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Abstract Background Bacterial blight of cotton (BBC), which is caused by the bacterium Xanthomonas citri pv. malvacearum (Xcm), is a destructive disease in cotton. Transcription activator-like effectors (TALEs), encoded by tal-genes, play critical roles in the pathogenesis of xanthomonads. Characterized strains of cotton pathogenic Xcm harbor 8–12 different tal genes and only one of them is functionally decoded. Further identification of novel tal genes in Xcm strains with virulence contributions are prerequisite to decipher the Xcm-cotton interactions. Results In this study, we identified six tal genes in Xss-V2–18, a highly-virulent strain of Xcm from China, and assessed their role in BBC. RFLP-based Southern hybridization assays indicated that Xss-V2–18 harbors the six tal genes on a plasmid. The plasmid-encoded tal genes were isolated by cloning BamHI fragments and screening clones by colony hybridization. The tal genes were sequenced by inserting a Tn5 transposon in the DNA encoding the central repeat region (CRR) of each tal gene. Xcm TALome evolutionary relationship based on TALEs CRR revealed relatedness of Xss-V2–18 to MSCT1 and MS14003 from the United States. However, Tal2 of Xss-V2–18 differs at two repeat variable diresidues (RVDs) from Tal6 and Tal26 in MSCT1 and MS14003, respectively, inferred functional dissimilarity. The suicide vector pKMS1 was then used to construct tal deletion mutants in Xcm Xss-V2–18. The mutants were evaluated for pathogenicity in cotton based on symptomology and growth in planta. Four mutants showed attenuated virulence and all contained mutations in tal2. One tal2 mutant designated M2 was further investigated in complementation assays. When tal2 was introduced into Xcm M2 and expressed in trans, the mutant was complemented for both symptoms and growth in planta, thus indicating that tal2 functions as a virulence factor in Xcm Xss-V2–18. Conclusions Overall, the results demonstrated that Tal2 is a major pathogenicity factor in Xcm strain Xss-V2–18 that contributes significantly in BBC. This study provides a foundation for future efforts aimed at identifying susceptibility genes in cotton that are targeted by Tal2.

Bacterial blight of cotton (Gossypium hirsutum L.), caused by Xanthomonas citri pv. malvacearum, induces serious economic damage throughout all major cotton producing areas in the world. In 2020, the disease was confirmed in five commercial fields in the Regional Unit of Drama in Greece with yield losses reaching 30%. The symptoms on leaves included angular necrotic spots, narrow necrotic stripe along the veins of the leaf and dark lesions on petioles. On bolls circular water-soaked spots, brown necrotic spots and large irregular necrotic areas developed, eventually resulting in boll rot. Xanthomonas citri pv. malvacearum was isolated and subsequently identified morphologically, biochemically and molecularly, based on PCR with the specific primers MSCT1-P2F/ MSCT1-P2R and partial 16S rRNA gene sequencing. The pathogenicity of the isolates was confirmed using artificial inoculations on cotton seedlings with subsequent re-isolation and re-identification. This is the first time that the causal agent of bacterial blight of cotton, Xanthomonas citri pv. malvacearum, although earlier observed and isolated, is fully identified by biochemical, molecular and pathogenicity tests in Greece. [ABSTRACT FROM AUTHOR]

Background: Bacterial blight of cotton (BBC), which is caused by the bacterium Xanthomonas citri pv. malvacearum (Xcm), is a destructive disease in cotton. Transcription activator-like effectors (TALEs), encoded by tal-genes, play critical roles in the pathogenesis of xanthomonads. Characterized strains of cotton pathogenic Xcm harbor 8–12 different tal genes and only one of them is functionally decoded. Further identification of novel tal genes in Xcm strains with virulence contributions are prerequisite to decipher the Xcm-cotton interactions. Results: In this study, we identified six tal genes in Xss-V2–18, a highly-virulent strain of Xcm from China, and assessed their role in BBC. RFLP-based Southern hybridization assays indicated that Xss-V2–18 harbors the six tal genes on a plasmid. The plasmid-encoded tal genes were isolated by cloning BamHI fragments and screening clones by colony hybridization. The tal genes were sequenced by inserting a Tn5 transposon in the DNA encoding the central repeat region (CRR) of each tal gene. Xcm TALome evolutionary relationship based on TALEs CRR revealed relatedness of Xss-V2–18 to MSCT1 and MS14003 from the United States. However, Tal2 of Xss-V2–18 differs at two repeat variable diresidues (RVDs) from Tal6 and Tal26 in MSCT1 and MS14003, respectively, inferred functional dissimilarity. The suicide vector pKMS1 was then used to construct tal deletion mutants in Xcm Xss-V2–18. The mutants were evaluated for pathogenicity in cotton based on symptomology and growth in planta. Four mutants showed attenuated virulence and all contained mutations in tal2. One tal2 mutant designated M2 was further investigated in complementation assays. When tal2 was introduced into Xcm M2 and expressed in trans, the mutant was complemented for both symptoms and growth in planta, thus indicating that tal2 functions as a virulence factor in Xcm Xss-V2–18. Conclusions: Overall, the results demonstrated that Tal2 is a major pathogenicity factor in Xcm strain Xss-V2–18 that contributes significantly in BBC. This study provides a foundation for future efforts aimed at identifying susceptibility genes in cotton that are targeted by Tal2. [ABSTRACT FROM AUTHOR]

Abstract Xanthomonas citri pv. malvacearum is a major pathogen of cotton, Gossypium hirsutum L.. In this study we report the complete genome of the X. citri pv. malvacearum strain MSCT1 assembled from long read DNA sequencing technology. The MSCT1 genome is the first X. citri pv. malvacearum genome with complete coding regions for X. citri pv. malvacearum transcriptional activator-like effectors. In addition functional and structural annotations are presented in this study that will provide a foundation for future pathogenesis studies with MSCT1.

In present research assessment of disease incidence was made between Bt and Non-Bt cotton against bacterial blight disease. Experiment was carried out in natural environmental conditions on twenty eight varieties/advance lines. Findings of the experiments depicted more disease incidence on Non-Bt varieties viz., Non Bt-FH 901 (41.7-43.4%), Non Bt-MNH 496 (47.6-49.5%), Non Bt-FH 1000 (48.6-51.2%), Non Bt-FH 207 (54.5-57.5%), Non BT-N 112 (54.7- 56.3%), Non BT-FH 942 (55.7-59.5%), Non BT-MNH 6070 (61.5-64.7%), Non Bt-FH 941 (63.4-61.6%), Non BT-N 814 (70.4-71.3%), Non Bt-FH 900 (74.7-77.4%), Non Bt-ANMOL (74.8-76.8%), Non Bt-FH 2015 (78.5-80.6%), Non BT REDACOLA (81.5-79.6%) and Non BT-C 26 (83.3-85.6%) while BT varieties BT-S-78 (25.8-26.7%), BT-Z-33 (26.7- 22.2%), BT-786 (28.6-31.5%), BT-A-ONE (28.8-26.5%), BT-282 (30.5-27.6%), BT-886 (33.5-35.3%), BT-3701 (38.3- 36. %), BT-SPECIAL (38.4-34.6%), BT-802 (41.3-43.4%), BT-92 (41.4-44.4%), BT-131 (43.8-41.7%), BT-905 (44.6- 42.3%), BT-SUPPER (45.6-46.8%) and BT-121 (48.6-52.4%) showed decreased response respectively. Hence, concluded that difference/variability in the resistant sources is present in Pakistan against the disease among BT varieties as compared to Non-Bt. [ABSTRACT FROM AUTHOR]

The phytohormone jasmonic acid (JA) and its derivatives, collectively referred to as jasmonates, regulate many developmental processes, but are also involved in the response to numerous abiotic/biotic stresses. Thus far, powerful reverse genetic strategies employing perception, signalling or biosynthesis mutants have broadly contributed to our understanding of the role of JA in the plant stress response and development, as has the chemical gain-of-function approach based on exogenous application of the hormone. However, there is currently no method that allows for tightly controlled JA production in planta. By investigating the control of the JA synthesis pathway in bacteria-infected cotton ( Gossypium hirsutum L.) plants, we identified a transcription factor (TF), named GhERF-IIb3, which acts as a positive regulator of the JA pathway. Expression of this well-conserved TF in cotton leaves was sufficient to produce in situ JA accumulation at physiological concentrations associated with an enhanced cotton defence response to bacterial infection. [ABSTRACT FROM AUTHOR]

Xanthomonas citri pv. malvacearum is a major pathogen of cotton, Gossypium hirsutum L.. In this study we report the complete genome of the X. citri pv. malvacearum strain MSCT1 assembled from long read DNA sequencing technology. The MSCT1 genome is the first X. citri pv. malvacearum genome with complete coding regions for X. citri pv. malvacearum transcriptional activator-like effectors. In addition functional and structural annotations are presented in this study that will provide a foundation for future pathogenesis studies with MSCT1. [ABSTRACT FROM AUTHOR]

• Endophytic Bacillus spp. reduced cotton bacterial blight disease. • Bacillus spp. inhibited pathogen in vitro and decreased disease incidence in vivo. • Bacillus spp. enhanced yields and growth of cotton plants. • B. amyloliquefaciens (ETL2) secreted number of antibacterial secondary metabolites. • Eight Anti-microbial peptide genes (AMPs) detected in B. amyloliquefaciens (ETL2) Bacterial antagonists against plant pathogens are widely exploited for the biological management of plant diseases. In the present study, antagonists were isolated from cotton plant associated bacteria such as endophytes (74 isolates), phylloplane (32 isolates) and cotton rhizosphere soils (48 isolates). Their efficacy against X. citri pv. malvacearum (Xcm) were evaluated in vitro by agar well diffusion technique. Among the isolates, the endophyte Bacillus amyloliquefaciens strain ETL2 was very effective in inhibiting the Xcm growth with an area of 983.76 mm2 followed by Bacillus velezensis strain ELS2 with an area of 944.41 mm2. PCR amplification of antimicrobial peptide (AMP) genes revealed that B. amyloliquefaciens strain ETL2 had maximum of 8 antibiotic biosynthesis genes namely, ItuC , bacA , bacD , bamC , fenCEA , sfrA , spaCS and mycC that produced antibiotics Iturin, bacilysin, bacillomycin, fengycin, surfactin, subtilin and mycosubtilin. Further, B. amyloliquefaciens strain ETL2 associated with Xcm inhibition was identified as aromatic hydrocarbons, phenols and fatty acids by Gas chromatography and mass-spectrometry (GC–MS) analysis of culture extracts. Delivery of B. amyloliquefaciens strain ETL2 and B. velezensis strain ELS2 as seed treatment and foliar spray was found promising for the management of bacterial blight of cotton in pot and field experiments. In pot and field experiments, the maximum plant growth promotion and seed cotton yield were observed in the plants treated with B. amyloliquefaciens strain ETL2 followed by B. velezensis strain ELS2 with better disease control efficiency compared to chemical control agents and chemical plant defense inducers. [ABSTRACT FROM AUTHOR]

Bacterial blight resistance gene B 5 has received little attention since it was first described in 1950. A near-isogenic line (NIL) of Gossypium hirsutum cotton, Ac B 5 , was generated in an otherwise bacterial-blight-susceptible 'Acala 44' background. The introgressed locus B 5 in Ac B 5 conferred strong and broad-spectrum resistance to bacterial blight. Segregation patterns of test crosses under Oklahoma field conditions indicated that Ac B 5 is likely homozygous for resistance at two loci with partial dominance gene action. In controlled-environment conditions, two of the four copies of B 5 were required for effective resistance. Contrary to expectations of gene-for-gene theory, Ac B 5 conferred high resistance toward isogenic strains of Xanthomonas citri subsp. malvacearum carrying cloned avirulence genes avrB4 , avrb7 , avrBIn , avrB101 , and avrB102 , respectively, and weaker resistance toward the strain carrying cloned avrb6 . The hypothesis that each B gene, in the absence of a polygenic complex, triggers sesquiterpenoid phytoalexin production was tested by measurement of cadalene and lacinilene phytoalexins during resistant responses in five NILs carrying different B genes, four other lines carrying multiple resistance genes, as well as susceptible Ac44E. Phytoalexin production was an obvious, but variable, response in all nine resistant lines. Ac B 5 accumulated an order of magnitude more of all four phytoalexins than any of the other resistant NILs. Its total levels were comparable to those detected in OK1.2, a highly resistant line that possesses several B genes in a polygenic background., Competing Interests: The author(s) declare no conflict of interest.

Cotton bacterial blight (CBB), caused by Xanthomonas citri pv. malvacearum , was a major disease of cotton in the United States in the early part of the twentieth century. The reemergence of CBB revealed many gaps in our understanding of this important disease. In this study, we employed a wild-type (WT) field isolate of X. citri pv. malvacearum from Georgia (U.S.A.) to generate a nonpathogenic hrcV mutant lacking a functional type-III secretion system (T3SS-). We tagged the WT and T3SS- strains with an auto-bioluminescent Tn 7 reporter and compared colonization patterns of CBB-susceptible and CBB-resistant cotton seedlings using macroscopic image analysis and bacterial load enumeration. WT and T3SS- X. citri pv. malvacearum strains colonized cotton cotyledons of CBB-resistant and CBB-susceptible cotton cultivars. However, X. citri pv. malvacearum populations were significantly higher in CBB-susceptible seedlings inoculated with the WT strain. Additionally, WT and T3SS- X. citri pv. malvacearum strains systemically colonized true leaves, although at different rates. Finally, we observed that seed-to-seedling transmission of X. citri pv. malvacearum may involve systemic spread through the vascular tissue of cotton plants. These findings yield novel insights into potential X. citri pv. malvacearum reservoirs for CBB outbreaks.