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Mizuna (Brassica rapa var. japonica), a member of family Brassicaceae, is a leafy vegetable having phenolic and other compounds beneficial to human health, such as natural antioxidants (Khanam et al. 2012). In October 2020, a field of mizuna (variety: Early) on Oahu island was observed having 20-30% diseased plants. Four randomly selected infected mizuna plants, showing the symptoms of wilt and stem rot (Figure 1A-D), were collected and isolations were made to determine the pathogen. Small sections of infected stems were cut, surface sterilized with 0.6% sodium hypochlorite solution for 30 sec, followed by three consecutive rinses in distilled water. The tissues were macerated in a sterile 1.5 ml centrifuge tube containing 100 μl sterile water-macerated tissues were streaked onto crystal violet pectate medium (CVP) (Helias et al. 2011) and incubated at 26 ± 2°C for 48 h. Isolated bacterial colonies that formed pits on the CVP plates were re-streaked onto dextrose peptone agar: Peptone (10 g/L), Dextrose (5 g/L) and Agar (17 g/L) (DPA-without tetrazolium chloride; Norman and Alvarez 1989) to obtain purified colonies for DNA isolation using DNeasy Blood and Tissue Kit (Qiagen, Germantown, MA). The two housekeeping genes (dnaA and gapA) were amplified and sequenced following the protocols used by Dobhal et al. (2020) and Boluk et al. (2020), for identity confirmation and phylogenetic analysis. Cleaned PCR products were sent to the GENEWIZ facility (Genewiz, La Jolla, CA) for sequencing of sense and antisense strands. The obtained sequences were aligned, manually edited, and consensus sequences were analyzed with BLASTn using the NCBI GenBank nucleotide and genome databases for identity confirmation. The BLASTn results demonstrated 100% query coverage of all four strains (PL248-PL251); and showed 100% identity of PL248 and PL249, and 99% identity of PL250 and PL251 with Pectobacterium brasiliense. All the sequences were submitted to the NCBI GenBank database under the following accession numbers: dnaA gene MW560271 - MW560274 (PL248 - PL251); and gapA gene MW560275 - MW560278 (PL248 - PL251). Pathogenicity was assessed by artificially inoculating 100 µl bacterial suspension of each strain (PL248 - 1.12x 10⁸ CFU/ml; PL249 - 1.32x 10⁸ CFU/ml; PL 250 - 1.2x 10⁸ CFU/ml and PL251 - 1.15x 10⁸ CFU/ml) onto four-week-old mizuna (variety: Leafy Asian Greens) plants in three replicates, using sterile pipette tips, which was stabbed into stem halfway and wrapped with parafilm. The inoculated plants were well maintained under controlled greenhouse conditions. As negative controls, three plants were inoculated with 100 µl distilled water. Soft rot and wilt symptoms (Figure 1E-H) were observed 24 hours post inoculation. No symptoms were observed on control plants (Figure 1F). All four strains were re-isolated from the inoculated plants and confirmed as P. brasiliense based on resequencing of the dnaA region and 100% homology with the sequences of original strain. In the phylogenetic tree (Figure 2), based on two housekeeping genes (dnaA and gapA), the bacterial strains from mizuna grouped with other P. brasiliense retrieved from the NCBI GenBank database. To our knowledge, this is the first report of P. brasiliense infecting mizuna plants in Hawaii or in the USA and is important because this species is one of the most aggressive pectolytic pathogens in the genus Pectobacterium. Understanding the diversity of different pectolytic phytopathogens is essential to formulating risk mitigation strategies as P. brasiliense could potentially pose a threat to additional vegetable crops, especially the crucifers vegetables (Arizala et al. 2019; Klair et al, 2021).

Potassium tetraborate tetrahydrate, K2B4O7⋅4H2O (PTB), was assessed as a preharvest spray in the greenhouse for reducing gray mold of tomato fruit caused by Botrytis cinerea. Efficacy of PTB was compared with a natural proprietary product formulated by Agrichem, which was previously shown to inhibit mycelial growth of B. cinerea in vitro and was used as a positive control for greenhouse studies. Mycelial growth and spore germination of B. cinerea were completely inhibited in vitro by PTB at 25 mM. Phytotoxicity was not observed on treated tomato plants with PTB at 25 mM. Preharvest sprays were applied at three ripening stages: turning, pink, and light red. After fruit reached the final ripening stage, all fruits were harvested and stored for 10 days at either 4 or 25°C. Disease severity was reduced compared with controls after storage at either temperature when PTB was applied at the turning stage. Preharvest applications of PTB improved the marketable quality of postharvest tomato fruit and significantly reduced the incidence of gray mold in comparison with inoculated control plants, which received no preharvest fungicidal treatment.

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.

Susceptibility of anthurium cultivars to systemic infection by the bacterial blight pathogen, Xanthomonas campestris pv. dieffenbachiae, was examined using a bioengineered bioluminescent strain (V108LRUH1) and compared with susceptibility to foliar infection. Eight cultivars with different levels of susceptibility to foliar infection were evaluated for their susceptibility to systemic infection. Petioles of second youngest leaves cut near the main stem were inoculated with strain V108LRUH1, and subsequent movement of this bacterium into other petioles was monitored by observing bioluminescence from the plants. The actual extent of systemic movement was determined by reisolating V108LRUH1 from dissected segments of the remaining petioles. In susceptible cultivars, the pathogen advanced very rapidly and nearly reached the distal end of petioles. In resistant cultivars, the pathogen was detected in none (or very few) of the petiole segments. However, the susceptibility ranking among the tested cultivars for systemic infection did not always correspond to the ranking determined for foliar infection: i.e., one cultivar that was susceptible to foliar infection was highly resistant to systemic infection, and vice versa. This suggests that cultivar susceptibility of anthuriums to bacterial blight may differ depending on the phase of disease progression, and thus evaluation for both disease phases is essential for complete understanding of cultivar susceptibility.

Edible ginger is a popular spice crop that is grown in Hawaii primarily for the fresh market, and as such, rhizome quality is of paramount importance. In our studies, a Gram-negative, facultative anaerobic, rod-shaped bacterium was consistently isolated from decayed as well as symptomless ginger rhizomes. The bacterium was identified as Enterobacter cloacae by biochemical assays and 16S rDNA sequence analysis. Rot symptoms, which usually occurred in the central cylinder of the rhizome, were characterized by yellowish-brown to brown discolored tissue and firm to spongy texture. In inoculation experiments, ginger strains of E. cloacae produced basal stem and root rot, with foliar chlorosis and necrosis in tissue-cultured ginger plantlets, and discolored and spongy tissue in mature ginger rhizome slices and whole segments. In other hosts, ginger strains of E. cloacae caused internal yellowing of ripe papaya fruit and internal rot of onion bulbs. All strains that caused symptoms in inoculated plants were reisolated and identified as E. cloacae. Our studies suggest that E. cloacae can exist as an endophyte of ginger rhizomes, and under conditions that are favorable for bacterial growth, or host susceptibility, including maturity of tissues, rhizome rot may occur. Rhizome quality may be impacted by the presence of E. cloacae under conditions such as high temperature, high relative humidity, and low oxygen atmosphere that may affect the development of decay, and such conditions should be avoided during post-harvest handling and storage. The association of E. cloacae with a rhizome rot of ginger is a new finding.

Bacterial canker of tomato, caused by Clavibacter michiganensis subsp. michiganensis (Cmm), occurs worldwide. This study focuses on three genes, clvA (clavicidin) and two associated genes (clvF and clvG, encoding a putative ABC-type multidrug transport system ATPase and permease component, respectively). Loop-mediated amplification of clvA and PCR of clvA, clvF and clvG showed that these genes were present only in Cmm and not in other Clavibacter species/subspecies, as well as other genera of plant-associated bacteria. Sequences of clvA, clvF and clvG from 48 geographically diverse strains of Cmm were analyzed phylogenetically to determine sequence variation. Maximum parsimony (MP), neighbour-joining (NJ) and maximum likelihood (ML) analyses placed strains into subgroups irrespective of their geographical origins. Multi-locus sequence analysis (MLSA) of these three genes produced the same results. In sum, all three clv genes are unique and conserved in Cmm, further supporting the use of the clvA gene for identification of Cmm, using either a previously designed LAMP assay or PCR with additional primers developed in this study. The genes investigated here are novel targets for specific detection of Cmm and have numerous molecular diagnostic applications.

Grey mold is the one of most important postharvest disease of tomato fruit worldwide. Treatments with edible, natural products are needed to reduce losses and contribute to food sustainability. Based on the hypothesis that inhibition of Botrytis spore germination will significantly reduce postharvest losses, botanicals were tested for their effects on conidia. Ten Botrytis isolates from rotting tomato fruit collected at seventeen different sites in Hawaii were identified morphologically and confirmed by DNA sequence analysis. Effects of plant extracts on spore germination were assessed at several dilutions. Leaves of candidate biocontrol plants were frozen at -20°C and plant fluids were sterilized by passing through a 0.22 μm millipore. The effect of plant extracts on germination of Botrytis spores (106/ml) in sterile malt extract broth was evaluated in multi-well microplates using preparations ranging from 10 to 40%. Changes in absorbance measured at 6, 12, and 24 hours after inoculation were analyzed with Gen5 software. Capsicum chinense cultivars Datil and C. annuum Carnival completely inhibited fungal germination at all evaluation times. Extracts from Capsicum species were superior to all other extracts tested. Treatments with 40% extracts increased the generation of intercellular reactive oxygen species in the fungal conidia. Plasma membrane damage was shown with fluorescence microscopy when extract-treated conidia were stained with propidium iodide. Loss of integrity in the spore plasma membrane appears to account for the inhibition of Botrytis spore germination. Extracts from the two pepper cultivars, Datil and Carnival, showed promise as pre-harvest sprays in the greenhouse and as edible coatings on tomato fruit postharvest to reduce grey mold.

Ralstonia solanacearum (Rs) race 4 strains cause bacterial wilt of edible ginger (Zingiber officinale). The survival of the pathogen was studied in plant-free soil and potting medium in the presence of plants inoculated by different methods (non-wounded, rhizome-wounded, and stem-wounded) and irrigated on different schedules (alternate and daily). Detection thresholds for Rs were determined for an enzyme-linked immunoabsorbent assay (ELISA), immunostrip assay, and polymerase chain reaction (PCR) using drainage water from soil and potting medium containing known concentrations of Rs. In the absence of a plant or in the presence of non-wounded plants, Rs populations declined rapidly in drainage water from potting medium during the first 9 days and were undetectable after 81 days. When plants were stem- or rhizome-wounded, Rs populations increased by two to three orders of magnitude from the initial population levels for the first 9 to 19 days and then gradually declined and became undetectable after 89 days. Results were similar in experiments with soil except for non-wounded ginger plants, where the initial decline in Rs populations was followed by an abrupt increase after day 11, reaching 7 log cfu/mL on day 21, then declining gradually to non-detectable levels after 137 days. The increase was attributed to natural infection of the plants followed by release of high populations of Rs into the irrigation water when plants wilted. When rhizome-inoculated plants were watered on alternate days, Rs was recovered from 97 to 129 days in soil and potting medium, but when the plants were watered daily, Rs was recovered in soil and potting medium up to 153 days after plant inoculation. ELISA using Ps1a monoclonal antibody detected the pathogen from >95% of the samples from soil and potting medium when viable populations were >5 log cfu/mL. The immunostrip assay (using the same antibody) detected the pathogen from 100% of the samples when viable populations were >3 log cfu/mL. PCR based on the flagellin gene fliC detected the pathogen from >95% of the samples from soil and from >74% of the samples from potting medium when viable populations were >4 log cfu/mL.

Palmarosa (Cymbopogon martini), lemongrass (C. citratus), and eucalyptus (Eucalyptus globulus) oils were investigated for their effects on Ralstonia solanacearum race 4 and their potential use as biofumigants for reducing bacterial wilt disease of edible ginger (Zingiber officinale). Three concentrations of the oils (0.04, 0.07, and 0.14% vol/vol) were evaluated by culture amendment assays, epifluorescence microscopy, and studies in potting medium. In culture amendment assays with palmarosa and lemongrass oils at 0.04%, both oils significantly reduced the growth of the bacterium compared with the control, and at 0.07 and 0.14% they showed complete inhibition of bacterial growth. Epifluorescence microscopic observations showed cell deterioration in 95 to 100% of the cells at all concentrations of palmarosa and lemongrass oils, indicating its bactericidal properties. Eucalyptus oil treatments at 0.04 and 0.07% had bacteriostatic effects on the cells. The pathogen was not detected in R. solanacearum–infested potting medium after treatment with palmarosa and lemongrass oils at 0.07 and 0.14% in any of the experiments. Bacterial wilt incidence on edible ginger was significantly reduced when planted in essential oil–treated potting medium. None of the essential oil treatments reduced the growth or yield of edible ginger grown for 180 days in 5-liter pots.

Fourteen species of ginger belonging to Zingiberaceae and Costaceae were evaluated for susceptibility to the bacterial wilt pathogen Ralstonia solanacearum (Rs) race 4 (ginger strains) by several methods of inoculation, including tests to simulate natural infection. Twelve of 14 species tested were highly susceptible to all strains of Rs race 4 upon stem inoculation, and susceptible plants wilted within 21 days. In contrast to previous reports that Rs strains from an invasive alien species, kahili ginger (Hedychium gardenarium), are nonpathogenic on ornamental gingers, the kahili ginger strain wilted both ornamental and edible ginger (Zingiber officinale) species within 21 days. Pour inoculation to the base of 11 plant species to simulate natural infection confirmed the ability of Rs to invade all the tested species without root wounds. Shampoo ginger (Zingiber zerumbet) was the most susceptible (wilted in 26 days) whereas pink ginger (Alpinia purpurata) and red ginger (A. purpurata) were the least susceptible and wilted in 71 and 76 days respectively. Pathogen survival in potting medium was evaluated by enumerating viable cells in effluent water from drenched pots with and without infected edible ginger after stem or rhizome inoculation. Ralstonia solanacearum survived in plant-free potting medium for 120 days and for 150 to 180 days in potting medium with infected edible ginger. The ability of Rs race 4 to infect many ginger species without wounding and to survive for long periods indicates that high risks will be incurred if the kahili ginger strain is inadvertently introduced from the forest reserves into ginger production areas.

Specificity of a monoclonal antibody (MAb), Cmm1, to geographically diverse strains of the seed-borne tomato pathogen, Clavibacter michiganensis subsp. michiganensis (Cmm), was assessed and the MAb was tested for its usefulness as a tool to separate the pathogen from saprophytes in naturally infested tomato seed. Of the 236 international Cmm strains tested, 99% reacted with MAb Cmm1. MAb Cmm1 was also strongly reactive with an additional 32 strains isolated from seed that were later identified as Cmm by the Biolog MicroLog™ microbial identification system (Biolog, Inc., Hayward, CA) and 16S rDNA sequence analysis. It correctly differentiated these strains from 12 MAb Cmm1-negative seed strains that possessed similar colony morphology but were later identified as other Gram-positive genera and species. The specificity of MAb Cmm1 to the pathogen and the near universality of the MAb Cmm1-reactive antigen among diverse Cmm strains make this antibody a useful detection and identification tool. The finding that a large proportion of the Cmm strains associated with naturally infested tomato seed were putatively hypovirulent or non-virulent indicates that such populations cannot be ignored and points to a need for studies to determine their significance in host-pathogen interactions.

Two cultivars of Anthurium andraeanum Hort. hybrids, `Paradise Pink' and `Tropic Flame', were transformed by Agrobacterium to contain gene sequences for Shiva-1, a cecropin-based lytic peptide. The antibacterial gene was driven by a 35-35S cauliflower mosaic viral (35-35S CaMV) promoter and the construct included the secretory signal sequence for pathogenesis-related protein 1b (PR1b). Blight tolerance of regenerated plants was tested by inoculation with a virulent strain of Xanthomonas axonopodis (formerly campestris) pv. dieffenbachiae (Xad) that is bioluminescent to allow detection of symptomless infections in Shiva-1 transformants. Primary regenerants for two Shiva-1 transgenic lines of `Paradise Pink' displayed significantly enhanced tolerance to bacterial blight over blight susceptible `Rudolph' and even the blight tolerant `Kalapana'. Two Shiva-1 transgenic lines of `Tropic Flame' showed no improved resistance when compared to the control at the mean percent leaf infection level. One Shiva-1 transgenic line of `Tropic Flame' was unexpectedly more susceptible to blight than the nontransgenic control. Low expression of Shiva-1 observed in this line is hypothesized to be the cause of its increased susceptibility to Xad.

The survival of the bacterial pathogen, Xanthomonas campestris pv. campestris (Xcc), was studied in plant debris-infested soil with different matric potentials (0, −10, −30, −50, −100, −200, and −900 kPa), and on the phylloplane of crops used for rotation with cabbage. Populations of cellulolytic and proteolytic microorganisms were studied in relation to soil matric potential and Xcc. The survival of Xcc was negatively correlated (r=−0.710; P=0.06) with soil matric potential and with the abundance of cellulolytic microorganisms (P=0.05). In saturated soil, Xcc survived for only 19–28 days, while at −900 kPa there was no significant change in the bacterial population within this period. Survival of Xcc on the phylloplane of cabbage (Brassica oleracea var. capitata) (host) was similar to that on mustard and lettuce (48 days), whereas the pathogen was detected for only 9 days on rice. It appears that high matric potentials reduced populations of Xcc in soil, whereas epiphytic survival of this pathogen depended on the plant species.

Xanthomonas campestris pv. campestris induces two types of symptoms, namely, black rot and blight. Black rot symptoms are V-shaped lesions and black veins on the leaf, and blight symptoms are sudden collapse of interveinal tissues following the lack of veinal necrosis at early stages of infection. These two symptoms can occur simultaneously. However, the tendency to induce either symptom type is strain-dependent. Six strains were evaluated for their rate and pattern of spread in misted seedbeds by using strain-specific monoclonal antibodies and miniplate enrichment/ELISA. Data on pathogen incidence was defined as the presence of the pathogen in or on plants rather than visual symptoms. The results indicated that blight-inducing strains spread to more seedlings than black rot-inducing strains. The high incidences of blight-inducing strains in experimental plots were associated with non-randomness of spatial pattern of pathogen spread, indicating that high incidence is primarily due to the spread from adjacent plants by leaf contact and water splash. Most ELISA-positive seedlings were symptomless, indicating that the sensitivity of the system used in this study was adequate for detection of latent or epiphytic spread.

Effect of temperature on leaf colonization in anthurium blight was studied using a bioluminescent strain of Xanthomonas campestris pv. dieffenbachiae. In a susceptible cultivar, colonization of leaf tissues (monitored by detection of bioluminescence) and symptom development (assessed visually) advanced rapidly at higher temperatures. For a susceptible cultivar, there was a linear relationship between degree-days and percent leaf area colonized by the pathogen, indicating that leaf colonization in a susceptible cultivar was a direct function of the cumulative effect of temperature. The degree-day intercept of the regression line represented the time from inoculation to detection of bioluminescence, and the slope indicated the increase of leaf colonization per degree-day. There also was a linear relationship between the logarithm of degree-days and the logarithm of percent leaf area showing visible symptoms in a susceptible cultivar. The degree-day intercept of this relationship represented the incubation period (about 500 degree-days). The degree-days required to detect bioluminescence was not considerably different between susceptible and resistant cultivars. However, the subsequent rates of leaf colonization were significantly lower for a resistant cultivar than for a susceptible cultivar in all temperature regimes. The results suggest that multiplication of the pathogen in the leaf tissues is optimized in the susceptible cultivar. In contrast, in the resistant cultivar, the defense mechanisms overshadow the temperature effect. The differential response to temperatures may be an additional indicator of cultivar susceptibility.

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.

Growth and survival of Xanthomonas campestris pv. dieffenbachiae in guttation fluids (xylem sap exuded from leaf margins) of anthuriums were suppressed by several bacterial strains indigenous to leaves of various anthurium cultivars. Inhibition of growth was not observed in filter-sterilized guttation fluids and was restored to original levels only by reintroducing specific mixtures of bacteria into filter-sterilized guttation fluids. The inhibitory effect was related to the species in the bacterial community rather than to the total numbers of bacteria in the guttation fluids. One very effective bacterial community consisted of five species isolated from inhibitory guttation fluids of two susceptible anthurium cultivars. The individual strains in this community had no effect on the pathogen, but the mixture was inhibitory to X. campestris pv. dieffenbachiae in guttation fluids. The populations of the individual strains remained near the initial inoculum levels for at least 14 days. The effect of the five inhibitory strains on reducing disease in susceptible anthurium plants was tested by using a bioluminescent strain of X. campestris pv. dieffenbachiae to monitor the progression of disease in leaves nondestructively. Invasion of the pathogen through hydathodes at leaf margins was reduced by applying the strain mixture to the leaves. When the strain mixture was applied directly to wounds created on the leaf margins, the pathogen failed to invade through the wounds. This bacterial community has potential for biological control of anthurium blight.

Summary and Future Perspectives Growers have been struggling with anthurium blight since the onset of the major disease outbreaks in the early 1980s. Good cultural practices help to reduce losses when growing anthuriums, but they are insufficient for blight control. Use of symptomless cuttings for propagation is a risk even when propagative materials are grown at high elevation, so establishment of pathogen-free microplants in vitro is essential for large-scale anthurium production. The A. Fig. 23. Disease reduction on ‘Marian Seefurth’ plants treated with beneficial bacteria (four plants on right) compared to four non-treated plants (left) 28 days after inoculation with X. axonopodis pv. dieffenbachiae . In repeated trials disease was reduced by 25 to 40% on treated plants, whereas all non-treated plants died within 28 to 35 days after inoculation. Photo by A. Alvarez. Fig. 24. ‘Marian Seefurth’ plants after continued weekly post-inoculation treatments. Diseased plants (Fig. 23) eventually recovered and produced flowers. Photo by A. Alvarez. APSnet Feature

These data point to but do not prove a bacterial etiology for gray kernel disease, and implicate Enterobacter cloacae as one of the causal agents. Other bacteria also may be involved. Accepted for publication 11 July 2003. Published 25 August 2003.

Bacterial black spot of mango (Mangifera indica) caused by Xanthomonas citri pv. mangiferaeindicae (Xcm), is an economically important disease in tropical and subtropical areas (3). Xcm can infect a wide range of mango cultivars and induces raised, angular, black leaf lesions, sometimes with a chlorotic halo. Fruit symptoms appear as small, water-soaked spots on the lenticels that become star-shaped, erumpent, and exude an infectious gum (3). The bacterium can also cause latent infections (2). Immature mango fruit with black spots on the epidermis were collected in August 2012 from mango trees of the cvs. Raposa and Pirie at a residence in Pukalani, Hawai'i, on the island of Maui. Similar symptoms were seen on a tree of the mango cv. Common (also known as ‘Spanish’ or ‘Lahaina’) at a nearby golf course. Mango fruit with black lesions, and leaves showing black lesions with yellow halos, were collected in August 2012 from mango trees of the cv. Haden at a residence in Kaimuki, Hawai'i, on the island of O'ahu. Xanthomonas-like bacterial colonies were isolated on TZC agar. Suspect colonies were non-pigmented on YDC agar. A fruit strain of the bacterium from Maui (A6081A) and a strain from each of a fruit (A6081B) and a leaf (A6082) from O'ahu were each gram-negative, oxidative, positive for both starch and esculin hydrolysis, and negative for nitrate reduction, resulting in presumptive identification as a Xanthomonas sp. The three strains were further characterized by Microlog (Biolog, Inc. Hayward, CA), which showed the closest match with X. campestris. In addition, 16S rDNA PCR assays showed the closest match (99% similarity) with X. citri strains, and RIF marker analysis of dnaA (4) grouped the three strains with Xcm strain LMG 941 (Accession No. CAHO01000002.1). Hypersensitivity responses typical of xanthomonads were observed when these strains were infiltrated into tobacco leaves, whereas no response was observed using sterile water. Leaves of 3-week-old mango seedlings were infiltrated using 10 μl (~108 CFU/ml) of each strain suspended in sterilized water (six to eight inoculations per leaf, four leaves per plant, and three replicate plants per strain). The negative control treatments consisted of inoculation with sterile water, as well as an incompatible pathogen, X. hortorum pv. vitians (A6076), isolated from lettuce. Typical symptoms of bacterial black spot were observed for all strains assayed approximately 2 weeks after inoculation. No lesions were observed on the negative control plants. Koch's postulates were satisfied following reisolation and identification of the Xanthomonas strains from the infected plant tissues, using the biochemical and PCR methods described above. Results for strains from the two islands confirmed published descriptions of the pathogen, indicating that the pathogen causing symptoms on these mango trees is Xcm (1). Cultures and infected plant samples were sent to USDA APHIS and CPHST NPGLB facilities where this identification was confirmed. To our knowledge, this is the first report of bacterial black spot of mango in Hawai'i or anywhere in the United States. It is unknown whether this disease is a new occurrence or has not been reported previously. The origin of the primary inoculum is unknown. References: (1) B. Manicom and F. Wallis. Int. J. Syst. Bacteriol. 34:77, 1984. (2) O. Pruvost et al. Microbial Ecol. 58:928. (3) O. Pruvost et al. Plant Dis. 95:774, 2011. (4) K. Schneider et al. PLoS 6:e18496, 2011.

A disease of papaya [Carica papaya L.] fruits was observed in Hawaii [USA] in fully ripe fruits that was characterized by soft, yellow, discolored flesh with diffuse margins and an offensive odor. The causal bacterium was isolated repeatedly from diseased fruit, hot-water treatment tanks, papaya flowers, and the crop and stomach of the oriental fruit fly (Dacus dorsalis). On the basis of biochemical and physiological characteristics, the bacterium was identified as Enterobacter cloacae. Fruits became increasingly susceptible to E. cloacae as they ripened. Hot-water-treated fruits had lower disease incidence than untreated fruits.

Etiologie, symptomatologie des principales pourritures d'entreposage et mesures generales prophylactiques ou curatives de lutte contre les organismes phytopathogenes

Experimentation de pulverisations d'eau chaude (54°C, 3 min.) en comparaison avec les traitements classiques par trempage (48°C, 20 min.) pour lutter contre les maladies des papayes (anthracnose, pourritures caulinaires et autres) apres simulation de periodes de transport (de 7 a 14 j a 10°C). Les traitements a l'eau chaude sont associes ou non a des traitements fongicides (thiabendazole)