Conidial Length Research Articles

First report of Verticillium dahliae Kleb. causing wilt symptoms in canola (Brassica napus L.) in North America

In Canada, Verticillium wilt of canola (Brassica napus L.), caused by Verticillium longisporum, was first confirmed in Manitoba in 2014. Verticillium dahliae, however, has not been reported to cause this disease. In 2016, a field survey in Alberta revealed canola plants with vascular wilt symptoms. Symptomatic plants were collected and infected stem tissue was cultured on agar medium, with one isolate designated A1-SS05 identified as a putative Verticillium spp. based on its colony characteristics. The colony was off-white in colour with a felt-like surface. On potato dextrose agar, the underside of the colony was dark only in the central area with radiating ridges. On Howell’s medium, only the test isolate exhibited polyphenol oxidase activity. The isolate formed conidiophores with 4–5 verticillate phialides. Mean conidial length was 5.96 µm (range of 4.65–6.64 µm) and mean width was 2.37 µm (range of 1.71–2.79 µm). The isolate also produced irregularly elongated chain-like microsclerotia of various sizes. Based on these criteria, isolate A1-SS05 was tentatively identified as V. dahliae. Sequencing of PCR products amplified with the primer sets ITS5/4 and VeruniF2/VeruniR3 revealed 99 and 100% identity, respectively, with V. dahliae sequences in GenBank, confirming the identity of this isolate. The isolate was pathogenic on the canola cultivar ‘Westar’, causing wilt symptoms, stunting, and leaf yellowing and senescence. Microscopic analysis of infected vascular tissues revealed irregular shaped microsclerotia, as were observed in pure culture. This is the first report of V. dahliae causing Verticillium wilt of canola in North America.

Monochaetia ilexae sp. nov. (Pestalotiopsidaceae) from Yunnan Province in China

Monochaetia is a pestalotiopsis-like genus characterized by 3–5-septate hyaline to brown conidia with single apical and basal appendages. Monochaetia species exhibit diverse conidial morphology, but many species lack molecular data and thus it is not clear if the genus is monophyletic. In this paper, combined LSU and ITS sequence data and morphological traits are used to introduce a new Monochaetia species, M. ilexae from Yunnan Province, China from dead leaves of Ilex species. Monochaetia ilexae shares similar morphology with the type, M. monochaeta and M. kansensis having fusiform conidia and has a similar range of conidia. However M. ilexae differs from M. monochaeta and M. kansensis having different conidia length, apical and basal appendage lengths. Phylogeny agrees with morphological differences allowing Monochaetia ilexae as a new species that clusters with Monochaetia species, but is separated from the main clade with high support.

Arf6 controls endocytosis and polarity during asexual development of Magnaporthe oryzae.

Asexual development of phytopathogenic fungi such as Magnaporthe oryzae involves morphological changes that require spatiotemporal regulation of polarized growth. ADP-ribosylation factor 6 (Arf6) is a small GTPase known to regulate membrane trafficking and organization of the actin cytoskeleton at the cell surface, and consequently has an impact on cell morphology and polarity. In this study, we have functionally characterized the Arf6 homolog in M. oryzae, showing that ▵arf6 exhibits hyperbranching at hyphal tips and morphologically abnormal conidia as a result of defective polarized growth. ▵arf6 hyphae are also defective in endocytosis as evidenced by a significant delay of FM4-64 uptake. Most ▵arf6 conidia display reduced conidial length, and have defects in conidial septum formation and nuclear distribution. Furthermore, ▵arf6 conidia show a disorganized actin cytoskeleton with random distribution of actin patches at the cell cortex and reduced accumulation of tropomyosin. Arf6-GFP is found to concentrate at the septum area and possibly in endocytic vesicles. Taken together, our data indicate that Arf6 plays an essential role in endocytosis and polarity establishment during asexual development of M. oryzae.

Stemphylium Leaf Blight of Garlic (Allium sativum ) in Spain: Taxonomy and In Vitro Fungicide Response.

The most serious aerial disease of garlic is leaf blight caused by Stemphylium spp. Geographical variation in the causal agent of this disease is indicated. Stemphylium vesicarium has been reported in Spain, whereas S. solani is the most prevalent species recorded in China. In this study, Stemphylium isolates were obtained from symptomatic garlic plants sampled from the main Spanish production areas. Sequence data for the ITS1–5.8S–ITS2 region enabled assignation of the isolates to the Pleospora herbarum complex and clearly distinguished the isolates from S. solani. Conidial morphology of the isolates corresponded to that of S. vesicarium and clearly discriminated them from S. alfalfae and S. herbarum on the basis of the size and septation pattern of mature conidia. Conidial morphology as well as conidial length, width and length:width ratio also allowed the Spanish isolates to be distinguished from S. botryosum and S. herbarum. Control of leaf blight of garlic is not well established. Few studies are available regarding the effectiveness of chemical treatments to reduce Stemphylium spp. incidence on garlic. The effectiveness of nine fungicides of different chemical groups to reduce Stemphylium mycelial growth in vitro was tested. Boscalid + pyraclostrobin (group name, succinate dehydrogenase inhibitors + quinone outside inhibitors), iprodione (dicar-boximide), and prochloraz (demethylation inhibitors) were highly effective at reducing mycelial growth in S. vesicarium with EC50 values less than 5 ppm. In general, the effectiveness of the fungicide was enhanced with increasing dosage.

Pseudoplagiostoma dipterocarpi sp. nov., a new endophytic fungus from Thailand

A new species of endophytic fungi, described herein as Pseudoplagiostoma dipterocarpi, was isolated from leaves of Dipterocarpus tuberculatus in Chiang Mai Province, Thailand. Morphological characteristics indicated that its conidial length was longer than in previously described Pseudoplagiostoma species. Phylogenetic analysis also supports the morphological results. A description, illustration and a key to species are provided.

Functional characterization of putative G protein-coupled receptors in the tomato pathotype of Alternaria alternata

G protein-coupled receptors (GPCRs) are a large transmembrane receptor superfamily that is involved in many cellular signaling pathways. In the present study, GPCR-family genes from the toxigenic and necrotrophic plant pathogen Alternaria alternata were cloned and characterized. Three GPCR-encoding genes, AaGPR1, AaGPR2, and AaGPR3 were identified in the draft genomic data of the A. alternata tomato pathotype, which produces the host-specific AAL-toxin. AaGPR1, AaGPR2, and AaGPR3 each encodes a protein containing a seven transmembrane domain that is characteristic of GPCRs. Targeted deletion of AaGPR1, AaGPR2, or AaGPR3 in the A. alternata tomato pathotype was conducted to understand the influence of G-protein signaling mechanisms on developmental processes and virulence of this pathogen. No changes in colony morphology or AAL-toxin production were observed for the deletion strain ΔAaGPR1, 2, and 3, compared with the wild-type strain. However, one deletion strain, ΔAaGPR3, exhibited aberrant conidial morphology including decreased conidial length and beak formation. The ability to induce the formation of necrotic lesions on susceptible leaves also significantly decreased in ΔAaGPR3, indicating a reduction in virulence. These defects are similar to the phenotypes found for the Gα gene (AGA1) mutant of A. alternata. These results indicate that the G-protein signal transduction pathway appears to be involved in conidial development and virulence of A. alternata.

Cultural and Reproductive Variability of Corynespora cassiicola from Different Host Plants

Natural rubber industry plays an important role in the economy of Sri Lanka. Therefore, improvement of productivity levels has become important. Corynespora leaf fall disease (CLFD) is the most destructive disease of rubber caused by Corynespora cassiicola. In Sri Lanka two epidemics occurred in 1986 and 1995. C. cassiicola has a wide host range including vegetables, ornamentals, weeds, yams, medicinal and other cash crops. Hence, there is a high risk of cross infection possibilities. The objective of this study was to examine the diversity of the pathogen isolates from several host plants; rubber-RRISL202 (A), RRISL 110 (B), RRISL201 (C), Eggplant (D), Papaya (E), Tomato (F). Diseased leaf samples were collected and isolated on potato dextrose agar (PDA). Single spore isolates were obtained and the cultural variations were studied. Except flat textured D and E, all the other isolates showed puffy growth. Colony appearance varied from olivaceous green colour to different shades of grey. Except A, B and C all the other isolates showed concentric rings on lower surface. Except A and B, the other isolates showed uneven margins. In microscopic view, all rubber isolates showed thread like hyphae with a width of (3.20-3.58) μm. However, in the isolates of alternative hosts, hyphae were wider (6.00-7.80 μm). Generally mycelia were branched and septate with conidiophores at the tips of hyphae. Isolates A, B and C were fast growers, D and E were moderate while F was slow. In reproductive studies, generally conidia of C. cassiicola were segmented and showed characteristic hilum at the pointed tips. There was no significant variation in the dimensions of spores among the isolates. The conidial length varied from (15-275 μm) and width varied from (3.75-12.50 μm). Straight, curved, cylindrical and obclavate shapes were observed. Mostly slender, straight conidia were observed in rubber isolates. Rubber isolates were poor sporulators compared to the alternative host isolates. Present study revealed that there is a significant variation in the morphology and reproductive characteristics among the selected C. cassiicola isolates. Further investigations will be carried out to examine the genetic and pathogenicity variations among the isolates. Keywords: Corynespora cassiicola, Alternative hosts, Morphology and reproductive Characteristics

Cultural and morphological variability among the Isolates of Alternaria alternata (Fr.) Keissler, incitant of fruit rot of chilli

Cultural and morphological variability studies on seven different media viz. , potato dextrose agar, host leaf extract agar, host fruit extract agar, oatmeal agar, Richards' agar, Czapek's Dox agar and Rose Bengal agar revealed considerable variation among the isolates of A. alternata indicated the existence of variability in the pathogen. Moreover, Oatmeal agar and potato dextrose agar were found as an excellent media to support the growth and spore formation of isolates of A. alternata , respectively. In case of isolates, Ahmedabad isolate (Aa-7) (61.90 mm) and Rajkot isolate (Aa-8) (61.71 mm) were at par in supporting the mycelium growth and Anand isolate (Aa-1) supports the sporulation abundantly. Among eight isolates of A. alternata , distinct differences in terms of conidial length, breadth, beak length and number of septa were recorded. The average conidial length varied from 16.93 to 59.24 μm and breadth ranges from 6.90 to 14.98 μm with beak length of 3.25 to 44.07 μm. The transverse and longitudinal septa varied from 2 to 10 and 0 to 4, respectively. In the present studies, glaring differences in conidial size were noticed among the isolates even when same medium was used for the growth of the isolates. It can be assumed that variation in the isolates may be inherent since isolates were collected from diverse agroclimatic zones of Gujarat. Hence, these variations in the conidial size indicated the existence of variability in this pathogen.

Molecular and Cultural Characterization of Alternaria brassicae Infecting Cauliflower in Uttar Pradesh, India

The Alternaria blight or leaf blight (Alternaria brassicae) causes severe damage to cauliflower at curd formation and seed setting stage. Roving survey revealed that the disease incidence on cauliflower in different farmer’s fields ranged from 10 to 40 % with an average incidence of 20 % in Uttar Pradesh. Twenty-three (23) isolates of A. brassicae were collected from different cultivars in Uttar Pradesh and characterized for cultural, morphological, pathogenic and molecular variations. Based on the pathogenicity, isolates of A. brassicae were rated as virulent or less virulent based on the percentage disease incidence on cv. Hajipur local. Most of the isolates showed smooth mycelial growth with circular, irregular margin and without concentric zonation. The colony colour is white, dark brown to light brown and pinkish in white. Significant morphological variations in conidial length, conidial width, and number of horizontal septa were observed in all the isolates. The maximum length of conidia ranged from 150 to 122 μm with 8 to 9 transverse and 2 vertical septation. Further the genetic diversity of isolates based on RAPD-PCR using sixteen random primers were produced on clarity, repeatability and the number of polymorphic bands in all the isolates. Cluster analysis of DNA fragments was performed using NTSYSpc V2.2 based on UPGMA method and Jacard coefficient. Based on the analysis the isolates represented four major groups with 75 % similarity.

Morphological, Pathogenic and Molecular Characterizations of Alternaria Species Causing Early Blight of Tomato in Northern India

Early blight disease samples were collected from six different states of India. Seventeen different isolates of Alternaria spp were obtained in pure culture which were designated as PB-2, PB-4, PB-13, PB-17, PB-19, HR-12, HR-44, HR-62, MP-6, MP-7, JT-4, JT-11, UP-7, UP-10, UP-15, UP-20 and RJ-T-1. Characterization based on culture colour and conidial dimensions (conidial length and breadth, and beak length) indicated that no distinguished variation of the isolates was observed on the colour parameters. Although, a wide variation was observed in the length of conidia and beak, no significant difference was observed in conidial breadth except RJ-T-1. Among the isolates, conidial length of five isolates viz., HR-12, UP-7, UP-10, UP-15 and RJ-T-1 ranged from 80 to 97 µm whereas others were of significantly lesser size (30–51 µm). Similarly, significant difference was observed in beak length. The PCR amplification of the fungal DNA using universal primers ITS1 and ITS4 and sequencing indicated that, out of 17 isolates, 12 (JT-4, JT-11, HR-62, HR-44, PB-2, PB-4, PB-13, PB-17, PB-19, UP-20, MP-6 and MP-7) were closely matching with A. alternata (JX993756) and five isolates (HR-12, UP-7, UP-10, UP-15 and RJ-T-1) with A. solani (JF796068). Further, pathogenicity test on tomato revealed that both A. alternata and A. solani isolates were of virulent category indicating that former is also an incitant of early blight in northern India.

Identification and characterization of pathogenic Pestalotiopsis species to pecan tree in Brazil

The objective of this work was to characterize and cluster isolates of Pestalotiopsis species and to identify those that are pathogenic to pecan, based on morphological and molecular characters. Pestalotiopsis spp. isolates were identified by sequencing the internal transcribed spacer (ITS) and β?tubulin regions. Identification methods were compared to indicate the key morphological characters for species characterization. Thirteen isolates were used for the pathogenicity tests. Morphological characterization was performed using the following variables: mycelial growth rate, sporulation, colony pigmentation, and conidial length and width. Ten pathogenic isolates were identified, three as -tubulin regions. Identification methods were compared to indicate the key morphological characters for species characterization. Thirteen isolates were used for the pathogenicity tests. Morphological characterization was performed using the following variables: mycelial growth rate, sporulation, colony pigmentation, and conidial length and width. Ten pathogenic isolates were identified, three as Pestalotiopsis clavispora and three as P. cocculi. The other isolates remained as an undefined species. The morphological characters were efficient for an initial separation of the isolates, which were grouped according to differences at species level, mainly colony diameter, which was identified as an important morphological describer. Beta-tubulin gene sequencing was less informative than the ITS region sequencing for species identification.

Incidence and Biology of Corynespora cassiicola (Berk. & Curt.) Wei. disease of okra in Bangladesh

Eight commercial okra cultivars were evaluated to determine the magnitude of incidence of Corynespora cassiicola (Berk. & Curt.) Wei. Maximum and significant incidence of C. cassiicola was 14.86 in the cultivar BARI 1. In rest of the cultivars, the occurrence of this fungus was very poor to nil. Corynespora cassiicola appeared to be a minor pathogen for okra. Effects of temperature, pH and culture media on growth and sporulation of the fungus were investigated. Potato dextrose agar medium was found to be the most suitable for optimum growth and sporulation of this fungus at pH 7 and 25ºC. The conidial length significantly varied with the changes of pH. The correlation between pH and conidial length was found negative and highly significant. DOI: http://dx.doi.org/10.3329/bjb.v42i2.18028 Bangladesh J. Bot. 42(2): 265-272, 2013 (December)

English

Alternaria blight (Alternaria brassicae) causes severe foliar damage to Indian mustard in Uttarakhand. Ten (10) isolates of A. brassicae were collected from different hosts and characterized for cultural, morphological, pathogenic and molecular variations. A. brassicae colonies varied in their cultural behaviour ranging from cottony, flurry to feathery, with smooth to rough margins. Colour of colonies ranged between white, off white to light brown. Colony growth varied from slow, medium to fast with fast growth in isolate KM and least in JD on the potato dextrose agar (PDA) medium. Significant morphological variations in conidia length, conidia width, and number of horizontal septa were observed in the isolates. Average conidial size ranged from 105 to 135 × 10 to 20 μm. Isolates exhibited variations in disease index, number and size of the lesions. The dendrogram analysis, based on molecular (random amplification of polymorphic DNA, RAPD) basis revealed two groups at 15% similarity coefficient. Group I was composed of seven isolates namely, VR, DV, P7, LM. P10, KR and ND with 18% similarity (82% dissimilarity) while group II was composed of only three isolates namely, JD, KA and AS with only 24% similarity (76% dissimilarity).   Key words: Pathogenic variability, Brassica, Alternaria brassicae, RAPD-PCR.

Morphological and molecular characterization of Fusarium spp pathogenic to pecan tree in Brazil.

The occurrence of Fusarium spp associated with pecan tree (Carya illinoinensis) diseases in Brazil has been observed in recent laboratory analyses in Rio Grande do Sul State. Thus, in this study, we i) obtained Fusarium isolates from plants with disease symptoms; ii) tested the pathogenicity of these Fusarium isolates to pecan; iii) characterized and grouped Fusarium isolates that were pathogenic to the pecan tree based on morphological characteristics; iv) identified Fusarium spp to the species complex level through TEF-1α sequencing; and v) compared the identification methods used in the study. Fifteen isolates collected from the inflorescences, roots, and seeds of symptomatic plants (leaf necrosis or root rot) were used for pathogenicity tests. Morphological characterization was conducted using only pathogenic isolates, for a total of 11 isolates, based on the mycelial growth rate, sporulation, colony pigmentation, and conidial length and width variables. Pathogenic isolates were grouped based on morphological characteristics, and molecular characterization was performed by sequencing TEF-1α genes. Pathogenic isolates belonging to the Fusarium chlamydosporum species complex, Fusarium graminearum species complex, Fusarium proliferatum, and Fusarium oxysporum were identified based on the TEF-1α region. Morphological characteristics were used to effectively differentiate isolates and group the isolates according to genetic similarity, particularly conidial width, which emerged as a key morphological descriptor in this study.

First Report of Colletotrichum karstii Causing Glomerella Leaf Spot on Apple in Santa Catarina State, Brazil.

Glomerella leaf spot (GLS) is an emerging disease of apple (Malus domestica Borkh.) that has been reported in regions with a humid subtropical climate, such as southern Brazil, the southeastern United States, and more recently eastern China. GLS is favored by high humidity and temperatures between 23 and 28°C and can result in extensive defoliation when the severity is high. The disease was first reported 1988 in Brazil on cvs. Gala and Golden Delicious in orchards in Paraná State (3), but now is widespread in the country's producing areas. Two Colletotrichum species of different complexes have been associated with GLS, C. gloeosporioides (Penz.) Penz. & Sacc. and its sexual stage Glomerella cingulata (Stoneman) Spaulding & Scherenk, and C. acutatum J. H. Simmonds, although GLS is more commonly associated with the former. In the summer of 2012, necrotic spots were observed on apple leaves (cv. Gala) in Santa Catarina state, Brazil. The first symptoms were reddish-brown spots, evolving to small necrotic lesions 1 to 10 mm long at 7 to 10 days after symptoms were first noted. Pure cultures were obtained by monosporic isolation and grown on PDA at 25°C and with a 12-h photoperiod under fluorescent light. The color of the upper surface of the colony varied from white to gray and the reverse was pink. The conidia length and width ranged from 9.1 to 17.1 μm ( = 12.8) and from 2.9 to 6.8 μm ( = 4.9), respectively, and were cylindrical, hyaline, and straight. After germination, conidia formed oval or circular appressoria measuring between 4.0 and 10.0 ( = 6.3) × 3.0 and 9.0 ( = 5.7). To confirm pathogenicity, susceptible apple seedlings (cv. Gala) were inoculated with a suspension of 1 × 106 conidia.mL-1. Seedlings sprayed with sterile distilled water served as controls. Seedlings were incubated in a moist chamber at 25°C and 100% RH for 48 h. First symptoms appeared 4 days after inoculation and were similar to those observed in the field. The control treatment remained symptomless. The pathogen was reisolated from lesions, confirming Koch's postulates. Fungus was molecularly characterized by sequencing the internal transcribed spacer (ITS) rDNA and glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and the nucleotide sequence was deposited in the GenBank database (KC876638 and KC875408). C. karstii, considered as part of the C. boninense species complex (1), was identified with 100% sequence homology. This species was previously reported in China (4), Thailand, and the United States, affecting Orchidaceae plants (2), and in Brazil it has been reported affecting Carica papaya, Eugenia uniflora, and Bombax aquaticum (1). To our knowledge, this is the first report of C. karstii causing GLS on apple in Brazil. The development of pre-harvest management practices may be warranted to manage this disease.

English

Dark leaf spot (Alternaria brassicae) is one of the important diseases in crucifers causing serious yield and quality loss in production due to the seed borne nature of the pathogen. Variation in morphology and cultural characteristics among 32 representative Indian geographical isolates of Alternaria brassicae, the causal agent of Alternaria blight of cauliflower (Vegetable) rapeseed-mustard (Oil seed), was studied. All the isolates showed high level of variability in vitro in respect of conidial length, width, and number of septa. Conidia of Uttar Pradesh isolate (CaAbU4) were smallest in size with lowest number of septa. Substantial variation was found in mycelial growth, sporulation among these isolates in different nutrient media. All the isolates did not grow and sporulate abundantly on the same nutrient medium. However, Potato Dextrose Agar, Cauliflower (Host) Agar medium and Carrot Potato Agar were good for all the cultures. Variation in mycelial growth, sporulation was also observed. Cluster analysis of data on cultural variability among thirty two A. brassicae isolates found a close relationship among isolates of both origins viz, from Cauliflower and mustard. Isolates from Uttar Pradesh, Delhi, Haryana and West Bengal were found to be more similar to each other whereas the Rajasthan isolates along with Tamil Nadu and Kerala isolate were distantly related to others. All the isolates were pathogenic in nature but not directly related to the cultural and the morphological characteristics. These isolates were further molecularly characterized by using internal transcribed spacer region where all the isolates were found 56% similar to each other and 99% similar to the A. brassicae isolates present in NCBI database.   Key words: Dark leaf spot, Alternaria brassicae, morphology, cultural variability,pathogenicity, ITS analysis.

First Report of Powdery Mildew of Snow Lotus (Saussurea involucrata) Caused by Leveillula taurica in China.

Snow lotus (Saussurea involucrata Kar. et Kir.) is a rare and beneficial traditional Chinese medicinal herb, growing in the mountains at heights of 4,000 to 4,300 m in the Tianshan and A'er Tai areas in China (2). Because of its very slow growth and exhaustive plant collection, the wild population has been listed as a protected plant by the Chinese government. In recent years, it has succeeded in artificial cultivation. Since 2010, severe powdery mildew infections were repeatedly observed on leaves of the plant of artificial cultivation in Urumqi, Xinjiang Autonomous Region of China. White superficial mycelia were present epiphyllously on both sides of the leaves as well as on young stems, forming a thin, irregular covering. Infections often cause leaf yellowing, reduced growth, and premature defoliation. On the basis of microscopic examination, the morphology of the fungus can be described as follows: Conidiophores emerged through leaf stomata, singly or branched, and form dimorphic conidia. Primary conidia are lanceolate with distinct apical points and 44 to 63 × 12 to 22 μm. Secondary conidia are ellipsoid to cylindrical and 41 to 59 × 12 to 20 μm. The germ tube has indistinct appressoria, is longer than conidia length, and arises from the subterminal region of conidia. These morphological features are typical of the anamorphic stage description of Leveillula taurica (Lév.) Arnaud (1). No ascomata were observed. Representative voucher specimens were deposited in the fungal herbarium of Xinjiang Agriculture University (HMACC 40731). To verify the identity of the fungus, the internal transcribed spacer (ITS) rDNA was amplified and sequenced, and the sequences were deposited as GenBank Accession No. KC292212. Comparison with sequences in the GenBank database revealed that the ITS sequence showed 99% homology with the sequence of L. taurica on Helianthus sp. (AB044378) and Gundelia tournefortii (AB667874). Thus, the pathogen was identified as L. taurica on the basis of the morphological characters and the ITS sequence. Pathogenicity was confirmed through inoculation by gently pressing diseased leaves onto leaves of healthy potted plants. Three inoculated plants were kept under a plastic humid chamber, whereas the same number of non-inoculated plants served as the control. The plants were placed under natural conditions (25 to 28°C) with 80 to 90% humidity. At 5 days after inoculation, typical symptoms of powdery mildew developed on the inoculated plants. No symptoms were seen on the control plants. To our knowledge, this is the first record of L. taurica on S. involucrata in the world. Because the plant is becoming widely cultivated in the Urumqi for use as a Chinese medicinal herb, the occurrence of powdery mildew poses a potential threat to the health of snow lotus.

Phytopathogenic, morphological, genetic and molecular characterization of a Verticillium dahliae population from Crete, Greece

A population of 84 V. dahliae isolates mainly originating from Crete, Greece, was characterized in terms of pathogenicity and virulence on different hosts, in parallel with morphological/physiological characterization, vegetative compatibility grouping and mating type determination. Tomato race 2 was found to have supplanted race 1 and was more virulent on a tomato-susceptible cultivar than race 1. Using a differential host classification system which tests pathogenicity to tomato, eggplant, sweet pepper and turnip, 59 isolates were assigned to tomato, 19 to eggplant, one to sweet pepper and five to tomato-sweet pepper pathogenicity groups. All isolates from Crete fell into VCG subgroups 2A, 2B and 4B, while a remarkably high incidence of bridging isolates (compatible with two or more VCGs) was recorded. The tomato-sweet pepper pathogenicity group was morphologically quite distinct from the others, while conidial length and pigment intensity were discriminatory parameters among VCGs 2A, 2B and 4B. PCR-based molecular marker Tr1/Tr2 was reliable in race prediction among tomato-pathogenic isolates, except for members of VCG 4B, while the application of markers Tm5/Tm7 and 35-1/35-2 was highly successful for tomato-pathogenic isolates. E10 marker was related to VCG 2B, rather than to pathogenicity groups. A single nucleotide polymorphism in the ITS2 region, and two novel molecular markers, M1 and M2, proved useful for the fast and accurate determination of major VCGs 2A, 2B and 4B, and can be used for high-throughput population analyses in future studies. The mating type was unrelated to VCG classification and probably does not control heterokaryon incompatibility in V. dahliae.

Identification of some Aspergillus species isolated from Dal Lake, Kashmir by traditional approach of morphological observation and culture

The current study on some species of genus Aspergillus revealed that any of the general purpose media like potato dextrose agar (PDA) or Rose-Bengal agar is only useful for identification of the molds upto genus level; however, the use of differential culture media like Czapek dox agar (CZ), Czapek yeast agar (CYA) and Malt extract agar (MEA) for their growth to study various macroscopic features like colony color (both conidium and reverse), colony diameter and microscopic features like conidia length, width, shape, ornamentation, stipe length, width, shape, ornamentation and branching Pattern is a key factor in the identification of these molds to species level. Different species of genusAspergillus isolated from the lake water samples showed slightly too large variations in their micro and macro morphological features leading to their species level identification. This study further revealed that follow up of the micro and macro morphological feature of the molds isolated from soil, water, damaged buildings, damp walls, paper or other surfaces is a reliable and simple technique for their identification. Key words: Apsergillus, morphological observation, culture, Dal Lake, Kashmir.

Aggressiveness, diversity and distribution of Alternaria brassicae isolates infecting oilseed Brassica in India

Alternaria brassicae (Berk.) Sacc., a necrotrophic fungus devastating oilseed Brassicacrops in India, causes up to 47% reduction in seed yield. Morphological characteristics of different isolates revealed variation in growth, shape and pigmentation of colony, conidial measurements and number of septa. Conidial length varied from 106.7 to 285.9 µm, width 33.5 to 57.0 µm and beak length 41.4 to 180.0 µm. Number of horizontal septa varied from 3.2 to 8.0 and vertical 0.3 to 1.4. Different synthetic media showed profound variation in mycelial growth of A. brassicae isolates and the poor sporulation indicated that the fungus requires some organic sources of nutrition for better growth and sporulation. The degree of sporulation of A. brassicae isolates is a function of nutrition proved for the first time. Per cent inhibition of mycelial growth showed diverge among A. brassicae isolates, which may be due to the variation towards fungicidal sensitivity among isolates. Pathogen aggressiveness study demonstrated the existence of considerable variation in tolerance ofBrassica species to A. brassicae, which is proved with the location specific disease severity. Key words: Variability, Alternaria brassicae, fungicides sensitivity, aggressiveness,Brassica.