Leaf Streak Disease Of Banana Research Articles

Convergent Adaptation to Quantitative Host Resistance in a Major Plant Pathogen.

ABSTRACTPlant pathogens can adapt to quantitative resistance, eroding its effectiveness. The aim of this work was to reveal the genomic basis of adaptation to such a resistance in populations of the fungus Pseudocercospora fijiensis, a major devastating pathogen of banana, by studying convergent adaptation on different cultivars. Samples from P. fijiensis populations showing a local adaptation pattern on new banana hybrids with quantitative resistance were compared, based on a genome scan approach, with samples from traditional and more susceptible cultivars in Cuba and the Dominican Republic. Whole-genome sequencing of pools of P. fijiensis isolates (pool-seq) sampled from three locations per country was conducted according to a paired population design. The findings of different combined analyses highly supported the existence of convergent adaptation on the study cultivars between locations within but not between countries. Five to six genomic regions involved in this adaptation were detected in each country. An annotation analysis and available biological data supported the hypothesis that some genes within the detected genomic regions may play a role in quantitative pathogenicity, including gene regulation. The results suggested that the genetic basis of fungal adaptation to quantitative plant resistance is at least oligogenic, while highlighting the existence of specific host-pathogen interactions for this kind of resistance.

Central American and Caribbean population history of the Pseudocercospora fijiensis fungus responsible for the latest worldwide pandemics on banana

Among the emerging fungal diseases threatening food security, the Pseudocercospora fijiensis fungus causing black leaf streak disease of banana is one of the most marked examples of a recent worldwide pandemic on a major crop. We assessed how this pathogen spread throughout the latest invaded region, i.e. Central America and the Caribbean. We retraced its population history combining detailed monitoring information on disease outbreaks and population genetic analyses based on large-scale sampling of P. fijiensis isolates from 121 locations throughout the region. The results first suggested that sexual reproduction was not lost during the P. fijiensis expansion, even in the insular Caribbean context, and a high level of genotypic diversity was maintained in all the populations studied. The population genetic structure of P. fijiensis and historical data showed that two disease waves swept northward and southward in all banana-producing countries in the study area from an initial entry point in Honduras, probably mainly through gradual stepwise spore dispersal. Serial founder events accompanying the northern and southern waves led to the establishment of two different genetic groups. A different population structure was detected on the latest invaded islands (Martinique, Dominica and Guadeloupe), revealing multiple introductions and admixture events that may have been partly due to human activities. The results of this study highlight the need to step up surveillance to limit the spread of other known emerging diseases of banana spread mainly by humans, but also to curb gene flow between established pathogen populations which could increase their evolutionary potential.

First Report of Banana Streak Virus Infecting Bananas (Musa spp.) in Georgia, U.S.A.

Banana streak virus (BSV) is a badnavirus containing a circular dsDNA genome of 7.4 kb that causes a viral leaf streak disease of banana (Musa spp.) worldwide (Dallot et al. 2001). On bananas, typical symptoms of BSV include broken or continuous chlorotic streaks or spindle-shaped patterns that are first chlorotic, become increasingly dark in color, and subsequently result in black streaking in older leaves (Dallot et al. 2001). In the summer of 2019, six symptomatic leaves from three different plants were collected from the University of Georgia Banana Research Plot, Tifton, GA. The cultivar is ‘Pisang Awak’, and it belongs to the tetraploid AABB genome group. Initial identification was performed by assessing disease symptoms including chlorotic streaks on leaves that became brown and black chlorotic streaks later, resembling those of banana streak disease (Lockhart 1986). BSV was verified via molecular and serological tests. Genomic DNA from leaf tissue of three different symptomatic plants and two healthy plants was extracted using a DNeasy Plant Mini Kit (Qiagen, Valencia, CA). Samples were tested for the presence of BSV by two separate PCR amplification methods. One was targeting the aspartic protease (AP) and reverse transcription (RT) regions of ORF3 using primer pair BSV 4673 (5′-GGAATGAAAGAGCAGGCC-3′) and BSV 5317 (5′-AGTCATTGGGTYCAACCTCTGTCCC-3′) with an amplicon size of 644 bp (Manoranjitham et al. 2012). Another PCR analysis was targeting the coat protein (CP) region of ORF3 with primer pair BSV 156 (5′-TTACCTCCAGCACAAAGTCG-3′) and BSV 962 (5′-TTCTCCACAGGCATAACACC-3′) designed in this study with a product size of 806 bp. Both PCR reactions for all six symptomatic samples produced the expected sizes of the fragments for BSV; however, two samples from the healthy plants did not produce any bands. The amplified products were then sequenced and subjected to BLAST analysis for further identification. Sequence analysis revealed that the obtained partial sequence of the AP and RT region (MN567071) shared 100% identity to corresponding sequences from BSV OL virus isolate BSOLV-IN2 (accession no. JQ409540). Furthermore, the obtained CP gene sequence (MN567072) also showed 100% identity with BSV isolate BSOLV-IN2. Samples were also tested for the presence of BSV by real-time PCR with primers BSV 1075 (5′-CACATTGACGGAAAGGACAACG-3′) and BSV 1198 (5′-TGTGAAATACCTCCTCCACTGC-3′) targeting the RNase H gene (Delanoy et al. 2003), and the results confirmed its identity as BSV. In addition to the molecular tests, a DAS-ELISA test was carried out on the remaining symptomatic leaf tissues for further confirmation of BSV according to the manufacturer’s protocol (Nano Diagnostics, Fayetteville, AR). All three samples tested by ELISA were positive for BSV. To the best of our knowledge, this is the first report of BSV infecting Musa spp. in Georgia. This virus could pose an imminent threat to the newly growing banana industry in this area if it spread in banana fields under conditions in Georgia. Our findings will be helpful for banana growers in Georgia by taking appropriate control strategies to combat this viral disease. Further research is needed to elucidate epidemiology, symptomatology, vector transmission, and crop losses due to BSV in Georgia and the United States.

Effects of Salicylic Acid and Acibenzolar-S-methyl on Phenols Content and Antioxidant Activity against Toxicity of Juglone in the Development of Black Leaf Streak Disease of Banana

Effects of Salicylic Acid and Acibenzolar-S-methyl on Phenols Content and Antioxidant Activity against Toxicity of Juglone in the Development of Black Leaf Streak Disease of Banana

A foliar disease simulation model to assist the design of new control methods against black leaf streak disease of banana

Black leaf streak disease (BLSD), caused by the fungal pathogen Mycosphaerella fijiensis, is considered as the most destructive foliar disease of banana. To advance our knowledge of the dynamics of the disease at plant scale as well as of the components of varietal resistance, we designed, calibrated and evaluated a mechanistic model to simulate the disease on a banana plant. The model runs in discrete time at plant scale and describes plant growth and pathogen dynamics under optimal epidemiological conditions. The model is divided into two modules: a deterministic plant sub-model that simulates the simplified architecture and growth of the banana, and a pathogen sub-model that simulates the detailed life cycle of the pathogen including infection, lesion growth, asexual and sexual sporulation, and the dispersal of spores on the plant. The three most influential epidemiological parameters identified by sensitivity analysis of the model (lesion growth rate, infection efficiency, and incubation period) were estimated in a Bayesian framework using Markov chain Monte Carlo methods and acquired data on the dynamics of leaf lesions under natural conditions. The posterior densities provided precise knowledge on pathogen life history traits. The evaluation of the model using an independent data set confirmed the good quality of the predictions. Simulations allowed us to evaluate the impact of host resistance components, auto-infection at plant scale, and of the leaf emergence rate, which is linked with cropping practices, on the severity of BLSD. This foliar disease simulation model will help design new methods of controlling BLSD.

Highly Efficient Immunodiagnosis of Episomal Banana streak MY virus Using Polyclonal Antibodies Raised Against Recombinant Viral‐Associated Protein

AbstractBanana streak MY virus (BSMYV) is the causal agent of viral leaf streak disease of banana, which leads to considerable losses in banana production in most of the banana‐growing regions worldwide. Developing high‐throughput virus detection system is essential for managing viral diseases especially in vegetatively propagated crops like banana. In this study, viral‐associated protein (VAP) coded by ORF II of BSMYV was expressed in Escherichia coli, and polyclonal antibodies were raised against purified recombinant VAP (rVAP) fusion protein in rabbits. Specificity and sensitivity of resulting antibodies were tested in Western blot, immunosorbent electron microscopy (ISEM) and enzyme‐linked immunosorbent assays (ELISAs). In direct antigen‐coated (DAC)‐ELISA, antibodies reacted specifically to BSMYV in crude sap, up to 1 : 8000 dilutions, but not to healthy leaf extracts. Using this antiserum, an immunocapture polymerase chain reaction (IC‐PCR) assay was developed and compared with DAC‐ELISA. VAP antibody‐based IC‐PCR is highly specific and could differentiate episomal virus infection from the integrated endogenous BSV (eBSV) sequences. The recombinant antibodies were validated by testing with a large number of banana germplasm conserved in the field gene bank. Field samples collected during surveys and mother cultures used in tissue culture propagation suggest that antibodies generated against rVAP are sensitive and useful for large‐scale detection of BSMYV. To the best of our knowledge, this is the first report on the production of polyclonal antiserum against recombinant VAP of BSMYV and its suitability for serology‐based testing by ELISA and IC‐PCR. This VAP‐based immunodiagnosis can be applied in quarantine, germplasm exchange and certification programmes.

Positive selection and intragenic recombination contribute to high allelic diversity in effector genes of Mycosphaerella fijiensis, causal agent of the black leaf streak disease of banana

Previously, we have determined the nonhost-mediated recognition of the MfAvr4 and MfEcp2 effector proteins from the banana pathogen Mycosphaerella fijiensis in tomato, by the cognate Cf-4 and Cf-Ecp2 resistance proteins, respectively. These two resistance proteins could thus mediate resistance against M. fijiensis if genetically transformed into banana (Musa spp.). However, disease resistance controlled by single dominant genes can be overcome by mutated effector alleles, whose products are not recognized by the cognate resistance proteins. Here, we surveyed the allelic variation within the MfAvr4, MfEcp2, MfEcp2-2 and MfEcp2-3 effector genes of M. fijiensis in a global population of the pathogen, and assayed its impact on recognition by the tomato Cf-4 and Cf-Ecp2 resistance proteins, respectively. We identified a large number of polymorphisms that could reflect a co-evolutionary arms race between host and pathogen. The analysis of nucleotide substitution patterns suggests that both positive selection and intragenic recombination have shaped the evolution of M. fijiensis effectors. Clear differences in allelic diversity were observed between strains originating from South-East Asia relative to strains from other banana-producing continents, consistent with the hypothesis that M. fijiensis originated in the Asian-Pacific region. Furthermore, transient co-expression of the MfAvr4 effector alleles and the tomato Cf-4 resistance gene, as well as of MfEcp2, MfEcp2-2 and MfEcp2-3 and the putative Cf-Ecp2 resistance gene, indicated that effector alleles able to overcome these resistance genes are already present in natural populations of the pathogen, thus questioning the durability of resistance that can be provided by these genes in the field.

Molecular characterisation of six badnavirus species associated with leaf streak disease of banana in East Africa

Banana leaf streak disease, caused by several species of Banana streak virus (BSV), is widespread in East Africa. We surveyed for this disease in Uganda and Kenya, and used rolling-circle amplification (RCA) to detect the presence of BSV in banana. Six distinct badnavirus sequences, three from Uganda and three from Kenya, were amplified for which only partial sequences were previously available. The complete genomes were sequenced and characterised. The size and organisation of all six sequences was characteristic of other badnaviruses, including conserved functional domains present in the putative polyprotein encoded by open reading frame (ORF) 3. Based on nucleotide sequence analysis within the reverse transcriptase/ribonuclease H-coding region of open reading frame 3, we propose that these sequences be recognised as six new species and be designated as Banana streak UA virus, Banana streak UI virus, Banana streak UL virus, Banana streak UM virus, Banana streak CA virus and Banana streak IM virus. Using PCR and species-specific primers to test for the presence of integrated sequences, we demonstrated that sequences with high similarity to BSIMV only were present in several banana cultivars which had tested negative for episomal BSV sequences.

Inferences on pathogenic fungus population structures from microsatellite data: new insights from spatial genetics approaches

Landscape genetics, which combines population genetics, landscape ecology and spatial statistics, has emerged recently as a new discipline that can be used to assess how landscape features or environmental variables can influence gene flow and spatial genetic variation. We applied this approach to the invasive plant pathogenic fungus Mycosphaerella fijiensis, which causes black leaf streak disease of banana. Around 880 isolates were sampled within a 50 × 50 km area located in a fragmented banana production zone in Cameroon that includes several potential physical barriers to gene flow. Two clustering algorithms and a new F(ST) -based procedure were applied to define the number of genetic entities and their spatial domain without a priori assumptions. Two populations were clearly delineated, and the genetic discontinuity appeared sharp but asymmetric. Interestingly, no landscape features matched this genetic discontinuity, and no isolation by distance (IBD) was found within populations. Our results suggest that the genetic structure observed in this production area reflects the recent history of M. fijiensis expansion in Cameroon rather than resulting from contemporary gene flow. Finally, we discuss the influence of the suspected high effective population size for such an organism on (i) the absence of an IBD signal, (ii) the characterization of contemporary gene-flow events through assignation methods of analysis and (iii) the evolution of the genetic discontinuity detected in this study.

Variable number of tandem repeat markers in the genome sequence of Mycosphaerella fijiensis, the causal agent of black leaf streak disease of banana (Musa spp)

We searched the genome of Mycosphaerella fijiensis for molecular markers that would allow population genetics analysis of this plant pathogen. M. fijiensis, the causal agent of banana leaf streak disease, also known as black Sigatoka, is the most devastating pathogen attacking bananas (Musa spp). Recently, the entire genome sequence of M. fijiensis became available. We screened this database for VNTR markers. Forty-two primer pairs were selected for validation, based on repeat type and length and the number of repeat units. Five VNTR markers showing multiple alleles were validated with a reference set of isolates from different parts of the world and a population from a banana plantation in Costa Rica. Polymorphism information content values varied from 0.6414 to 0.7544 for the reference set and from 0.0400 and 0.7373 for the population set. Eighty percent of the polymorphism information content values were above 0.60, indicating that the markers are highly informative. These markers allowed robust scoring of agarose gels and proved to be useful for variability and population genetics studies. In conclusion, the strategy we developed to identify and validate VNTR markers is an efficient means to incorporate markers that can be used for fungicide resistance management and to develop breeding strategies to control banana black leaf streak disease. This is the first report of VNTR-minisatellites from the M. fijiensis genome sequence.

Construction of a genetic linkage map of the fungal pathogen of banana Mycosphaerella fijiensis, causal agent of black leaf streak disease

A genetic linkage map of the fungal plant pathogen Mycosphaerella fijiensis, causal agent of black leaf streak disease of banana was developed. A cross between the isolates CIRAD86 (from Cameroon) and CIRAD139A (from Colombia) was analyzed using molecular markers and the MAT locus. The genetic linkage map consists of 298 AFLP and 16 SSR markers with 23 linkage groups, containing five or more markers, covering 1,879 cM. Markers are separated on average by around 5.9 cM. The MAT locus was shown to segregate in a 1:1 ratio but could not be successfully mapped. An estimate of the relation between physical size and genetic distance was approximately 39.0 kb/cM. The estimated total haploid genome size was calculated using the genetic mapping data at 4,298.2 cM. This is the first genetic linkage map reported for this important foliar pathogen of banana. The great utility of the map will be for anchoring contigs in the genome sequence, evolutionary studies in comparison with other fungi, to identify quantitative trait loci (QTLs) associated with aggressiveness or oxidative stress resistance and with the recently available genome sequence, for positional cloning.

Isolation and characterization of the mating type locus of Mycosphaerella fijiensis, the causal agent of black leaf streak disease of banana

SUMMARY Idiomorphs mat1-1 and mat1-2 from Mycosphaerella fijiensis, the causal agent of black leaf streak disease of banana, were isolated. Degenerate oligos were used to amplify the HMG box of the mat1-2 idiomorph from M. fijiensis, showing homology with the HMG box of Mycosphaerella graminicola. Using a DNA walking strategy, anchored on the DNA lyase gene towards the HMG box, a 9-kb-long region of mat1-2 was obtained. A 5-kb fragment from the mat1-1 region was obtained by long-range PCR using primers on the flanking regions, which have close to 100% identity between both idiomorphs. High-identity (77-89%), inverted regions within both idiomorphs were found, which suggest unique inversion events, which have not been found before, and that could have been significant in the evolution of this species. The predicted genes showed the conserved introns in both idiomorphs as well as an additional intron within the alpha box. The implications for the evolution of species in the Mycosphaerella complex on banana are discussed.

Banana streak virus is very diverse in Uganda

Banana streak virus (BSV) is a badnavirus that causes a viral leaf streak disease of banana and plantain ( Musa spp.). Identified in essentially all Musa growing areas of the world, it has a deleterious effect on the productivity of infected plants as well as being a major constraint to Musa breeding programmes and germplasm dissemination. Banana is a staple food in Uganda which is, per capita, one of the worlds largest banana producers and consumers. BSV was isolated from infected plants sampled across the Ugandan Musa growing area and the isolates were analysed using molecular and serological techniques. These analyses showed that BSV is very highly variable in Uganda. They suggest that the variability is, in part, due to a series of introductions of banana into Uganda, each with a different complement of infecting viruses.

Spraying bananas in Fiji to control black leaf streak disease

SUMMARYThree sprays, maneb in water applied by hydraulic knapsack sprayer and maneb in an oil/water emulsion or an oil/water emulsion alone applied by mistblower were compared for the control of black leaf streak disease of banana caused by Mycosphaerella sp.Although there were no differences in yield in the ‘plant’ crop, maneb, especially as a water‐based spray, resulted in much better disease control and leaf survival. Oil seemed to have an adverse effect on fruit quality but not on plant growth.Since it is unlikely that oil alone will adequately control the disease in ratoon crops fungicides may be necessary.