Vasicola Pv Research Articles

Identification of quantitative trait loci associated with maize resistance to bacterial leaf streak

AbstractBacterial leaf streak (BLS), a foliar disease of maize (Zea mays L.) caused by Xanthomonas vasicola pv. vasculorum, recently emerged in the Americas as a disease of major importance. Little is known about the disease cycle, and consequently, management is difficult. No chemical control is available. Host resistance will likely play a major role in controlling the disease, but to date, no data regarding the resistance of maize germplasm to X. vasicola pv. vasculorum have been published. The objective of this study was to examine the genetic architecture of resistance to BLS. We conducted quantitative trait locus (QTL) mapping for BLS resistance in three maize populations: the Z022 (B73 × Oh43 recombinant inbred line) nested association mapping (NAM) population, the Z023 (B73 × Oh7B recombinant inbred line) NAM population, and the DRIL78 (NC344 × Oh7B chromosome segment substitution line) population. A total of five QTL were detected across two of the mapping populations. Of the QTL detected, one conferred a moderate effect, whereas the others conferred small effects. We also examined the relationship between resistance to BLS and resistance to three foliar diseases of maize, which had been mapped previously. The only significant correlation we found for BLS was with northern corn leaf blight [caused by Exserohilum turcicum (Pass.) K. J. Leonard & Suggs] in one of the populations, although two of the five BLS regions were involved in resistance to other diseases. These data will be useful for developing maize varieties resistant to BLS to mitigate the impact of bacterial leaf streak on maize production.

First Report of Bacterial Leaf Streak of Corn Caused by Xanthomonas vasicola pv. vasculorum in Illinois

First Report of Bacterial Leaf Streak of Corn Caused by <i>Xanthomonas vasicola</i> pv. <i>vasculorum</i> in Illinois

A new Multi Locus Variable Number of Tandem Repeat Analysis Scheme for epidemiological surveillance of Xanthomonas vasicola pv. musacearum, the plant pathogen causing bacterial wilt on banana and enset.

Xanthomonas vasicola pv. musacearum (Xvm) which causes Xanthomonas wilt (XW) on banana (Musa accuminata x balbisiana) and enset (Ensete ventricosum), is closely related to the species Xanthomonas vasicola that contains the pathovars vasculorum (Xvv) and holcicola (Xvh), respectively pathogenic to sugarcane and sorghum. Xvm is considered a monomorphic bacterium whose intra-pathovar diversity remains poorly understood. With the sudden emergence of Xvm within east and central Africa coupled with the unknown origin of one of the two sublineages suggested for Xvm, attention has shifted to adapting technologies that focus on identifying the origin and distribution of the genetic diversity within this pathogen. Although microbiological and conventional molecular diagnostics have been useful in pathogen identification. Recent advances have ushered in an era of genomic epidemiology that aids in characterizing monomorphic pathogens. To unravel the origin and pathways of the recent emergence of XW in Eastern and Central Africa, there was a need for a genotyping tool adapted for molecular epidemiology. Multi-Locus Variable Number of Tandem Repeat Analysis (MLVA) is able to resolve the evolutionary patterns and invasion routes of a pathogen. In this study, we identified microsatellite loci from nine published Xvm genome sequences. Of the 36 detected microsatellite loci, 21 were selected for primer design and 19 determined to be highly typeable, specific, reproducible and polymorphic with two- to four- alleles per locus on a sub-collection. The 19 markers were multiplexed and applied to genotype 335 Xvm strains isolated from seven countries over several years. The microsatellite markers grouped the Xvm collection into three clusters; with two similar to the SNP-based sublineages 1 and 2 and a new cluster 3, revealing an unknown diversity in Ethiopia. Five of the 19 markers had alleles present in both Xvm and Xanthomonas vasicola pathovars holcicola and vasculorum, supporting the phylogenetic closeliness of these three pathovars. Thank to the public availability of the haplotypes on the MLVABank database, this highly reliable and polymorphic genotyping tool can be further used in a transnational surveillance network to monitor the spread and evolution of XW throughout Africa.. It will inform and guide management of Xvm both in banana-based and enset-based cropping systems. Due to the suitability of MLVA-19 markers for population genetic analyses, this genotyping tool will also be used in future microevolution studies.

First Report of the Occurrence of Bacterial Leaf Streak of Corn Caused by Xanthomonas vasicola pv. vasculorum in Brazil

Bacterial leaf streak of corn, caused by Xanthomonas vasicola pv. vasculorum, was recently reported in the United States and Argentina (Korus et al. 2017; Lang et al. 2017; Plazas et al. 2018). Further, the disease has reached epidemic levels in some corn-growing states of the United States (Korus et al. 2017; Lang et al. 2017). In April 2018, diseased corn leaf samples were collected in commercial fields in the western region of the state of Parana, Brazil. The leaves with initial symptoms of the disease had translucent yellow to brown narrow linear lesions with irregular margins, confined to the interveinal spaces. Older symptoms on highly susceptible corn hybrids had coalescing long lesions of dark coloration, reaching large extension along the leaf blade. Preliminary examinations did not show any structure of fungi but revealed the presence of bacterial ooze. Bacterial isolates established on nutrient agar medium produced yellow mucoid colonies typical of bacteria of the genus Xanthomonas. The pathogenicity of the bacterial isolates was confirmed by spray inoculation of a 10⁸ CFU/ml suspension in plants at the V4 stage of the Zea mays hybrid JM 2M77, kept under greenhouse conditions. Lesions similar to those observed in the samples from commercial corn fields started to show up 9 days after inoculation. We reisolated consistently from the affected leaf tissues bacteria identical to those originally inoculated. The bacterium obtained had a rod-shaped cell, was gram negative, nonfluorescent and nonfermentative. Based on the analysis of polymerase chain reaction amplified sequences of the 16S rDNA region, using the universal primers fD1 and rD1 (Weisburg et al. 1991), the bacterial isolates showed genetic similarity of 99% with X. vasicola pv. vasculorum strain SAM119 (NCCPB no. 4614), isolated from corn in South Africa, the pathotype strain of the pathovar (Lang et al. 2017). Further, a neighbor-joining phylogenetic tree reconstructed based on partial 16S rDNA sequences alignment using MEGA7 (Kumar et al. 2016) confirmed that our bacterial strains clustered with X. vasicola pv. vasculorum strain SAM119. The sequences of two bacterial strains established in our studies were deposited in GenBank as accessions MH497007 and MH497008. The disease was present in commercial fields in at least eight municipalities of corn-producing regions of the state of Parana, Brazil. In addition, bacterial leaf streak of corn was detected under natural conditions on Z. mays plants of at least 30 different commercial hybrids. Although the occurrence of X. vasicola pv. vasculorum causing bacterial leaf streak of corn has been suspected in Brazil for previous years, this is the first confirmed report.

A highly specific tool for identification of Xanthomonas vasicola pv. musacearum based on five Xvm-specific coding sequences

Xanthomonas vasicola pv. musacearum (Xvm) is a bacterial pathogen responsible for the economically important Xanthomonas wilt disease on banana and enset crops in Sub-Saharan Africa. Given that the symptoms are similar to those of other diseases, molecular diagnosis is essential to unambiguously identify this pathogen and distinguish it from closely related strains not pathogenic on these hosts. Currently, Xvm identification is based on polymerase chain reaction (PCR) with GspDm primers, targeting the gene encoding general secretory protein D. Experimental results and examination of genomic sequences revealed poor specificity of the GspDm PCR. Here, we present and validate five new Xvm-specific primers amplifying only Xvm strains.

First Report of Xanthomonas vasicola pv. vasculorum Causing Bacterial Leaf Streak of Maize (Zea mays) in Brazil.

First Report of Xanthomonas vasicola pv. vasculorum Causing Bacterial Leaf Streak of Maize (Zea mays) in Brazil.

Gluconacin from Gluconacetobacter diazotrophicus PAL5 is an active bacteriocin against phytopathogenic and beneficial sugarcane bacteria.

This study aimed to explore the possibility of using the Gluconacin from Gluconacetobacter diazotrophicus strain PAL5 in the biological control of diverse sugarcane phytopathogenic bacteria. An in silico analysis was first employed to determine the phylogenetic relationship between Gram-negative/positive bacteriocin producers and Gluconacin. The analysis showed that this trait is widespread among tested bacterial species and a well-conserved gene within the Acetobacteraceae family. The bacteriocin gene (GDI_0415) present in the genome of strain PAL5 was than cloned in pDEST™17 and expressed in Escherichia coli BL21-AI™. A bioassay showed growth inhibition of Xanthomonas albilineans by the recombinant bacteriocin. Subsequent bioassays indicated different levels of antagonistic activity against the majority of the sugarcane phytopathogenic bacteria (Xanthomonas axonopodis pv. vasculorum, Acidovorax avenae subsp. avenae, Pseudomonas syringae pv. syringae, Xanthomonas vasicola pv. vasculorum). In addition, the bacteriocin was also antagonistic to some beneficial bacterial strains belonging to G. diazotrophicus and endophytic Bacillus species, which also colonize sugarcane plants. The GDI_0415 gene, responsible for the production of Gluconacin, is well conserved within the Acetobacteraceae family and presented antagonistic activity against phytopathogenic and a few beneficial sugarcane bacteria. The production of a recombinant protein, named Gluconacin, opens new avenues for the agro-biotechnology application in agriculture, mainly with regard to the sugarcane crop.

First Report of Xanthomonas vasicola pv. vasculorum Causing Bacteria Leaf Streak of Maize (Zea mays) in Argentina

Bacterial leaf streak of maize is caused by the bacterial pathogen Xanthomonas vasicola pv. vasculorum (Xvv). The disease is known to naturally infect maize in South Africa (Karamura et al. 2015) and was recently reported in the United States (Korus et al. 2017; Lang et al. 2017). Since 2010 the Plant Pathology Laboratory at the Universidad Catolica de Cordoba has observed the presence of bacterial leaf streak symptoms on maize leaves in the northern region of Cordoba, Argentina. The disease has since expanded its range and prevalence, from a few of the more susceptible hybrids to infecting all of the commercial hybrids available in the region. The severity can reach up to 60% of leaf area affected in the most severe cases. Each year from 2010 to 2017, the range of the disease has expanded from the initial reports in northern Cordoba province to the rest of the corn producing areas of Argentina confirmed by isolation. By the 2017 growing season, which in Argentina is from September to May with some variat...

First Report of Bacterial Leaf Streak of Corn Caused by Xanthomonas vasicola pv. vasculorum in Oklahoma

Following reports of a new bacterial disease of corn (Zea mays) caused by Xanthomonas vasicola in the nearby states of Colorado, Kansas, and Nebraska (Korus et al. 2017), irrigated corn fields in Caddo, Garvin, Kingfisher, and Texas Counties of Oklahoma were surveyed for symptoms of bacterial leaf streak in August 2016. Symptoms consisting of elongated necrotic lesions mostly confined within leaf veins, with irregular yellow to orange colored margins, were observed in several fields in Texas County, although disease severity was low (less than 5%). Bacterial streaming was observed from excised leaf sections, and yellow mucoid bacterial colonies were present on nutrient agar cultures obtained by streaking aqueous bacterial suspensions from lesion sections. Isolates were purified and grown on nutrient agar for 3 days, and DNA was extracted using a quick method. The quick method consisted of heating an aqueous bacterial suspension (one colony picked with sterile toothpick in 100 μl) for 15 min at 100°C and retaining supernatant following centrifugation at 1,200 rpm for 5 min. The primers Xvv3 that targets membrane protein and Xvv5 that targets putative exported protein of X. vasicola pv. vasculorum (Lang et al. 2017) were used in polymerase chain reaction (PCR) assays to identify the pathogen. Isolates OK-6-1, OK-6-3-1, OK-6-3-2, and OK-8-1 were PCR positive for the expected 207-bp product for Xvv3 and for the 200-bp product for Xvv5 primer pairs, confirming the pathogen in 2 of the 19 fields surveyed. Other bacteria including nonpathogens isolated from the corn leaves and X. euvesicatoria were PCR negative. Pathogenicity tests were performed on 21-day-old plants of corn hybrid 208-71VT2PRIB (two plants per isolate and inoculation method) grown in the greenhouse at 22 to 29°C. Bacterial suspensions (10⁷ CFU/ml of sterile tap water) were sprayed to run-off on plants incubated for 48 h pre- and postinoculation in humidity chambers in the greenhouse at 100% relative humidity (RH), or were infiltrated into leaves of plants left on the greenhouse bench at 50 to 60% RH. Sterile tap water served as the noninoculated control. Typical bacterial leaf streak lesions developed within 7 days postinoculation with the four PCR-positive isolates. Symptoms on spray-inoculated plants were more severe, and the pathogen often killed symptomatic leaves compared with infiltrated leaves, which remained intact 14 days postinoculation. The other bacteria described above and the water control did not cause symptoms. The pathogen was reisolated as described above from a symptomatic leaf representing each isolate and inoculation method. Reisolated bacteria were identified by colony characteristics and the two PCR primers. This is the first report of bacterial leaf streak of corn caused by X. vasicola pv. vasculorum in Oklahoma and expands the current reported geographic range of this new disease in the United States (Korus et al. 2017). The pathogen is synonymous with X. vasicola (Korus et al. 2017) and X. campestris pv. zeae (Qhobela et al. 1990).

Detection and Characterization ofXanthomonas vasicolapv.vasculorum(Cobb 1894) comb. nov. Causing Bacterial Leaf Streak of Corn in the United States

Bacterial leaf streak of corn (Zea mays) recently reached epidemic levels in three corn-growing states, and has been detected in another six states in the central United States. Xanthomonas vasicola was identified as the causal agent of this disease. A multilocus sequence alignment of six housekeeping genes and comparison of average nucleotide identity from draft genome sequence were used to confirm phylogenetic relationships and classification of this bacteria relative to other X. vasicola strains. X. vasicola isolates from Nebraska and South Africa were highly virulent on corn and sugarcane and less virulent on sorghum but caused water-soaking symptoms that are typical of X. vasicola infection on the leaves of all three hosts. Based on host range and phylogenetic comparison, we propose the taxonomic designation of this organism to X. vasicola pv. vasculorum ( Cobb 1894 ) comb. nov. Polymerase chain reaction-based diagnostic assays were developed that distinguish X. vasicola pv. vasculorum and X. vasicola pv. holcicola from each other and from other Xanthomonas spp.

English

Bacterial plant pathogens belonging to the Xanthomonas genus are adapted to their host plants and are not known to colonize other environments. Xanthomonas colonize host parts such as leaves, stems and roots before entering vascular tissues and engaging in an invasive pathogenic phase. These bacterial strains have evolved strategies to adapt to life in this environment. The host-pathogen interactions of Xanthomonas vasicola (Xv) need to be well understood to properly map the target genes in the host and pathogen so as to understand the mechanism of resistance. Genotypic characterization, based on the analysis of restriction fragment length polymorphism of virulence factor fragment products was performed on members of the X. vasicola pv. musacearum (Xcm) and X. vasicola pv. vasculorum (Xvv) from varying geographical locations. The study showed that Xcm and Xvv are different from each other based on amplification of virulence factors within fragments of their DNA. Bacterial strains of similar species can have unique Type four pili (Tfp) and Tfp pilus assembly protein PilF a fimbrial biogenesis protein was amplified in all Xanthomonas strains except NCPPB1131 only. Type III effector protein RipT was confirmed to be present in all strains of Xcm and Xvv but not NCPPB1131 and NCPPB1132. All the Xcm and Xvv strains under test yielded bands of type III effector HopAF1 except Xvv206, NCPPB1131 and NCPPB1132. YopJ type III secretion system effector protein hybridizes in DNA of all Xcm strains tested but not in NCPPB1131 or NCPPB1132. This study confirmed the predicted presence or absence of virulence factors especially effectors across bacterial strains and within strains of the same species and other clusters conserved in gram negative bacteria. Key words: Banana, effectors, pathogen-host, Xanthomonas wilt, Xanthomonas campestris, Xanthomonas vasicola.

English

Previous biochemical and molecular sequence analyses of Xanthomonas campestris pathovar musacearum, the etiological agent of banana Xanthomonas wilt, suggest that it belongs within the species Xanthomonas vasicola (X. vasicola pv. vasculorum and X. vasicola pathovar holcicola. However, the X. vasicola pathovar names were considered invalid according to pathovar naming standards and placed as one X. vasicola species; this was also not helped by the lack of sufficient comparative pathogenicity studies. Hence the proposal to rename X. campestris pathovar musacearum was no longer further supported. This study therefore carried out large scale comparative pathogenicity trial studies on the X. vasicola strains and X. campestris pathovar musacearum on 112 plants for banana and maize, and 84 plants for sugarcane, to establish or support the proper X. vasicola pathovar designations. The study also included nine common plant pathogenic Xanthomonas pathovars and one non-Xanthomonas strain. The six strains of X. campestris pathovar musacearum used in the study caused disease in sugarcane and banana but not on maize. 2 and 4 strains of X. vasicola pathovar vasculorum and X. vasicola pathovar holcicola, respectively were not only pathogenic on maize and sugarcane but each also caused distinct symptoms on maize. X. vasicola pathovar vasculorum caused deformation of the plant while X. vasicola pathovar holcicola caused stunted growth. Key words: Pathogenicity, X. axonopodis pv. vasculorum, X.campestris pv. musacearum, X vasicola pv. holcicola, X. vasicola pv. vasculorum, Xanthomonas wilt of bananas.

Xanthomonas vasicola pv. musacearum down-regulates selected defense genes during its interaction with both resistant and susceptible banana

Expression of specific R, NPR1 and PR genes was investigated to ascertain their role in the resistance of Musa balbisiana to Xanthomonas vasicola pv. musacearum (Xvm). Following inoculation, wilt symptoms developed in test plants though their incidence and severity climaxed merely at 30% and 20% respectively before recovery. Xvm was limited to the inoculated and the immediate follower leaves and its population in a 50 mg tissue dropped from 3.06 × 107 cfu at 18 days to 0 cfu by 150 days after inoculation (DAI). In susceptible banana, it instead increased from 3.41 × 108 to 1.08 × 1011 cfu by 21 DAI culminating in plant death. Expression of MbNBS, MdNPR1 and PR3 sharply declined during the first 6 h, recovering in the later stages though this did not stop later wilt symptoms developed in resistant and susceptible plants. We concluded that neither hypersensitive response, nor Systemic Acquired Resistance nor Induced systemic resistance is the resistance mechanism for M. balbisiana against Xvm as it suppresses key genes in these pathways.

Draft genome sequence of Xanthomonas axonopodis pathovar vasculorum NCPPB 900.

Xanthomonas axonopodis pathovar vasculorum strain NCPPB 900 was isolated from sugarcane on Reunion island in 1960. Consistent with its belonging to fatty-acid type D, multi-locus sequence analysis confirmed that NCPPB 900 falls within the species X. axonopodis. This genome harbours sequences similar to plasmids pXCV183 from X. campestris pv. vesicatoria 85-10 and pPHB194 from Burkholderia pseudomallei. Its repertoire of predicted effectors includes homologues of XopAA, XopAD, XopAE, XopB, XopD, XopV, XopZ, XopC and XopI and transcriptional activator-like effectors and it is predicted to encode a novel phosphonate natural product also encoded by the genome of the phylogenetically distant X. vasicola pv. vasculorum. Availability of this novel genome sequence may facilitate the study of interactions between xanthomonads and sugarcane, a host-pathogen system that appears to have evolved several times independently within the genus Xanthomonas and may also provide a source of target sequences for molecular detection and diagnostics

Banana &lt;i&gt; Xanthomonas&lt;/i&gt; wilt in Ethiopia: Occurrence and insect vector transmission

Bacterial wilt caused by Xanthomonas vasicola pv. musacearum (Xvm) is an important disease of enset and banana in south and south-western Ethiopia where, the diversity of the insect fauna on banana inflorescences was unknown and the role of insects as vectors of the disease had not been studied. The objectives of this study were to assess the occurrence of bacterial wilt and male bud infection, the diversity of insect families in banana plantations and the presence of the bacteria on insects collected from diseased inflorescences in south and southwestern Ethiopia. Surveys were carried out and insects were collected from three different zones in 2005. The diversity and richness of the insect families was assessed across sites and genotypes and comparisons were made using the Shannon Diversity Index and the Jack knife estimator, respectively. Correlations were made between the abundance and incidence of insects with the incidence of male bud infection on ‘Pisang Awak’ plants. A wide range of insect families were recorded and they varied according to banana genotype and altitude. The Drosophilidae and Apinae families were most frequently recorded across sites and genotypes. The ‘Wendo’ variety (AAA Cavendish group) had the highest diversity and richness of insect families within and across sites. In contrast to the Kembata Tembaro and Bench Maji zones, severe and widespread male bud infection of banana was found in Kaffa, where there was a high diversity of insects on the ‘Pisang Awak’ and ‘Abesha muz’ plants. The incidence of male bud infection on ‘Pisang Awak’ plants was highly correlated with the incidence of insects (R2 = 0.964). The incidence of male bud infection however depends on the floral morphology and altitude. Artificial inoculation with Xvm ooze on fresh male bract and flower scars resulted in infections on ‘Pisang Awak’ and ‘Abesha muz’ plants, but the ‘Dwarf Cavendish’ plants with persistent bracts and flowers remained healthy. Few male bud infections were observed at altitudes above 1,700 masl. Xvm was isolated from Apinae, Lonchaeidae, Muscidae, Tephritidae and Vespidae insect families. Lonchaeidae (Silba spp.) were frequently observed on banana bract and flower scars and could thus be an important insect vector of Xvm in Ethiopia.

A Polymerase Chain Reaction Assay for the Detection ofXanthomonas campestrispv.musacearumin Banana

Polymerase chain reaction (PCR) primers (BXW-1 and BXW-3) for conventional PCR were developed from conserved sequences in the hrpB operon of the hrp gene cluster from Xanthomonas campestris pv. musacearum, the causative agent of banana Xanthomonas wilt (BXW). All 50 strains of X. campestris pv. musacearum, isolated from Uganda, Rwanda, and Tanzania, produced a 214-bp amplicon when whole cells, bacterial ooze from infected tissue, and genomic DNA purified from bacterial ooze or infected tissue were used as template. The BXW primers also detected strains of X. axonopodis pv. vasculorum isolated from sugarcane and maize and strains of X. vasicola pv. holcicola isolated from sorghum. All of the strains of X. campestris pv. musacearum were clonal when compared using enterobacterial repetitive intergenic consensus PCR.

Characterization of the Xanthomonas sp. causing wilt of enset and banana and its proposed reclassification as a strain of X. vasicola

Comparative analyses were undertaken to characterize Xanthomonas campestris pv. musacearum, the causal agent of a wilt of enset and banana, and to assess its relatedness to other xanthomonads by fatty acid methyl esters, genomic fingerprinting using rep‐PCR and partial nucleotide sequencing of the gyrase B gene. The results from all three analyses indicated that strains of X. campestris pv. musacearum are homogeneous and very similar to X. vasicola strains isolated from sugarcane and maize from Africa. Pathogenicity studies indicated that strains of X. vasicola pv. holcicola and X. vasicola from sugarcane induced no symptoms on banana, whereas X. campestris pv. musacearum produced severe disease. These data will support a future proposed reclassification of X. campestris pv. musacearum as X. vasicola pv. musacearum when more data are available.

Banana Xanthomonas wilt: a review of the disease, management strategies and future research directions

Banana production in Eastern Africa is threatened by the presence of a new devastating bacterial disease caused by Xanthomonas vasicola pv. musacearum (formerly Xanthomonas campestris pv. musacearum). The disease has been identified in Uganda, Eastern Democratic Republic of Congo, Rwanda and Tanzania. Disease symptoms include wilting and yellowing of leaves, excretion of a yellowish bacterial ooze, premature ripening of the bunch, rotting of fruit and internal yellow discoloration of the vascular bundles. Plants are infected either by insects through the inflorescence or by soil-borne bacterial inoculum through the lower parts of the plant. Short- and long-distance transmission of the disease mainly occurs via contaminated tools and insects, though other organisms such as birds may also be involved. Although no banana cultivar with resistance to the disease has been identified as yet, it appears that certain cultivars have mechanisms to ‘escape’ the disease. Management and control of the disease involve methods that reduce the inoculum’s density and spread of the pathogen. Removal of the male bud (de-budding) has proven to be very effective in preventing the disease incidence since the male bud appears to be the primary infection site. The economic impact of banana Xanthomonas wilt is not fully understood but its impact on food security in the region is very significant. While germplasm screening for the disease is ongoing, efforts to genetically engineer resistance in some banana cultivars are also making good progress. This paper presents a review of the disease and management strategies that have been successful in curtailing its spread.

Banana Xanthomonas wilt: a review of the disease, management strategies and future research directions

Banana production in Eastern Africa is threatened by the presence of a new devastating bacterial disease caused by Xanthomonas vasicola pv. musacearum (formerly Xanthomonas campestris pv. musacearum). The disease has been identified in Uganda, Eastern Democratic Republic of Congo, Rwanda and Tanzania. Disease symptoms include wilting and yellowing of leaves, excretion of a yellowish bacterial ooze, premature ripening of the bunch, rotting of fruit and internal yellow discoloration of the vascular bundles. Plants are infected either by insects through the inflorescence or by soil-borne bacterial inoculum through the lower parts of the plant. Short- and long-distance transmission of the disease mainly occurs via contaminated tools and insects, though other organisms such as birds may also be involved. Although no banana cultivar with resistance to the disease has been identified as yet, it appears that certain cultivars have mechanisms to ‘escape’ the disease. Management and control of the disease involve methods that reduce the inoculum’s density and spread of the pathogen. Removal of the male bud (de-budding) has proven to be very effective in preventing the disease incidence since the male bud appears to be the primary infection site. The economic impact of banana Xanthomonas wilt is not fully understood but its impact on food security in the region is very significant. While germplasm screening for the disease is ongoing, efforts to genetically engineer resistance in some banana cultivars are also making good progress. This paper presents a review of the disease and management strategies that have been successful in curtailing its spread.

Variation among Strains of Xanthomonas campestris pv. vasculorum from Mauritius and other Countries Based on Fatty Acid Analysis

Fatty acid profiling was used to study variation amongst strains of Xanthomonas campestris pv. vasculorum (Xcv). They could be divided into five groups using cellular fatty acid profiles. Group A strains represent a new and little known taxon and all came from plants of broom bamboo (Thysanolaena maxima) from Mauritius. Group B strains included the Xcv pathotype reference strain and were from palms, broom bamboo and sugarcane from Mauritius, Reunion and Australia. Group C contained southern African and Malagasy strains from sugarcane and maize, together with X. campestris pv. holcicola strain. No Mascarene strains fell into this group. Group D strains isolated from sugarcane, maize and royal palm (Roystonea regia) were from Mauritius and Reunion, the earliest known strains coming from Réunion. These groups represented in the Mascarene Islands possibly belong to three different Xanthomonas species. A further Group E comprised one Xcv strain (NCPPB 182) from Puerto Rico, one X. vasicola pv. holcicola strain plus 6 other unclassified Xanthomonas strains causing red stripe disease symptoms in sugarcane. Three of these groups occur on Mauritius and two occur on Réunion. Group B strains originally caused serious problems in noble canes. As resistant interspecific hybrids were introduced, group D strains appeared in Mauritius possibly being introduced from Reunion but having similar host ranges within the Gramineae and Palmae. The findings that 3 of these groups (A, B, D) can cause gumming disease in a grass species (T. maxima) and that 2 of them (B, D) also cause gumming disease in sugar cane (Gramineae) and palms (Palmae) is unusual.