Genetic Structure and Population Dynamics of Xanthomonas axonopodis pv. manihotis in Colombia from 1995 to 1999

Abstract

Restriction fragment length polymorphisms (RFLPs) were used to study the population genetics and temporal dynamics of the cassava bacterial pathogen Xanthomonas axonopodis pv. manihotis. The population dynamics were addressed by comparing samples collected from 1995 to 1999 from six locations, spanning four different edaphoclimatic zones (ECZs). Forty-five different X. axonopodis pv. manihotis RFLP types or haplotypes were identified between 1995 and 1999. High genetic diversity of the X. axonopodis pv. manihotis strains was evident within most of the fields sampled. In all but one site, diversity decreased over time within fields. Haplotype frequencies significantly differed over the years in all but one location. Studies of the rate of change of X. axonopodis pv. manihotis populations during the cropping cycle in two sites showed significant changes in the haplotype frequencies but not composition. However, variations in pathotype composition were observed from one year to the next at a single site in ECZs 1 and 2 and new pathotypes were described after 1997 in these ECZs, thus revealing the dramatic change in the pathogen population structure of X. axonopodis pv. manihotis. Disease incidence was used to show the progress of cassava bacterial blight in Colombia during the 5-year period in different ecosystems. Low disease incidence values were correlated with low rainfall in 1997 in ECZ 1.Cassava, Manihot esculenta Crantz, is a starchy root crop that is among the most important tropical foods. About 80% of the cassava produced is consumed in developing countries and constitutes the principal carbohydrate source for more than 500 million people (14). Cassava bacterial blight (CBB) has caused extensive damage to the crop during the past 2 decades (6, 14, 30). The causal agent, Xanthomonas axonopodis pv. manihotis, can induce a wide variety of symptoms, including angular leaf spots, blight, gum exudation, stem cankers, shoot wilt, vascular necrosis, and dieback (15). Resistance, which has been identified in M. esculenta and the wild relative Manihot glaziovii, is thought to be polygenic and additively inherited (9). Molecular markers have been employed to construct a genetic map of the cassava genome consisting of several hundred markers (8). The mapping of CBB resistance has recently been reported both in controlled conditions and in the field (10, 11). Resistance to X. axonopodis pv. manihotis strains is controlled by several quantitative trait loci (QTL) located in different linkage groups, suggesting a specific interaction between the plant and the pathogen. Some of these QTL are specific to one strain, showing the complexity of this host plant-pathogen interaction (10). Since 1983, the entire cassava breeding strategy has been based on improving varieties for different edaphoclimatic zones (ECZs) (1). The ECZs were defined according to the importance of cassava production in that region, climatic conditions, predominant soil type, and pest and disease problems (2). Seven zones exist: ECZ 1, subhumid tropics;...

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

“…Although a lower number of clearly scorable bands were observed in some isolates (Figure 5), the three repeats of rep-PCR amplifications revealed that the absent bands are reproducible. The findings from the present study are in agreement with reports by Restrepo et al [33] demonstrating the high discriminatory power of rep-PCR when characterizing Xam populations with low levels of genetic diversity in Colombia.…”

Temporal and Spatial Scaling of the Genetic Structure of a Vector-Borne Plant Pathogen

“…If that were the case, one would expect locally adapted populations to be recalcitrant to introduction of less-fit genotypes from other regions. Because replacement of bacterial plant pathogen populations has been observed in crops (38), it is important to determine whether pathogen population replacement has occurred over time for diseases of perennial crops. The replacement of pathogen populations could, in the long term, lead to dissimilar disease control strategies, because distinct populations would differentially affect host crops (41).…”

Genetic Diversity and Pathogenicity of Xanthomonas axonopodis Strains Inducing Citrus Canker Disease in Iran and South Korea

“…AFLP has proven to be useful for identifying bacterial strains at subgeneric level [5,10,11,14,15,17,18,20]. Although the results of AFLP fingerprinting are specific and show high resolution to differentiate bacterial strains at the subgeneric level, it is very clear that the efficacy of this method not only depends on the choice of a suitable restriction enzyme that cleaves the most stable site in the bacterial genome but also depends on application of suitable primer to amplify the unique fragment of bacterial genome which can differentiate one strain from the others.…”

“…manihotis from each other and also from other Xanthomonas strains. Restrepo et al [18] characterized genetic structure and population dynamics of X. axonopodis pv. manihotis in Colombia from 1995 to 1999 and identified 45 RFLP types or haplotypes.…”