Bacterial blight, historically a seed-borne disease of cotton (Gossypium hirsutum) is caused by Xanthomonas citri pv. malvacearum, resulted in significant economic losses prior to development of resistant varieties and implementation of acid-delinting of planting seed. Periodic outbreaks have been associated with seed since the early twentieth century; of note, the disease has experienced a resurgence since 2011. Effective management of bacterial blight is dependent on accurate diagnosis and detection of the pathogen. Currently, detection of X. citri pv. malvacearum is performed by time-consuming microbiological methods. In this study, a novel and sensitive TaqMan-based qPCR protocol was developed to test for X. citri pv. malvacearum in cotton plant tissue. The primers developed are specific to five races of X. citri pv. malvacearum, but not to other Xanthomonas species or cotton-associated nonpathogenic bacteria. The efficiency of this assay was evaluated on artificially inoculated cotton leaves and seed, on naturally infected cotton leaves, and on bolls and seed originating from bacterial blight symptomatic bolls. The protocol's efficiency from artificially inoculated plant tissue was 102 copies g-1 and 37 copies from 1 g seed for leaves and seed, respectively. In addition, X. citri pv. malvacearum was detected from 94% of the seed samples originating from blight symptomatic bolls. The qPCR protocol provides a rapid and accurate method for diagnosis and detection of bacterial blight and offers a tool for monitoring X. citri pv. malvacearum and potentially reducing its spread in seed.

Strain JX22, exhibiting a broad range of antimicrobial activities to fungal pathogens, was isolated and classified as representing Pseudomonas kilonensis. In this study, the mutant JX22MT1 was obtained by the EZ-Tn5 transposon mutation and showed no antifungal activity against Fusarium oxysporum f. sp. lycopersici as compared with wild-type strain JX22. The pqqC gene was disrupted in the mutant. Antifungal activity at the wild-type level was restored from the mutant JX22MT1 with the introduction of the functional pqqC gene, which encodes pyrroloquinoline–quinone synthesis protein C. The results suggest that pqqC is essential for antifungal activity of P. kilonensis JX22 against F. oxysporum f. sp. lycopersici.

Strain JX22, exhibiting a broad range of antimicrobial activities to fungal pathogens, was isolated and classified as representing Pseudomonas kilonensis. In this study, the mutant JX22MT1 was obtained by the EZ-Tn5 transposon mutation and showed no antifungal activity against Fusarium oxysporum f. sp. lycopersici as compared with wild-type strain JX22. The pqqC gene was disrupted in the mutant. Antifungal activity at the wild-type level was restored from the mutant JX22MT1 with the introduction of the functional pqqC gene, which encodes pyrroloquinoline-quinone synthesis protein C. The results suggest that pqqC is essential for antifungal activity of P. kilonensis JX22 against F. oxysporum f. sp. lycopersici.

Strain MS14, exhibiting antifungal activity, was classified to belong to Burkholderia contaminans. When compared with the wild type strain, antifungal activities of mutants MS14MT13 and MS14MT18 against Geotrichum candidum were eliminated, and the activity of mutant MS14MT15 was reduced by approximately 80%. Sequence analysis of a 22.7-kb DNA segment revealed the presence of six open-reading frames (ORFs), including the genes disrupted in the mutants. The wild type level of antifungal activity was observed for mutant MS14MT15 (ambR2::Tn5) complemented in trans with the intact ambR2 gene, which encodes a LuxR type regulator. AmbR2 positively regulates the transcription of the other five ORFs identified, which including two nonribosomal peptide synthetase genes required for biosynthesis of antifungal compound. The compound consists of amino acid residues having a molecular weight of 1200.6 Da. These results show that strain MS14 possesses a novel set of genes dedicated to the biosynthesis of an antifungal oligopeptide.