Omnipresence of Partitiviruses in Rice Aggregate Sheath Spot Symptom-Associated Fungal Isolates from Paddies in Thailand

Partitiviruses are one of the most prevalent double-stranded RNA viruses that have been identified mostly in filamentous fungi and plants. Partitiviruses generally infect host fungi asymptomatically but infrequently exert significant effect(s) on morphology and virulence, thus being considered a potential source of biological control agents against pathogenic fungi. In this study, we performed a screening for mycoviruses of a collection of Thai isolates of rice fungal pathogen Rhizoctonia oryzae-sativae, a causal agent of rice aggregated sheath spot disease. As a result, 36% of tested isolates carried potentially viral double-stranded RNAs with sizes ranging from 2 to 3 kbp. By conventional cDNA library construction and RNA-seq, we determined six new alphapartitiviruses that infected three isolates: tentatively named Rhizoctonia oryzae-sativae partitivirus 1 to 6 (RosPV1-6). Furthermore, RT-PCR detection of each virus revealed their omnipresent nature in different R. oryzae-sativae isolates. Although virus-curing of basidiomycetous fungi is generally difficult, our repeated attempts successfully obtained virus-free (for RosPV1, RosPV2, and uncharacterized partitiviruses), isogenic strain of R. oryzae-sativae TSS190442. The virus-cured strain showed slightly faster colony growth on the synthetic media and severe symptom development on the rice sheath compared to its virus-infected counterpart. Overall, this study shed light on the distribution of partitiviruses in R. oryzae-sativae in a paddy environment and exemplified a virus-curing protocol that may be applicable for other basidiomycetous fungi.

Phytotoxin of Rice Aggregate Sheath Spot Pathogen Rhizoctonia oryzae-sativae and Its Biological Activities

Rice aggregate sheath spot disease occurs in many countries, causing serious yield losses. In China, the disease-causing fungus Rhizoctonia oryzae-sativae was reported in 1985, and since then, it has rarely been reported in major rice-growing areas after almost 30 years. Compared with Rhizoctonia solani, R. oryzae-sativae has a significantly different physiological morphology and growth status, although both fungi affect rice leaves in very similar ways. The optimum temperature for the suitable growth of R. oryzae-sativae is 31 °C, which is consistent with previous reports. We extracted phytotoxins from R. oryzae-sativae and analyzed its biological activity via the detached leaf and radicle inhibition methods. Rhizoctonia solani and R. oryzae-sativae exhibit differences in terms of pathogenicity and toxins activity, which indicates that these fungi may produce different toxins components. Based on gas chromatography–mass spectrometry data, esters, phenols, and other components were present in the crude toxins extract of R. oryzae-sativae. Our research provides a new method for studying the phytotoxins of R. oryzae-sativae. However, further studies are needed to elucidate the pathogenic mechanisms responsible for the aggregate sheath spot disease on rice.

Ekstrak Metanol Daun Binahong (Anredera cordifolia) Menekan Pertumbuhan Koloni Jamur Rhizoctonia oryzae dan Kejadian Penyakit Hawar Bibit Padi

Penyakit bercak pelepah yang disebabkan oleh Rhizoctonia oryzae merupakan salah satu penyakit penting pada tanaman padi. Penyakit ini umumnya dikendalikan dengan menggunakan fungisida sintetik meskipun pengendalian cara ini dipercaya dapat memberikan efek negatif terhadap lingkungan dan kesehatan manusia. Dalam upaya pengembangan pengendalian penyakit tanaman yang lebih ramah lingkungan, pemanfaatan bahan-bahan alami seperti tumbuhan sebagai pestisida nabati telah mendapat banyak perhatian pada saat ini. Tanaman binahong (Anredera cordifolia) telah banyak digunakan sebagai obat tradisional terutama di bidang kesehatan manusia. Penelitian ini bertujuan untuk menguji keefektifan ekstrak metanol daun binahong dalam menekan pertumbuhan koloni jamur R. oryzae serta menekan perkembangan penyakit hawar bibit pada benih padi akibat infeksi R. oryzae. Percobaan dilakukan di Laboratorium Bioteknologi, Departemen Hama dan Penyakit Tumbuhan, Fakultas Pertanian, Universitas Padjadjaran. Metode penelitian menggunakan Rancangan Acak Lengkap (RAL). Pengujian penghambatan pertumbuhan koloni jamur R. oryzae dilakukan menggunakan teknik poisoned food dengan 7 perlakuan yaitu 5 konsentrasi ekstrak 0,25%, 0,5%, 1%, 1,5%, dan 2%, serta perlakuan kontrol akuades steril dan fungisida propineb 0,3% yang diulang 4 kali. Pengujian pada benih dilakukan dengan 4 perlakuan dan 5 ulangan yang masing-masing terdiri atas 25 benih padi menggunakan teknik perendaman. Hasil pengujian menunjukkan ekstrak metanol daun binahong 2% mampu menghambat pertumbuhan koloni dan pembentukan sklerotia jamur R. oryzae serta mampu menekan kejadian penyakit akibat infeksi R. oryzae pada bibit padi dengan penekanan tertinggi sebesar 46,2%.

Pengaruh senyawa volatil yang dihasilkan bakteri endofit asal padi terhadap Rhizoctonia oryzae dan Cercospora oryzae

Penggunaan fungisida dalam mengendalikan penyakit pada tanaman telah banyak dilaporkan menimbulkan dampak negatif terutama terhadap lingkungan. Oleh karena itu diperlukan alternatif pengendalian lain yang lebih ramah lingkungan. Bakteri endofit telah banyak dimanfaatkan sebagai agens biokontrol pada berbagai penyakit tanaman karena dikenal sebagai sumber penghasil senyawa-senyawa yang bersifat antifungal. Laboratorium Bioteknologi Proteksi Tanaman Fakultas Pertanian Universitas Padjadjaran memiliki koleksi beberapa bakteri endofit hasil isolasi asal tanaman padi yang masih dalam tahap pengujian. Penelitian ini dilakukan dengan tujuan untuk mengetahui potensi antijamur dari senyawa volatil yang dihasilkan oleh bakteri endofit dalam menekan pertumbuhan jamur Rhizoctonia oryzae penyebab penyakit bercak pelepah daun dan jamur Cercospora oryzae penyebab penyakit bercak daun secara in vitro. Percobaan dilakukan dengan metode dual culture dengan menggabungkan dua cawan dimana isolat bakteri endofit dan jamur patogen ditumbuhkan secara terpisah. Hasil pengujian menunjukkan bahwa isolat bakteri endofit Os1 dan Os2 memiliki kemampuan terbaik dalam menghambat patogen R. oryzae dengan persentase penghambatan pertumbuhan masing-masing sebesar 68,7% dan 65,4%. Sedangkan isolat bakteri endofit Os3 adalah isolat bakteri endofit yang mempunyai kemampuan terbaik dalam menghambat perkembangan patogen C. oryzae dengan persentase penghambatan sebesar 87,1%. Pengamatan mikroskopis memperlihatkan bahwa senyawa volatil yang dikeluarkan oleh isolat-isolat bakteri endofit tersebut dapat menyebabkan terjadinya malformasi pada miselia jamur R. oryzae dan C. oryzae.

Morphological and Molecular characterization of rhizoctonia oryzae sativae in Bangladesh

Aggregate sheath spot disease of rice caused by Rhizoctonia oryzaesativae has emerged in higher incidence in North-Western region of Bangladesh. Thirty isolates of R. oryzae-sativae were studied by using morphological and molecular marker. Isolates were confirmed using specific primer where a single band of 1200bp was amplified. Two distinct groups relatively slow and faster were found in mycelal growth. Molecular characterization was done using four primers and DNA band ranged from 0.25 to 2.21 kb. A combined dendrogram was constructed which separated the isolates into three groups at 69.6% similarity level. All isolates placed in two major clusters except isolate RA-1 placed in cluster group III but were not grouped according to their geographic origins. Fast growing isolates have been placed in Group II while slow growing isolates in cluster group I. The similarity coefficient values of the dendrogram profile ranged from 0.36 to 0.98 with an average of 0.67. Diversity of different isolate showed that significant variation was present among the isolate and were not genetically identical. SAARC J. Agri., 16(2): 119-128 (2018)

Seed germination and development of orchid seedlings (Cyrtopodium saintlegerianum) with fungi

Fungi of Rhizoctonia complex are mycorrhizal of orchids and may to germinate yours seeds and development the seedlings. In this context, our objective was to select a fungal isolate to promote seed germination and seedling development of Cyrtopodium saintlegerianum. Pelotons were found in the roots and three mycorrhizal fungi were isolated. We tested mycorrhizal isolates obtained from C. saintlegerianum roots and six mycorrhizal fungi from other orchids as well three pathogenic isolates (of rice and bean) to germinate the seeds in oatmeal-agar medium. Seeds not inoculated were used as control. The isolates En07 (Waitea circinata), Cs10 (Tulasnella sp.) and Ro88 (Rhizoctonia oryzae) were efficient to promote seed germination, but only En07 differing statistically of the control. The non-specific isolate En07 promoted germination in 81% of seeds and the specific isolate (Cs10) promoted 60%, evidencing the non-specificity mycorrhizal association in this orchid during germination. Axenic seedlings were inoculated with four mycorrhizal fungi (non-inoculated seedlings - control). After six months, the isolates En07 and Cs10 were efficient in the interaction with the seedlings, but did not differ to the control. Therefore, our results suggested that fungi of the Rhizoctonia complex can be used in the germination and seedling development of C. saintlegerianum.

Adaptabilidade e danos potenciais de Rhizoctonia oryzae-sativae ao milho

RESUMO Espécies do gênero Rhizoctonia estão associadas ao complexo de manchas da bainha do arroz, sendo que R. oryzae-sativae, em particular, causa a mancha agregada da bainha. Neste estudo objetivou-se determinar o potencial adaptativo de duas populações de Rhizoctonia oryzae-sativae à cultura do milho, uma das culturas comerciais amplamente cultivadas no estado de São Paulo e que pode ser utilizada em rotação com o arroz irrigado. Não há relatos da doença em milho no Brasil. Foram inoculados, em plantas de milho, isolados de duas populações de R. oryzae-sativae e determinou-se componentes de evolucionabilidade ou do potencial adaptativo de uma população (i.e., medidas de resposta à seleção) como os coeficientes de variância genotípica (IG), variância ambiental (IE) e a herdabilidade (h2) para os níveis de agressividade da doença. Comparou-se também a diferenciação fenotípica por caracteres quantitativos (QST) e a diferenciação genética neutra (baseada em dados de microssatélites) nas duas populações (FST). Experimentos similares usando plantas de arroz inoculadas com as duas populações do patógeno foram conduzidos como controle. Os isolados das populações de R. oryzae-sativae foram patogênicos e apresentaram variação na agressividade ao milho, com predominância de baixa herdabilidade para este atributo. Os valores estimados de QST não diferiram significativamente de FST indicando que a neutralidade teve importante papel na adaptação regional de populações do patógeno.