Transfection of Sclerotinia sclerotiorum withIn VitroTranscripts of a Naturally Occurring Interspecific Recombinant of Sclerotinia sclerotiorum Hypovirus 2 Significantly Reduces Virulence of the Fungus

ABSTRACTA recombinant strain ofSclerotinia sclerotiorumhypovirus 2 (SsHV2) was identified from a North AmericanSclerotinia sclerotiorumisolate (328) from lettuce (Lactuca sativaL.) by high-throughput sequencing of total RNA. The 5′- and 3′-terminal regions of the genome were determined by rapid amplification of cDNA ends. The assembled nucleotide sequence was up to 92% identical to two recently reported SsHV2 strains but contained a deletion near its 5′ terminus of more than 1.2 kb relative to the other SsHV2 strains and an insertion of 524 nucleotides (nt) that was distantly related toValsa ceratospermahypovirus 1. This suggests that the new isolate is a heterologous recombinant of SsHV2 with a yet-uncharacterized hypovirus. We named the new strainSclerotinia sclerotiorumhypovirus 2 Lactuca (SsHV2L) and deposited the sequence in GenBank with accession numberKF898354.Sclerotinia sclerotiorumisolate 328 was coinfected with a strain ofSclerotinia sclerotiorumendornavirus 1 and was debilitated compared to cultures of the same isolate that had been cured of virus infection by cycloheximide treatment and hyphal tipping. To determine whether SsHV2L alone could induce hypovirulence inS. sclerotiorum, a full-length cDNA of the 14,538-nt viral genome was cloned. Transcripts corresponding to the viral RNA were synthesizedin vitroand transfected into a virus-free isolate ofS. sclerotiorum, DK3. Isolate DK3 transfected with SsHV2L was hypovirulent on soybean and lettuce and exhibited delayed maturation of sclerotia relative to virus-free DK3, completing Koch's postulates for the association of hypovirulence with SsHV2L.IMPORTANCEA cosmopolitan fungus,Sclerotinia sclerotioruminfects more than 400 plant species and causes a plant disease known as white mold that produces significant yield losses in major crops annually. Mycoviruses have been used successfully to reduce losses caused by fungal plant pathogens, but definitive relationships between hypovirus infections and hypovirulence inS. sclerotiorumwere lacking. By establishing a cause-and-effect relationship betweenSclerotinia sclerotiorumhypovirus Lactuca (SsHV2L) infection and the reduction in host virulence, we showed direct evidence that hypoviruses have the potential to reduce the severity of white mold disease. In addition to intraspecific recombination, this study showed that recent interspecific recombination is an important factor shaping viral genomes. The construction of an infectious clone of SsHV2L allows future exploration of the interactions between SsHV2L andS. sclerotiorum, a widespread fungal pathogen of plants.

Saccothecium sepincola. [Descriptions of Fungi and Bacteria].

A description is provided for Saccothecium sepincola. Some information on its dispersal and transmission and conservation status is given, along with details of its geographical distribution (Morocco, Canada (British Columbia), USA (Florida, North Carolina, Oregon, Virginia, Washington), Chile, Armenia, Republic of Georgia, India (Uttar Pradesh), Pakistan, Austria, Belgium, Bosnia-Hercegovina, Czech Republic, Denmark, France, Germany, Hungary, Italy, Luxembourg, Montenegro, Norway, Poland, Portugal, Romania, Russia (Leningradskaya oblast), Spain, Sweden, Switzerland, Ukraine and UK), hosts (Aruncus sylvestris, Celtis planchoniana, Cornus sanguinea, Cornus sp., Corylus avellana, Crataegus laevigata, Crataegus pojarkoviae, Elaeagnus angustifolia, Forsythia intermedia, Hippophae rhamnoides, Laurus nobilis, Philadelphus sp., Pistacia mutica, Populus tremula, Rosa canina, Rosa centifolia, Rosa moschata, Rosa multiflora, Rosa pendulina, Rosa trachyphylla, Rosa sp., Rubus amoenus, Rubus discolor, Rubus floridus, Rubus fruticosus, Rubus idaeus, Rubus laciniatus, Rubus leucodermis, Rubus grabowskii, Rubus villicaulis, Rubus sp., Physocarpus opulifolius, Spiraea salicifolia and Staphylea pinnata) and associated fungi (Leptosphaeria fuscella, Valsa ceratosperma, Valsa ambiens and Valsa sp.).

Valsa ceratosperma. [Distribution map].

A new distribution map is provided for Valsa ceratosperma (Tode) Maire Ascomycota: Diaporthales Principal hosts: Apple (Malus pumila), peach (Prunus persica), pear (Pyrus communis) and quince (Cydonia oblonga). Information is given on the geographical distribution in EUROPE, Austria, Czech Republic, Germany, Greece, Italy, Lithuania, Portugal, Romania, Central Russia Russian Far East, Southern Russia, Western Siberia, Slovakia, Sweden, Switzerland, UK, Ukraine, ASIA, Azerbaijan, China, Gansu, Hebei, Heilongjiang, Henan, Hubei, Jiangsu, Jilin, Liaoning, Nei, Menggu, Ningxia, Shaanxi, Shandong, Shanxi, Xinjiang, Zhejiang, Republic of Georgia, India, Rajasthan, Uttar Pradesh, Japan, Hokkaido, Honshu, Korea Republic, Pakistan, NORTH AMERICA, Canada, Ontario, USA, New Jersey, Washington, SOUTH AMERICA, Argentina, OCEANIA, Australia, New South Wales, Tasmania, Victoria.

Extending Chestnut Blight Hypovirus Host Range Within Diaporthales by Biolistic Delivery of Viral cDNA

Biolistic bombardment was used to successfully transform three phytopathogenic fungal species with an infectious cDNA clone of the prototypic hypovirus, CHV1-EP713, a genetic element responsible for the virulence attenuation (hypovirulence) of the chestnut blight fungus, Cryphonectria parasitica. The fungal species included two strains each of C. parasitica and Valsa ceratosperma, as well as one strain of Phomopsis G-type (teleomorph Diaporthe Nitschke); all are members of the order Diaporthales but classified into three different genera. A subset of transformants for each of the fungal species contained CHV1-EP713 dsRNA derived from chromosomally integrated viral cDNA. As has been reported for CHV1-EP713 infection of the natural host C. parasitica, biolistic introduction of CHV1-EP713 into the new fungal hosts V. ceratosperma and Phomopsis G-type resulted in altered colony morphology and, more importantly, reduced virulence. These results suggest a potential for hypoviruses as biological control agents in plant-infecting fungal pathogens other than the chestnut blight fungus and closely related species. In addition, the particle delivery technique offers a convenient means of transmitting hypoviruses to potential host fungi that provides new avenues for fundamental mycovirus research and may have practical applications for conferring hypovirulence directly on infected plants in the field.

Valsa ceratosperma. [Descriptions of Fungi and Bacteria].

A description is provided for Valsa ceratosperma. Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. DISEASE: Valsa ceratosperma is known to be a pathogen, causing Valsa canker of apple trees in Japan (Sawamura et al., 1990). HOSTS: Dead or dying twigs and branches of numerous woody angiosperms. GEOGRAPHICAL DISTRIBUTION: Asia: Azerbaijan, China, Republic of Georgia, Japan, India, Korea, Russia. Australasia: Australia. Europe: Austria, Czech Republic, Germany, Greece, Italy, Lithuania, Portugal, Rumania, Russia, Slovakia, Sweden, Switzerland, UK, Ukraine. North America: USA. South America: Argentina. Spielman (1985) describes distribution as worldwide. TRANSMISSION: By air-borne conidia and ascospores in humid conditions. Conidial and ascospore dispersal of V. ceratosperma was studied in apple tree orchards in Japan (Fujita et al., 1980; Saito et al., 1972).