Nit Mutants Research Articles

Quantitative Assessment of the Combined Effect of the Nitrogen Status, Light and Dehydration of Mycelium on Conidiation in Neurospora crassa

We performed a quantitative assessment of the conidia yield in Neurospora crassa in response to treatment with different conidiation effectors. Depending on nitrogen source and intactness of nitrite reductase (NiR) and nitrate reductase (NR), light and dehydration affected the number of viable conidia produced by the ascomycete. In most variants of the nitrogen status, the combined action of light and dehydration synergistically increased the conidia yield. Conidiation in wild-type cells cultivated on the medium with NH4Cl as a sole nitrogen source did not respond to light, whereas illumination of the same culture grown on NH4NO3- or NaNO3-containing medium stimulated the process of spore formation. In response to light exposure, conidia formation occurred in the same way in the nit-2 (no NR and NiR) and nit-6 (no NiR) mutants cultivated in the presence of NH4Cl, but differed greatly when grown on the medium with NH4NO3. The results obtained indicate the possibility that NR and NiR participate in the photoconidiation regulation (wild-type strain on the medium with secondary nitrogen source); however, they cannot be necessary because light-dependent stimulation of spore formation was observed in nit-2 and nit-6 mutants.

Characterization of Aspergillus section Flavi from pistachio soils in Iran

Abstract During 2012, soil samples from commercial pistachio orchards in three major production regions include Rafsanjan (Kerman Province, center of Iran), Damghan (Semnan Province, north-central Iran) and Feyz-Abad (Khorasan-e Razavi Province, northeastern Iran), were assayed on Dichloran Rose-Bengal Chloramphenicol agar (DRBC) and Aspergillus flavus-parasiticus agar media to quantify populations of Aspergillus species from the section Flavi. The mean propagule density of Aspergillus species from the Flavi section [log10 (CFU/g soil)] was higher in Feyz-Abad (3.06, 2.88–3.24), compared to Damghan (2.55, 2.44–2.65) and Rafsanjan (2.40, 2.26–2.54). A. flavus (69.7, 65.3 and 57.9%), A. parasiticus (19.6, 25.4, and 29.3%), and A. nomius (10.7, 9.3, and 12.8%) were the predominant species in the regions of Rafsanjan, Damghan, and Feyz-Abad, respectively. There were significant differences among sclerotia producing isolates of A. flavus in the sampling regions (p < 0.05). The percentage of sclerotium-producing isolates of A. flavus from Rafsanjan (14.5%) was much lower than Damghan (39.5%) and Feyz-Abad (41.4%). The A. flavus isolates from Damghan, Rafsanjan, and Feyz-Abad were toxigenic at 53.7%, 61.6%, and 60.4%, respectively. In Rafsanjan, aflatoxin B1 (AFB1), and AFB1 + AFB2 (aflatoxin B2) ranged from 274 to 553 ppb (393±17.11) and 394 to 3745 ppb, respectively, while AFB1, and AFB1 + AFB2 ranged from 257 to 392 ppb (285±13.18) and 415 to 1658 ppb, respectively, in Damghan. We found 16 and 20 vegetative compatibility groups (VCGs) for 41 and 37 nit mutant producing isolates of A. flavus from Rafsanjan and Damghan, respectively. From Damghan the VCG diversity for A. flavus isolates was greater (54%) than from Rafsanjan (39%). Because there were a few number of sclerotium-producing isolates of A. flavus, we did not determine the relationships between sclerotium production with VCGs and/or geographical distribution in the three pistachio production regions. This study was the first to determine the strain and VCG diversity of A. flavus soil isolates from Iranian pistachio orchards.

Evidence for Genetic Similarity of Vegetative Compatibility Groupings in Sclerotinia homoeocarpa.

Vegetative compatibility groups (VCGs) are determined for many fungi to test for the ability of fungal isolates to undergo heterokaryon formation. In several fungal plant pathogens, isolates belonging to a VCG have been shown to share significantly higher genetic similarity than those of different VCGs. In this study we sought to examine the relationship between VCG and genetic similarity of an important cool season turfgrass pathogen, Sclerotinia homoeocarpa. Twenty-two S. homoeocarpa isolates from the Midwest and Eastern US, which were previously characterized in several studies, were all evaluated for VCG using an improved nit mutant assay. These isolates were also genotyped using 19 microsatellites developed from partial genome sequence of S. homoeocarpa. Additionally, partial sequences of mitochondrial genes cytochrome oxidase II and mitochondrial small subunit (mtSSU) rRNA, and the atp6-rns intergenic spacer, were generated for isolates from each nit mutant VCG to determine if mitochondrial haplotypes differed among VCGs. Of the 22 isolates screened, 15 were amenable to the nit mutant VCG assay and were grouped into six VCGs. The 19 microsatellites gave 57 alleles for this set. Unweighted pair group methods with arithmetic mean (UPGMA) tree of binary microsatellite data were used to produce a dendrogram of the isolate genotypes based on microsatellite alleles, which showed high genetic similarity of nit mutant VCGs. Analysis of molecular variance of microsatellite data demonstrates that the current nit mutant VCGs explain the microsatellite genotypic variation among isolates better than the previous nit mutant VCGs or the conventionally determined VCGs. Mitochondrial sequences were identical among all isolates, suggesting that this marker type may not be informative for US populations of S. homoeocarpa.

High‐Throughput Assessment and Genetic Investigation of Vegetative Compatibility in Verticillium dahliae

AbstractClassification of isolates into vegetative compatibility groups (VCGs) using nitrate‐non‐utilizing (nit) mutants has been widely used for the characterization of Verticillium dahliae populations. However, certain methodological limitations prevent its application on a large scale. Furthermore, systematic investigations into the genetics underlying complementation tests between nit mutants of fungal isolates (i.e. heterokaryon formation) are lacking for Verticillium species. In this work, a diverse collection of 27 V. dahliae isolates – including representatives of all VCGs, both mating types, and heterokaryon self‐incompatible isolates – was employed for the development and optimization of (i) a protocol for the rapid generation of nit mutants of V. dahliae isolates using UV‐irradiation and (ii) a reproducible high‐throughput procedure for complementation tests between nit mutants in liquid cultures using 96‐well microplates. The genetic analysis of selected heterokaryons demonstrated that the frequently encountered ‘weak’ cross‐reactions between VCGs and their subgroups can be actually heterokaryotic, implying the absence of strict genetic barriers between VCGs. In conclusion, we provide in this work an optimized method for the high‐throughput VCG assignment of V. dahliae populations and a genetic analysis of heterokaryons that may have serious implications for the interpretation of VCG classification data. These advancements in the available methodology and the genetic background of vegetative compatibility grouping may contribute to a better understanding of the population biology of V. dahliae and possibly other mitosporic fungi.

Barrage formation is independent from heterokaryon incompatibility in Verticillium dahliae

Barrage formation has been traditionally used for the assessment of mycelial compatibility in many fungi and has often been assumed to represent a non-self recognition phenotype that is directly associated with vegetative incompatibility in these organisms. In this work, the optimal growth conditions for large-scale studies of barrage formation in the asexual fungus Verticillium dahliae were determined, and they were used for the analysis of a diverse collection comprising 69 isolates of V. dahliae and related species. Barrage formation was very frequent on a defined complete agar medium within V. dahliae and between species of the genus. However, it was not correlated with the classification of V. dahliae isolates into Vegetative Compatibility Groups (VCGs) (based on the standard method using complementary nit mutants), as it was recorded at high frequencies both within and between V. dahliae VCGs. The high overall frequency of barrage formation demonstrated the presence of a higher level of mycelial incompatibility in V. dahliae than heterokaryon incompatibility assessed by forcing complementary nit mutants to form heterokaryons under selective conditions. The possible association of barrage formation with morphological characteristics of the fungal colonies was investigated, and a negative correlation of frequency and intensity of barrages with the isolates’ capacity for pigment production was detected.

Vegetative compatibility groups and sexual reproduction among Spanish Monilinia fructicola isolates obtained from peach and nectarine orchards, but not Monilinia laxa

The frequency of occurrence of Monilinia fructicola in the Ebro Valley, Spain has increased since its first appearance in 2006, and M. fructicola has displaced Monilinia laxa, the native species which is the main cause of brown rot in peaches in this valley. In order to determine the characteristics that may be related to the displacement, we studied the capacity to generate new genotypic combinations of M. fructicola under laboratory conditions. The morphology and parasitic ability from ten field isolates of M. fructicola and M. laxa collected from three different orchards in the valley, and sampling from five different lesions were studied. Nitrate-non-utilising (nit) mutants were generated in order to test the isolates for vegetative compatibility which was done by assessing their colony growth when cultured singly or in pairs on media that contained different nitrogen sources. For the M. fructicola isolates, five vegetative compatibility groups (VCGs) were identified using the nit mutants and six VCGs were identified when they were grown on potato dextrose agar dishes. In all instances, the vegetatively compatible M. fructicola isolates came mainly from the same orchard. Only one VCG displays the same morphological and competition characteristics. No VCGs were identified among the M. laxa isolates. We did not find any apothecia of M. laxa and M. fructicola isolates in the soil of the three orchards, but we were able to produce apothecia of M. fructicola in the laboratory. Our finding of sexual reproduction and VCGs in the M. fructicola isolates suggests that the genetic variability of M. fructicola could be maintained by sexual and/or parasexual recombination.

Chlamydomonas NZF1, a tandem‐repeated zinc finger factor involved in nitrate signalling by controlling the regulatory gene NIT2

The Chlamydomonas reinhardtii NIT2 gene plays a central role in nitrate assimilation, thus, nit2 mutants are not able to sense or to use nitrate for growth. NIT2 protein is an RWP-RK-type transcriptional factor related to nodule inception (Nin, NLP) proteins from plants. NIT2 expression is down-regulated in ammonium and up-regulated under nitrogen deprivation. However, intracellular nitrate is required to activate NIT2 for subsequent expression of NIA1 and other nitrate assimilation genes. In this work, mutants defective in nitrate sensing have been studied. The identification of genomic regions affected allows proposing putative loci/genes for nitrate signalling in the alga. Among them, a CrNZF1 (Nitrate Zinc Finger 1) that encodes a tandem zinc finger protein CCCH-type. In the nzf1 mutant, the expression of the regulatory gene NIT2 is decreased and also that of nitrate assimilation genes. In this mutant, polyadenylated forms of NIT2 with different lengths could be detected, whereas in the wild type there appeared preferentially the longest forms. CrNZF1 is proposed to regulate NIT2 polyadenylation and thus nitrate signalling and nitrate-dependent growth in the alga.

Pathogenicity and vegetative compatibility grouping among Indian populations of Fusarium oxysporum f. sp. ciceris causing chickpea wilt

Thirty-nine isolates of Fusarium oxysporum f. sp. ciceri – the causal agent of chickpea (Cicer arietinum) wilt – collected from different parts of India and representing eight races of the pathogen, were analyzed for virulence and classified on the basis of vegetative compatibility grouping (VCG). The wilt incidence ranged from 24% to 100% on a highly susceptible cultivar JG 62. Six isolates, from Delhi, Gujarat, Karnataka, Punjab and Rajasthan and belonging to six different races of the pathogen, caused 100% wilt incidence. Five isolates belonging to four different races, namely, Foc 143 from Andhra Pradesh, Foc 161 from Chhattisgarh, Foc 146 from Karnataka, Foc 158 from Madhya Pradesh and Foc 50 from Rajasthan, caused low wilt incidence. For VCG analysis, nitrate non-utilizing mutants (nit) were obtained by culturing wild-type isolates on 2.5% potassium chlorate and selecting resistant sectors. Complementary nit mutants were paired in all possible combinations to determine varying degrees of heterokaryon formation within the isolates, which showed that most of the isolates were self-compatible. Pairing of all the mutants showed that the isolates included in the present study belonged to a single VCG (0280). Thus, in spite of variability in the virulence, the Indian populations of the pathogen have only one VCG.

Genetic diversity of Fusarium mangiferae isolated from mango malformation disease in China

Mango malformation disease, caused by Fusarium mangiferae, is one of the most important diseases affecting mango production. Thirty-eight isolates from MM-affected mango tissues were collected from two cities and assessed for genetic diversity using vegetative compatibility groups (VCGs) and inter simple sequence repeats (ISSRs). VCGs were determined among all isolates, using nitrate non-using (nit) mutants. Out of the 455 nit mutants generated, 78.02% used both nitrite and hypoxanthine (nit1), 13.63% used hypoxanthine but not nitrite (nit3) and 7.91% used nitrite but not hypoxanthine (NitM). Five different VCGs were identified by pairing the mutants on nitrate medium. Seventy-two bands were amplified by 14 ISSR primers, with an average of 5.14 bands per primer. The size of the amplified products ranged from 300 to 2000bp. At a genetic similarity of 0.76, the unweighted pair-group method with arithmetic mean analysis separated the isolates into five distinct clusters, comprising 33, 2, 1, 1 and 1 isolates. The VCG and ISSR data support the conclusion that the isolates of F. mangiferae are not necessarily related by geographic origin, type of host tissue, or the mango cultivar from which they were isolated.

VEGETATIVE COMPATIBILITY GROUPS OF PHYSIOLOGICAL RACES OF PYRICULARIA GRISEA IN Egypt

One hundred forty Pyricularia grisea isolates were collected from the six main rice growing governorates; Kafrelsheikh, Beheira, Sharkia, Gharbia, Dakahlia and Damietta, and from different research stations during 2008, 2009 and 2010 growing seasons. The isolates were identified to their group races as IA (1); IB (12); IC (15); ID (45); IE (1); IF (4); IG (22); IH (32) and II (8) using the international differential varieties under greenhouse conditions. Vegetative compatibility groups (VCGs) among the races were studied through producing nitrate nonutilizing (nit) mutants for the races on chlorate minimal medium (CMM). The results revealed that the nit mutants were grouped into eight VCGs. VCG 1 included members of the IB race group (70.59 %). VCG 2 included members of IC race group with 87.5% and two isolates were identified as IH and II. The largest group, VCG 3 included 44 isolates, most of these isolates were identified as ID (86.36 %). All isolates in VCG 4 were identified as IF. 95.65% of isolates in VCG 5 represented IG and one belonged to II (4.35%). All isolates in VCG 6 corresponded to IH (96.43 %), and only one as ID. VCG 7 included eight isolates, 5 isolates represented ID and one each of IG, IF and IH. Only one isolate was identified as IE race group in VCG 8. The reaction among different nit mutants was examined using a scanning electron microscope and revealed that heterokaryon, incompatibility and inhibition zone were observed. This investigation revealed that the correspondence between VCGs and races ranged from 62.5 to 100 %; however, the latter percentage was relevant to very small number of isolates

Identification of Aspergillus flavus Isolates as Potential Biocontrol Agents of Aflatoxin Contamination in Crops

Aspergillus flavus, a haploid organism found worldwide in a variety of crops, including maize, cottonseed, almond, pistachio, and peanut, causes substantial and recurrent worldwide economic liabilities. This filamentous fungus produces aflatoxins (AFLs) B1 and B2, which are among the most carcinogenic compounds from nature, acutely hepatotoxic and immunosuppressive. Recent efforts to reduce AFL contamination in crops have focused on the use of nonaflatoxigenic A. flavus strains as biological control agents. Such agents are applied to soil to competitively exclude native AFL strains from crops and thereby reduce AFL contamination. Because the possibility of genetic recombination in A. flavus could influence the stability of biocontrol strains with the production of novel AFL phenotypes, this article assesses the diversity of vegetative compatibility reactions in isolates of A. flavus to identify heterokaryon self-incompatible (HSI) strains among nonaflatoxigenic isolates, which would be used as biological controls of AFL contamination in crops. Nitrate nonutilizing (nit) mutants were recovered from 25 A. flavus isolates, and based on vegetative complementation between nit mutants and on the microscopic examination of the number of hyphal fusions, five nonaflatoxigenic (6, 7, 9 to 11) and two nontoxigenic (8 and 12) isolates of A. flavus were phenotypically characterized as HSI. Because the number of hyphal fusions is reduced in HSI strains, impairing both heterokaryon formation and the genetic exchanges with aflatoxigenic strains, the HSI isolates characterized here, especially isolates 8 and 12, are potential agents for reducing AFL contamination in crops.

Vegetative Compatibility, Pathogenicity and Virulence Diversity of Fusarium oxysporum f. sp. melongenae Recovered from Eggplant

AbstractFusarium oxysporum (Schlechtend.: Fr.) f. sp. melongenae (Fomg) recovered from symptomatic eggplants from five eggplant‐growing areas in Turkey, including the south, west, north‐west, north and south‐east regions. The objective of this study was to investigate the genetic diversity of the Fomg isolates from different geographical location by pathogenicity and VCG tests. Three hundred and seventy‐four Fomg isolates were classified as highly virulent, virulent, moderately virulent and low virulent through pathogenicity assays. No correlation was observed between virulence of Fomg isolates and their locations. The nitrate non‐utilizing mutants (nit) were generated as nit1, nit3 and NitM, based on phenotyping of Fomg growth characteristics of the Fomg isolates on diagnostic media with various sources of nitrogen. The majority of nit mutants (39.4%) recovered were nit1 from minimal medium (MM) containing of 2.0% potassium chlorate (MMC). The most of Fomg isolates were identified as heterokaryon self‐compatible (HSC) based on their ability to form a stable heterokaryon, while four isolates were classified as heterokaryon self‐incompatible (HSI). A large amount of Fomg isolates were vegetatively compatible and assigned as members of the same VCG, whereas nit mutants of 10 Fomg isolates that did not complement with tester strains only paired by themselves (HSC), these isolates were termed vegetative incompatible (vic). The complementation of 33 isolates with tester strains was slow and quite weak, but not paired with themselves even though they are HSC. About 96.3% of the Fomg isolates were assigned to VCG 0320, while the remaining 3.7% were classified as vegetative incompatible group.

Characterization of Magnaporthe grisea populations associated with rice and weeds in Iran

In this study, host-specific forms of the blast pathogen Magnaporthe grisea in Iran were characterized from distinct hosts using a combination of molecular and biological assays. A total of 106 isolates of M. grisea were obtained from north of Iran besides of seven international standards mating type (ISMT) tester isolates achieved from France. Population genetically analyzed with selected markers, such as complementation tests of nit mutants and rep-PCR to evaluate such events. Compatible isolates by complementation tests were assigned to the same vegetative compatibility group (VCG) detected as VCG1 to VCG9 among isolates from rice and weeds. During rep-PCR analysis a total of 42 polymorphic banding patterns were scored from 106 isolates which clustered by host with high bootstrap support (72 to 100 %). Genetic structure between rice and weeds isolates differed significantly. Eleven clonal lineages were identified with only two fingerprinting groups for ISMT isolates considering similarity coefficient of approximately 60 % with rice isolates. Additionally, the majority of the isolates from weeds (78.43 %) were gashed from rice isolates in 43 % similarity. Clear differences in cultivar compatibility within and between lineages suggest Distinctive patterns of genetic diversity of host-specific forms of M. grisea populations linked to crop domestication and agricultural intensification.

The L-Cysteine Desulfurase NFS1 Is Localized in the Cytosol where it Provides the Sulfur for Molybdenum Cofactor Biosynthesis in Humans

In humans, the L-cysteine desulfurase NFS1 plays a crucial role in the mitochondrial iron-sulfur cluster biosynthesis and in the thiomodification of mitochondrial and cytosolic tRNAs. We have previously demonstrated that purified NFS1 is able to transfer sulfur to the C-terminal domain of MOCS3, a cytosolic protein involved in molybdenum cofactor biosynthesis and tRNA thiolation. However, no direct evidence existed so far for the interaction of NFS1 and MOCS3 in the cytosol of human cells. Here, we present direct data to show the interaction of NFS1 and MOCS3 in the cytosol of human cells using Förster resonance energy transfer and a split-EGFP system. The colocalization of NFS1 and MOCS3 in the cytosol was confirmed by immunodetection of fractionated cells and localization studies using confocal fluorescence microscopy. Purified NFS1 was used to reconstitute the lacking molybdoenzyme activity of the Neurospora crassa nit-1 mutant, giving additional evidence that NFS1 is the sulfur donor for Moco biosynthesis in eukaryotes in general.

Vegetative compatibility of Verticillium dahliae isolates from potato and sunflower using nitrate non-utilizing (nit) mutants and PCR-based approaches

Vegetative compatibility groups (VCGs) of 12 potato and nine sunflower isolates of Verticillium dahliae were determined using both nitrate non-utilizing (nit) mutants and multiplex-nested-PCR approaches. Based on analysis of nit mutants, most potato isolates showed strong compatibility with VCG 4A and weak compatibility with VCG 4B; one potato isolate was also weakly compatible with VCGs 2A, 2B and 3. Sunflower isolates were more variable and most of them showed weak reactions with VCG 4A and 4B. One sunflower isolate, Vs06-14, was compatible only with VCG3 testers, whereas another isolate, Vs06-20, was compatible with all VCG groups except VCG2A. Vegetative compatibility of four selected isolates, two from potato and two from sunflower, was also investigated after passing them through potato or sunflower for four generations. The VCG of one potato isolate did not change, whereas the other one changed from VCG4B to 4A. One sunflower isolate, initially compatible with both VCG4A and 4B, became incompatible with both. The other sunflower isolate was not compatible with any VCG and remained so. In a second part of this work, multiplex-nested-PCR was carried out to characterize VCGs of the same isolates of V. dahliae. Vegetative compatibility grouping using this approach assigned the V. dahliae isolates to VCG1, 2A, 3 or 4A. Six of the 12 potato isolates and four of the nine sunflower isolates of V. dahliae could not be identified or placed in any VCG group based on PCR results. In the present study, the multiplex-nested-PCR results were confirmed using nit mutants. As such, PCR-based methods will require more specific primers before they can replace the approach based on nit mutants. Current address of A.F. El-Bebany: Department of Plant Pathology, Faculty of Agriculture, Alexandria University, El-Shatby, 21545, Alexandria, Egypt.

The use of vegetative compatibility tests for identification of biodiversity of phytopathogenic fungi

Visual assessment of phenotypes, performed when two strains of one fungal species are cultivated in a mixed culture on specific media, is known as vegetative or heterokaryotic compatibility or incompatibility test, which enables identification of fungal clones and their classification based on phylogenetic groups. Hyphae of strains that have identical alleles at all vic loci can anastomose into a form of a visible heterokaryon. Strains that divide compatible loci and can anastomose each other belong to a subpopulation termed the vegetative compatibility group (VCG), which is genetically distinguishable from other VCGs. Each VCG is specific regarding its host plant or related host groups and can, but does not have to be virulent on other hosts. Vegetative compatibility can be established in different ways, but complementary auxotrophic strains or strains formed by spontaneous mutation during nutrition, capable of forming a prototrophic heterokaryon are predominantly used. The nit mutants are considered excellent genetic markers for determination of vegetative compatibility and grouping of strains or clones of one fungus into the same or different VCGs. The ability only to determine whether strains are the same or not, but not the degree of their relatedness using VCG, is a limiting factor in analyses that could be performed. VCGs are the most efficient when they are employed to detect the presence of a specific strain in a population. This paper provides an overview of the importance of the phenomenon of vegetative compatibility. Vegetative compatibility is one of the most important genetic traits in ascomycetes by which one subpopulation can be identified as a distinct genetic group. Furthermore, the procedures for isolation, identification and determination of nit mutant phenotypes, and for identification of complementary strains and VCGs are described in detail.

Differential Chlorate Inhibition of Chaetomium globosum Germination, Hyphal Growth, and Perithecia Synthesis

Chaetomium globosum Kunze:Fr is a dermatophytic, dematiaceous fungus that is ubiquitous in soils, grows readily on cellulolytic materials, and is commonly found on water-damaged building materials. Chlorate affects nitrogen metabolism in fungi and is used to study compatibility among anamorphic fungi by inducing nit mutants. The effect of chlorate toxicity on C. globosum was investigated by amending a modified malt extract agar (MEA), oat agar, and carboxymethyl cellulose agar (CMC) with various levels of potassium chlorate (KClO(3)). C. globosum perithecia production was almost completely inhibited (90-100 %) at low levels of KClO(3) (0.1 mM) in amended MEA. Inhibition of perithecia production was also observed on oat agar and CMC at 1 and 10 mM, respectively. However, hyphal growth in MEA was only inhibited 20 % by 0.1-100 mM KClO(3) concentrations. Hyphal growth was never completely inhibited at the highest levels tested (200 mM). Higher levels of KClO(3) were needed on gypsum board to inhibit perithecia synthesis. In additional experiments, KClO(3) did not inhibit C. globosum, Fusarium oxysporum, Aspergillus niger, Penicillum expansum, and airborne fungal spore germination. The various fungal spores were not inhibited by KClO(3) at 1-100 mM levels. These results suggest that C. globosum perithecia synthesis is more sensitive to chlorate toxicity than are hyphal growth and spore germination. This research provides basic information that furthers our understanding about perithecia formation and may help in developing control methods for fungal growth on building materials.

Fusarium verticillioides from sugarcane, vegetative compatibility groups and pathogenicity

Sugarcane plant samples affected by the disease pokkah boeng were collected from the major sugarcane producing areas in Iran. Fifty isolates of Fusarium verticillioides were recovered from diseased sugarcanes. Results of pathogenicity tests revealed that all isolates were pathogenic to sugarcane. Four hundred and eighty-five nitrate non-utilising mutants were generated from F. verticillioides isolates. Media used for nit mutant generation included potato dextrose agar, minimal medium and Czapeck agar amended with 1.8%, 2%, 2.5%, and 3% potassium chlorate. Nit mutants were divided into three phenotypic (nit1, nit3, and nitM) classes based on their growth on different nitrogen sources in the culture media. Among the isolates tested, 280, 115 and 90 nit1, nit3, and nit M were generated, respectively. Nit mutants were used to force the heterokaryon formation to determine the distribution of VCGs and their relation to pathogenicity and geographic origin. Forty-eight VCGs of F. verticillioides were isolated from sugarcane. Forty-six of the VCGs were represented by a single isolate, whereas the remaining two comprised two isolates. None of the VCGs was common.

Genetic, pathogenic and toxigenic variability by F. proliferatum isolated from maize kernels

Genetic (mating population and vegetative compatibility), pathogenic and toxigenic variability of F. proliferatum isolated from maize kernels originating from different localities in Serbia were studied. Investigated isolates of F. proliferatum were fertile and most of them (8/13) belonged to the mating type MATD-2. Based on the complementary test isolates, F. proliferatum were grouped into 11 vegetative compatibility groups (VCGs) and two isolates were self-incompatible. All tested field isolates of F. proliferatum and nit mutants were pathogenic and most expressed medium pathogenicity. Field isolates of F. proliferatum showed a higher potential for biosynthesis of FB1 (up to 1,246.00 µg g -1 ) in relation to their nit1 (up to 53.41 µg g -1 ) and NitM mutants (up to 56.17 µg g -1 ). Based on genetic, pathogenic and

Vegetative compatibility groups and pathogenicity of verticillium dahliae ısolates from potato plants in Erzurum province

One hundred eleven isolates of Verticillium dahliae were obtained from potato plants in Erzurum province, Turkey. The pathogen was isolated from 7.6% of the stems collected. All isolates were assigned to vegetative compatibility groups (VCGs) using nitrate-nonutilizing ( nit ) mutants. In total, 240 nit mutants were obtained from V. dahliae isolates, and classified as nit 1 (71%) and nit M (29%). Two VCGs were found and identified as VCG 2B (34 isolates) and VCG 4B (77 isolates) by using tester isolates of known VCGs. Pathogenicity of V. dahliae isolates was tested on potato (cv. Marfona) by the root-dip method. Both VCG 2B and VCG 4B isolates showed similar aggressiveness on potato. This is the first study of VCGs of V. dahliae isolates from potato plants in Turkey.