Genetic diversity of Cryphonectria parasitica causing chestnut blight in South Tyrol (northern Italy)

European chestnut (Castanea sativa) is threatened by the invasive fungus Cryphonectria parasitica, which causes chestnut blight. The virulence of the fungus can be reduced by a group of mycoviruses that can spread among vegetatively compatible strains through hyphal anastomosis. Hypovirulent isolates are used as biocontrol agents, but their efficiency can be diminished by restricted hyphal anastomosis if the variability of vegetative compatibility (vc) types in a population is high. Sexual reproduction could increase the vc type diversity and further complicate biocontrol in a region. Therefore, knowledge of genetic diversity of C. parasitica is important to assess the effectiveness of a biological control program. The present study was performed in the Autonomous Province of Bozen-Bolzano (South Tyrol) in northern Italy, where chestnut cultivation provides an additional income to farmers. The genetic characterization of C. parasitica isolates from 35 chestnut stands and one forest population in different districts of South Tyrol was performed based on the analysis of vegetative incompatibility loci, the mating type locus, and the internal transcribed spacer (ITS) region. In this study, a total of 23 different vc types were found all over South Tyrol with a Shannon diversity index of 1.86. EU-2, EU-1, and EU-13 were the most widespread vc types comprising 51%, 13%, and 9% of the fungal isolates, respectively. Both mating types were present in the region with a ratio close to 1:1. Three different haplotypes were identified based on ITS sequence analysis, which pointed to two introduction events of the fungus to the region and allowed placing C. parasitica from South Tyrol into a larger phylogeographic context.

A COMPREHENSIVE REVIEW ON MYCOVIRUSES AS BIOLOGICAL CONTROL AGENT

Mycoviruses are viruses that infect fungi. They have been reported in all major taxa of fungi. Generally extracellular phase is not present in mycoviruses and are transmitted during cell division intracellularly in sporogenesis, and/or hyphal anastomosis. The genome of mycoviruses has dsRNA, but a number of positive- or negative-strand ssRNA and ssDNA viruses have been isolated and characterized. There is an increasing interest for use of mycoviruses as novel biocontrol agent as they reduce the virulence of their phytopathogeinc fungal hosts. Mycoviruses can also infect endophytic fungi and encode killer toxins. Better understanding of mycoviruses assembly, function, and evolution have been done through their structural analyses. Recent report on virus taxonomy suggested that mycoviruses genome mostly consists of double-stranded RNA (dsRNA), and about 30% of mycoviruses genome is composed of a positive, single-stranded RNA (+ssRNA). Recently a mycovirus that is related to Gemini viruses has been reported. Scientists have reported mycoviruses in Chytridiomycota, Zygomycota, Ascomycota, Deuteromycota, and Basidiomycota. Many mycoviruses and their fungal hosts still remain unknown recently developed metagenomics approaches will be useful for detecting and identifying new mycoviruses

Some characteristic of Rhizoctonia spp. in sharp eyespot of wheat

Isolates of <i>Rhizttctonia</i> sp. with multinucleate and binucleate cells were obtained from sharp eyespot lesions on wheat culms in Olsztyn region. (NE Poland). These isolates were compared to isolates of AG-4 and GAG-1 testers with reference to cultural morphology of colony, growth rate, hyphal anastomosis and pathogenicity to wheat seedlings. The wheat binucleate isolates were similar in morphology of colonies and anastomosed with the <i>Ceratubasidium</i> anastomosis group GAG-1 tester isolates of <i>R. cerealis</i>. Growth rates on PDA ranged from 9 to 11 mm/24h for wheat isolates and from l to 11 mm/24 h for tester isolates GAG-1 of <i>R. cerealis</i>. The wheat multinucleate isolates were similar in morphology of colonies and anastomosed with <i>Rhizoctonia solani</i> Kühn group AG-4 tester isolate. <i>R. solani</i> AG-4 isolates were morphologically distinct from the <i>R. cerealis</i> isolates. These isolates on PDA were dark and grow rapidly (20-30 mm diam./24 h/20°C) and significantly contrasted with slowly growing white-creamy isolates of <i>R. cerealis</i> (GAG-1). Isolates of <i>R. solani</i> (AG-4) and <i>R. cerealis</i> (GAG-I) developed sharp eyespot lesions on culms and white head symptoms typical of the disease. None of the wheat isolates of <i>R. cerealis</i> (GAG-I) caused root-rot on wheat seedlings. In the present work the classification system of vegetative groups of <i>Rhizoctonia</i> spp. in present work is also discussed.

A Rare case of Subcutaneous Mycosis due to Rhizoctonia solani

Rhizoctonia solani is a very common soil borne pathogen with a great diversity of host plants. A 52 year old lady presented with sole manifestation of subcutaneous swelling over the left leg for 3 months Pus was collected by aspiration revealed septate fungal hyphae. After culture on SDA at 25 C showed white cottony growth initially, progressed to buff colored to black colonies on further incubation. On LPCB mount we found septate hyphae with acute and right angled branching without any conidia and hyphal anastomosis which resembled features of Rhizoctonia solani. Patient was put on Fluconazole and responded well to the treatment. DOI: http://dx.doi.org/10.3329/bjms.v13i2.15060 Bangladesh Journal of Medical Science Vol.13(2) 2014 p.228-230

Potentiation of Mycovirus Transmission by Zinc Compounds via Attenuation of Heterogenic Incompatibility in Rosellinia necatrix

ABSTRACTHeterogenic incompatibility is considered a defense mechanism against deleterious intruders such as mycovirus.Rosellinia necatrixshows strong heterogenic incompatibility. In the heterogenic incompatibility reaction, the approaching hyphae hardly anastomosed, a distinctive barrage line formed, and green fluorescent protein (GFP)-labeled hyphae quickly lost their fluorescence when encountering incompatible hyphae. In this study, transmission of a hypovirulence-conferring mycovirus to strains with different genetic backgrounds was attempted. Various chemical reagents considered to affect the programmed cell death pathway or cell wall modification were examined. Treatment with zinc compounds was shown to aid in transmission of mycoviruses to strains with different genetic backgrounds. In incompatible pairings, treatment with zinc compounds accelerated hyphal anastomosis; moreover, cytosolic GFP was transmitted to the newly joined hyphae. These results suggest that zinc compounds not only increase hyphal anastomosis but also attenuate heterogenic incompatibility.

Deletion of the Fungal Gene soft Disrupts Mutualistic Symbiosis between the Grass Endophyte Epichloë festucae and the Host Plant

ABSTRACT Hyphal anastomosis, or vegetative hyphal fusion, establishes the interconnection of individual hyphal strands into an integrated network of a fungal mycelium. In contrast to recent advances in the understanding of the molecular basis for hyphal anastomosis, knowledge of the physiological role of hyphal anastomosis in the natural habitats of filamentous fungi is still very limited. To investigate the role of hyphal anastomosis in fungal endophyte-plant interactions, we generated mutant strains lacking the Epichloë festucae soft ( so ) gene, an ortholog of the hyphal anastomosis gene so in the endophytic fungus E. festucae . The E. festucae Δ so mutant strains grew similarly to the wild-type strain in culture but with reduced aerial hyphae and completely lacked hyphal anastomosis. The most striking phenotype of the E. festucae Δ so mutant strain was that it failed to establish a mutualistic symbiosis with the tall fescue plant host ( Lolium arundinaceum ); instead, it killed the host plant within 2 months after the initial infection. Microscopic examination revealed that the death of the tall fescue plant host was associated with the distortion and disorganization of plant cells. This study suggests that hyphal anastomosis may have an important role in the establishment/maintenance of fungal endophyte-host plant mutualistic symbiosis.