Onion Leaf Blight Research Articles

Improving management of Stemphylium leaf blight of onion

Improving management of Stemphylium leaf blight of onion

First report of Stemphylium vesicarium causing leaf blight of onion in Slovakia

AbstractDuring the 2022 growing season, commercial crops of onion (Allium cepa cv. Medusa) were found to be affected by an extensive leaf blight in south western Slovakia. The pathogen present on diseased leaves was isolated and identified as Stemphylium vesicarium through morphological and molecular analyses, utilizing three DNA markers (ITS, tef1-α, and β-tubulin). A detailed description and illustration of the fungus are provided. Although this pathogen is already present in Slovakia, this is the first record of S. vesicarium causing leaf blight on A. cepa in the country. Pathogenicity tests with a fungal isolate were performed on three local cultivars of onion plants in the laboratory, indicating varying susceptibility of the cultivars to S. vesicarium.

First Report of Pantoea ananatis and Pantoea eucalypti causing onion leaf blight and bulb decay in Central Chile.

Nearly 5,400 hectares of long-day onions (Allium cepa) are cultivated in the Central Zone of Chile (UTM 33°3´S to 37°24´S). During summer 2021-22 and 2022-23 (December to February), followed by high temperatures (around 35°C) and high humidity conditions, symptoms showing yellowing, soft rot, blight on old leaves, necrotic tips, and soft bulbs were observed. The affected plants were observed in "spots" into the fields, and the incidence reached 5-10%. The severity was high, and 70-80% of the affected plants died. Symptomatic plants from different fields from the Coquimbo, Metropolitan, O´Higgins and Maule regions were sampled. Isolations were made using casamino-acid peptone glucose (CPG) agar medium (Schaad, 2001). Yellow-pigmented, circular to irregular shaped colonies were observed. Molecular identification was carried out by partial 16S rRNA gene sequencing, resulting in the identification of 18 isolates of Pantoea spp. from twelve different fields. Selected strains were biochemically analyzed using the GEN III BIOLOG microtest system (Hayward, CA) and were identified as Pantoea spp. BLAST analyses of the 16S rRNA sequences (602 nt) of selected strains (GenBank Accession No. OR527817 to OR527819) against the NCBI Database resulted in the identification of Pantoea species with 100% coverage and 100% identity. To determine the Pantoea species of each strain, housekeeping gene gyrB (Delétoile et al. 2009) was amplified and sequenced (GenBank Accessions No. OR544061 to OR544063). BLAST analysis (802 nt) of selected strains resulted in 100% coverage and 100% identity, identifying three different species: P. ananatis, P. eucalypti, and P. agglomerans. Pantoea species were isolated from both leaves and bulbs and no more than one species was observed per field. Pathogenicity assays in onion plants and bulbs were performed based on the methodology described by Asselin et al. (2018). Five onion plants cv. Cimarron of thirteen-week-old were inoculated by wounding an external leave with a sterile toothpick previously immersed in a bacterial suspension at ~ 108 CFU/mL and maintained at 26-28°C for 30 days in high humidity conditions. Control plants were inoculated with sterile water. Plants inoculated with Pantoea spp. showed chlorosis, soft rot, and necrosis mainly in older leaves, as observed in the field, while negative control plants remained healthy. Pantoea spp. were re-isolated from the inoculated onion plants. Toothpicks dipped in the inoculum were stuck 4 cm into the shoulders of onion bulbs and incubated at 26°C for 20 days. Water was inoculated as a negative control. At the end of the incubation period, the bulbs were opened longitudinally across their inoculation sites and shrunken, brownish, watery scales were observed. Pantoea species have been previously described as causing leaf blight of onions in Georgia and Michigan in the USA and South Africa, Brazil, and Uruguay (Hattingh and Walters 1981; Gitaitis and Gay 1997; Edens et al. 2006; Tho et al. 2015; De Armas et al. 2022; Rosende et al. 2022). P. agglomerans was recently reported in Chile (Sepúlveda et al. 2023), but this is the first report of P. ananatis and P. eucalypti affecting onions in central Chile. This detection is an alert call for the onion's growers and exporters in Chile for upcoming seasons, where conditions predisposing to disease may continue to occur. It is crucial to continue analyzing the factors that caused the appearance of this new disease in onions.

First Report of Stemphylium vesicarium Causing Onion Stemphylium Leaf Blight in Mauritius.

In August 2021, severe leaf blight symptoms were observed on onion (Allium cepa L. cvs Francia and Askari F1 hybrid) in commercial fields located in Mauritius, namely La Forêt (20°19'56.1"S57°30'04.9"E), St Aubin (20°29'47.0"S57°32'29.4"E) and Chapiron (20°20'46.8"S 57°29'12.8"E). Infected leaves displayed small circular to oblong yellow-pale-brown and spindle shaped lesions which later coalesced and formed necrotic areas with black sporulation. Three fields were selected from each region, and along a W-pattern across the fields a disease incidence ranging 53-93% and a severity of 9-28% were recorded. Ten symptomatic leaves were collected in each region and small pieces of infected tissue were surface disinfected using 1% NaOCl for 2 min, rinsed with sterile distilled water, air-dried, transferred to potato dextrose agar (PDA) and incubated for 7 days at 20°C under a 12-h light/dark cycle. Fungal cultures with uniform appearance forming multi-septated conidia typical of the genus Stemphylium (Simmons 1969) were consistently isolated. Monosporic colony of isolates SVCWLF24/3, SVSSA23/1 and SVCWLMC26/1 developed similar olivaceous green to light and dark grey mycelium with an average daily growth rate of 6.5 mm at 25°C in the dark. Conidiophores were straight, light brown with a distinct swollen apex on which olive brown to dark brown, oblong to ovoid, septate conidia formed with dimensions 16.2-44.7 × 8.0-22.9 μm (av. 29.5 x 14.7 μm; n = 50) typical of Stemphylium vesicarium (Wallr) E.G. Simmons 1969 (Woudenberg et al. 2017). Genomic DNA of the three isolates was extracted from fungal mycelium (Ranghoo and Hyde 2000).. The ITS, cmdA and gapdh genes of the isolates were amplified with primers ITS4/ITS5 (White et al. 1990), CALDF1/CALDR1 (Lawrence et al. 2013) and Gpd1/Gpd2 (Beerbee et al. 1999) and sequenced. Sequences were submitted to GenBank under accession numbers OR131271, ON620213, OR188702 (ITS), OR350623, OR350622, OR166368 (cmdA) and OR684516, OR684517, OR684518 (Gapdh). The BLAST search of the sequences showed 100% similarity with S. vesicarium strain CBS 155.24 under accession numbers KU850555 (ITS), KU850702 (Gapdh) and KU850845 (cmdA) (Woudenberg et al. 2017). Phylogenetic trees inferred from the ITS, cmdA and Gapdh concatenated datasets with the maximum-likelihood algorithm allowed clustering of the isolates within S. vesicarium clade, confirming the morphological identification. Pathogenicity tests were performed using all three isolates, cultured on PDA at 25°C in a 12-h dark/light cycle. Ten 60-day-old onion plants (cv. Francia) were spray inoculated each with 10 ml of conidial suspension (1 × 104/ml) of each isolate while 10 healthy plants sprayed with sterile distilled water served as control. They were incubated in a greenhouse at 25°C with a 12-h photoperiod and > 80% humidity. Necrotic circular lesions appeared on leaves after 7-10 days while control plants remained symptomless. Re-isolations made from symptomatic leaf tissues on PDA consistently yielded cultures with similar morphology as the original isolates, thus fulfilling Koch's postulates. This is the first report of S. vesicarium as the causal agent of leaf blight of onion in Mauritius. It is a re-emerging fungal disease (Hay et al. 2021) with a wide host range threatening local onion production. This finding will contribute to early detection of leaf blight, implementation of surveillance and integrated disease management in affected regions.

Onion leaf blight caused by Alternaria alternata sensu lato and Stemphylium vesicarium in Michoacán, México

México is among the main producers of onions, which are cultivated mainly in the states of Baja California, Chihuahua, Guanajuato, Michoacán, and Zacatecas. During June and November 2017, foliar blight symptoms were observed in commercial onion crops in the municipality of Copándaro, Michoacán. The incidence of the disease was 20% in June and 80% in November. The objective of this work was to identify the causal agent or agents of this disease. Fungal isolates recovered from symptomatic plants presented conidia typical of Alternaria and Stemphylium. Molecular identification and phylogenetic analysis using partial sequences of the nuclear ribosomal internal transcribed spacer (ITS) region, the translation elongation factor-1 alpha (TEF1), and RNA polymerase subunit II (RPB2) genes confirmed the identity of the isolates as species within the Alternaria alternata species complex, and Stemphylium vesicarium. The isolates reproduced foliar blight symptoms in inoculated onion plants in pathogenicity tests. This is the first report of Alternaria alternata sensu lato and Stemphylium vesicarium causing foliar blight in commercial onion crops in Michoacán.

First Report of Pantoea agglomerans Causing a Leaf Blight and Bulb Rot of Onion in Chile.

Onion (Allium cepa L) is an important vegetable crop in Chile with 3.675 ha (ODEPA, www.odepa.gob.cl). Since 2017, a series of symptoms has been increasingly observed, mainly in mature bulbs which include water-soaked lesions on mature leaves and external and central cataphylls, which evolve to necrotic lesions and rot, reducing yields and affecting the postharvest life. As the season progresses over 90% incidence has been estimated in severely affected fields. Symptomatic plants were collected for disease identification in summer (February 2022) in Santa Cruz, O´Higgins, Chile, (34º41'32"S and 71º27'17"W). Isolations were done on semi-selective OEM medium (Zaid et al. 2012) and isolated colonies were transferred and maintained on King's B (KB) medium. Colonies on OEM medium were yellow slightly green in the center, circular to irregular shape, elevated, smooth margin, and mucoid texture (Tho et al. 2015). On KB medium colonies were yellow cream, slightly darker in the center, with smooth margins and circular or slightly irregular. Two isolates (CHS B3, CHS B1), obtaining in three different onion fields, were further identified by PCR amplification of partial 16S rRNA using primers 27F/1492R (Frank et al., 2008). The resulting sequencing were deposited in GenBank under accession numbers OP934962.1 and OP934961.1. A BLAST search of GenBank showed that these sequences exhibited 99,89 to 100 % nucleotides similarities with multiple Pantoea agglomerans sequences. Three isolates were used to test pathogenicity on detached cataphylls and onion plants tests in the laboratory and greenhouse, respectively. Cataphylls (n=10) were surface disinfected with 2% NaOCl for 2 min, placed in sterile Petri dishes, and injected with 50 µL (106 UFC/mL) inoculum suspension with the aid of a hypodermic syringe. Cataphylls were incubated in humid chamber at 22 + 2ºC for 14 days. Additionally, three-month-old onion plants (n=10), growing in pod, were inoculated by injecting leaves with 1 mL inoculum suspension (106 UFC/mL). Plant were incubated under greenhouse for 30 days to 28ºC. An equal number of cataphylls and onion plants, injected with sterile water, were left as controls. Water soaked lesions on inoculated cataphylls appeared five days after inoculation. While onions plants develop water soaked lesion 1- 4 days after inoculation. Blight and bulb rot were observed only on inoculated plants. Symptoms were identical to those previously observed in the field. Reisolations were accomplished for 100% of the inoculated cataphylls and leaves fulfilling Koch's postulates (Biochemical characterization and PCR amplification of partial 16S rRNA). Previously, Pectobacterium carotovorum was reported causing a similar disease in Chile (Acuña 2008). However, to our knowledge this is the first report of P. agglomerans causing onion leaf blight and bulb rot in O'Higgins Region, Chile. In agreement with other reports (De Armas et al. 2015, Tho et al. 2015), leaf blight and bulb has been a very aggressive disease in Chile. These results do not exclude the possibility that other Pantoea species (Armas et al. 2015) may be involved in the leaf blight and bulb rot of onions.

First report of Stemphylium leaf blight of onion (Allium cepa) caused by Stemphylium vesicarium in Italy.

In July 2019, severe leaf symptoms were observed on onion plants (Allium cepa L. cv. Dorata di Parma) in a commercial field located in the municipality of Medicina (Bologna, Emilia-Romagna region), in northern Italy. Diseased leaves showed yellowish-pale-brown and oval-shaped lesions, which later coalesced in larger necrotic areas, and black leaf tips. As the disease progressed, conidia developed on the necrotizing leaves, until premature desiccation of the whole plants. Disease incidence of approximately 70% was calculated in the affected field, together with yield losses that were estimated to be above 30%. Symptomatic tissue fragments excised from the leaf lesions were surface disinfested with NaOCl 1% for 2 minutes, rinsed with sterile water and transferred onto potato dextrose agar (PDA). Fungi were consistently isolated after 5 days of incubation at 27 ± 1°C in the dark. Single spore isolation was performed on PDA to obtain 7 pure cultures, whose morphological characteristics were consistent with the description of Stemphylium vesicarium (Ellis 1971). DNA from a representative single spore isolate was extracted and the internal transcribed spacer region (ITS) of ribosomal DNA (rDNA) was amplified using the universal primers P-ITS1 and P-ITS4 (White et al. 1990). The PCR product was sequenced and deposited in GenBank (Accession No. OP144057). A BLAST search in CBS-KNAW collection bank (Westerdijk Fungal Biodiversity Institute, Utrecht, The Netherlands) showed 100% identity for the ITS gene with the strain of S. vesicarium under accession number CBS 124749. Moreover, the PCR assay using the primer pair KES 1999 and KES 2000 (Graf et al. 2016) for the cytochrome b gene displayed the specific fragments of 420 bp for S. vesicarium. The isolate was tested for pathogenicity on onion (potted plants cv. Texas Early Gran, fourth leaf stage) by spraying 4 ml of a conidial suspension (1 × 104 conidia/ ml) per plant. Inoculated and non-inoculated (sprayed with sterile distilled water) plants were kept at 24 ± 1°C and 90% relative humidity with a 16-h photoperiod. Seven days after inoculation, disease assessment was performed. Inoculated plants showed typical Stemphylium leaf blight (SLB) symptoms, similar to those observed in the field. No symptoms developed on the water-inoculated plants. S. vesicarium was consistently reisolated from the artificially inoculated onion plants and identified using a PCR assay, according to Graf et al. (2016). The assay was repeated twice with the same results. SLB is currently reported worldwide and it is considered a re-emerging threat and a truly challenging fungal disease, which can result in yield and quality losses of up to 90% in onion crops (Hay et al. 2021). In Italy, S. vesicarium has been reported several years ago on pear (Ponti et al. 1982) and, more recently, on radish sprouts (Belisario et al. 2008), chili pepper (Vitale et al. 2017) and spinach (Gilardi et al. 2022). To our knowledge, this is the first report of S.vesicarium on onion in Italy. Our results stress that development and implementation of innovative Integrated Pest Management (IPM) strategies are urgently needed to ensure an effective control of SLB, since only a few moderately resistant onion varieties are available (Hay et al. 2021) and no fungicides are currently registered to specifically control SLB in Italy. Further studies are underway to elucidate the pathogen geographic distribution and assess the impact of this disease on the onion crop in Italy.

Relative performance of fungicides and crude leaf extract of Azadirachta indica against leaf blight of onion

Relative performance of fungicides and crude leaf extract of Azadirachta indica against leaf blight of onion

Botryotinia squamosa (leaf blight of onion)

Botryotinia squamosa (leaf blight of onion)

Stemphylium vesicarium (onion leaf blight)

Stemphylium vesicarium (onion leaf blight)

New species and new record of Alternaria from onion leaf blight in Myanmar

New species and new record of Alternaria from onion leaf blight in Myanmar

Stemphylium Leaf Blight of Onion

Stemphylium Leaf Blight of Onion

Piriformospora indica Primes Onion Response against Stemphylium Leaf Blight Disease.

The root-endophytic fungus Piriformospora indica (=Serendipita indica) has been revealed for its growth-promoting effects and its capacity to induce resistance in a broad spectrum of host plants. However, the bioefficacy of this fungus had not yet been tested against any pathogen affecting onion (Allium cepa). In this study, the biocontrol potency of P. indica against onion leaf blight, an impacting disease caused by the necrotrophic fungal pathogen Stemphylium vesicarium, was evaluated. First, it was proved that colonisation of onion roots by P. indica was beneficial for plant growth, as it increased leaf development and root biomass. Most relevantly, P. indica was also effective in reducing Stemphylium leaf blight (SLB) severity, as assessed under greenhouse conditions and confirmed in field trials in two consecutive years. These investigations could also provide some insight into the biochemical and molecular changes that treatment with P. indica induces in the main pathways associated with host defence response. It was possible to highlight the protective effect of P. indica colonisation against peroxidative damage, and its role in signalling oxidative stress, by assessing changes in malondialdehyde and H2O2 content. It was also showed that treatment with P. indica contributes to modulate the enzymatic activity of superoxide dismutase, catalase, phenylalanine ammonia-lyase and peroxidase, in the course of infection. qPCR-based expression analysis of defence-related genes AcLOX1, AcLOX2, AcPAL1, AcGST, AcCHI, AcWRKY1, and AcWRKY70 provided further indications on P. indica ability to induce onion systemic response. Based on the evidence gathered, this study aims to propose P. indica application as a sustainable tool for improving SLB control, which might not only enhance onion growth performance but also activate defence signalling mechanisms more effectively, involving different pathways.

The Role of Ascospores and Conidia, in Relation to Weather Variables, in the Epidemiology of Stemphylium Leaf Blight of Onion.

Stemphylium leaf blight (SLB), caused by Stemphylium vesicarium, is an important foliar disease of onion in northeastern North America. The pathogen produces conidia and ascospores, but the relative contributions of these spore types to epidemics in onion is not known. Determining the abundance of ascospores and conidia during the growing season could contribute to a disease forecasting model. Airborne ascospores and conidia of S. vesicarium were trapped during the growing season of 2015 and 2016 at an onion trial in southern Ontario, Canada, using a Burkard 7-day volumetric sampler. Meteorological data were recorded hourly. Ascospore numbers peaked before the crop was planted and declined rapidly with time and at daily mean air temperatures >15°C. Conidia were present throughout the growing season and appear to be closely related to the development of SLB on onion. Daily spore concentrations were variable, but 59 to 73% of ascospores and approximately 60% of conidia were captured between 0600 and 1200 h. Spore concentrations increased 24 to 72 h after rainfall and precipitation and leaf wetness duration were consistently and positively associated with increases in numbers of conidia and subsequent SLB incidence. The first symptoms of SLB coincided with high numbers of conidia, rainfall, leaf wetness duration ≥8 h, and days with average daily temperature ≥18°C. The number of airborne ascospores was very low by the time SLB symptoms were observed. Ascospores may initiate infection on alternative hosts in early spring, while conidia are the most important inoculum for the epidemic on onions.

Emergence of Stemphylium Leaf Blight of Onion in New York Associated With Fungicide Resistance.

A complex of foliar diseases affects onion production in New York, including Botrytis leaf blight (Botrytis squamosa), purple blotch (Alternaria porri), Stemphylium leaf blight (SLB; Stemphylium vesicarium), and downy mildew (Peronospora destructor). Surveys were conducted in 2015 and 2016 to evaluate the cause of severe premature foliar dieback in New York onion fields. SLB was the most prevalent disease among fields with the greatest incidence, surpassing downy mildew, purple blotch, and Botrytis leaf blight. Sequencing of the internal transcribed spacer region of ribosomal DNA and the glyceraldedyhe-3-phosphate dehydrogenase and calmodulin genes identified S. vesicarium as the species most commonly associated with SLB. S. vesicarium was typically associated with a broad range of necrotic symptoms but, most commonly, dieback of leaf tips and asymmetric lesions that often extended over the entire leaf. Because of the intensive use of fungicides for foliar disease control in onion crops in New York, the sensitivity of S. vesicarium populations to various fungicides with site-specific modes of action was evaluated. Sensitivity of S. vesicarium isolates collected in 2016 to the quinone outside inhibitor (QoI) fungicide, azoxystrobin, was tested using a conidial germination assay. Isolates representing a broad range of QoI sensitivities were selected for sequencing of the cytochrome b gene to evaluate the presence of point mutations associated with insensitivity to azoxystrobin. The G143A mutation was detected in all 74 S. vesicarium isolates with an azoxystrobin-insensitive phenotype (effective concentrations reducing conidial germination by 50%, EC50 = 0.2 to 46.7 µg of active ingredient [a.i.]/ml) and was not detected in all 31 isolates with an azoxystrobin-sensitive phenotype (EC50 = 0.01 to 0.16 µg a.i./ml). The G143A mutation was also associated with insensitivity to another QoI fungicide, pyraclostrobin. Sensitivity to other selected fungicides commonly used in onion production in New York was evaluated using a mycelial growth assay and identified isolates with insensitivity to boscalid, cyprodinil, and pyrimethanil, but not difenoconazole. The frequency of isolates sensitive to iprodione, fluxapyroxad, and fluopyram was high (93.5 to 93.6%). This article discusses the emergence of SLB as dominant in the foliar disease complex affecting onion in New York and the complexities of management posed by resistance to fungicides with different modes of action.

The current outbreak of stemphylium leaf blight of onion in New Zealand – identification of cause and review of possible risk factors associated with the disease

During the 2017–18 growing season, significant outbreaks of leaf blight occurred in Pukekohe, Hawke’s Bay and Canterbury commercial onion fields. It was unknown if the causal agent was Stemphylium vesicarium, a pathogen already present in New Zealand that causes stemphylium leaf blight (SLB), or a new introduction of another Stemphylium species. Morphological and molecular characterisation methods were used to identify the pathogen present on diseased onion leaves. The possibility that climate may have been a contributor to the outbreak was evaluated using hourly temperature and relative humidity data, and comparing the 2017–18 growing season with the previous four seasons in these regions when no disease was observed. Our research indicates that the recent leaf blight outbreak in New Zealand was caused by S. vesicarium, and not the introduction of a novel species of Stemphylium. The warm, and wet summer of 2017–18 possibly contributed to the SLB outbreak.

Botrytis squamosa - the causal agent of onion leaf blight in Bosnia and Herzegovina

Over the past several decades, necrotic spots, lesions and blight symptoms have been observed on onion leaves in several locations in Bosnia and Herzegovina, where the crop is grown intensively. The type of symptoms indicated a possible infection with Botrytis squamosa, a widespread pathogen of onion. As symptoms of leaf spots and necrotic lesions can also be caused by some other biotic and abiotic factors, our research focused on identifying the causal agent of the observed symptoms. The pathogen was isolated from diseased tissue using standard phytopathological procedure and identified based on pathogenic and morphological features. Identification was confirmed by amplification and sequencing of the internal transcribed spacer (ITS) region of ribosomal DNA (rDNA). The influence of temperature and growth medium on mycelial growth rate of the isolates was also studied.

A standard area diagram set for severity assessment of botrytis leaf blight of onion

This work aimed to develop and validate a standard area diagram set (SADs) to estimate the severity of botrytis leaf blight of onion caused by Botrytis squamosa. For this purpose, a SADs with nine levels of severity (0.3; 1.0; 2.5; 5.0; 10; 20; 30; 40; and 57.7%) was developed from 193 symptomatic leaves collected in the field. The SADs was validated by 16 raters with no experience in evaluating plant diseases. Both precision and accuracy improved when they used the SADs. The statistical parameters for the 16 raters were: coefficient of bias - Cb (no SADs = 0.592, with SADs = 0.988); correlation coefficient – r (no SADs = 0.864, with SADs = 0.921); and Lin’s concordance correlation coefficient – ρc (no SADs = 0.513, with SADs = 0.909). In addition, estimates were more reliable: coefficient of determination - R2 (no SADs = 0.681, with SAD = 0.796); intra-class correlation coefficient - ρ (no SADs = 0.729, with SADs = 0.876). The SADs proposed here is a useful tool for improving visual assessments of severity of botrytis leaf blight of onion.

Cultivar resistance and chemical, biological and fertilizer treatments for controling Botrytis leaf blight of onion

Botrytis leaf blight, caused by Botrytis squamosa, is an important disease of onion, mainly in the Southern region of Brazil. Studies on disease management that include host resistance, chemical, biological and alternative methods are scarce in the region. This work aimed to evaluate the effect of control treatments and 40 onion genotypes with varying resistance levels on disease management. Control treatments included seven fungicides, one biocontrol agent, and a calcium phosphite treatment. Among the genotypes, Onix and Liborio cv. exhibited the lowest levels of disease severity in the 2015 experiment, while the Bola Agroecologica, Preciosa, Onix, and Super Agroecologica cv. were least affected in the 2016 experiment. Trifloxistrobin (75 g/ha) + tebuconazole (150 g/ha); boscalid (200 g/ha) + kresoxim-methyl (100 g/ha); and fluazinam (398.4 g/ha) best controlled the disease, while dicarboximides, Bacillus subtilis and phosphorus pentoxide (600 g/ha) + calcium (120 g/ha) did not differ from the control. We updated the data on host resistance to Botrytis squamosa and report for the first time the inefficacy of iprodione and procymidone for controlling Botrytis leaf blight in Brazil.

Pathogenicity of Xanthomonas campestris pv. allii causing bacterial leaf blight of onion in sudan and antibacterial efficacy of plant extracts

Bacterial leaf blight of onion, caused by Xanthomonas campestris pv. allii, is a new disease of green bulb onion in Sudan. A study was conducted to test pathogenicity of the causative agent of onion bacterial leaf blight and evaluate the efficacy of certain plant extracts against the pathogen. Antibacterial activity of aqueous ethanolic plant extracts of desert rose (Adenium obesum), eucalyptus (Eucalyptus microtheca), button wood (Conocarpus erectus), tamarind (Tamarindus indica) and mesquite (Prosopis julifora), at different concentrations, was assayed in vitro by well diffusion technique. The bacterium X. campestris pv. allii was isolated from leaf lesions and its pathogenicity was confirmed on onion leaves. There were significant differences between the extracts in their effect on bacterial growth and the best results were obtained at a high concentration (420 ppm) of plant extracts. Among the test plant extracts, mesquite extract revealed a high anti-bacterial activity with inhibition zone up to 38.6 mm. It was followed by eucalyptus extract with inhibition zone of 38.3mm, button wood and tamarind with inhibition zone of 38 mm each. Desert rose extract displayed lower inhibition zone of 20.2 mm as dcompare to the standard control of stryptomicin having inhibition zone of 36 mm. Thus plant extracts of eucalyptus, mesquite, button wood, and tamarind were promising and may help in the non-toxic, eco-friendly management of onion bacterial leaf blight disease.