Mating type-correlated molecular markers and demonstration of heterokaryosis in the phytopathogenic fungus Thanatephorus cucumeris (Rhizoctonia solani) AG 1-IC by AFLP DNA fingerprinting analysis

Global distribution, traditional and modern detection, diagnostic, and management approaches of Rhizoctonia solani associated with legume crops

Sustainable development relies heavily on a food system that is both safe and secure. Several approaches may lead to sustainability and food safety. An increase in the cultivation of legume crops is one of the approaches for enhancing agricultural viability and ensuring adequate food supply. Legumes may increase daily intake of fiber, folate, and protein as substitutes for meat and dairy. They are also crucial in various intercropping systems worldwide. However, legume production has been hampered by Rhizoctonia solani due to its destructive lifestyle. R. solani causes blights, damping off, and rotting diseases in legume crops. Our knowledge of the global distribution of R. solani associated with legume crops (alfalfa, soybean, chickpea, pea, lentil, common bean, and peanut), detection, diagnosis, and management of legume crops diseases caused by R. solani is limited. Traditional approaches rely on the incubation of R. solani, visual examination of symptoms on host legume crops, and microscopy identification. However, these approaches are time-consuming, require technical expertise, fail to detect a minimal amount of inoculum, and are unreliable. Biochemical and molecular-based approaches have been used with great success recently because of their excellent sensitivity and specificity. Along with conventional PCR, nested PCR, multiplex PCR, real-time PCR, magnetic-capture hybridization PCR, and loop-mediated isothermal amplification have been widely used to detect and diagnose R. solani. In the future, Next-generation sequencing will likely be used to a greater extent to detect R. solani. This review outlines global distribution, survival, infection and disease cycle, traditional, biochemical, molecular, and next-generation sequencing detection and diagnostic approaches, and an overview of the resistant resources and other management strategies to cope with R. solani.

Evolution of uni- and bifactorial sexual compatibility systems in fungi

Mating systems, that is, whether organisms give rise to progeny by selfing, inbreeding or outcrossing, strongly affect important ecological and evolutionary processes. Large variations in mating systems exist in fungi, allowing the study of their origin and consequences. In fungi, sexual incompatibility is determined by molecular recognition mechanisms, controlled by a single mating-type locus in most unifactorial fungi. In Basidiomycete fungi, however, which include rusts, smuts and mushrooms, a system has evolved in which incompatibility is controlled by two unlinked loci. This bifactorial system probably evolved from a unifactorial system. Multiple independent transitions back to a unifactorial system occurred. It is still unclear what force drove evolution and maintenance of these contrasting inheritance patterns that determine mating compatibility. Here, we give an overview of the evolutionary factors that might have driven the evolution of bifactoriality from a unifactorial system and the transitions back to unifactoriality. Bifactoriality most likely evolved for selfing avoidance. Subsequently, multiallelism at mating-type loci evolved through negative frequency-dependent selection by increasing the chance to find a compatible mate. Unifactoriality then evolved back in some species, possibly because either selfing was favoured or for increasing the chance to find a compatible mate in species with few alleles. Owing to the existence of closely related unifactorial and bifactorial species and the increasing knowledge of the genetic systems of the different mechanisms, Basidiomycetes provide an excellent model for studying the different forces that shape breeding systems.

New and classic families of secreted fungal heme peroxidases

Heme-containing peroxidases secreted by fungi are a fascinating group of biocatalysts with various ecological and biotechnological implications. For example, they are involved in the biodegradation of lignocelluloses and lignins and participate in the bioconversion of other diverse recalcitrant compounds as well as in the natural turnover of humic substances and organohalogens. The current review focuses on the most recently discovered and novel types of heme-dependent peroxidases, aromatic peroxygenases (APOs), and dye-decolorizing peroxidases (DyPs), which catalyze remarkable reactions such as peroxide-driven oxygen transfer and cleavage of anthraquinone derivatives, respectively, and represent own separate peroxidase superfamilies. Furthermore, several aspects of the "classic" fungal heme-containing peroxidases, i.e., lignin, manganese, and versatile peroxidases (LiP, MnP, and VP), phenol-oxidizing peroxidases as well as chloroperoxidase (CPO), are discussed against the background of recent scientific developments.

Genetic structure of populations of Rhizoctonia solani anastomosis group-1 IA from soybean in Brazil

The Basidiomycete fungus Rhizoctonia solani anastomosis group (AG)-1 IA is a major pathogen of soybean in Brazil, where the average yield losses have reached 30 to 60% in some states in Northern Brazil. No information is currently available concerning levels of genetic diversity and population structure for this pathogen in Brazil. A total of 232 isolates of R. solani AG1 IA were collected from five soybean fields in the most important soybean production areas in central-western, northern, and northeastern Brazil. These isolates were genotyped using 10 microsatellite loci. Most of the multilocus genotypes (MLGTs) were site-specific, with few MLGTs shared among populations. Significant population subdivision was evident. High levels of admixture were observed for populations from Mato Grosso and Tocantins. After removing admixed genotypes, three out of five field populations (Maranhao, Mato Grosso, and Tocantins), were in Hardy-Weinberg (HW) equilibrium, consistent with sexual recombination. HW and gametic disequilibrium were found for the remaining soybean-infecting populations. The findings of low genotypic diversity, departures from HW equilibrium, gametic disequilibrium, and high degree of population subdivision in these R. solani AG-1 IA populations from Brazil are consistent with predominantly asexual reproduction, short-distance dispersal of vegetative propagules (mycelium or sclerotia), and limited long-distance dispersal, possibly via contaminated seed. None of the soybean-infecting populations showed a reduction in population size (bottleneck effect). We detected asymmetric historical migration among the soybean-infecting populations, which could explain the observed levels of subdivision.

Heterokaryon formation in Thanatephorus cucumeris (Rhizoctonia solani) AG-1 IC

Approximately 50 single-basidiospore isolates (SBIs) obtained from each of 16 field isolates of Thanatephorus cucumeris AG-1 IC were examined for heterokaryon formation. All SBIs obtained from each field isolate were divided into two mating groups (SBIs-M1 and SBIs-M2), and tufts of mycelia were formed in the contact zone between colonies of paired SBIs-M1 and -M2 based on 0.5 % charcoal agar medium. Tufts were produced from all possible pairing between SBIs from non-parental field isolates. Hyphal anastomosis reactions indicated no cell death and random cell death at the contact cell, and was not related to tuft formation. AFLP phenotypes of SBIs from each field isolate were not identical to each other and were different from their parental field isolate. AFLP phenotypes of the tuft isolates formed from SBIs-M1 and SBIs-M2 from each field isolate were heterokaryotic. Moreover, several SBIs also formed tufts with their parental and non-parental field isolates. AFLP phenotypes of these tuft isolates suggested that they were all heterokaryotic. Results of these experiments suggest that T. cucumeris AG-1 IC is heterothallic and bipolar, and that genetic exchange can occur between homokaryotic and heterokaryotic isolates (Buller phenomenon).

Vegetative compatibility groups in indigenous and mass-released strains of the entomopathogenic fungus Beauveria bassiana: likelihood of recombination in the field

Using nitrate non-utilizing (nit) mutants, we determined vegetative compatibility groups (VCG) among strains of Beauveria bassiana representing strains indigenous to North America, isolated from diverse insect hosts, and strains that have been mass released for insect control. Genetic similarity among these strains was analyzed using random amplified polymorphic DNA (RAPD) markers. Our data revealed 23 VCGs among the 34 strains tested, with most of these groups comprised of only a single strain. We also observed a VCG comprised of eight genetically similar strains isolated from Colorado potato beetles (CPB). Co-inoculation studies of CPB larvae with complementary nit mutants from the same or from different VCGs revealed heterokaryosis in four out of five same-VCG pairs, with only 5-17% of the sporulating cadavers generating few parasexual recombinants. In contrast, none of the infected beetles treated with non-compatible pairs generated recombinants. The large number of VCGs observed and the low frequency of in vivo recombination limited to vegetatively compatible strains indicate that this self/non-self recognition system may be an effective barrier preventing genetic exchange between dissimilar strains in the field.

Analysis of genetic variation in Ganoderma lucidum after space flight

A modified CTAB method was used in the extraction of total cellular DNA of Ganoderma lucidum. Four strains Cx, Ch, C3 and C4, and their counterparts, four space flown strains Sx, Xh, S3 and S4, were analysed by amplified fragment length polymorphism (AFLP) with several primer combinations. Polymorphic bands were detected between Sx and Cx, S3 and C3, respectively. Somatic incompatibility tests further confirmed their heterogeneity. However, no disparity between Sh and Ch, S4 and C4 was detectable. The results suggest that spaceflight may be used to accelerate breeding of Ganoderma lucidum strains for commercial cultivation.

Potential failsafe mechanisms against the spread and introgression of transgenic hypervirulent biocontrol fungi

Microbial biocontrol agents are typically inefficient owing to the evolutionary necessity to be in balance with their hosts to survive. If transgenetically rendered hypervirulent, however, they could be competitive alternatives to pesticides. Potential means are delineated to prevent, contain or mitigate uncontrollable spread of hypervirulent biocontrol organisms, mutations that increase their host range, and the sexual or asexual introgression of hypervirulence genes into pathogens of other organisms. The use of asporogenic deletion mutants as a platform for generating transgenic hypervirulent biopesticides would prevent such spread. Hypervirulence genes flanked with available 'transgenetic mitigator' (TM) genes (genes that are neutral or positive to the biocontrol agent but deleterious to recombinants) would decrease virulence to non-target species.

Evaluation of different PCR-based DNA fingerprinting techniques for assessing the genetic variability of isolates of the fungus Epicoccum nigrum

Thirty-six strains of the fungus Epicoccum nigrum, isolated from different substrata and ecosystems of Europe, America and Africa, were analysed using 14 molecular markers included in 5 different genetic fingerprinting techniques: AP-PCR, tDNA-PCR, microsatellite-primed PCR, ARDRA and AFLP. All of the techniques used were able to differentiate the isolates, showing a high genetic diversity within the species. However, the different techniques detected different levels of similarity among the strains; ARDRA shows the most homogeneous results whilst AP-PCR shows the most heterogeneous. The similarity indices achieved for each strain were compared for the different techniques. The distribution obtained by microsatellite-primed PCR was similar to those shown by AP-PCR techniques. tDNA-PCR and AFLP rendered similar distributions, and ARDRA showed remarkably different results from the other techniques. The results also reveal the lack of an overall correlation between geographical or ecological origin of the isolates and their genotypes.