Conidial Length Research Articles

Molecular and Morphological Characterization of Exserohilum turcicum (Passerini) Leonard and Suggs Causing Northern Corn Leaf Blight of Maize in Bihar.

Maize is considered the third most important cereal crop in Asia after rice and wheat. Many diseases affect this crop due to the cultivation of various hybrids. This research aimed to characterize the causative agent of northern corn leaf blight disease in Bihar, India, caused by Exserohilum turcicum (Passerini) Leonard and Suggs. Leaf samples were collected from infected fields in five maize growing districts of Bihar in 2020–2022. A total of 45 fungal isolates from 135 samples were examined for cultural, morphological, and molecular characteristics and were identified as E. turcicum. The isolates were grouped into four groups based on colony color, i.e., olivaceous brown, blackish brown, whitish black, and grayish, and into two groups based on regular and irregular margins. The conidial shapes were observed to be elongated and spindle-shaped with protruding hilum, with conidial septa ranging from 2–12. Similarly, conidial length varied from 52.94 μm to 144.12 μm. β-tubulin gene sequences analysis made it possible to verify the identities of fungal strains and the phylogenetic relationships of all isolates, which were clustered in the same clade. The β-tubulin gene sequences of all the isolates showed a high level of similarity (100%) with reference isolates from GenBank accession numbers KU670342.1, KU670344.1, KU670343.1, KU670341.1, and KU670340.1. The findings of this study will serve as a baseline for future studies and will help to minimize yield losses.

Morphocultural and pathogenic characterization of Colletotrichum gossypii and Colletotrichum gossypii var. cephalosporioides under different temperatures

ABSTRACT Considering the importance of identifying Colletotrichum species associated with cotton plants, this study aimed to characterize the morphological and pathogenic isolates of C. gossypii var. cephalosporioides and C. gossypii under different temperatures. Five isolates of C. gossypii var. cephalosporioides and C. gossypii were incubated at 20, 25 and 30 °C. The cultural characteristics data were analyzed through ANOVA and the means compared by the Tukey test. There were differences between the isolates of the two species concerning mycelial growth and sporulation at different temperatures. Temperatures between 20 to 30 °C increased the length of conidia but did not influence the width, whereas between 25 and 30 °C, there was the highest mycelial growth. Colletotrichum gossypii expressed anthracnose symptoms, and ramulosis symptoms were observed only in plants inoculated with C. gossypii var. cephalosporioides.

Morphologically Diversity of Colletotrichum sp. Conidia Associated With Anthracnose on Chili

Abstract The research conducted to observe the diversity of Colletotrichum sp. associated with anthracnose on chili. The diversity was observed from morphology of conidia. Colletotrichum sp. was isolated from Capsicum frustescens, C. annum (big chili variety and red curly chili) with anthracnose symptoms. In the isolation process, two isolates were obtained from C. annum big chili variety (BA and BB), 5 isolates were isolated from C. annum red curly chili (DPTK1, DPTK2, KA, KC, and KD), and 7 isolates from C. frustescens (DPTR1, DPTR2, RA, RB, RC, RD, and UPN4). Conidia length, shape, and color were observed. Isolate BA from C. annum big chili variety has the longest conidia than other isolate in average (16.10). Isolate RA from C. frustescens has the shortest conidia than other isolates (10.05). All isolates have hyaline color. Isolate BA, DPT K-1, RC, RD, and UPN4 have Fusiform shape. Isolate with cylindrical with rounded apices is BB, DPT K-2, KA, KD, DPT R-1, DPT R-2, RA, and RB. Conidia of Colletotrichum sp. isolated from Capsicum frustescens and C. annum have hyaline colour and diversity on the length and shape.

Cultural, Morphological and Pathogenic Variability in Alternaria cyamopsidis Causing Alternaria Blight of Clusterbean in Rajasthan

Background: Alternaria cyamopsidis (Rang. and Rao) causes Alternaria blight of clusterbean and it is one of the significant disease of clusterbean. Studies were conducted to compare the Cultural, morphological and pathogenic variability among ten isolates of Alternaria cyamopsidis from clusterbean, in five districts of Rajasthan viz., Bikaner, Barmer, Churu, Hanumangarh and Jaipur. Methods: During 2016-17 exhaustive survey was conducted in clusterbean growing areas of Rajasthan and collected diseased samples of clusterbean caused by Alternaria. All the samples were processed for isolation, purification and their pathogenicity was proved in cagehouse and laboratory and standard methods were adopted for cultural and morphological variability study. Result: All the isolates showed variation in their morphological characters, i.e., colony color and shape; conidial number, size, width, length, shape and septation on PDA. Out of ten isolates two isolate, viz., AlcyJp1 and AlcyJp2 showed maximum colony diameter 89.50 and 86.30 mm, respectively. All the isolates varied in their spore length and width and virulent on the tested variety of clusterbean for virulence. AlcyJp1 was the most virulent and produced maximum (65.50%) disease intensity, followed by AlcyJp2 isolate (61.22%).

Morphological and Biometric Diversity of <i>Colletotrichum capsici</i> Isolates, Causal Agent of Cowpea Brown Blotch Disease (<i>Vigna unguiculata</i> (L.) Walp) in the Sudano-Sahelian Zone of Cameroon

Cowpea [Vigna unguiculata (L.) Walp] is an important legume in the midst of about 170 species of its genus because it is an important source of protein and other essential nutrients for humans and animals. Its production faces many constraints such as the cowpea brown blotch disease caused by Colletotrichum capsici which contributes in wet conditions of the field to losses ranging from 42% to 100%. This study was conducted to identify Colletotrichum capsici isolates responsible for cowpea brown blotch disease and to determine their diversity in the Sudano-Sahelian zone of Cameroon. Identification and isolation were made from cowpea organ samples on the Potato Dextrose Agar (PDA) medium and, morphological and biometric characteristics such as: the colony color, the mycelium shape, the abundance of acervules, the presence or absence of saltations, the mycelial growth rate, the conidia length and width were used to assess the diversity. The results obtained indicate that 55 Colletotrichum capsici isolates have been identified in the Sudano-Sahelian zone of Cameroon. Statistical analysis showed that there is a significant difference between isolates. Isolates showed multiple colony colours and were brown coloured as presented by 36.36% of isolates, compact mycelium is found in 56.36% of isolates, 56.36% of isolates have abundant acervulis, and saltations were absent in 45.45% of C. capsici isolates. The mycelial growth rate is between 6.69 mm/d and 12.33 mm/d. The principal component analysis (PCA) made indicated that there are differences between the observed and measured characteristics. The Hierarchical Ascending Classification (HAC) was done and 10 morphotypes of C. capsici in the Sudano-Sahelian zone were identified.

The integrative taxonomy of Beauveria asiatica and B. bassiana species complexes with whole-genome sequencing, morphometric and chemical analyses.

Fungi are rich in complexes of cryptic species that need a combination of different approaches to be delimited, including genomic information. Beauveria (Cordycipitaceae, Hypocreales) is a well-known genus of entomopathogenic fungi, used as a biocontrol agent. In this study we present a polyphasic taxonomy regarding two widely distributed complexes of Beauveria: B. asiatica and B. bassiana s.lat. Some of the genetic groups as previously detected within both taxa were either confirmed or fused using population genomics. High levels of divergence were found between two clades in B. asiatica and among three clades in B. bassiana, supporting their subdivision as distinct species. Morphological examination focusing on the width and the length of phialides and conidia showed no difference among the clades within B. bassiana while conidial length was significantly different among clades within B. asiatica. The secondary metabolite profiles obtained by liquid chromatography-mass spectrometry (LC-MS) allowed a distinction between B. asiatica and B. bassiana, but not between the clades therein. Based on these genomic, morphological, chemical data, we proposed a clade of B. asiatica as a new species, named B. thailandica, and two clades of B. bassiana to respectively represent B. namnaoensis and B. neobassiana spp. nov. Such closely related but divergent species with different host ranges have potential to elucidate the evolution of host specificity, with potential biocontrol application. Citation: Kobmoo N, Arnamnart N, Pootakham W, et al. 2021. The integrative taxonomy of Beauveria asiatica and B. bassiana species complexes with whole-genome sequencing, morphometric and chemical analyses. Persoonia 47: 136-150. https://doi.org/10.3767/persoonia.2021.47.04.

First Report of Passion Fruit Anthracnose Caused by Colletotrichum constrictum.

Passion fruit (Passiflora edulis) is widely cultivated in tropic and subtropic regions. Because of its unique and intense flavour and high acidity, passion fruit juice concentrate is used in making delectable sauces, desserts, candy, ice cream, sherbet, or blending with other fruit juices. Anthracnose of passion fruit is favored by frequent rainfall and average temperatures above 27°C. In August 2018, anthracnose on passion fruit was observed in commercial plantings in Lincang, Yunnan, China (23.88 N, 100.08 E). Symptoms included lesions of oval to irregular shapes with brown to dark brown borders. Infection covered most of the fruit surface with pink-to-dark sporulation as reported by Tarnowski and Ploetz (2010). A conidial mass from an individual sorus observed on an infected fruit was isolated and cultured on potato dextrose agar (PDA) supplemented with 50 μg ml-1 of streptomycin. From a single microscopic field, two monospore isolates were dissected using a sterile needle, subcultured, and referred to as BXG-1 and BXG-2. Morphological characters including conidia colour, size, and shape were similar between the two isolates. Conidia were aseptate and cylindrical with apex and rounded base. Conidial length ranged from 12.3 to 16.1 µm (avg. 13.5) and width ranged from 5.5 to 6.2 µm (avg. 5.7). Morphologic data were consistent with Colletotrichum constrictum (Damm et al., 2012). To further confirm the fungal species, the ribosomal internal transcribed spacer (ITS), partial sequences of actin (ACT), chitin synthase (CHS-1), glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and β-tubulin 2 (TUB2) were amplified and sequenced. Primers and PCR amplification were described by Damm et al. (2012). The sequences were compared to type sequences in GenBank. The results showed the ITS (GenBank accession MW828148 and MW828149), ACT (MW855882 and MW855883), CHS-1 (MW855884 and MW855885), GAPDH (MW855886 and MW855887), and TUB2 (MW855888 and MW855889) sequences of the isolates BXG-1 and BXG-2 were 98% identical with sequence data from strain CBS:128504 of C. constrictum. A maximum likelihood tree was constructed using MEGA-X version 10.1.6 (Kumar et al., 2018) based on a combined dataset of the ITS, ACT, CHS-1, GAPDH, and TUB2 sequences of BXG-1 and BXG-2, and those of 18 Colletotrichum spp. previously deposited in GenBank (Damm et al., 2012). The phylogenetic analysis showed that BXG-1 and BXG-2 belong to the C. constrictum clade. Based on morphology and DNA sequencing, BXG-1 and BXG-2 were identified as C. constrictum. To verify pathogenicity, passion fruit were sprayed with a suspension of 1 × 105 conidia ml-1. Control fruit were sprayed with sterilized water. After inoculation, fruit were incubated in an Artificial Climate Box at 27°C and 80% RH. Necrotic symptoms appeared 8 days after inoculation and were similar to those observed on fruit form the field. The pathogen was reisolated from lesions thus fulfilling Koch's postulates. C. constrictum has been reported to cause anthracnose of citrus from Australia (Wang et al., 2021) and mango from Italy (Ismail et al., 2015). To our knowledge, this is the first report of C. constrictum causing anthracnose on passion fruit worldwide, and these data will provide useful information for developing effective control strategies.

Morphological Variety in Distoseptispora and Introduction of Six Novel Species.

Distoseptispora is one of the sporidesmium-like taxa with great variation in asexual morphology and delineation of species. Phylogenetic analyses of four gene regions LSU, ITS, TEF1α, and RPB2 revealed the placement of several sporidesmium-like species in Distoseptispora (Distoseptisporaceae, Distoseptisporales, Sordariomycetes), collected on submerged decaying twigs from streams in China and Thailand. Based on morphological examination and molecular DNA data, six new species, Distoseptispora amniculi, D. atroviridis, D. effusa, D. fusiformis, D. hyalina, and D. verrucosa, are proposed. Among them, D. hyalina is the first sexual morph confirmed in the genus. A new geographical record is reported for D. lignicola in China. Conidial length proved to be of less taxonomic significance for some Distoseptispora species, whereas the type of conidial septa is informative at species level.

Morphological Characterization of Corynespora cassiicola Isolates in Culture Media

Corynespora cassiicola threatens soybean and cotton production in Brazil. The objective of this study was to evaluate cultural and morphological aspects of C. cassiicola isolated from soybean and cotton of different Brazilian regions, in culture media. The isolates were grown in PDA (Potato Dextrose Agar) and V8 juice agar media. The characteristics evaluated were: color, aspect, and growth rate of mycelia, as well as production and dimension of conidia, and number of septa per conidium. Culture media and isolates were compared using the Kruskal-Wallis or Tukey’s test at 5% significance level. The mycelia of the isolates were predominantly dark gray and light brown. C. cassiicola isolates grew better in V8 juice agar medium, presenting a higher mycelial growth rate. In PDA medium, the production of conidia was higher in isolates from cotton, compared with soybean isolates. There was great variation in the production of conidia in V8 juice agar medium, regardless of the host origin. Conidia length and width varied for isolate and culture medium. The isolates of C. cassiicola coming from cotton presented a higher number of septa per conidium when grown in PDA medium. The morphological aspects of C. cassiicola vary depending on the host of origin and the culture medium.

Diplodia parva sp. nov., a novel species of the family Botryosphaeriaceae isolated from soil in Korea

A fungal strain designated KNU16-007, belonging to the family Botryosphaeriaceae, was isolated from soil in Daegu, Korea. Phylogenetic analyses based on the concatenated nucleotide sequences of the ITS and TEF-1α regions, showed that the isolate resides in a clade together with Diplodia species but occupies a distinct phylogenetic position. Conidial dimensions of strain KNU16-007 (22.7–29.3 μm × 8.9–10.9 μm) or its conidial length:width ratio were significantly differed from those of the closely related D. sapinea, D. intermedia, D. scrobiculata, D. seriata, D. crataegicola, D. rosacearum, and D. citricarpa clearly indicating morphological differences from these species. Detailed descriptions, illustrations, and discussions regarding the morphological and phylogenetic analyses of the closely related species are provided to support the novelty of the isolated species. The results of phylogenetic analysis and morphological observations indicate that strain KNU16-007 represents a novel species in the genus Diplodia, for which the name Diplodia parva sp. nov. is proposed.

The integrative taxonomy of Beauveria asiatica and B. bassiana species complexes with whole-genome sequencing, morphometric and chemical analyses.

Fungi are rich in complexes of cryptic species that need a combination of different approaches to be delimited, including genomic information. Beauveria (Cordycipitaceae, Hypocreales) is a well-known genus of entomopathogenic fungi, used as a biocontrol agent. In this study we present a polyphasic taxonomy regarding two widely distributed complexes of Beauveria: B. asiatica and B. bassiana s.lat. Some of the genetic groups as previously detected within both taxa were either confirmed or fused using population genomics. High levels of divergence were found between two clades in B. asiatica and among three clades in B. bassiana, supporting their subdivision as distinct species. Morphological examination focusing on the width and the length of phialides and conidia showed no difference among the clades within B. bassiana while conidial length was significantly different among clades within B. asiatica. The secondary metabolite profiles obtained by liquid chromatography-mass spectrometry (LC-MS) allowed a distinction between B. asiatica and B. bassiana, but not between the clades therein. Based on these genomic, morphological, chemical data, we proposed a clade of B. asiatica as a new species, named B. thailandica, and two clades of B. bassiana to respectively represent B. namnaoensis and B. neobassiana spp. nov. Such closely related but divergent species with different host ranges have potential to elucidate the evolution of host specificity, with potential biocontrol application. Citation: Kobmoo N, Arnamnart N, Pootakham W, et al. 2021. The integrative taxonomy of Beauveria asiatica and B. bassiana species complexes with whole-genome sequencing, morphometric and chemical analyses. Persoonia 47: 136-150. https://doi.org/10.3767/persoonia.2021.47.04.

Morphological characteristics and distribution of colletotrichum isolates morphotypes infecting mango (Mangifera indica L.) in the north of Côte d’Ivoire

Anthracnose caused by Colletotrichum species is the most important field and postharvest disease infecting mango worldwide. A survey was conducted in the seven mango producing districts in the north of Cote d'Ivoire to identify and characterize Colletotrichum species isolates associated with mango leaves necrosis and fruit rots. A total of 70 isolates were identified based on morphological and cultural characters. Most of isolate colour were grey or grey whitish (36%), cottony (71%) with cylindrical conidia (97%) rounded on both ends (57%). Three texture types were observed in colonies of the seventy isolates. Most of the isolates were cottony (71%) followed by abundant aspect (23%) and closely appressed (6%). According to conidia shape, two species of Colletotrichum; Colletotrichum gloeosporioides (97%) and C. acutatum(3%) were identified in the seventy isolates. Conidia length and width varied respectively from 15.4to 19.7μm and 4.8 to 5.2 μm. The Average Linear Growth Rate (ALGR) 7 days after culture varied from 0.76 to 0.91 cm day-1. Multivariate analysis grouped the 70 isolates into four morphotypes containing, respectively: 5 (7%), 7 (10%), 17 (24%) and 41 (59%) isolates. Isolates of morphotype 1 were characterized by whitish obverse and reverse colour with an abundant mycelia aerial aspect. The second morphotypes were represented by isolates with obverse and reverse brownish grey colour and contained both conidia with two rounded ends, and one rounded and one sharped ends. The third morphotype consisted of isolates with obverse and reverse grey whitish colour. The fourth morphotype consisted of isolates with obverse and reverse respectively dark grey and grey or vice versa. Conidial length and width of morphotypes varied, respectively, from 14.5 to 17.2 μm and 4.6 to 5.2 μm. ALGR of morphotypes varied from 0.84 to 0.87 μm day-1. The present study highlighted that morphological variation of Colletotrichum species existed among the different isolates and the districts surveyed. However, to overcome the inadequacies of this traditional morphological identification, sequence analyses are needed to be carried out to confirm the identity of these Colletotrichum species isolates.

Characterization and pathogenicity of six Cytospora strains causing stem canker of wild apple in the Tianshan Forest, China

AbstractCytospora species are capable of causing destructive cankers of stems belonging to a wide range of woody plant species. In severe cases, cankers may lead to dieback of twigs and branches. Little is known about the Cytospora species causing canker disease of wild apple (Malus sieversii) trees in the Wild Fruit Forest Reserve in Tianshan Forest, Xinjiang Uygur Autonomous Region, China. In this study, six Cytospora isolates belonging to two species were isolated from cankerous lesions of wild apple twigs. Based on multi‐locus phylogenetic analysis using three DNA markers (ITS, tef1‐α and tub2) and morphological characterization, these isolates were identified as Cytospora mali and Cytospora parasitica. Temperature trials (15, 20, 25 and 30°C) showed that the optimal growth temperature for six isolates was 25°C. At a variety of temperatures, C. mali isolates tended to grow faster than isolates of C. parasitica, with the C. mali isolate, EGI1 performing better than others with regard to growth rate. Morphological observations showed that these species exhibited a single locule without conceptacles, and the conidia length was 3–5 μm. In vitro inoculation trials of twigs and leaves of M. sieversii seedlings revealed that the C. mali isolates were highly virulent phytopathogenic fungi, whereas the C. parasitica isolates were less virulent. The isolate EGI1 was the most virulent isolate among the six isolates. This paper presents the first report of pathogenic Cytospora spp. of the M. sieversii Tianshan Wild Fruit Forest Reserve of Yili, Xinjiang in China. It will aid in the understanding of how apple tree cankers are induced and provide disease management guidelines for M. sieversii forest conservation.

Morphology characterization and in vitro study of bio agents, plant extracts and chemicals against Pestalotiopsis mangiferae in Manipur

A study was conducted in vitro condition to analyse the morphology and efficacy of bio agent, plant extract and some chemical against P. mangiferae which was collected from different districts of Manipur. The morphological characters under study consist of colony and conidial characteristics such as colour, shape, size and appendages. The cultural growth colour of P. mangiferae on PDA varied from concolour to versicolour fuliginous. The conidial shape varied from oval and spherical to elliptical with prominent appendages. The conidial length and widths were 22.9 and 5.7 μm respectively. The diseased sample which was collected from different district of Manipur consists of three septation and the number of conidial appendages was found 2-3 numbers. Among seven antagonists namely Penicillium citrinum, Trichoderma atroviride, T. ovalisporum, Hypocrea lixii, T. harzianum (69 and 131) and T. asperellum evaluatedin vitro, T. asperellum showed the best in inhibiting the growth of the fungus (85.8%). Among three plant extracts viz. garlic, neem and sweet flag evaluated in vitro, garlic extract (3.0%) showed the best result (100.0%). Among the seven chemicals viz. carbendazim, thiophenate methyl, mancozeb, imidacloprid, fipronil, profenophos and thiomethoxam evaluated in vitro, thiophenate methyl (0.05%) and carbendazim (0.05%) showed the best result with 100.0 percent inhibition in fungal growth.

Cultural, Morphological and Molecular Characterization of Fusarium Oxysporum f.sp. Ciceris Inciting Wilt of Chickpea

Thirty two isolates of Fusarium oxysporum f.sp. ciceris (Foc) were collected from six districts of Andhra Pradesh (A.P) and three districts of Telangana. Based on wilting % in pathogenicity test, the isolates were grouped into three categories. All the isolates differed in cultural characters like mycelium colour, margin, texture, pigmentation and morphological characters like macro conidia, micro conidia length, width and chlamydospores diameter. There was no correlation between cultural and morphological characters of Foc isolates except three isolates (Foc-6, Foc-12 and Foc-17). These three isolates have white mycelium, cream colour pigmentation, slow radial growth and highly pathogenic (100% wilt incidence) in nature. Sporulation ability and radial growth of all isolates were also measured. All the isolates exhibited genetic variation in RAPD banding pattern and three major clusters (I, II and III) were found in the dendrogram. Maximum genetic similarity of 80.3% was observed between Foc-27 and Foc-28 isolates.

Morphology and phylogeny reveal two novel Coryneum species from China.

Coryneum is currently the sole genus of Coryneaceae in Diaporthales, distinguished from other diaporthalean genera by transversely distoseptate brown conidia. However, Coryneum species are presently difficult to identify because of variability and overlap of morphological characters and the lack of sequence data for most described species. During fungal collection trips in China, 13 Coryneum isolates were obtained from cankered branches of Ilex and Quercus. Morphological and phylogenetic analyses (ITS, LSU, TEF1-α and RPB2) revealed that these strains belong to two new species (viz. Coryneumilicissp. nov. and C.songshanensesp. nov.), and three known species, C.gigasporum, C.sinense, and C.suttonii. Coryneumilicis has larger conidia and more distosepta than most Coryneum species. Coryneumsongshanense was similar to C.sinense from the same host genus, Quercus, in conidial length, but distinct in conidial width and by molecular data.

Diversity in Alternaria brassicae (Berk.) Sacc. isolates and characterization of host response in different oilseed Brassica species

Alternaria brassicae (Berk.) Sacc., a necrotrophic fungus devastating oilseed Brassica crops in India, causes up to 47% reduction in seed yield. So the study is conducting to develop the knowledge about the variability of A. brassicae in terms of cultural, morphological, pathogenic characters and their effects on different Brassica species of rapeseed mustard, for minimizing the losses caused by A. brassicae and help to stabilize the rapeseed mustard production. In variability study, all the isolates showed cultural, morphological variability. Average conidial length was maximum in isolate Ab2 (21.7μ) followed by Ab4 (20.7μ) and minimum in Ab8 (15.6μ). Septation in conidia, both horizontal and vertical also showed variation in different isolates. Finally it was revealed that smallest size of conidia in isolates Ab8 and longest size of conidia in isolates Ab4 were observed. On solid medium, maximum sporulation was observed in Ab7 followed while minimum sporulation recorded in Ab8. On liquid medium, maximum sporulation was observed in Ab7 while minimum sporulation recorded in Ab8. All the isolates showed the variability in qualitative characters i.e. spot colour, presence or absence of central point, concentric rings and yellow halo and as well as in quantitative characters i.e. incubation period and Percent Disease Index.

Cultural, morphological and bio-chemical variability of different isolates of Colletotrichum truncatum causing anthracnose of greengram

A laboratory experiment was conducted to study the variability among the eight isolates of Colletotrichum truncatum of greengram collected from different locations on the basis of cultural, morphological and biochemical characteristics by using nine different culture media viz., Potato Dextrose Agar (PDA), Potato Carrot Agar (PCA), Oat Meal Agar (OMA), Corn Meal Agar (CMA), Carrot Agar (CA), Sabouraud’s Agar (SA), Czapek’s Dox Agar (CDA), Richard’s Agar (RA) and V8 Juice Agar. Colony colour varied in different media from white or white with light brown centres which later changed to black or dark to light brown with increase in the age of the fungal cultures. Mostly, the colonies had fluffy or cottony mycelial growth with slight variations and regular to irregular white margin. PDA, PCA, CA and RA produced maximum mycelial growth (90 mm) at 10 DAI (days after inoculation). Minimum growth was observed on SA (69.56 mm) and V8 juice agar media (55.42 mm) and their difference was statistically significant. Morphological variability among the isolates was studied by comparing their conidial length, breadth and length and breadth of setae and their differences were statistically significant. Biochemical variability among the isolates was based on α- and β-esterase and peroxidise profiling. Positive activity was observed for both α- and β-esterase. α-Esterase enzyme showed the highest enzyme activity in terms of maximum numbers of banding loci among the three isozymes tested. The findings of the present study clearly revealed that cultural, morphological and biochemical variability did exist among the different isolates of C. truncatum.

RESISTANCE OF HELMINTHOSPORIUM SOLANI STRAINS TO SELECTED FUNGICIDES APPLIED FOR TUBER TREATMENT

Helminthosporium solani strains were isolated from potato tubers collected in Russia or taken from imported German and Dutch seed tubers. Sequences of the nuclear ribosomal genes and internal transcribed spacers (ITS) for all 24 tested strains were identical and had 100% similarity to the sequences from GenBank identified as Helminthosporium solani. The obtained molecular data confirmed the morphological identification based on the width and length of conidia, the shape of conidiophores and the colony morphology. Screening for resistance to the fungicides Score 250 SC (active ingredient difenoconazole 250 g/l), Quadris (azoxystrobin 250 g/l), Tecto 500 SC (thiabendazole 500g/l), Zeroxxe (colloidal silver particles (3 g/l) stabilized with amphoteric surfactant) was done. Agar blocks with pure cultures of the fungal strains were placed in the centre of Petri dishes containing malt agar amended with fungicide concentrations of 0.1, 1, 10, 100 and 1000 mg/l (accounted for the concentration of the active ingredient). Malt agar free of fungicide was used as the control. 2 Growth inhibition of 50% (EC50) compared to the control was detected based on the doseresponse curves. Difenoconazole (EC50 100 mg/l). Thiabendazole appears to be effective against the sensitive strains of H. solani (EC50 1000 mg/l). The sequence of their β-tubulin gene contained a SNP mutation in the 198 codon or 200 codon, translating to Gln (CAG) instead of Glu (GAG) or Tyr (TAC) instead of Phe (TTC), respectively. Thus, the resistance to thiabendazole of the Russian, European, and American strains had the same genetic background and was conferred by the same mutations.

BIOLOGICAL CONTROL OF SPILOCAEA OLEAGINA, THE CAUSAL AGENT OF OLIVE LEAF SPOT DISEASE, USING ANTAGONISTIC BACTERIA

Olive leaf spot (OLS) caused by the fungus Spilocaea oleagina (Cast.) Hugh. is one of the serious diseases of olive trees in many parts of the world. The disease is controlled by application of copper-containing fungicides prior to winter rains. Timing of fungicide applications and their high costs and possible effects on human health and the environment are critical for an effective control. Since biological control may be a realistic alternative to chemicals, in this work about 176 bacterial isolates were screened for their efficacy against OLS. Six bacterial isolates, belonging to the genera Pseudomonas and Bacillus proved to have an inhibitory effect on conidial germination under in vitro conditions. A Pseudomonas isolate (ORS3) and a Bacillus isolate (BAT) were most effective with inhibition rates of 96.95 and 94.78%, respectively. The length of the germ tube in the presence of the bacteria was three times the length of the conidia in the control treatments. The results of this work provide new possibilities to control using bacteria as biocontrol agents. Further analysis and experiments are required to evaluate the efficacy of the bacteria under field conditions.