Mycelial Compatibility Groups Research Articles

Мицелна съвместимост на изолати от Phomopsis helianthi (Munt.- Cvet. еt al.)

In the present study, the genetic diversity of 30 isolates of the pathogen Phomopsis helianthi was studied using the mycelial compatibility groups (MCGs) method. Mycelial compatibility tests were carried out on two media - PDA + 80 µl/L and PSA +80 µl/L, with added colorant (Christmas red - Sly Commerce OOD) and without added colorant. The use of PDA medium was found to be inadvisable due to the indistinct dividing line (groove) in isolates having an incompatible phenotypic response. Based on the tests done, 416 combinations were carried out and the four types of reaction were observed- NC-N – incompatible with necrosis, NC-Gincompatible, mycelium do not approach with a pronounced distance between them, NC-DL- both lines (black) are spaced, C-compatible. Their percentage ratio is presented. Isolates are grouped into 20 MCGs, with two of the groups containing only one isolate due to their incompatibility. The remaining isolates were found to occur in more than one MCG. The isolates originating from the region of Ruse were marked with the greatest genetic diversity, and the isolates from the area of Karnobat with the least.

Characterizing genetic diversity of Sclerotium rolfsii isolates by biomapping of mycelial compatibility groupings and multilocus sequence analysis.

Genetic diversity in Sclerotium rolfsii is useful for understanding its population structure, identifying different mycelial compatibility groups (MCGs), and developing targeted strategies for disease management in affected crops. In our study, a comprehensive genetic analysis was conducted on 50 isolates of S. rolfsii, collected from various geographic regions and host plants. Two specific genes, TEF1α and RPB2, were utilized to assess the genetic diversity and relationships among these isolates. Notably, out of 1225 pairings examined, only 154 exhibited a compatible reaction, while the majority displayed antagonistic reactions, resulting in the formation of a barrier zone. The isolates were grouped into 10 distinct MCGs. These MCGs were further characterized using genetic sequencing. TEF1α sequences distinguished the isolates into 17 distinct clusters, and RPB2 sequences classified them into 20 clusters. Some MCGs shared identical gene sequences within each gene, while others exhibited unique sequences. Intriguingly, when both TEF1α and RPB2 sequences were combined, all 10 MCGs were effectively differentiated, even those that appeared identical with single-gene analysis. This combined approach provided a comprehensive understanding of the genetic diversity and relationships among the S. rolfsii isolates, allowing for precise discrimination between different MCGs. The results shed light on the population structure and genetic variability within this plant pathogenic fungus, providing valuable insights for disease management and control strategies. This study highlights the significance of comprehending the varied virulence characteristics within S. rolfsii isolates, categorizing them into specific virulence groups based on disease severity index (DSI) values. The association with MCGs provides additional insights into the genetic underpinnings of virulence in this pathogen. Furthermore, the identification of geographical patterns in virulence implies the influence of region-specific factors, with potential implications for disease control and crop protection strategies.Please confirm if the author names are presented accurately and in the correct sequence (given name, middle name/initial, family name). Author 1 Given name: [G. M. Sandeep] Last name [Kumar]. Author 2 Given name: [Praveen Kumar] Last name [Singh]. Also, kindly confirm the details in the metadata are correct.I confirm that the given names are accurate and presented in the correct sequence.

Genetic, Phenotypic, and Pathogenic Variation Among Athelia rolfsii, the Causal Agent of Peanut Stem Rot in China.

Peanut stem rot caused by Athelia rolfsii is a serious soilborne disease worldwide and is becoming increasingly important in China. A total of 293 A. rolfsii isolates were collected from four representative peanut producing provinces in northern, central, and southern China. These isolates were assigned to 45 mycelial compatibility groups (MCGs) through pairing testing. The MCG diversity among isolates was greater in the southern sampled provinces compared with the northern provinces. A high level of genetic variability was found among the isolates from Guangdong Province in southern China. Variations were found in mycelial growth rate and sclerotial number, size, and dry weight of isolates sampled from places in different latitudes. Size and dry weight of sclerotia were positively correlated with latitude (P < 0.01), but the number of sclerotia was negatively correlated with latitude (P < 0.01). All tester isolates were pathogenic on peanut but varied in disease index. Inter-simple sequence repeat analysis and unweighted pair-group method with arithmetic average clustering resulted in three distinct clusters that were associated with the geographical location of the collection sites and sclerotial traits but were not associated with virulence of these isolates. These findings imply that genetic diversity, morphological traits, and virulence among A. rolfsii isolates varied in diverse geographical regions in China, and genetic diversity and sclerotial traits might be affected by latitude.

Morpho-Cultural and Pathogenic Variability of Sclerotinia sclerotiorum Causing White Mold of Common Beans in Temperate Climate.

The present systematic research on cultural, morphological, and pathogenic variability was carried out on eighty isolates of Sclerotinia sclerotiorum collected from major common bean production belts of North Kashmir. The isolates were found to vary in both cultural and morphological characteristics such as colony color and type, colony diameter, number of days for sclerotia initiation, sclerotia number per plate, sclerotial weight, and size. The colony color ranged between white and off-white with the majority. The colony was of three types, in majority smooth, some fluffy, and a few fluffy-at-center-only. Colony diameter ranged between 15.33 mm and 29 mm after 24 h of incubation. The isolates took 4 to 7 days for initiation of sclerotia and varied in size, weight, and number per plate ranging between 14 and 51.3. The sclerotial arrangement pattern on plates was peripheral, sub peripheral, peripheral, and subperipheral, arranged at the rim and scattered. A total of 22 Mycelial compatibility groups (MCGs) were formed with seven groups constituted by a single isolate. The isolates within MCGs were mostly at par with each other. The six isolates representing six MCGs showed variability in pathogenicity with isolate G04 as the most and B01 as the least virulent. The colony diameter and disease scores were positively correlated. Sclerotia were observed to germinate both myceliogenically and carpogenically under natural temperate conditions of Kashmir. Germplasm screening revealed a single resistant line and eleven partially resistant lines against most virulent isolates.

Molecular detection, virulence, and mycelial compatibility of Macrophomina phaseolina isolates associated with chickpea wilt in Sinaloa and Sonora, Mexico

Three Macrophomina species (M. phaseolina, M. pseudophaseolina, and M. euphorbiicola) associated with various crops worldwide have been distinguished to date by DNA sequence analysis; however, no studies have been conducted to identify Macrophomina species occurring on chickpea in Mexico. The aims of this study were to identify Macrophomina isolates associated with chickpea wilt through the use of species-specific primers, as well as to determine their virulence and mycelial compatibility. During the 2019 growing season, 58 Macrophomina isolates were obtained from symptomatic plants collected from 19 chickpea crops distributed in the states of Sinaloa and Sonora, Mexico. The identity of all 58 isolates was determined by PCR using three sets of primers specific to three Macrophomina species (M. phaseolina, M. pseudophaseolina, and M. euphorbiicola). Virulence was determined by inoculating chickpea seedling roots with a mycelial suspension and disease severity was assessed 30 days after inoculation. Molecular detection with species-specific primers indicated that all isolates belong to M. phaseolina, with significant differences found in their virulence. Mycelial compatibility testing showed that there are at least six mycelial compatibility groups of M. phaseolina distributed in chickpea fields in Sinaloa and Sonora. This information will serve as a basis for future studies on the epidemiology and management of the disease caused by M. phaseolina on chickpea in Mexico.

The Population of Sclerotinia sclerotiorum in Brazil Is Structured by Mycelial Compatibility Groups.

The genetic structure of the population of Sclerotinia sclerotiorum was analyzed using 238 individuals collected from different hosts. Individuals were characterized for microsatellite genotypes and mycelial compatibility groups (MCGs). A total of 22 MCGs and 64 multilocus lineages (MLLs) were identified. There was a close relationship between the MCGs and MLLs, but there was no association between MLLs and hosts or regions. At least 39 MCGs are present in Brazil, and 68.5% of the isolates were assigned to either MCG 1 or MCG 2. Eight new MCGs were found. Seven genetic groups were identified and associated with MCGs. Most genetic variation (70.0%) was because of differences among MCGs. High values of estimates of linkage disequilibrium among loci were more frequent in the total population (all MCGs). By contrast, there was evidence of random mating in subpopulations defined by MCGs 1 and 2. Additionally, there was evidence of outcrossing in the population of S. sclerotiorum in Brazil. The population was structured by MCGs; lineages originating from asexual reproduction or selfing prevail and are widely distributed in space, are persistent in time, and affect many hosts, but there is evidence of some degree of outcrossing, which may lead to a more genetically variable population in the future.

MYCELIAL INCOMPATIBILITY OF SCLEROTINIA SCLEROTIORUM ISOLATES FROM A SINGLE RAPESEED FIELD IN SLOVAKIA

Sclerotinia sclerotiorum (Lib.) de Bary (1884) is economically important pathogen of rapeseeds damaging up to 20% of plants in Slovakia. There is a suggestion that S. sclerotiorum reproduces predominantly asexually, thus genetically identical clonal populations are dominating in fields. Genetically distinct isolates can be distinguished by mycelial compatibility-incompatibility grouping system. The aim of the study was to determine genetic variability of S. sclerotiorum based on mycelial interaction within a single oilseed rape field in Slovakia. S. sclerotiorum isolates were obtained from flower petals of commercial rapeseeds field in Hul, Slovakia (2018) by transferring a single hyphal tip to the plates with potato dextrose agar (PDA). Two sets of 20 isolates were paired in all possible combination and cultivated on PDA amended by bromophenol blue. Mycelial interactions were scored after 7 days.Each of the 20 isolates in 1st set was unique and belonged to the different mycelial compatibility groups (MCGs). In the 2nd set, 18 MCGs was determined with one isolate and only 1 MCGs consisted of 2 isolates. No prevalent MCG was found in this study, suggesting that S. sclerotiorum population affecting the target rapeseed field consisted of a very diverse group of isolates. The high level of incompatible reactions found in this first study from Slovakia may indicate that S. sclerotiorum undergoes frequent outcrossing in rapeseed stands.

Impact of Preconditioning Temperature and Duration Period on Carpogenic Germination of Diverse Sclerotinia sclerotiorum Populations in Southwestern Australia.

The soilborne pathogen Sclerotinia sclerotiorum (Lib.) de Bary is the causal agent of Sclerotinia stem rot, a severe disease of broad-leaf crops including canola/rapeseed (Brassica napus) that can result in significant yield losses. Sclerotia, the hard melanized resting structure of the pathogen, requires preconditioning before carpogenic germination can occur. We investigated the effect of preconditioning temperature (4, 20, 35, 50°C, and field conditions) and duration (0, 30, 60, 120, 179, 240, and 301 days) on germination of S. sclerotiorum sclerotia collected from five canola fields in the southwestern Australia grain belt. The ecological diversity of each population was characterized using mycelial compatibility group (MCG) typing. No response was observed for isolates conditioned at 4°C at any time period, indicating that chilling is not a preconditioning requirement for these isolates. Sclerotia required preconditioning for a minimum of 60 days before any significant increase in germination occurred, with no further increases in germination recorded in response to longer conditioning after 60 days. The highest germination was observed in sclerotia conditioned at 50°C. The MCG results indicated significant diversity within and between populations, suggesting local adaptation to different environments as well as ensuring the ability to respond to seasonal variation between years.

Population genetics and gene sequence analysis of Athelia rolfsii collected from Northern Iran

Athelia rolfsii is a globally dispersed pathogenic fungus, causing white root rot disease in many crops and horticultural plants. In this study, 90 isolates were collected from three provinces of Guilan, Mazandaran and Golestan in northern Iran. Eighteen isolates were selected for sequence analyses based on their host, sampling sites and Mycelial Compatibility Groups (MCG). Translation elongation factor 1-α(tef1-α), β-tubulin (tub2) genes and rDNA large subunit (LSU) were partially amplified and sequenced in order to conduct phylogenetic analyses. Approximately, all Iranian isolates clustered together in both tef1-α and LSU phylogenetic trees. However, after deletion of ambiguous sites, no variations were observed in tub2 sequences. ISSR and SCoT were also used to investigate the genetic structure of the population. Results of the molecular variance analysis (AMOVA) showed that 70 and 30% of the observed variance corresponded to the difference between and within the populations, respectively. According to these findings, we suggest that mating between populations would be less likely and thus, gene flow is restricted.

Entoleuca sp. infected by mycoviruses as potential biocontrol agents of avocado white root rot

Rosellinia necatrix Prill. the causal agent of white root rot diseases causes major losses in avocado crops in Spain. To study the biocontrol of this disease, 31 antagonistic isolates were collected from the avocado rhizosphere and identified as Entoleuca sp. Studies were carried out in mycovirus detection, in vitro optimal growth temperature, mycelial compatibility groups of these isolates, and their inhibition of R. necatrix growth. The pathogenicity of these antagonistic isolates and their biocontrol of white root rot on avocado plants were also studied. The presence of mycoviruses was detected in all 31 Entoleuca sp. isolates studied and the optimal growth temperature for almost all the isolates (> 80%) was 25 °C. Dual culture showed different responses, with some isolates compatible and others incompatible with each other, showing inhibition halos and black lines. Twenty-five of the 31 isolates showed significant growth inhibition to a virulent R. necatrix isolate in in vitro conditions. In addition, none of the Entoleuca sp. isolates produced any symptoms on inoculated avocado plants and in 24 of them, symptoms of avocado white root rot were reduced, with significant differences among the Entoleuca sp. isolates when they were used as biocontrol agents. New virus-carrying Entoleuca sp. isolates were obtained, which are capable of controlling avocado white root rot.

Carpogenic Germinability of Diverse Sclerotinia sclerotiorum Populations Within the Southwestern Australian Grain Belt.

Sclerotinia stem rot, caused by the necrotrophic plant pathogen Sclerotinia sclerotiorum (Lib.) de Bary, is a major disease of canola and pulses in Australia. Current disease management relies greatly on cultural and chemical means of control. Timing of fungicide applications remains a challenge, because efficacy is dependent on accurate prediction of ascospore release and presence on the plant. The aims of this study were to determine the optimal temperature for carpogenic germination of S. sclerotiorum populations sampled from canola and lupin fields in southwestern Australia and characterize diversity using mycelial compatibility groupings (MCGs). Sclerotia were collected from four diseased canola and one diseased lupin field from across southwestern Australia. Forty sclerotia from each population were incubated at four alternating temperatures of 30/15, 20/15, 20/4, and 15/4°C (12-h/12-h light/dark cycle) and assessed every 2 to 3 days for a 180-day period. MCG groupings for populations were characterized using 12 reference isolates. Results indicated the time to initial carpogenic germination decreased as diurnal temperature fluctuations decreased, with a fluctuation of 5°C (20/15°C) having the most rapid initial germination followed by 11°C (15/4°C) followed by 16°C (20/4°C). Optimal germination temperature for all five populations was 20/15°C; however, population responses to other diurnal temperature regimes varied considerably. No germination was observed at 30/15°C. MCG results indicate extensive diversity within and between populations, with at least 40% of sclerotia within each population unable to be characterized. We suggest that this diversity has enabled S. sclerotiorum populations to adapt to varying environmental conditions within southwestern Australia.

Genetic diversity and pathogenic characteristics of Phomopsis asparagi obtained from Asparagus officinalis and A. kiusianus in Japan

Phomopsis asparagi has been reported as a serious disease, causing stem blight on asparagus cultivars (Asparagus officinalis), and this fungus was also recorded as a common spot disease on wild asparagus (A. kiusianus). In this study, isolates of P. asparagi obtained from A. officinalis and A. kiusianus in different locations of the Kyushu island were successfully assessed the genetic variation through mycelial compatibility grouping (MCG) and random amplified polymorphic DNA (RAPD). Thirty fungal isolates were identified into six MCGs; of these, fifteen isolates were representatively chosen for the RAPD analysis, pathogenicity and extracellular enzyme test. Eight RAPD primers, B62, B66, B68, B71, C83, D22, D32 and E10, generated 100 different patterns from the isolates with 91% of the polymorphic bands. Based on RAPD analysis, P. asparagi isolates were divided into 3 distinct genetic clusters, namely RAPD-I, RAPD-II and RAPD-III at a similarity of 73%. The result indicated that there was a great genetic variation within the isolates from A. kiusianus, presenting in the three clusters. While the isolates from A. officinalis showed high genetic homology and they belonged to the RAPD-II cluster. There is no conflict between genetic clusters distinguished by the RAPD markers and those of MCG. On the other hand, the pathogenicity test revealed that the isolates of RAPD-II and RAPD-III were highly virulent pathogens. In contrast, the isolates of RAPD-I were weak virulent pathogens when inoculated on A. officinalis. Screening of extracellular enzyme activities concluded that all isolates were positive for laccase, lipase and protease activity.

Genetic Diversity and Recombination in the Plant Pathogen Sclerotinia sclerotiorum Detected in Sri Lanka.

Sclerotinia sclerotiorum is an important fungal pathogen on many economically important crops including cabbage worldwide. Even though population structure and genetic diversity of S. sclerotiorum is well studied in temperate climatic conditions, only a few studies have been conducted in tropical countries. It is also not clear whether the populations are clonal or recombining in the tropics. In filling this information gap, 47 isolates of S. sclerotiorum were collected from commercial cabbage (Brassica oleracea L.) fields in Nuwara Eliya district of Sri Lanka, where the disease has been previously reported. All the isolates were subjected to genetic diversity study using mycelial compatibility grouping and microsatellite markers. Fourteen mycelial compatibility groups (MCGs) and 23 multilocus haplotypes (MLHs) were recorded. Mean expected heterozygosity of the population was 0.56. MLHs were weakly correlated with MCGs. Population genetic structure analysis and principal coordinates identified three genetic clusters. Genetic recombination was inferred within each genetic cluster when isolates were subjected to clone correction. There was evidence of multiple infections on single plant as detected by the presence of more than one MCG on each cabbage plant. However, multiple infections did not increase the disease severity in detached leaf assay. We found high genetic diversity and recombination of S. sclerotiorum population in a tropical country, Sri Lanka. Importance of detecting genetic structure when inferring recombination was also highlighted.

Population Structure and Aggressiveness of Sclerotinia sclerotiorum From Rapeseed (Brassica napus) in Chongqing City.

Sclerotinia sclerotiorum is one of the most devastating fungal plant pathogens of oilseed Brassica and is distributed worldwide. In particular, Sclerotinia stem rot has always been a serious threat to rapeseed production in Chongqing City, China. In this study, simple sequence repeat (SSR) markers and mycelial compatibility groups (MCGs) were used to characterize the population structure of 90 geographic isolates of S. sclerotiorum collected from rapeseed in nine counties of Chongqing. A total of 52 microsatellite haplotypes were identified, and a few haplotypes were found with high frequency. Gene diversity ranged from 0.1570 to 0.4700 in nine populations. A constructed unweighted pair group with arithmetic mean dendrogram based on Nei genetic distance and a STRUCTURE analysis revealed that the genetic composition of the isolates collected in the five counties located in western Chongqing are different from those collected in the two eastern counties, suggesting that breed lines should be cultivated in both the western and eastern regions to effectively evaluate resistance levels. A total of 47 MCGs were identified, and 72% of the MCGs was represented by single isolates. Seven of 13 MCGs that included at least two isolates contained isolates from only one county. SSR haplotypes were not correlated with MCGs. A subset of 34 isolates were inoculated on rapeseed stems, and the aggressiveness showed variation. This research revealed the population genetic structure and aggressiveness of this pathogen in Chongqing, and the results will help to develop disease management and resistance screening strategies.

Molecular characterization, mycelial compatibility grouping, and aggressiveness of a newly emerging phytopathogen, Sclerotinia sclerotiorum, causing white mold disease in new host crops in Bangladesh

Sclerotinia sclerotiorum is a newly emerging phytopathogen in Bangladesh causing white mold disease in many plants, including important horticultural and field crops. In this study, we isolated S. sclerotiorum strains from infected parts of various host crops and characterized them using morphophysiological and genetic approaches. White mold of mustard; pod rot or fruit rot of bush bean and garden pea; head rot of cauliflower; flower rot or blossom rot of rose and Salvia; fruit rot of squash; inflorescence rot and pod rot of country bean; and leaf drop or rot of coriander and lettuce were observed in several regions of Bangladesh. From the infected crops, a total of 36 fungal strains were isolated and identified as S. sclerotiorum using internal transcribed spacer (ITS) sequencing. The S. sclerotiorum isolates showed white to off-white mycelial growth with loose to dense velvety aerial mycelia. Round to irregular shaped sclerotia formation was observed, with 4-38 sclerotia present per Petri plate. Apothecia formation from sclerotia was also noted under both natural and artificial conditions. In the present study, as many as 13 crops: Cosmos bipinnatus, Amaranthus cruentus, Leucas aspera, Glycine max, Dahlia hortensis, Hibiscus rosa-sinensis, Rosa chinensis, Salvia officinalis, Cucurbita pepo, Lagenaria siceraria, Brassica oleracea var. italica, Coriandrum sativum, and Lactuca sativa were identified as new host crops of S. sclerotiorum in Bangladesh based on morphological characteristics and ITS sequences.

Phenotypic and genotypic characterization of single isolate-derived monoascospore strains of Sclerotinia sclerotiorum from common bean

White mold is a highly destructive disease caused by Sclerotinia sclerotiorum, a polyphagous fungus that infects several hosts including common bean grown that is widely cultivated in Brazil. The pathogenic populations are known to exhibit genetic variability but studies rarely used single ascospore-derived strains. In this study, 12 monoascospore strains originated from a same isolate (UFLA 54), but from different apothecia, were compared among them and with the mother strain with regards: days to first sclerotium formation, mycelial growth rate mycelial compatibility groups, microsatellite markers and mating type locus (MAT1–1 and MAT1–2). Their pathogenicity was assessed on three common bean lines. Cluster analysis of growth rates data separated UFLA 54 from all monoascospore strains, which shared same alleles in the microsatellite locus. Inversion of MAT1–1 region was found for both UFLA 54 and half of monoascospore strains. Aggressiveness of the monoascospore strains was not consistent across common bean lines. Our study reveals significant variability of S. sclerotiorum at the single isolate level.

Mycelial compatibility groups, pathogenic diversity and biological control of Sclerotium rolfsii on turfgrass

Sclerotium rolfsii Sacc. (the sclerotial state of Athelia rolfsii (Cruzi) Tu and Kimbrough), the soil-borne pathogen on several plants all over the world, has been previously reported from Turkey on certain plants. In this study, turfgrass areas in 9 provinces of Turkey were firstly surveyed for S. rolfsii, and samples showing chlorotic, reddish-brown, and frog-eye shaped circular patches were collected. Totally, 32 Sclerotium rolfsii isolates were obtained from these areas. One mycelial compatibility group (MCG) was identified among S. rolfsii isolates. Disease severity in pathogenicity tests carried out in the greenhouse ranged from 83.74 to 92.87%. Identification of fungal and bacterial isolates used in the study was performed by DNA sequencing analysis. Five antagonistic bacterial strains, previously found as effective on controlling some fungal pathogens, were tested to determine their antifungal effects against the southern blight by using seed coating method in greenhouse conditions. In consequence of the biological control studies, Bacillus cereus 44bac and Stenotrophomonas rhizophila 88bfp were found more effective than the other strains with the ratio of 91.00 and 90.11%, respectively.

The population of Sclerotinia sclerotiorum affecting common bean in Brazil is structured by mycelial compatibility groups

The genetic structure of a population of Sclerotinia sclerotiorum causing white mold on common bean in Brazil was studied using microsatellite (SSR) loci and mycelial compatibility groups (MCGs). A total of 300 isolates were analyzed and 154 SSR haplotypes and 32 MCGs were identified. Two MCGs were widely distributed and accounted for 70% of the isolates. Six SSR haplotypes were associated with more than one closely related MCG. There was no evidence of random association of alleles among loci when the population comprised by all MCGs was analyzed, suggesting that outcrossing is absent or rare. Nevertheless, there was evidence of random mating within the major MCGs. Seven genetic groups were identified, one of them comprising only highly pigmented isolates. Isolates of distinct MCGs did not differ in virulence. There was strong genetic differentiation among MCGs: more than 95% of the total genetic variation was attributed to differences among these groups. Therefore, MCGs contribute to the structure of the population of S. sclerotiorum in Brazil.

Something in the agar does not compute: on the discriminatory power of mycelial compatibility in Sclerotinia sclerotiorum

Mycelial compatibility, the ability for fungal isolates to grow together and form one single colony, was defined for Sclerotinia sclerotiorum nearly 30 years ago and has since been used as a marker to describe clonal variation in population genetic studies. While evidence suggests an associative relationship between mycelial compatibility and vegetative compatibility, contemporary research has treated these traits as analogous. As molecular markers have been developed to describe genetic variation, researchers combined these with the mycelial compatibility groups to assess and to define clonal lineages. However, several inconsistent relationships between mycelial compatibility groups, haplotypes, and even vegetative compatibility groups have been observed throughout the literature, suggesting that mycelial compatibility may not accurately reflect self-recognition. We argue that the Sclerotinia community needs to move beyond using MCG data in population genetic studies.

Partial stem resistance in Brassica napus to highly aggressive and genetically diverse Sclerotinia sclerotiorum isolates from Australia

Sclerotinia sclerotiorum is a fungal pathogen that causes stem rot in oilseed rape (Brassica napus). Previously, B. napus accessions with partial stem resistance to a Canadian S. sclerotiorum isolate (#321) were identified using a stem test in which flowering plants were inoculated with mycelium plugs. The present study examined the partial stem resistance of four of these accessions, PAK54, PAK93, DC21 and K22, following inoculation with Australian isolates. Mycelial compatibility groups and intergenic spacer (IGS) region haplotypes were identified among 71 isolates from Australian oilseed rape and lupin fields. Eleven genetically diverse isolates showed differences in aggressiveness when inoculated onto nine oilseed rape varieties and one Chinese accession. Isolates CU8.24, CU10.17 and CU11.19 were selected based on genetic diversity, growth rate in vitro and high aggressiveness in the initial screen and subsequently inoculated onto the four B. napus accessions. These accessions developed significantly smaller lesions compared with the susceptible control varieties (‘AV Garnet’ and ‘Westar’), with the average frequency of soft and collapsed lesions being less than 20% in PAK54, DC21 and K22, 29% in PAK93 and greater than 88% in the susceptible controls. Microscopic examination revealed that hyphae were typically confined to the stem cortex in the smallest lesions, but could be found in the stem pith in larger lesions. These results show that B. napus accessions PAK54, PAK93, DC21 and K22 can be used in Australia for development of varieties with partial stem resistance to S. sclerotiorum.