, , 2005Taylor et al, 2004;Tomkins et al, 2004;Zhang et al, 2005). Whilst the host-pathogen interaction, the genetic diversity of the pathogen, and genetic determinants of resistance in the host have been studied (Jorge et al, 2000;Lopez et al, 2005;Verdier et al, 2004), no clear mechanism for controlling the disease through either breeding or biotechnology is available. Like a surprisingly high proportion of food plants, cassava is cyanogenic (Jones, 1997).…”