First Report of Binucleate Rhizoctonia AG-L Causing Root and Stem Rot of Wishbone Flower (Torenia fournieri) in Taiwan

Wishbone flower (Torenia fournieri L.) is a common ornamental plant for flower bed in Taiwan. In August 2018, root and stem rot of wishbone flower occurred on the flower bed in the campus of National Chung Hsing University, Taichung city, with 100% incidence. Symptoms were dark brown discoloration of basal stems and brown necrosis of roots. Lesions from base of stems were excised into 5 mm long fragments, which were then surface sterilized in 1% sodium hydrochloride for 1 min, rinsed in sterile distilled water, dried on filter paper and thereafter placed onto 2% water agar. After 24 h, hyphae characteristic of Rhizoctonia (Sneh et al. 1991) appeared and dominated in every isolation. Hyphal tips were transferred to potato dextrose agar (PDA). After 5 days of incubation at 28°C, characteristic brown colonies of Rhizoctonia (Sneh et al. 1991) were observed. Hyphal width was 4.29±0.52 μm. No sclerotia were visibly present after 21 days of growth on PDA at 28°C. Hyphae were stained by 0.3% safranin-O and 1% KOH. There were two nuclei in each hyphal compartment, suggesting a binucleate Rhizoctonia fungus. ITS sequence has been used as the best tool to identify specific anastomosis group (AG) of Rhizoctonia as shown by Sharon et al. (2006, 2008). ITS sequence was amplified using the primers Bd1a and ITS4 (Goka et al. 2009; White et al. 1990). Blast search analysis of this acquired sequence (acc. no. LC498494) revealed the highest similarity (98.75 to 99.83%) with the reference sequences (acc. nos. AB286934, AB286933, and AB196653) of binucleate Rhizoctonia AG-L, namely Ceratobasidium sp. AG-L. Pathogenicity test was carried out using seedlings of 4-week-old wishbone flower each grown in a pot of 6.35 cm diameter. To prepare the inoculum, a PDA agar block (6 mm in diameter) excised from the growing front of 5-day-old colony was transferred into a flask with 200 ml of potato dextrose broth (PDB) incubated in a shaker at 26°C and 120 rpm for 6 days. The PDB broth was then blended into slurry. Ten pots each with a seedling were inoculated by pouring 50 ml of slurry onto the potting medium. Five pots were served as the controls by pouring PDB only. Pots were maintained in a greenhouse (26 to 33°C). Three days after inoculation, all inoculated plants exhibited symptom of root and stem rot. The same fungus was reisolated and confirmed by sequencing rDNA-ITS. This is the first report of root and stem rot of wishbone flower caused by binucleate Rhizoctonia AG-L in Taiwan and in the world. Although this is the second cases, since Wang and Hsieh (1993), for binucleate Rhizoctonia AG-L to be pathogenic, this study shows that this fungus has the potential to cause damages and is worth of further investigations.

Can Biological Control Agents Reduce Multiple Fungal Infections Causing Decline of Milkwort in Ornamental Nursery?

This research evaluates biological control agents (BCAs) and fungicide alone and in combination for the management of decline caused by multiple fungi on milkwort (Polygala myrtifolia). Four experiments were performed in a greenhouse within a nursery located in Catania province (southern Italy). The activity of fungicides and biological control agents was evaluated by calculating the plant mortality (%) and recovery frequency (%) of different fungi associated with symptomatic tissue. Comprehensively, boscalid + pyraclostrobin and fosetyl-Al showed the best results in managing disease complex on milkwort. Biological control agents provided, on average, the lowest performances; nevertheless, in most cases, they were able to significantly reduce multiple infections and sometimes when combined with fungicide enhanced the effectiveness. The molecular analysis of 86 isolates obtained from symptomatic tissue allowed to identify the fungi involved in the disease as Calonectriapauciramosa, C. pseudomexicana, Fusariumoxysporum, Neocosmospora solani (syn. F. solani) and binucleate Rhizoctonia AG-R. Calonectriapseudomexicana never reported on milkwort and in Europe was inoculated on P. myrtifolia potted healthy cuttings and produced crown and root rot after 40 days. Our findings represent the first worldwide report about disease complex of milkwort caused by several fungi (Calonectria spp., Fusarium spp. and binucleate Rhizoctonia) and on the effects of integrated control strategies to manage this disease in the nursery.

Short Communication: Characterization of Rhizoctonia-like mycorrhizae associated with five Dendrobium species in Java, Indonesia

Soelistijono R, Utami DS, Daryanti, Faizin M, Dian R. 2020. Plankton biodiversity in various typologies of inundation in Paminggir swamp, South Kalimantan, Indonesia on dry season. Biodiversitas 21: 1007-1011. This study aims to determine the morphological and anatomical characteristics of Rhizoctonia-like mycorrhizae associated with the roots of five Dendrobium species; to determine the association between Rhizoctonia-like mycorrhizae with the root of five Dendrobium sp.; to obtain difference between Rhizoctonia-like mycorrhizae with the other in adjacent location Mycorrhizal observations of Rhizoctonia-like mycorrhizae in this study were carried out macroscopically (morphologically) and microscopically (anatomically). The macroscopic observation was performed by observing directly the development of fungal colonies on culture media. Microscopic observations were performed to determine the shape of the hyphal of fungi and the number of nuclei. The results showed that the Rhizoctonia-like mycorrhizae associated with the root of five species of Dendrobium sp. in Java were the binucleate Rhizoctonia groups (BNR). The binucleate Rhizoctonia has white colonies, right-angle branching hyphae, two nuclei, and brown hyphae. The association of the root of five species of Dendrobium sp.with Rhizoctonia-like mycorrhizae fungi was indicated by the existence of a peloton structure in cortical root tissue.