▪ Abstract Disease diagnosis is based on a number of factors, including laboratory tests for pathogen identification. Rapid development of genomic techniques for characterization of bacteria over the past decade has greatly simplified and improved pathogen detection and identification, but DNA-based methods have not yet entirely replaced traditional culture and phenotypic tests in the plant industry. The first section of this review focuses on rapid immunodiagnostic and DNA-based detection methods for known bacterial pathogens in plants or plant products, which often manifest no symptoms of disease. The second section covers the broader topic of disease diagnosis and new methods for identifying and characterizing bacteria.

The bacterial wilt pathogen, first known as Bacillus solanacearum, has undergone numerous taxonomic changes since its first description in 1896. The history and significance of this pathogen is covered in this review with an emphasis on the advances in technology that were used to support each reclassification that finally led to the current separation of Ralstonia solanacearum into three genomic species. Frequent name changes occurred as methodology transitioned from phenotypic, biochemical, and molecular studies, to genomics and functional genomics. The diversity, wide host range, and geographical distribution of the bacterial wilt pathogen resulted in its division into three species as genomic analyses elucidated phylogenetic relationships among strains. Current advances in phylogenetics and functional genomics now open new avenues for research into epidemiology and control of the devastating bacterial wilt disease.

The genus Clavibacter contains one recognized species, Clavibacter michiganensis . Clavibacter michiganensis is subdivided into subspecies based on host specificity and bacteriological characteristics, with Clavibacter michiganensissubsp.michiganensis causing bacterial canker of tomato. Clavibacter michiganensissubsp.michiganensis is often spread through contaminated seed leading to outbreaks of bacterial canker in tomato production areas worldwide. The frequent occurrence of non-pathogenic Clavibacter michiganensissubsp.michiganensis -like bacteria (CMB) is a concern for seed producers because Clavibacter michiganensissubsp.michiganensis is a quarantine organism and detection of a non-pathogenic variant may result in destruction of an otherwise healthy seed lot. A thorough biological and genetic characterization of these seed-associated CMB strains was performed using standard biochemical tests, cell wall analyses, metabolic profiling using Biolog, and single-gene and multilocus sequence analyses. Combined, these tests revealed two distinct populations of seed-associated members of the genus Clavibacter that differed from each other, as well as from all other described subspecies of Clavibacter michiganensis . DNA–DNA hybridization values are 70 % or higher, justifying placement into the single recognized species, C. michiganensis , but other analyses justify separate subspecies designations. Additionally, strains belonging to the genus Clavibacter isolated from pepper also represent a distinct population and warrant separate subspecies designation. On the basis of these data we propose subspecies designations for separate non-pathogenic subpopulations of Clavibacter michiganensis : Clavibacter michiganensissubsp.californiensis subsp. nov. and Clavibacter michiganensissubsp.chilensis subsp. nov. for seed-associated strains represented by C55^T( = ATCC BAA-2691^T = CFBP 8216^T) and ZUM3936^T( = ATCC BAA-2690^T = CFBP 8217^T), respectively. Recognition of separate subspecies is essential for improved international seed testing operations.

Effects of single versus multiple biological control agents (BCAs) on suppression of bacterial blight of anthurium were studied using a bioluminescent strain (V108LRUH1) of Xanthomonas campestris pv. dieffenbachiae. When five BCAs (GUT3, GUT4, GUT5, GUT6, and GUT9) were coinoculated in various combinations with V108LRUH1 into filter-sterilized guttation fluids of anthurium plants, a mixture of all five strains or four strains without GUT9 was most inhibitory to V108LRUH1. None of the individual BCAs inhibited V108LRUH1 in the guttation fluid. When BCAs were sprayed at ≅10⁸ CFU/ml on the foliage of a susceptible cultivar 1 day prior to inoculation with V108LRUH1, GUT6 alone and any mixtures containing GUT6 were highly effective in suppressing wound invasion and subsequent leaf infection by V108LRUH1. When tested on several cultivars that differed in susceptibility to the disease, the mixture of five strains or four strains without GUT9 consistently suppressed leaf infection regardless of the cultivars. In some cultivars, BCAs completely suppressed both wound and hydathode invasion by V108LRUH1, resulting in no infection in many leaves. These results indicate that application of bacterial mixtures provides anthurium cultivars with bacterial communities suppressive to X. campestris pv. dieffenbachiae. The results also suggest that selecting an effective mixture of BCAs first and then removing ineffective strains may be a better general approach to finding the most effective BCAs than finding individual strains and combining them.

Gray mold and soft rot are the most important postharvest diseases of tomato worldwide. A survey of fresh-market tomato fruit was conducted in Oahu to determine which fungal and bacterial pathogens were most commonly associated with postharvest disease. Alternaria, Botrytis, Colletotrichum, Fusarium, Geotrichum, Mucor, Stemphyllium, Rhizopus and Penicillium were the most frequently isolated fungi and Acetobacter, Gluconobacter, Klebsiella, Leuconostoc and Pectobacterium were the prevalent bacteria. Fifty-one percent of the diseased tomatoes had been imported from California and Mexico and 49% had been grown locally at three sites in Oahu. Pathogenicity tests revealed that 33 of 99 fungal isolates and 10 of 17 bacterial isolates were pathogenic on tomato types known as common market, cherry and grape tomato. Based on fruit assays, Botrytis cinerea (B03) and Pectobacterium carotovorum (BA17) were the most virulent isolates. Tested leaf extracts of Capsicum annuum cv. Stocky Red, C. annuum cv. Criolla de cocina, Capsicum chinense cv. NuMexsuave, Tagetes tenuifolia, Aloe vera, Origanum vulgare and Azadirachta indica were ineffective as biopesticides and did not reduce spore germination or mycelial growth of B. cinerea (B03) nor P. carotovorum (BA17). In contrast, a proprietary product (PF) reduced mycelial growth of B. cinerea (B03) and was further evaluated at doubling concentrations ranging from 0.0625 to 1 ml/L. Mycelial growth of B. cinerea and other fungi was completely inhibited by exposure to PF at 1 ml/L. On the other hand, PF was not an effective biopesticides against P. carotovorum. PF shows promise for reducing gray mold and will be evaluated as a preharvest spray on tomato plants in the greenhouse. Key words: Survey, postharvest diseases, tomato, natural product, Botrytis cinerea, Pectobacterium carotovorum.