Silvia María Wolcan

Molecular phylogeny and evolution of the genus Neoerysiphe (Erysiphaceae, Ascomycota)

The genus Neoerysiphe belongs to the tribe Golovinomyceteae of the Erysiphaceae together with the genera Arthrocladiella and Golovinomyces. This is a relatively small genus, comprising only six species, and having ca 300 species from six plant families as hosts. To investigate the molecular phylogeny and evolution of the genus, we determined the nucleotide sequences of the rDNA ITS regions and the divergent domains D1 and D2 of the 28S rDNA. The 30 ITS sequences from Neoerysiphe are divided into three monophyletic groups that are represented by their host families. Groups 1 and 3 consist of N. galeopsidis from Lamiaceae and N. galii from Rubiaceae, respectively, and the genetic diversity within each group is extremely low. Group 2 is represented by N. cumminsiana from Asteraceae. This group also includes Oidium baccharidis, O. maquii, and Oidium spp. from Galinsoga (Asteraceae) and Aloysia (Verbenaceae), and is further divided into four subgroups. N. galeopsidis is distributed worldwide, but is especially common in western Eurasia from Central Asia to Europe. N. galii is also common in western Eurasia. In contrast, the specimens of group 2 were all collected in the New World, except for one specimen that was collected in Japan; this may indicate a close relationship of group 2 with the New World. Molecular clock calibration demonstrated that Neoerysiphe split from other genera of the Erysiphaceae ca 35-45M years ago (Mya), and that the three groups of Neoerysiphe diverged between 10 and 15Mya, in the Miocene. Aloysia citriodora is a new host for the Erysiphaceae and the fungus on this plant is described as O. aloysiae sp. nov.

Enanismo y podredumbre basal de eustoma grandiflorum y su relación con la densidad de fusarium solani en el suelo

Fusarium solani was recorded in 100% of the commercial crops of lisianthus (Eustoma grandiflorum) located around La Plata (Argentina). The pathogen causes stunt and basal rot. A trial was carried out to analyse the F. solani soil density and its relation to the development of both diseases. Soil samples were analysed at three times: before transplant (October), at the beginning of flowering (January) and at the ending of flowering (March) of flowering. The incidence of each disease was evaluated in January and March, and the plants harvested were quantified. The soil density of F. solani was not altered during the three times for each treatment, and fumigants and steam decrease it significantly. In January the stunt incidence reached 0 to 9.5% with the fumigants and 31.4% with the steam treatment. In the control and fungicide plots, the incidence reached 87.9 to 100%, and a consequent reduction of flower production was observed. Stem rot began after the flowers were harvested as a result of pathogen entry through the wounds. The major values of harvested plants were obtained with fumigants (90.7 to 99%) and steam (76.8%), so the greatest stem rot incidence was 15.7 to 22.2 and 10.1%, respectively, in March, and the productive period was shortened. The need of reducing F. solani soil density before lisianthus transplant is emphasized. Among soil control treatments, Metham sodium and Dazomet could be effective substitutes for Methil bromide followed by steam treatment.

First Confirmed Report of Powdery Mildew Caused by Erysiphe aquilegiae on Casuarina cunninghamiana in Argentina

Casuarina cunninghamiana Miq. (Fam. Casuarinaceae) is native toAustralia and was introduced to Argentina and used as a windbreak,shade tree and for ornamental purposes. In autumn 2009, the pottedseedlings in the nursery of La Plata University were found to beinfected with a powdery mildew. Symptoms first appeared as thinwhite colonies, which subsequently developed into an abundantgrowth on the leavesand y oung stems (Fig. 1A)The . damage causedby the powdery mildew infection has been observed every year afterthis initial infection and was again confirmed in April, 2011. Therehave been a few reports on the presence of powdery mildew onCasuarina spp. (Mantz et al., 2008; Farr and Rossman, 2011). In allthe reports, the pathogen was cited to be Oidium sp. Thus, the aim ofthis work was to identify the causal agent of the powdery mildewobserved on casuarina in Argentina. A detailed microscopic examination of a representative sample(KUS-F24744) deposited in Korea University was made to identifythe pathogen. Conidiophores were cylindrical, 70–145 × 6–8.5 µm,moderately flexuous to straight in foot-cells and produced conidiasingly, followed by 2–3 cells (Fig. 1B–D). Appressoria weremultilobed or moderately lobed (Fig. 1J). Conidia were oblong-elliptical, 28–54 × 11–18 µm, without conspicuous fibrosin bodiesand produced germ tubes in the perihilar position (Fig. 1F–I). First-formed conidia (Fig. 1E) were apically conical, basally subtruncate,and generally smaller than the secondary conidia. No chasmotheciawere found but the above characteristics were consistent with theconidial state of Erysiphe aquilegiae DC. (Braun, 1987; Liberatoand Cunnington, 2006). To confirm the identity of the causal fungus, the complete internaltranscribed spacer (ITS) region of rDNA from KUS-F24744 wasamplified using primers ITS5 and P3, and then directly sequenced.The resulting sequence of 553 bp was deposited in GenBank(Accession No. JN003594). Phylogenetic analysis was performedusing MEGA4 with the neighbor-joining method and the Tajima-Nei distance calculation. A comparison with the sequencesavailable in the GenBank database revealed that the ITS sequenceshared over 99% (552/553 bp) similarity with those of E. aquilegiaeon several host genera of the Ranunculaceae (Fig. 2). Therefore, thesequence analysis verified that the pathogen was E. aquilegiae.Powdery mildew caused by E. aquilegiae has been shown tooccur on plants belonging to the Ranunculaceae with one exception(Farr and Rossman, 2011). Catharanthus roseus (L.) G. Don, whichbelongs to the Apocynaceae, was found to be naturally infected byE aquil. egiae as demonstrated by morphological and moleculardata (Liberato and Cunnington, 2006). To the best of our knowledge, thisis the second report where E. aquilegiae was found on a host outsideof the Ranunculaceae. An occurrence of powdery mildew diseaseon this tree was previously recorded in Argentina; however, in thatstudy, the causal fungus was not identified (Mantz et al., 2008).Their description of the causal fungus was actually identical to thecharacteristics reported here. Therefore, we believe that their funguswas also E. aquilegiae .

Phytophthora nicotianae causing root and stem rot on Dieffenbachia picta in Argentina

Dieffenbachia picta is a worldwide appreciated crop due to its ornamental value. In Argentina it is cultivated in warm provinces and in the outskirts of Buenos Aires city, where in spring 2007 a great amount of plants were lost in commercial greenhouses. Symptoms such as wilting and soaked lesions in the basal leaves began in four- to six-month-old plants causing plants to wilt due to basal stem and root rot processes. A Peronosporomycete was consistently isolated from diseased tissues. The pathogen was identified as Phytophthora nicotianae based on cultural characteristics, morphology of vegetative and reproductive structures, and on the analysis of the sequence of the nuclear ribosomal internal transcribed spacer (ITS) region. Pathogenicity tests were carried out and Koch’s postulates were fulfilled. In complementary studies, the dieffenbachia varieties Alex, Compact, Camilla and Marianne were susceptible to the infection caused by P. nicotianae, whereas Tropic snow (D. amonea) was resistant. This is the first report of P. nicotianae causing stem and root rot of D. picta in Argentina and in the Americas.

Basal rot of Chamelaucium uncinatum caused by Phytophthora nicotianae in Argentina

Since 1995 severe losses were recorded on the production of Chamelaucium uncinatum in the vicinity of La Plata. In 2010, with the aim to confirm the identity of the causal agent of Geraldton waxplant basal rot, molecular studies were added to the morphological observations of the pathogen. P. nicotianae was identified as the causal agent of the disease.

First Report of Septoria centellae Associated with Leaf Spot of Centella asiatica in Korea

Septoria centellae associated with leaf spot of Centella asiatica is reported for the first time in Korea. The fungus is described and illustrated in detail. It is also compared with related species of Septoria present on Centella and Hydrocotyle spp. with taxonomic comments. Two monoconidial isolates from Jeju and Wando were successfully cultured and have been deposited in the Korean Agricultural Culture Collection.