Blight Disease Research Articles

Molecular marker validation for bacterial leaf blight resistant genes Xa21 and Xa4 in Ld 99-12- 38 / IRBB 60 genetic background

Bacterial leaf blight (BLB) disease is an emerging issue in rice cultivation of Sri Lanka. Xanthomonas oryzae pv. oryzae is causal organism. There is no chemical control method practice in the world to control the disease. Use of resistance varieties is most appropriate mode of control. Bacterial blight resistance Xa21 and Xa4 are dominant genes responsible for durable resistance of rice varieties for the disease. The advanced rice line, Ld 99-12-38 is farmer demanding, non lodging type, high yielding rice line and is susceptible to BLB. Therefore, an attempt was taken to improve it resistant to BLB through markerassisted backcross breeding (MAB) by crossing rice line with resistant variety IRBB60, and advanced plants up to BC3F2 level. At the beginning selected two molecular markers namely pTA248 (Xa21) and PM1+MP2 (Xa4) were tested for their polymorphism with parental materials. To identify BLB resistance Xa21 and Xa4 alleles, markers were validated in thirty five BC3F2 progenies derived from a cross between Ld 99-12- 38/IRBB60. As the results selected two molecular markers were polymorphic with parental materials with the expected fragment sizes. Out of the tested 35 progenies, eight were confirmed with possessing both Xa21 and Xa4 with resistant to the disease, twenty one lines carried only the resistant allele Xa4. A paired t- test revealed that there is a significant difference in the resistance level exerted by progeny carrying resistance alleles of two genes than with one (p = 0.0064). In addition, six progeny lines were heterozygote for Xa4 locus; one progeny line was heterozygous at both loci. No lines were identified carrying only the Xa21. Therefore it can be concluded that resistant genes Xa4 and Xa21 has been pyramided to rice lines derived from cross between Ld 99-12-38/IRBB60 in BC3F2 progenies with similar morphological characters of Ld 99-12-38 to withstand BLB. The rice line Ld 99-12-38 does not carry any resistance genes regarding BLB and IRBB 60 consist of Xa21 and Xa4 alleles. The selected markers pTA248 and MP1+MP2 can be recommended to in marker- assisted selection of Xa21 and Xa4 genes in crosses involving the tested genetic background.

Characterization of fungi causing lesion blight on Papaver dubium in Iran.

Papaver dubium (common name, blindeyes, Papaveraceae) is widespread throughout Europe and America and is an important weed in western Iran. Since 2009, a blight disease has occurred in several areas in Hamedan Province, Iran, causing significant damage to plants of P. dubium. Small, yellow-brown lesions appeared on lower leaves and eventually expanded to the whole plant, resulting in necrosis and complete wilting. This study was conducted to identify the causal agent(s) of the blight disease on blindeyes plants. On the basis of cultural and microscopic characters, as well as representative DNA sequence data of the 5.8S rRNA (ITS), partial LSU rRNA partial β-tubulin (TUB2), and partial G3PD genes, 82 isolates were identified as follows: Ascochyta pisi M. A. Libert. (42), Neodidymelliopsis longicolla L.W. Hou, Crous & L. Cai. (28), and Allophoma zantedeschiae (Dippen.) Q. Chen & L. Cai (12). Pathogenicity tests in the greenhouse showed that all the isolates of A. pisi and Neod. longicolla caused typical spots on inoculated blindeyes plants, and the fungi were successfully re-isolated from the symptomatic tissues. Based on the high isolation frequency for A. pisi, and the severity of symptoms induced by this species in pathogenicity tests, this fungus was indicated as the major pathogen causing the blight disease on blindeyes. It has potential as a biocontrol agent against P. dubium. To the best of our knowledge, Al. zantedeschiae and Neod. longicolla observed in this study are new taxa for the mycobiota of Iran.

Biological Components Efficiency on Safety and Productivity of Different Tomato Cultivars

Biological agent plays an outstanding and also effective role in agricultural systems with the reducing chemical components applications. This three yr study investigated the bio-growth regulators (with anti stress activity and plant resistance against diseases) efficacy on productivity and safety of four tomato varieties with the goal of sustainable agriculture during 2013 – 2015. Biological active substances were epin extra, zirkon, tekamin max and immunotsitofit that were performed as following levels: Soaking in 0.2% solution for 6 hours, Soaking in a 0.2% solution for 6 hours and one time foliar treatment, Soaking in a 0.2% solution for 6 hours and two time foliar treatments, one time foliar treatment, two time foliar treatments and control as a water treatment respectively. Tomato (Lycopersicon esculentum) cultivars in this study were Sultan F1, Lodzheyn, Dar Zavolzhja and Beta. Results of this study revealed that epin extra caused the highest germination of Sultan f1 and Dar Zavoljia significantly; germination of Beta was improved when tekamin max (TM3) was used. Bio-agent tekamin max in all cases had favorable improvement on tomato morphology of all tomato cultivars. Three records of observation on blight spread on tomato cultivar Dar Zavoljia concluded that blight disease was significantly diminished when tekamin max (TM3) was performed. Overall, tekain max as a biological growth regulator was distinguished as the most efficient on growth and development of tomato, and also the lowest blight infection was observed when tekamin max was applied.

Study on alternative technologies for the production of tomato during the rainy season in subhumid climate of Bahir Dar, Ethiopia

Tomato production is not common during main rainy season, especially in sub-humid climatic conditions like in Bahir Dar. Therefore, an experiment was conducted to study the production potential of tomato using rainshelter and management practices during the 2013 rainy season (June-October) in Bahir Dar. The experimental treatments were laid down in split-plot-design at three replications, where with and without plastic rain-shelter were assigned as main plots and management practices (fungicide and stalking) as sub-plots. The results revealed that tomatoes grown in protected structure were significantly (P<0.01) longer (100.5 cm), had more branches (8.9) and flowered earlier (49.1 days) than those grown under open field condition with the mean values of 50.9 cm, 6.3 and 54 days, respectively. Incidence and severity of late blight and yield of tomatoes were also influenced significantly by growth conditions, management practices and their interactions. Tomatoes grown under rain-shelter structure produced significantly higher total fruit yield (31.3 t ha -1 ) and exhibited low disease incidence (16.7%) and severity indexes (26.7%) on leaves and as well as on fruits with the mean values of 22.4% and 37.9%, respectively. Similarly, sprayed and staked tomatoes produced the highest marketable (35.2 t ha -1 ) and total (41.8 t ha -1 ) fruit yields and exhibited significantly lower late blight incidence and severity. In rainshelter structure, the management practices had similar effects on both disease and yield parameters, where higher yield and lower late blight incidence and severity were generally observed. In open field condition, however, only sprayed and staked tomatoes exhibited lower late blight incidence (23.3%) and severity (24%) on leaves and fruits with the mean values of 39% and 40%, respectively. The highest marketable yield (36.4 t ha -1 ) obtained from such tomatoes in open field condition was statistically similar with the yield obtained from the corresponding treatment in rain-shelter structure (34.1 t ha -1 ). Generally, the present findings showed that rain-shelter technology reduced incidence of late blight and thus it can be used as alternative technology for the production of tomato during the rainy season in and around Bahir Dar. Moreover, tomato can also be produced in open field using improved management practices such as staking and spraying with appropriate fungicides against late blight and similar diseases. Further research is required to select tomato varieties suitable for rainshelter technology as well as to optimize frequency of pesticide applications as their application may have residual effect on fresh vegetables like tomato. Keywords: Disease incidence, growth condition, late blight, rain-shelter, Ridomil, staking

Survey of biological components efficiency on safety and productivity of different tomato cultivars

Biological agents play an outstanding and effective role in agricultural systems with the reduction of chemical components’ applications. This study carried out during 2013 to 2015 investigated the efficiency of some bio-growth regulators, with anti-stress activity and plant resistance against diseases, on productivity and safety of four tomato cultivars with the goal of sustainable agriculture. Biological active substances were Epin extra, Zirkon, Tekamin max and Immunotsitofit that were performed as the following levels: soaking in 0.2% solution for 6 h, soaking in a 0.2% solution for 6 h and one time foliar treatment, soaking in a 0.2% solution for 6 h and two times foliar treatments, one time foliar treatment, two times foliar treatments and control as a water treatment, respectively. Tomato (Lycopersicon esculentum Mill.) cultivars in this study were Sultan F1, Lodzheyn, Dar Zavolzhja and Beta. Results of this study revealed that Epin extra caused the highest germination of Sultan F1 and Dar Zavoljia significantly; germination of Beta was improved when Tekamin max [(TM3) soaking in a 0.2% solution for 6 h and two times foliar treatment] was used. Bio-agent Tekamin max in all cases had favourable improvement on tomato morphology of all tomato cultivars. Three records of observation on blight spread on tomato cultivar Dar Zavoljia concluded that blight disease was significantly diminished when Tekamin max [(TM3) soaking in a 0.2% solution for 6 h and two times foliar treatment] was performed. Overall, Tekain max as a biological growth regulator was distinguished as the most efficient on growth and development of tomato, and also the lowest blight infection was observed when Tekamin max was applied.

Field evaluation of bt and non bt cotton hybrids to foliar diseases

Identification of resistant sources is a prerequisite for management of diseases through the use of resistant varieties/hybrids that constitutes an important strategy of integrated plant protection. Ninety two Bt and five Non Bt cotton hybrids were evaluated at Regional Agricultural Research Station, Guntur using infector row technique under unprotected conditions. Reaction of these hybrids to bacterial blight and fungal foliar diseases was recorded by adopting 0 to 4scale and percent disease intensity was calculated. Four entries viz., RCH-368 Bt, Brahma BG-I, MRC-7347 BG-II and MRC-6918 Bt recorded moderately susceptible reaction to bacterial blight; RCH-530 BG-II was resistant and 38 were moderately resistant to Helminthosporium leaf spot; 28 hybrids showed moderately resistant reaction to Myrothecium leaf spot; Tulasi-118 BG-II was free from Cercospora leaf spot while seven hybrids viz., ABCH-1020 Bt, GK-207 Bt, RCH-368 Bt, Dhruv Bt, ACH-33-1 Bt, NCS-854 BG-II and NHH-44 Bt recorded resistant reaction. Six hybrids viz., MRC-7347 BG-II, PRCH-505 BG-II, NCS-854 BG-II, GK-217 BG-II, ACH-6 BG-II and VBCH-1506 BG-II were free from rust while Tulasi-118 BG-II, MRC-7351 BG-II, ACH-5 BG-II, ACH-111 BG-II, MRC-7201 BG-II and NCEH-2R F Bt were resistant. MRC-7347, Brahma BG I, RCH-368 Bt, RCH-530 BG II, Tulasi-118 BG II and MRC-6918 showed multiple disease resistance/tolerance. Cotton farmers should grow best Bt cotton hybrids with multiple disease resistance/tolerance to reduce the cost of plant protection and increase net returns.

Genome Analysis and Development of a Multiplex TaqMan Real-Time PCR for Specific Identification and Detection of Clavibacter michiganensis subsp. nebraskensis.

The reemergence of the Goss's bacterial wilt and blight disease in corn in the United States and Canada has prompted investigative research to better understand the genome organization. In this study, we generated a draft genome sequence of Clavibacter michiganensis subsp. nebraskensis strain DOAB 395 and performed genome and proteome analysis of C. michiganensis subsp. nebraskensis strains isolated in 2014 (DOAB 397 and DOAB 395) compared with the type strain, NCPPB 2581 (isolated over 40 years ago). The proteomes of strains DOAB 395 and DOAB 397 exhibited a 99.2% homology but had 92.1 and 91.8% homology, respectively, with strain NCPPB 2581. The majority (99.9%) of the protein sequences had a 99.6 to 100% homology between C. michiganensis subsp. nebraskensis strains DOAB 395 and DOAB 397, with only four protein sequences (0.1%) exhibiting a similarity <70%. In contrast, 3.0% of the protein sequences of strain DOAB 395 or DOAB 397 showed low homologies (<70%) with the type strain NCPPB 2581. The genome data were exploited for the development of a multiplex TaqMan real-time polymerase chain reaction (PCR) tool for rapid detection of C. michiganensis subsp. nebraskensis. The specificity of the assay was validated using 122 strains of Clavibacter and non-Clavibacter spp. A blind test and naturally infected leaf samples were used to confirm specificity. The sensitivity (0.1 to 1.0 pg) compared favorably with previously reported real-time PCR assays. This tool should fill the current gap for a reliable diagnostic technique.

Occurrence and identification of Stemphylium lycopersici causing Stemphylium leaf spot disease on tomato in Taiwan

Tomato leaves showing severe leaf spot symptoms have been observed and sampled in the central west and southwest Taiwan during 2015 and 2016. The symptoms were similar to those of bacterial leaf spot/late blight diseases, but only Stemphylium-like fungi were consistently isolated from the diseased tomato. Upon spray inoculation of tomato, Stemphylium-like isolates caused leaf spot symptoms identical to those of naturally infected plants, and the pathogenic isolates were successfully re-isolated from inoculated leaves. The tomato-pathogenic isolates were identified as S. lycopersici based on morphological characterization and molecular identification. S. lycopersici has been previously reported to cause gray leaf spot of tomato in the temperate regions, but the majority of S. lycopersici-caused lesions were black/dark brown rather than gray in our surveillance. Accordingly, it is suggested that S. lycopersici-caused disease of tomato is named Stemphylium leaf spot of tomato more appropriately than tomato gray leaf spot. Moreover, S. lycopersici-caused leaf spot disease on tomato has been distributed in major tomato production regions in Taiwan. The information provided by our study will be important for future breeding of tomato cultivars, especially for tomato producers in Taiwan.

XopN-T3SS effector of Xanthomonas axonopodis pv. punicae localizes to the plasma membrane and modulates ROS accumulation events during blight pathogenesis in pomegranate

Bacterial blight caused by Xanthomonas axonopodis pv. punicae (Xap) is a major disease of pomegranate. Xap secretes effector proteins via type III secretion system (T3SS) to suppress pathogen-associated molecular pattern (PAMP)-triggered plant immunity (PTI). Previously we reported that XopN, a conserved effector of Xap, modulate in planta bacterial growth, and blight disease. In continuation to that here we report the deletion of XopN from Xap caused higher accumulation of reactive oxygen species (ROS) including H2O2 and O2−. We quantitatively assessed the higher accumulation of H2O2 in pomegranate leaves infiltrated with Xap ΔxopN compared to Xap wild-type. We analysed that 1.5 to 3.3 fold increase in transcript expression of ROS and flg22-inducible genes, namely FRK1, GST1, WRKY29, PR1, PR2 and PR5 in Arabidopsis when challenged with Xap ΔxopN; contrary, the up-regulation of all the genes were compromised when challenged with either Xap wild-type or Xap ΔxopN+xopN. Further, we demonstrated the plasma-membrane based localization of XopN protein both in its natural and experimental hosts. All together, the present study suggested that XopN-T3SS effector of Xap gets localized in the plasma membrane and suppresses ROS-mediated early defense responses during blight pathogenesis in pomegranate.

A Brief Comparative Effectiveness Research (CER) about Conventional and Homeopathic Treatment of Type 2 Diabetic Patients

A Brief Comparative Effectiveness Research (CER) about Conventional and Homeopathic Treatment of Type 2 Diabetic Patients Bacterial leaf blight (BB) disease caused by Xanthomonas oryzae pv. oryzae is one of the most severe diseases effecting Basmati rice production in India. CSR-30 is widely grown in Haryana and is extremely popular amongst rice farmers and consumers because of its salt tolerance, aroma, high yield, medium slender grains and excellent cooking and eating qualities. CSR-30 lacks tolerance to BB. The present investigation was therefore planned to introgress BB resistance genes (xa5, xa13 & Xa21) from IRBB-60 to CSR-30. The pyramided BC3 F1 genotypes were evaluated for BB incidence under artificial field inoculation. Scoring of inoculated plant was done 14 days after inoculation. The triple and double resistance genes pyramided genotypes provided enhanced resistance as expressed by smaller mean lesion length in comparison to genotypes with individual genes...

Evaluation of Pyramided Rice Genotypes Derived from Cross Between CSR-30 and IRBB-60 Basmati Variety against Bacterial Leaf Blight

Evaluation of Pyramided Rice Genotypes Derived from Cross Between CSR-30 and IRBB- 60 Basmati Variety against Bacterial Leaf Blight Bacterial leaf blight (BB) disease caused by Xanthomonas oryzae pv. oryzae is one of the most severe diseases effecting Basmati rice production in India. CSR-30 is widely grown in Haryana and is extremely popular amongst rice farmers and consumers because of its salt tolerance, aroma, high yield, medium slender grains and excellent cooking and eating qualities. CSR-30 lacks tolerance to BB. The present investigation was therefore planned to introgress BB resistance genes (xa5, xa13 & Xa21) from IRBB-60 to CSR-30. The pyramided BC3 F1 genotypes were evaluated for BB incidence under artificial field inoculation. Scoring of inoculated plant was done 14 days after inoculation. The triple and double resistance genes pyramided genotypes provided enhanced resistance as expressed by smaller mean lesion length in comparison to genotypes with individual genes.

Validation of IPM module against major insect-pests and diseases of cabbage in mid-hills of Uttarakhand

Field trials were conducted to validate the formulated IPM programme for the management of insect-pests and diseases in cabbage grown in Jadipani village of Chamba block of district Tehri-Garhwal, Uttarakhand. The result showed that the IPM program provided 59.12, 57.12, 43.88, 55.98, 52.67, 49.41 and 52.24% reduction in white-grub, cut worm, cabbage butterfly, DBM, aphids, tobacco caterpillar, painted bug infestation, respectively, as compared to non-IPM practiced fields. Similarly, there was 52.15, 52.94 and 49.41% control of damping-off, black leg and white blight or head rot diseases, respectively, over non-IPM practice. Analysis of cost benefit ratio of IPM practice revealed that there was 58.88% increase in yield with net return of Rs. 65.59 thousand per ha over non-IPM practiced field. The B: C ratio of IPM practice field was 2.19. Overall study revealed that the cabbage production under IPM situation proved to be economically more viable in terms of reduction in crop losses by suppression of pest and consequently increase in yield.

Alternaria species associated with araliaceous plants in Korea

In this work, we assess the taxonomy of Alternaria species associated with leaf spot and blight disease on araliaceous plants in Korea. Alternaria araliae and A. panacis are recognized and a novel species, A. dendropanacis, is proposed based on sequence analysis and morphology. They can be differentiated by the combined analysis of Alt a 1, BT1, BT2, EF-1α, gpd and RPB2 gene sequences. Morphologically, the species are distinct by pigment production and conidial characteristics produced under standardized cultural conditions.

Evaluation of Maize Hybrids Against Leaf Blight (&lt;i&gt;Helminthosporium maydis&lt;/i&gt; and &lt;i&gt;H. turcicum&lt;/i&gt;) and Brown Spot Diseases (&lt;i&gt;Physoderma zea maydis&lt;/i&gt;) of Maize Under Mid Hills of North Western Himalayas

A line x tester set was obtained by crossing 24 inbred lines with three testers in maize. Seventy two F 1 S along with twenty seven parents and one standard check were evaluated for resistance against leaf blight and leaf spot diseases under natural epiphytotic conditions at the experimental Farm of Seed Production Unit, CSKHPKV Palampur during Kharif 2004 and 2005. The ten cross combinations viz., Line-3 x Early Composite, Line-5 x Early Composite, Line-10 x Early Composite, Line-13 x Early Composite, Line-15 x Early Composite, Line-19 x Early Composite, Line-18 x Girija, Line-5 x KH-2001, Line-18 x KH-2001 and Line-19 x KH-2001 exhibited resistance for leaf blight and brown spot in both the years. Thus, these hybrids appear to be suitable for cultivation in maize growing areas of Himachal Pradesh where blight and brown spot are the prominent diseases. Hence it was concluded from the present study that the cross combinations Line-13 x Early Composite and Line-19 x KH-2001 showed resistance against leaf blight and spot disease of maize with desirable high specific combining ability (SCA) effects for majority of traits under studied in both the years. These hybrids should be involved in the crop improvement programmes.

English

Tissue culture technique can be used for normal callus culture and regeneration of a new clone. Nowadays the technique is used for establishment of dual culture of host and parasite, and regeneration of disease free plants. Normal callus was established and maintained on MS-medium supplemented with 6-benzylaminopurine (BAP, 1.0 mgl-1) and naphthalene acetic acid (NAA, 4.0 mgl-1). Efficient shoot bud and regeneration of cumin plant from callus was observed on combination of Kinetin (0.5 mgl-1) + indole-3-acetic acid (IAA, 1.0 mgl-1), BAP (0.1 mgl-1) + NAA (1.0 mgl-1) with 25 mgl-1 adenine sulphate (AS). Dual culture of Alternaria burnsii on cumin (Cuminum cyminum) callus was established on MS medium by using infected seeds. Dual culture was developed on MS-medium supplemented with NAA (4.0 mgl-1), BAP (1.0 mgl-1), biotin (1.0 mgl-1), thiamine hydrochloride (1.0 mgl-1), ascorbic acid (25.0 mgl-1) and casein hydrolysate (1.0 mgl-1). The dual culture developed from the infected seeds which were surface sterilized, indicates that the blight disease is basically seed borne in nature. Casein hydrolysate (1.0 mgl-1) and ascorbic acid (25 mgl-1) was found to be best for the growth of the fungus in the dual culture. It was concluded that the study can be used for disease free plants and enhance the growth of the fungus through control the nutrients from the host during disease development. Key words: Cumin, Alternaria burnsii, callus, dual culture.

English

Due to premature defoliation, early blight epidemics can cause major yield losses. Large-spore Alternaria species such as A. solani and A. tomatophila have long been recognized as important pathogens responsible for such blight disease in the family Solanaceae and thus represent a serious risk for crop production. Small-spore Alternaria species have also been frequently isolated from plant samples with typical blight symptoms but their incidence as primary pathogens is often controversial. In order to study the diversity of small-spore Alternaria species, 32 isolates were selected from a larger collection of 130 isolates from infected leaves, fruits and stems of tomato from various growing regions of North-West Algeria. Morphological characterization under standard conditions and polymerase chain reaction (PCR) analyses using specific primers to amplify a part of the ITS regions and the 5.8S gene were conducted to confirm their identification as members of the alternata section. They were then examined according to morphological characteristics of conidia and sporulation patterns on potato carrot agar (PCA) and were segregated into three morphological species: A. alternata, A. tenuissima and A. arborescens. Colony type, substrate colour, margin, zonation, pigmentation, colony diameter and conidia production were studied on potato sucrose agar (PSA). Physiological parameters and nutritional requirements of the isolates were also assessed and a data matrix based on cluster analysis and Euclidean distance was constructed. Results of pathogenicity test on tomato showed obvious diversity among the isolates and they could be separated into two groups based on their virulence. The dendrogram based on the influence of cultural, nutritional and physiological characters suggests moderate heterogeneity within the populations of A. alternata and A. tenuissima. The small-spore species formed five clusters that fundamentally paralleled the morphological groupings. However, the results provided no evidence for geographical and pathogenicity clustering of isolates. Key words: Epidemiology, Solanaceae, small-spore Alternaria species, pathogenic variability, cultural characters, physiological diversity.

Study on the antifungal effect of silver nano particle-chitosan prepared by irradiation method on Phytophthora capsici causing the blight disease on pepper plant

The colloidal silver nano particles with particle sizes of 5, 10 and 15 nm using chitosan (1%) as a stabilizer were prepared by irradiation method using gamma rays from a Co-60 source. The researches of in vitro antifungal activity by silver nano particle-chitosan products on Phytophthora capsici pointed out that the treatments of the products with silver concentrations from 20 to 100 ppm inhibited the growth of P. capsici from 22.6% to 92.9%, respectively. The antifungal activity of P. capsici increased from 62.5 to 100% by the decreasing of silver nano particle size in product from 15 to 5 nm. The antifungal activity on P. capsici by silver nano particle-chitosan product with particle size of 5 nm was 100% at the concentration of 40 ppm, while that by silver nano particle-chitosan product with particle size of 10 nm was 92.9% at the concentration of 100 ppm. The silver nano particle-chitosan prepared by radiation technique may be potentially used as a high-tech, effective and safe fungicide for preventing and treating the foot rot disease caused by P. capsici, a very serious problem on pepper plant.

Bacterial leaf spot and blight of crucifer plants (Brassicaceae) caused by Pseudomonas syringae pv. maculicola and P. cannabina pv. alisalensis

Bacterial leaf spot and blight diseases caused by Pseudomonas syringae pv. maculicola (Psm) and P. cannabina pv. alisalensis (Pcal) are becoming a significant concern for producers of crucifer crops worldwide. Since Psm was first described in 1911, many have reported on its diverse phenotypic, genetic and pathogenic characteristics. Japanese isolates of Psm are also heterogeneous and differ in their host preferences. Pcal was first described in 2002 and has quickly spread globally. Recent work demonstrated that some isolates that had been identified as Psm are actually Pcal. Pcal was also shown to be split into two groups, A and B, based on bacteriological properties, genetic traits and pathogenicity. Group A of Pcal consists mostly of isolates from Japanese radish and radish, isolated before 1990s, that are more aggressive on radish leaves but less aggressive on other Brassica plants compared with group B. Group B of Pcal consists of recent isolates from various crucifer plants including the pathotype of Pcal. In this review, we suggest that group A of Pcal may have existed since the 1950s and survived as a relatively minor pathogen on radish or Japanese radish, whereas group B emerged in the late 1990s, causing global epidemics because of its stronger virulence on various Brassica crops. We also suggest that emergence of a new group of a pathogenic bacterium may cause a re-emergence or new epidemics of a disease that previously was of minor importance.

アブラナ科植物黒斑細菌病 歴史と現状

Bacterial leaf spot and blight diseases caused by Pseudomonas syringae pv. maculicola (Psm) and P. cannabina pv. alisalensis (Pcal) are becoming a significant concern for producers of crucifer crops worldwide. Since Psm was first described in 1911, many have reported on its diverse phenotypic, genetic and pathogenic characteristics. Japanese isolates of Psm are also heterogeneous and differ in their host preferences. Pcal was first described in 2002 and has quickly spread globally. Recent work demonstrated that some isolates that had been identified as Psm are actually Pcal. Pcal was also shown to be split into two groups, A and B, based on bacteriological properties, genetic traits and pathogenicity. Group A of Pcal consists mostly of isolates from Japanese radish and radish, isolated before 1990s, that are more aggressive on radish leaves but less aggressive on other Brassica plants compared with group B. Group B of Pcal consists of recent isolates from various crucifer plants including the pathotype of Pcal. In this review, we suggest that group A of Pcal may have existed since the 1950s and survived as a relatively minor pathogen on radish or Japanese radish, whereas group B emerged in the late 1990s, causing global epidemics because of its stronger virulence on various Brassica crops. We also suggest that emergence of a new group of a pathogenic bacterium may cause a re-emergence or new epidemics of a disease that previously was of minor importance.

First Report of Petiole (Rachis) Blight of Washingtonia filifera Caused by Phoma glomerata in Greece.

In July 2007, a severe petiole (rachis) blight disease was observed on several California fan palms (Washingtonia filifera) in the vicinity of Heraklion (Crete), Greece. Typical symptoms included discolored (brown to reddish-brown), reversed V-shaped lesions on the petiole bases of the oldest (lowest) leaves, and elongated yellow to dark-brown stripes along the petiole. The lesions progressively expanded and penetrated the petioles, resulting in gradual discoloration (from tan to brown-black) of the internal petiole tissues, including the vascular tissue. The bases of infected petioles occasionally became fragile and burst open, while the corresponding leaf blades were characterized initially by yellowing and one-sided or uneven wilt and, later, desiccation and death with the entire leaves curving downwards. The disease gradually moved upward to younger leaves, severely debilitating but rarely killing the infected trees. A filamentous fungus was consistently isolated onto potato dextrose agar (PDA) plates from sections of diseased petioles, forming dense, dark green colonies with abundant light to dark brown, subglobose pycnidia (diameter ranging between 36.4 to 177.4 μm, and averaging 99.4 μm, n = 50) on the agar surface or immersed in the medium. Chlamydospores and numerous dictyochlamydospores were also observed, with the latter being initially light to dark brown and later becoming black. The numerous conidia were hyaline, ovoid to ellipsoid, and single-celled. Their dimensions were 5.3 to 7.3 × 2.4 to 4.9 μm, averaging 6.5 × 3.2 μm (n = 100). The ITS1-5.8S-ITS2 region, together with parts of the flanking 18S and 28S rRNA genes (3), were amplified with PCR from total DNA extracted from two representative isolates, and sequenced (GenBank Accession Nos. KC802086 to KC802087). Using BLASTn, both sequences were 100% identical to Phoma glomerata ITS sequences (FJ427018, FJ427011, AF126816). Based on morphological and molecular analyses, the pathogen was identified as Phoma glomerata (Corda) Wollenw. & Hochapfel, also known as Peyronellaea glomerata (Corda) Goid. ex Togliani or Coniothyrium glomeratum Corda (1,2). To prove pathogenicity and fulfill Koch's postulates, petioles of the older leaves of eight W. filifera 2-year-old seedlings were wounded with a sterile scalpel (shallow cuts 0.5 to 1.0 cm wide, made parallel to the surface), inoculated with agar discs from a 2-week-old PDA culture of the fungus, and sealed with Parafilm. For controls, sterile PDA plugs were placed on the artificial wounds of five more seedlings. All plants were maintained in the greenhouse at 15 ± 5°C, with 90% humidity. Petiole blight and leaf necrosis symptoms-identical to those observed in the infected plants-were evident 5 weeks post-inoculation, and P. glomerata was consistently reisolated from all inoculated plants. No symptoms were observed on control plants. This is the first report of petiole blight of a palm species caused by P. glomerata in Greece. Due to the extensive use of palms as ornamentals in Greece, the occurrence of P. glomerata can potentially cause economic loss to the local ornamental industry.