Mycelial Compatibility Research Articles

Independently founded populations of Sclerotinia sclerotiorum from a tropical and a temperate region have similar genetic structure.

Sclerotinia sclerotiorum populations from tropical agricultural zones have been suggested to be more variable compared to those from temperate zones. However, no data were available comparing populations from both zones using the same set of markers. In this study, we compared S. sclerotiorum populations from the United States of America (USA, temperate) and southeast Brazil (tropical) using the frequency of mycelial compatibility groups (MCGs) and 13 microsatellite (SSR) markers. Populations were sourced from diseased plants within leguminous crops in New York, USA (NY; n = 78 isolates), and Minas Gerais State, Brazil (MG; n = 109). Twenty MCGs were identified in NY and 14 were previously reported in MG. The effective number of genotypes based on Hill’s number of order 0, which corresponded to the number of multilocus genotypes (MLGs) were 22 (95% CI = 15.6–28.4) and 24 (95% CI = 18.9–29.1) in NY and MG, respectively. Clonal fractions of MLGs were 71.8% (NY) and 78.0% (MG). The effective number of genotypes based on Hill’s number of orders 1 and 2 in NY were 8.9 (95% CI = 5.2–12.6) and 4.4 (95% CI = 2.6–6.1), respectively. For MG these indices were 11.4 (95% CI = 8.7–14.1) and 7.1 (95% CI = 5.1–9.0), respectively. There were no significant differences of allelic richness, private allelic richness, gene diversity, effective number of alleles and genotype evenness between the NY and MG populations. The populations were differentiated, with 29% of total variance attributed to differences between them and G''ST and Jost’s D indices higher than 0.50. Cluster analysis revealed dissimilarity higher than 80% among most MLGs from both populations. Different alleles segregated in the populations but both had similar levels of genotypic variability.

Mycelial compatibility in Valsa malicola, the causal agent of canker disease in Iran

Mycelial compatibility of 62 isolates of Valsa malicola from different hosts and areas of Iran were investigated on potato dextrose agar (PDA) and oat meal agar (OMA). Four mycelial compatibility groups (MCGs) on PDA, 1–4, including three single membered (1–3) and a 58 membered (4) were identified. However, 8 MCGs, 1–8, consisting of 6 single membered (1–3, 5, 6 and 8), a 6 membered (4) and a 50 membered (7) were identified on OMA. On PDA, the number of groups and the time to achieve results were less than on OMA as well as the barrage zones were clearer on PDA than OMA. There was no correlation between groups and host or geographical origins of the isolates. The low number of identified MCGs on both culture media revealed low genetic diversity of investigated isolates of V. malicola.

Are Sclerotinia sclerotiorum populations from the tropics more variable than those from subtropical and temperate zones?

The genetic variability of Sclerotinia sclerotiorum populations has been investigated in many countries and, consequently, under different ecological conditions. The first studies were conducted to gather information about the genetic structure of populations sampled in temperate climate areas. Based on DNA fingerprinting analysis of restriction fragment length polymorphism (RFLP) data and mycelial compatibility groups, most studies revealed a clonal population structure. Later, using DNA sequences, populations from subtropical regions of North America were reported to be more variable than those from temperate regions. In the past few years, new analyses in temperate, sub-tropical and tropical areas were conducted using microsatellite (SSR) markers. Most studies using SSR reported both high variability and evidence of outcrossing in S. sclerotiorum populations, but evidence of clonality has also been found. Some authors argue that populations from subtropical and tropical areas are more diverse. We argue that the reports of high variability of S. sclerotiorum in tropical or subtropical regions may be due to an increase in the number of studies performed with SSR markers in these regions and in some cases due to inappropriate interpretations of the results.

Characterization of the Mycelial Compatibility Groups and Mating Type Alleles in Populations of Sclerotinia minor in Central China.

Ninety-five single-sclerotium isolates were obtained from lettuce and weeds in three counties in central China. They were identified belonging to Sclerotinia minor based on colony morphology and the S. minor-specific DNA marker. Mycelial compatibility groups (MCGs) and the mating type (MAT) alleles in these isolates were determined using the methods of paired cultures and specific PCR, respectively, and the MCG data were used to calculate Shannon's H index (H) and Simpson index (S), thereby evaluating diversity of S. minor. Eight MCGs (MCG1 to MCG8) and two MAT alleles (Inv+, Inv-) were identified in these isolates. Low diversity was detected for the total 95 isolates (H = 1.748, S = 0.786). Isolates of different MCGs or with different MAT alleles did not significantly differ (P > 0.05) in mycelial growth rate on potato dextrose agar (PDA, 20°C) or lesion diameter on lettuce leaves (20°C), but slightly differed in the number of sclerotia produced on PDA (20°C). Furthermore, this study reported five new host plants of S. minor in China, including Capsella bursa-pastoris, Oenanthe javanica, Fragaria gracilis, Ranunculus ternatus, and Salvia plebeia, and identified three hypovirulent isolates. These results broaden our understanding about the population biology of S. minor.

Characterization of Alternaria isolates and reaction of potato genotypes to early blight

ABSTRACT: Early blight is one of the most important fungal diseases of potato. The objective of this study was to evaluate the in vitro reaction of potato genotypes to the severity of early blight and compare the species Alternaria solani and Alternaria grandis , etiologic agents of disease, through the evaluation of physiological characteristics. Twenty-two genotypes of the Potato Breeding Program at UFLA, two cultivars, Aracy and Bintje, patterns of resistance and susceptibility, respectively were evaluated. For inoculation, three isolates of A. grandis and two isolates of A. solani were used. Plantlets obtained in vitro were inoculated with a 5mm diameter mycelial disk of isolates Alternaria spp. of. These were incubated in severity and classified according to the rating scale. Isolates of Alternaria spp. were evaluated for mycelial growth index (MGI) and for formation of mycelial compatibility groups (MCG). The methodology for evaluating the in vitro reaction of genotypes to severity of early blight was efficient for both isolates. The isolates of A. solani and A. grandis were similar in their aggressiveness. The isolates of A. grandis MGI's had higher, and therefore mycelium grew faster when compared to those isolated from A. solani . The occurrence of mycelial compatibility among isolates of A. solani and A. grandis indicated the possible occurrence of parasexual cycle.

Analysis of genetic diversity of Sclerotinia sclerotiorum from eggplant by mycelial compatibility, random amplification of polymorphic DNA (RAPD) and simple sequence repeat (SSR) analyses

ABSTRACTThe genetic diversity and pathogenicity/virulence among 60 eggplant Sclerotinia sclerotiorum isolates collected from six different geographic regions of Turkey were analysed using mycelial compatibility groupings (MCGs), random amplified polymorphic DNA (RAPD) and simple sequence repeat (SSR) polymorphism. By MCG tests, the isolates were classified into 22 groups. Out of 22 MCGs, 36% were represented each by a single isolate. The isolates showed great variability for virulence regardless of MCG and geographic origin. Based on the results of RAPD and SSR analyses, 60 S. sclerotiorum isolates representing 22 MCGs were grouped in 2 and 3 distinct clusters, respectively. Analyses using RAPD and SSR markers illustrated that cluster groupings or genetic distance of S. sclerotiorum populations from eggplant were not distinctly relative to the MCG, geographical origin and virulence diversity. The patterns obtained revealed a high heterogeneity of genetic composition and suggested the occurrence of clonal and sexual reproduction of S. sclerotiorum on eggplant in the areas surveyed.

GENETIC DIVERSITY OF SCLEROTINIA SCLEROTIORUM WITHIN A SINGLE SUNFLOWER FIELD IN WENQUAN, XINJIANG PROVINCE, CHINA

To unravel the genetic diversity of Sclerotinia sclerotiorum, 90 isolates collected from a single sunflower field in Wenquan of Xinjiang were studied using the method of mycelial compatibility grouping (MCG). Meanwhile, the oxalic acid (OA) secretion ability, polygalacturonases (PG) enzymatic activity and pathogenicity of the isolates within the same and between different MCGs were studied. The distribution of inversion minus (Inv-) and inversion plus (Inv+) isolates of S. sclerotiorum at MAT locus within the same MCGs and also in the whole population were identified using specific PCR primers. The sensitivity of S. sclerotiorum isolates to both carbendazim and dimethachlon fungicides were also tested in this study. The results suggested that the 90 isolates from a single sunflower field in Wenquan, Xinjiang region, can be grouped into 15 MCGs. MCG1, the biggest group, contained 34 isolates, representing 37.8% of all the tested isolates; 6 MCGs contained only a single isolate; 8 MCGs include 2 to 13 isolates each. The dramatically variation on OA level, PG enzyme activities and pathogenicity was observed among isolates from the same and between different MCGs, and no obvious positive correlation was detected between OA, PG and pathogenicity. For mating type distribution ratio, 17:17 (1:1) ratio of Inv+ and Inv- isolates at mating type locus (MAT) was observed only in MCG1, however, 12:1, 7:2 and 9:1 of Inv+ to Inv- ratio at MAT locus was detected in MCG2, MCG4 and MCG6, respectively. The distribution ratio of Inv+ and Inv- in the whole population is 56:34, which is deviated from the 1:1 steady state. The results of fungicide sensitivity test within MCG1 and MCG2 suggested that 84% of isolates is more sensitive to dimethachlon than to carbendazim. Seven isolates, three from MCG1 and four from MCG2, showed the opposite tendency of sensitivity to both fungicides. Three isolates, one from MCG1 and two from MCG2, showed the same sensitivity to both fungicides. Based on above results, we concluded that dramatic genetic diversity do exist within S. sclerotiorum population collected from a single sunflower field in Wenquan of Xinjiang.

Mycelial Compatibility and Cultural Grouping ofSclerotinia sclerotiorumIsolates Causing Root Rot and Stem Rot of Sunflower in Punjab

Variability among 23 isolates of Sclerotinia sclerotiorum (Lib) associated with root rot, stem rot and head rot of sunflower collected from different locations of Punjab is reported. The isolates varied in colony morphology, mycelial growth rate, sclerotium formation and sclerotia size. Variability among the isolates on the basis of mycelial compatibility was also observed. Five groups of isolates were identified based on cluster analysis. The field population of S. sclerotiorum was genetically heterogenous as lot of variation existed in cultural characters and mycelial incompatibility reactions.

Similar Aggressiveness of Phenotypically and Genotypically Distinct Isolates of Sclerotinia sclerotiorum.

Understanding how Sclerotinia sclerotiorum aggressiveness varies among isolates may be useful for breeding programs aimed at developing common bean cultivars resistant to white mold. The aggressiveness of 20 S. sclerotiorum isolates collected in common bean fields from four Brazilian states was tested against two common bean genotypes (Pérola and A195) using two inoculation methods. The isolates were characterized using 10 microsatellite (SSR) loci, mycelial compatibility groups (MCGs), partial sequences of the oxaloacetate acetylhydrolase (OAH) gene, and morphological traits. Twenty SSR and seven OAH haplotypes, 10 MCGs, and high variability in colony morphology were found. One isolate was more aggressive when inoculated on plants of the genotype A195, but all other isolates had similar aggressiveness. Aggressiveness was not related with MCGs, SSR, OAH haplotypes, mycelial pigmentation, growth rate, or sclerotia production.

Effect of some fungicides against the growth inhibition of Sclerotinia sclerotiorum mycelial compatibility groups

Abstract Sclerotinia sclerotiorum (Lib.) de Bary, the causal agent of Sclerotinia stem rot, is one of the most important pathogens of Brassica napus L. in northern Iran. In this study, 13 mycelial compatibility groups (MCGs) of the fungus were identified among 31 isolates sampled from four regions of Mazandaran province, Iran. Effective fungicides are useful in the integrated management of the disease. So, the effect of tebuconazole, propiconazole, cyproconazole, and Rovral-TS at five doses (0.0001, 0.001, 0.01, 0.1, and 1 ppm) was studied on the growth inhibition of S. sclerotiorum as in vitro tests. Maximum inhibition (100%) of S. sclerotiorum mycelial growth was obtained by the highest dose (1 ppm) of all tested fungicides, as well as by the doses of 0.1 and 0.01 ppm of propiconazole, cyproconazole, and tebuconazole. In this investigation, the reaction of S. sclerotiorum isolates belonging to different MCGs was evaluated against tebuconazole, propiconazole, cyproconazole, and Rovral-TS at their EC50 ranges. The results revealed that there was high variation of S. sclerotiorum MCGs against different fungicides. The inhibition percentage varied between 4.29% and 71.72%.

Genetic Variation of Sclerotinia sclerotiorum from Multiple Crops in the North Central United States.

Sclerotinia sclerotiorum is an important pathogen of numerous crops in the North Central region of the United States. The objective of this study was to examine the genetic diversity of 145 isolates of the pathogen from multiple hosts in the region. Mycelial compatibility groups (MCG) and microsatellite haplotypes were determined and analyzed for standard estimates of population genetic diversity and the importance of host and distance for genetic variation was examined. MCG tests indicated there were 49 different MCGs in the population and 52 unique microsatellite haplotypes were identified. There was an association between MCG and haplotype such that isolates belonging to the same MCG either shared identical haplotypes or differed at no more than 2 of the 12 polymorphic loci. For the majority of isolates, there was a one-to-one correspondence between MCG and haplotype. Eleven MCGs shared haplotypes. A single haplotype was found to be prevalent throughout the region. The majority of genetic variation in the isolate collection was found within rather than among host crops, suggesting little genetic divergence of S. sclerotiorum among hosts. There was only weak evidence of isolation by distance. Pairwise population comparisons among isolates from canola, dry bean, soybean and sunflower suggested that gene flow between host-populations is more common for some crops than others. Analysis of linkage disequilibrium in the isolates from the four major crops indicated primarily clonal reproduction, but also evidence of genetic recombination for isolates from canola and sunflower. Accordingly, genetic diversity was highest for populations from canola and sunflower. Distribution of microsatellite haplotypes across the study region strongly suggest that specific haplotypes of S. sclerotiorum are often found on multiple crops, movement of individual haplotypes among crops is common and host identity is not a barrier to gene flow for S. sclerotiorum in the north central United States.

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Low genetic variability in Sclerotinia sclerotiorum populations from common bean fields in Minas Gerais State, Brazil, at regional, local and micro‐scales

Sclerotinia sclerotiorum, causal agent of white mould, is the most destructive and widely distributed soilborne pathogen of common bean during the autumn–winter season in Brazil. Nevertheless, little is known about the genetic structure of the pathogen population. Microsatellite (SSR) markers and mycelial compatibility groups (MCGs) were used to characterize 118 isolates collected from 20 bean fields located in the most important growing regions of Minas Gerais State (MG). Additionally, the genetic variability among 10 isolates obtained from a single sclerotium was investigated in 10 different sclerotia. Seventy SSR haplotypes and 14 MCGs were identified among the 118 isolates. The genetic differences within bean growing areas accounted for most of the genetic variation (72%). Despite the relatively high genotypic diversity, the SSR loci were at linkage disequilibrium. Moreover, 70% of the isolates were assigned to only two MCGs, and haplotypes of a given MCG were closely related. The discriminant analysis of principal components revealed five groups. There was strong genetic differentiation between isolates collected in one municipality in southern MG when compared to other regions. Common bean resistance to white mould should be assessed with representative isolates of the five genetic groups and, if possible, of the different MCGs detected in the present study. One to five haplotypes were detected among the 10 isolates obtained from a single sclerotium. Therefore, in order to ensure genetic identity of an isolate, hyphal tip or monoascosporic isolates should be used.

Investigation of Sclerotinia sclerotiorum strains variability in Brazil.

White mold is a common bean disease caused by the fungus Sclerotinia sclerotiorum, resulting in economic losses in Brazil and worldwide. Lack of knowledge about the population structure of the pathogen makes it difficult to control the disease. The aim of this study was to characterize strains of S. sclerotiorum obtained from ex-perimental and commercial common bean fields in Brazil. We analyzed 50 strains of S. sclerotiorum collected at several locations in the state of Minas Gerais. The strains were characterized according to their ability and time for developing apothecia. Morphological and physiological analyses such as the mycelial growth index, colony color, the time re-quired to form the first sclerotia on media, the number of sclerotia per plate, average sclerotium size, and sclerotium shape were performed. We determined the mycelial compatibility, conducted molecular analy-sis of microsatellites, and evaluated the aggressiveness of 28 strains. Most strains had the ability to form apothecia. A small group of strains showed mycelial compatibility, and the strains showed different aggres-siveness levels. Overall, the population studied here demonstrated wide variability based on the morphological, physiological, and molecular traits analyzed. The average size and shape of sclerotia presented a cor-relation of 0.617, whereas the times required to form sclerotia and the number of sclerotia per plate showed a correlation of -0.455. The char-acterization of the pathogen population described herein will provide an important tool for promoting the development of bean cultivars re-sistant to white mold.

Evaluation of the virulence of Sclerotium rolfsii isolates on Arachis hypogaea and screening for resistant genotypes in greenhouse conditions

Summary Sclerotium rolfsii is a soil borne pathogen responsible for root and stem rot on a wide range of crops. This study was conducted to identify the virulence of different S. rolfsii isolates on a susceptible local peanut germplasm and determine the resistance of 20 peanut genotypes to the most virulent isolate and also the relationship between virulence and mycelial compatibility groups (MCGs). Seventy eight isolates of this fungus from 10 host plants and six known MCGs were used in the experiment. The experiment was done in greenhouse conditions (25±5°C) using a complete randomized block design with three replications. Pots containing sterile soil (pH=6.7) were inoculated with barley seeds colonized by each isolate separately before being seeded with the peanut germplasm. Disease severity was assessed by scoring the wilting, yellowing or death of plants, mycelia or sclerotia production on the soil surface or on plant stem, stem area affected (%) and stem lesion length, at the stage of plant maturity. Also, shoot wet weight and plant height were recorded at this stage. According to the results of the pathogenicity tests, all of the isolates were virulent on the susceptible peanut germplasm and the virulence diff ered signifi cantly between the isolates (P≤0.01). There was no relationship between the virulence of the five groups of isolates identified in the present study and the MCGs. The peanut genotype 140, which was better than the others based on seed size, plant height and the canopy size, was also the most resistant one

English

Sclerotinia sclerotiorum , infection of bean fields, has increased in Brazil. Fungicides application is the control strategy used due to lack of cultivars with complete disease resistance. To guide the use of isolates in resistance screening 25 S. sclerotiorum isolates from Brazilian dry bean fields were characterized using microsatellite markers, mycelial compatibility groups (MCGs) and aggressiveness. Microsatellite primer pairs were used to identify polymorphisms among the S. sclerotiorum isolates and MCGs were determined from interaction of all isolates grown side-by-side. Aggressiveness was derived from a straw test where fungal mycelium was placed over a cut bean stem and rated for disease progress. Data from microsatellite profiles grouped the 25 isolates into four clusters and seven MCGs were identified. No association among host cultivar and cluster or MCG of isolates was observed. For MCGs, 57% contained isolates sampled frequently over multiple locations and 43% contained isolates unique to locations. There were significant differences among isolates in aggressiveness within and between MCGs. The most aggressive isolates in resistance screening will be helpful in the identification of higher levels of resistance in bean germplasm/lines.

Mycelial Compatibility and Pathogenic Diversity Among Sclerotium rolfsii Isolates in the Southern United States.

Sclerotium rolfsii is a soilborne fungus that causes southern blight on a wide range of plants in tropical and subtropical regions of the world. Eighty-four isolates collected from Florida, Georgia, Louisiana, South Carolina, Texas, and Virginia were paired and assigned to 23 mycelial compatibility groups (MCGs), of which 11 MCGs consisted of a single isolate. Isolates within an MCG typically originated from different hosts and different geographical areas, with the exception of MCG 11. In all, 13 of the 15 isolates in MCG 11 originated from peanut in Georgia and Florida, while the other 2 isolates originated from potato in Virginia and from the ornamental Barlaeria cristata in Florida. Significant differences in the size and number of sclerotia produced in vitro existed between isolates from peanut and other hosts. Nineteen isolates representative of the most common MCGs (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 13, 14, 15, 16, 17, and 18) were tested for pathogenicity on tomato, pepper, and peanut. All isolates were pathogenic on all hosts but virulence differed significantly among isolates. Isolates collected from peanut were the most virulent on all three hosts compared with isolates collected from tomato and pepper. 'Georgia Green' peanut was more susceptible to peanut isolates from Georgia than to the other tested isolates. Of the two tomato entries, the commercial tomato 'Tygress' was less susceptible than the previously reported resistant breeding line 5635M to many of the S. rolfsii isolates tested, with the exception of the peanut isolates collected from Georgia. These initial findings suggest that considerable variation exists among S. rolfsii isolates throughout the southern United States, with some indications of specialization for the isolates collected from peanut.

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.

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An experiment was carried out to find the variability among twenty sclerotial isolates of Rhizoctonia solani collected from potato growing areas of Gilgit-Baltistan. These isolates were grown in different culture media, mycelial compatibility and fungus protein profile were investigated. Culture media were used to study radial colony growth and sclerotial production of isolates. Radial colony growth (RCG) and sclerotial production (SP) of isolates against culture media ranged from 12.31-21.55; 3.66-22.66 in potato dextrose agar, 12.67-18.56; 4.66-10.66 in czpedox agar, 12.02-20.42; 2.00-8.66 in corn meal agar and 10.54-14.16; 0.00-3.00 in water agar, respectively. These isolates were further classified into three categories on the basis of RCG and SP. Result revealed that out of total isolates, 60% showed medium RCG and 40% fast growth, while 10, 60 and 30% isolates showed low, medium and high SP. Furthermore, sclerotial characteristic such as size, shape and distribution pattern were also recorded. Mycelial compatibility and incompatibility among the R. solani isolates was also studied. The results indicated that out of 190 combinations, 72.10% were compatible, whereas 27.90% were incompatible. Fungus protein profile of twenty isolates of R. solani by sodium dodecyl suplphate gel electrophoresis (SDS-PAGE) recovered sixty one bands with different frequencies among the isolates. Cluster analysis of twenty isolates divided them into two major lineage groups, A and B. Lineage A contained 65% isolates whereas lineage B contained 35% isolates. These lineages were further divided into thirteen clusters (C1-C13); A was comprised of eight and B five clusters, respectively. Key words: Rhizoctonia solani, sclerotial isolates, radial colony growth, sclerotial feature, mycelial compatibility, sodium dodecyl suplphate gel electrophoresis (SDS-PAGE), Gilgit-Baltistan.

Mycelial Compatibility Groups and Microsatellite Markers Reveal Genetic Diversity Within and Among Populations of Sunflower Sclerotinia Sclerotiorum in China

The genetic variability and differentiation among 101 sunflower Sclerotinia sclerotiorum isolates collected from four different geographic regions of China were analyzed using mycelial compatibility groupings (MCGs) and microsatellite markers. Twenty three MCGs were identified among all tested isolates. The majority of isolates collected from the same region were grouped in to the same MCGs, indicating less genetic variation of S. sclerotiorum within the same region. But there still have exceptions for some isolates. Also microsatellite marker data revealed that all tested isolates from four geographic populations could be divided into three distinct clusters, isolates from Inner Mongolia and Ninxia regions formed cluster I, isolates from Heilongjiang and Xinjiang formed separate clusters II and III . The percentage of variance within and among different geographic populations was 84.54% and 15.46% respectively and both variances were significantly different from each other (p0.01). Meanwhile, association between the microsatellite haplotype and MCGs was observed but not so significant; majority isolates from the same MCG showed the same haplotype, but certain samples showed different haplotypes, although they belonged to the same MCG. Based on the virulence test results, we also found that MCGs not only represent the genetic variation of tested isolates, but also reflect their pathogenic ability to a certain extent.