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 2. Eight new MCGs were found. Seven genetic groups were identified and associated with MCGs. Most genetic variation (70.0%) was due to differences among MCGs. High values of estimates of linkage disequilibrium among loci were more frequent in the total population (all MCGs). In 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 originated 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 compatibility, anastomosis, and nucleus numbers of eight Mexican Hirsutella citriformis strains isolated from Diaphorina citri

Background Among entomopathogenic fungi, H. citriformis has been recognized as potential biocontrol agent against the Asian citrus psyllid Diaphorina citri (Hemiptera: Liviidae). Nevertheless, this fungus is poorly characterized. Previous molecular studies have shown high sequence similarities among strains, but significant differences in Diaphorina citri virulence. Objective The aim of the present study was to determine mycelial compatibility and anastomosis, and nucleus numbers in mycelium and conidia of eight H. citriformis strains isolated from mycosed D. citri adults collected from several Mexican states. Methods Mycelial compatibility and anastomosis evaluation was performed after pairing strains, leading to 36 confrontations, and cultured in chlorate minimum medium to obtain mutants for vegetative compatibility group. Results Hypha or conidia nuclei were visualized with safranin-O and 3% KOH, and 0.05% trypan blue–lactophenol solution. H. citriformis strains showed compatibly and anastomosis events after confrontation. In addition, they showed one nucleus per conidium and mycelium section. It was not possible to obtain H. citriformis nit mutants from the chlorate concentrations tested. Conclusions To date, this is the first report demonstrating mycelial compatibility, anastomosis occurrence, and hyphae and conidia nuclei number among H. citriformis strains.

Impact of preconditioning temperature and duration period on carpogenic germination of diverse Sclerotinia sclerotorium (Lib.) de Bary populations in south-western Australia

The soil-borne pathogen Sclerotinia sclerotorium 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 pre-conditioning temperature (4°C, 20°C, 35°C, 50°C and field conditions) and duration (0, 30, 60, 120, 179, 240, 301 days) on germination of S. sclerotorium sclerotia collected from five canola fields in the south-western Australian grain-belt. The ecological diversity of each population was characterised using mycelial compatibility groups (MCGs) typing. No response was observed for isolates conditioned at 4°C at any time period indicating 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 within and between population diversity suggesting local adaptation to different environments as well as ensuring the ability to respond to seasonal variation between years.

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.

Investigation of the mycelial compatibility of Macrophomina phaseolina

Macrophomina phaseolina (Tassi) Goid. is found on all five crop-growing continents. In hot and dry seasons, this fungus is capable of causing considerable damage. In this study, mycelial compatibility of M. phaseolina isolates was investigated. In total the 30 samples collected were tested to examine their compatibility. The sunflower samples examined were collected in 2019 and 2020 in different regions of Hungary (29 isolates) and Slovakia (1 isolate). A total of 465 pairing tests were made with 30 isolates. The results of our examination showed incompatibility in 12 pairings. In our studies, we also measured the size of the microsclerotia of the isolates in order to determine which group they belong to. The diameter of the microsclerotia ranged from 74 to 182 μm. Based on this, microsclerotia belong to group ‘C’, as well as the data of previous studies in Hungary.

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.

Mycelial growth variation and compatibility of the selected isolates of Bipolaris sorokiniana (Sacc.) Shoemaker

Bipolaris sorokiniana (Sacc.) Shoemaker is a phytopathogenic fungus, causal agent of leaf blight disease of wheat. This fungus is difficult to control because of its immense cultural, morphological, physiological, pathogenic and genetic variability. The aim of this investigation was to study the cultural variability of the selected isolates of B. sorokiniana by means of mycelial compatibility. One hundred fifty isolates of B. sorokiniana from eight districts (Dhaka, Gazipur, Dinajpur, Joypurhat, Pabna, Sirajgonj, Kushtia and Chuadanga) of Bangladesh were studied and cultural variation was characterized on the basis of colony color and texture on PDA medium. They were - Black-Mat (B-M), Black-Fluffy (B-F), Ash-Mat (A-M), Brownish Ash-Fluffy (Br. A-F), Blackish Ash-Mat (Bl.AM), Whitish Ash-Mat (W. A-M), Greenish Ash-Fluffy (G. A-F) and Pinkish White-Mat (P.W-M). To compare and understand cultural variability, mycelial compatibility test was done among the cultural groups. Results revealed that selected isolates of different cultural groups showed incompatible reaction. Incompatibility was also noticed between the isolates of same district and different districts. Dhaka Univ. J. Biol. Sci. 28(2): 195-209, 2019 (July)