Molecular epidemiology studies further our understanding of migrations of phytopathogenic bacteria, the major determining factor in their emergence. Asiatic citrus canker, caused by Xanthomonas citri pv. citri, was recently reported in Mali and Burkina Faso, a region remote from other contaminated areas. To identify the origin and pathways of these emergences, we used two sets of markers, minisatellites and microsatellites, for investigating different evolutionary scales. Minisatellite typing suggested the introduction of two groups of strains in Mali (DAPC 1 and DAPC 2), consistent with microsatellite typing. DAPC 2 was restricted to Bamako district, whereas DAPC 1 strains were found much more invasive. The latter strains formed a major clonal complex based on microsatellite data with the primary and secondary founders detected in commercial citrus nurseries and orchards. This suggests that human activities played a major role in the spread of DAPC 1 strains via the movement of contaminated propagative material, further supported by the frequent lack of differentiation between populations from geographically distant nurseries and orchards. Approximate Bayesian Computation analyses supported the hypothesis that strains from Burkina Faso resulted from a bridgehead invasion from Mali. Multi-locus variable number of tandem repeat analysis and Approximate Bayesian Computation are useful for understanding invasion routes and pathways of monomorphic bacterial pathogens.
Bacterial leaf streak (BLS) caused by Xanthomonas oryzae pv. oryzicola was first reported in Africa in the 1980s. Recently, a substantial reemergence of this disease was observed in West Africa. Samples were collected at various sites in five and three different rice-growing regions of Burkina Faso and Mali, respectively. Sixty-seven X. oryzae pv. oryzicola strains were isolated from cultivated and wild rice varieties and from weeds showing BLS symptoms. X. oryzae pv. oryzicola strains were evaluated for virulence on rice and showed high variation in lesion length on a susceptible cultivar. X. oryzae pv. oryzicola strains were further characterized by multilocus sequence analysis (MLSA) using six housekeeping genes. Inferred dendrograms clearly indicated different groups among X. oryzae pv. oryzicola strains. Restriction fragment length polymorphism analysis using the transcriptional activator like effector avrXa7 as probe resulted in the identification of 18 haplotypes. Polymerase chain reaction-based analyses of two conserved type III effector (T3E) genes (xopAJ and xopW) differentiated the strains into distinct groups, with xopAJ not detected in most African X. oryzae pv. oryzicola strains. XopAJ functionality was confirmed by leaf infiltration on 'Kitaake' rice Rxo1 lines. Sequence analysis of xopW revealed four groups among X. oryzae pv. oryzicola strains. Distribution of 43 T3E genes shows variation in a subset of X. oryzae pv. oryzicola strains. Together, our results show that African X. oryzae pv. oryzicola strains are diverse and rapidly evolving, with a group endemic to Africa and another one that may have evolved from an Asian strain.
Cashew's (Anacardium occidentale L.) production in Burkina Faso suffers from several biotic constraints. The aim of this study was to inventory the diseases associated with the tree. Cashew orchards were prospected in the production belt of Burkina Faso including Hauts Bassins, Cascades, South-Western and, Center-Western regions. Four major diseases were observed including anthracnose (Colletotrichum gloeosporioides), Pestalotia leaf spot (Pestalotia heterocornis), bacterial leaf and nut spot (Xanthomonas citri pv. anacardii), and gummosis (Lasiodiplodia theobromae). The incidence of the diseases varied according to the locations; in addition, anthracnose was the most spread disease with high incidence. Gummosis was observed in all the locations and was the second threat to cashew production in South-West and West Center regions. The bacterial disease which affects all parts of the cashew tree was mainly observed in the Hauts Bassins region. No virus was detected during this survey. Altogether, the results of this study represent an important baseline data for the design and implementation of strategies for cashew protection in Burkina Faso.
Background: Environmental heterogeneity, emerging pathogens and limited access to financial and agricultural inputs prevent farmers from producing consistent crop yields in many developing countries. Yield instability impedes establishment of processing and export industries, thereby inhibiting economic development. Modern varieties offer significant increases in yield stability. Results:A deeply collaborative, multi-national germplasm trialing network was established in West Africa to identify tomato varieties well adapted to each country and mobilize those varieties into local seed distribution networks alongside an integrated pest management program. Research partners in seven West African countries evaluated over 100 tomato varieties for resistance to tomato leaf curl disease (ToLCD). Using biotechnology, the identity and distribution of the key viruses (begomoviruses) causing ToLCD in these countries were identified, and a vector-independent inoculation method (agroinoculation) was developed. The trials identified a set of high-performing varieties with resistance. Agroinoculation with the three prevalent begomoviruses confirmed resistance. Conclusions:These trial results fulfill the new Economic Community of West African States harmonized seed regulation policy, which requires at least 2 years of national performance trials prior to commercialization of a tomato variety. To compete with a rapidly expanding canned tomato import industry, West African growers need to increase productivity and processing capacity; therefore, we also assessed processing and export trade data for fresh and processed tomatoes from each of the seven countries.
Citrus canker, caused by Xanthomonas citri pv. citri, is a bacterial disease of economic importance in tropical and sub-tropical citrus-producing areas (EPPO-PQR online database). X. citri pv. citri causes severe infection in a wide range of citrus species, and induces erumpent, callus-like lesions with water-soaked margins leading to premature fruit drop and twig dieback. It has consequently been subjected to eradication efforts and international regulations. It was first described on the African continent in South Africa at the beginning of the 20th century, from which it was eventually eradicated. Since 2006, several outbreaks caused by phylogenetically diverse strains of X. citri pv. citri have been reported from several African countries (Ethiopia, Mali, Senegal, and Somalia). In July 2011, citrus canker in Burkina Faso was suspected in the area adjacent to the Sikassso Province of Mali where X. citri pv. citri has been confirmed. In November and December 2012, leaves of clementine (Citrus clementina), lemon (C. limon), Volkamer lemon (C. volkameriana), sweet orange (C. sinensis), tangelo (C. paradisi× C. reticulata), and mandarin (C. reticulata) were collected from orchards with trees showing symptoms of citrus canker in the Comoé, Houet, and Kénédougou provinces of Burkina Faso. Isolations performed using KC semi-selective medium (4) recovered 45 Xanthomonas-like strains. All Xanthomonas-like strains were tentatively identified as X. citri pv. citri by PCR (4/7 primers) using IAPAR 306 and sterile distilled water as the positive and negative controls, respectively (3). Among these, two strains (LK4-4 and LK4-5) produced a ‘fuscans’-like brown diffusible pigment, a phenotype never reported previously for X. citri pv. citri. MultiLocus Sequence Analysis targeting six housekeeping genes (atpD, dnaK, efp, gltA, gyrB, and lepA) (1,2) fully identified seven strains from Burkina Faso (LJ301-1, LJ303-1, LK1-1, LK2-6, LK4-3, LK4-4, and LK4-5) as X. citri pv. citri (and not to any other Xanthomonas pathovars pathogenic to citrus or host range-restricted pathotypes of pathovar citri), and more specifically as sequence type ST2 which is composed mostly of pathotype A strains of X. citri pv. citri (2). The same seven strains were inoculated to at least four leaves of each of grapefruit cv. Henderson, Mexican lime SRA 140 (C. aurantifolia), Tahiti lime SRA 58 (C. latifolia), and sweet orange cv. Washington Navel, using a detached leaf assay (2). All strains developed typical erumpent, callus-like tissue at wound sites on all citrus species inoculated. No lesions developed on the negative control (sterile 10 mM tris buffer). Koch's postulate was fulfilled after reisolation of Xanthomonas-like yellow colonies from symptoms on Mexican lime produced by the seven strains. Boiled bacterial suspensions were assayed by PCR with 4/7 primers (3) and produced the expected 468-bp amplicon in contrast with the PCR negative control. To our knowledge, this is the first report of X. citri pv. citri in Burkina Faso. Citrus canker-free nurseries and grove sanitation should be implemented for reducing the prevalence of Asiatic canker in Burkina Faso and a thorough survey of citrus nurseries and groves in the region should be conducted. References: (1) N. F. Almeida et al. Phytopathology 100:208, 2010. (2) L. Bui Thi Ngoc et al. Int. J. Syst. Evol. Microbiol. 60:515, 2010. (3) J. S. Hartung et al. Phytopathology 86:95, 1996. (4) O. Pruvost et al. J. Appl. Microbiol. 99:803, 2005.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.