VIRUS NILAM: IDENTIFIKASI, KARAKTER BIOLOGI DAN FISIK, SERTA UPAYA PENGENDALIANNYA

Infeksi virus pada tanaman nilam dapat menyebabkan penurunan produksi dan kualitas minyak. Sembilan jenis virus diidentifikasi menginfeksi tanaman nilam, yaitu Patchouli mosaic virus (PatMoV), Patchouli mild mosaic virus (PatMMV), Telosma mosaic virus (TeMV), Peanut stripe virus (PStV), Patchouli yellow mosaic virus (PatYMV), Tobacco necrosis virus (TNV), Broad bean wilt virus 2 (BBWV2), Cucumber mosaic virus (CMV), dan Cymbidium mosaic virus (CymMV). Kesembilan virus tersebut memiliki genom RNA, tetapi panjang dan bentuk partikelnya berbeda. Deteksi dan identifikasi berdasarkan bagian partikel virus dapat dilakukan secara serologi dengan teknik ELISA dan secara molekuler dengan RT-PCR. Gejala awal tanaman nilam terserang virus yaitu mosaik atau belang pada daun pucuk dan pada gejala berat tanaman menjadi kerdil. Infeksi virus dapat bersifat tunggal, tetapi ada pula infeksi oleh beberapa virus. Virus menular secara mekanis dan sebagian melalui penyambungan dan vektor. TNV, BBWV2, dan CMV memiliki kisaran inang yang luas, sedangkan virus yang lain inangnya terbatas. Virus nilam umumnya memiliki titik panas inaktivasi dan titik batas pengenceran yang tinggi, sedangkan ketahanan in vitro tidak stabil. Pendekatan terbaik pengendalian virus ialah menggunakan bahan tanaman bebas virus atau tahan virus dan pengendalian vektor. Tanaman bebas virus dapat diperoleh melalui kultur meristem, sedangkan pengendalian vektor dapat menggunakan pestisida nabati atau kimia.

First Report of Bean common mosaic virus Infecting Mungbean (Vigna radiata) in China

Bean common mosaic virus (BCMV) is a member of the genus Potyvirus and one of the numerous viruses that can infect Phaseolus vulgaris. In May of 2013, we planted more than 100 varieties of mungbean in fields and a greenhouse of Nanjing. Mungbean (Vigna radiata (Linn.) Wilczek.) with leaves displaying mosaic and shrinkage typical of viral infection was observed in a greenhouse and a field in Nanjing. About 60% of the varieties can be infected. The symptoms in some sources from Southeast Asian countries and wild germplasm are heavier, while the symptoms are lighter on the local varieties. It can be transmitted to mungbean via aphid or mechanical inoculation, or by seeds. The infected leaves were collected for electron micrograph analysis. Pinwheel inclusion and filamentous virus particles were observed, indicating a Potyvirus infection. To confirm the presence of Potyvirus infection, total RNA was extracted from plants from the greenhouse and field, and RT-PCR was performed using universal Potyvirus primers (Sprimer (+) 5′-GGXAAYAAYAGYGGXCAZCC-3′; X=A, G, C or T, Y=T or C, Z=A or G); M4T (5′-GTTTTCCCAGTCACGAC(T)-3′), which amplify a region of the 3′ fragment of the RNA-dependent RNA polymerase of potyviruses (1). The 596-bp sequence was found to be 95% identical to the BCMV isolate HB (GenBank Accession No. KC478389.1). To confirm the presence of BCMV, three leaf samples were randomly collected and all were determined to be positive when subjected to ELISA using BCMV-specific antibodies. The virus infecting mungbean was identified as BCMV and the strain was named BCMV-JAAS (KJ866945). Using gene-specific primers (BCMV-cp-F: 5′-CAAAAGGACAAGGATTGAGGA, BCMV-cp-R: 3′-ACAACAAACATTGCCGTAGC) for the reported coat protein gene in BCMV, a 1,080-bp gene fragment was amplified from the total RNA of the isolate, and subsequent sequence analysis indicated that an 862-bp region contained the complete cp gene that encodes a 228 amino acid protein. The nucleotide sequences of the cp gene from the isolate shared 96% homology with the reported BCMV-HB. The phylogenetic trees based on the CP gene show that BCMV-JAAS (KJ866945) was most closely related to other Chinese BCMV isolates (KF439722.1 and AJ132145.1) followed by Azuki mosaic virus (AB012663.1) and Peanut stripe virus (U34972.1). These results indicate that the virus associated with the mosaic disease in mungbean is an isolate of BCMV. To our knowledge, this is the first report of BCMV infecting mungbean in China. BCMV affects a wide range of legume crops and can spread rapidly, causing serious harm. The discovery could effectively control BCMV and characterize the prevalent BCMV strains. Research utilizing whole-genome sequencing of the mungbean isolate is continuing and is currently being expanded to characterize the genetic diversity of the virus, assisting in the study of the evolution of the virus. Reference: (1) J. Chen and J. P. Chen. Chin. J. Virol. 18:372, 2002.

PYRAMIDING IMPORTANT DISEASE-RESISTANT CHARACTERS BY HYBRIDIZATION OF TRANSGENIC AND NON-TRANSGENIC PEANUTS (ARACHIS HYPOGAEA L.)

We have produced transgenic peanut lines carrying a coat protein gene of peanut stripe virus (PStV) and showing resistance to the virus. However, their susceptibility to leafspot disease caused by Cercospora sp. and their lower productivity compared to their genetic background cultivar make them commercially less undesireable. The objective of this research was to test whether crossing the transgenic peanut plants with a non-transgenic peanut line WS, which was resistant to leafspot disease and high-yielding, could produce progenies in F2 generation that were resistant to both PStV and leafspot disease as well as of higher yield campared to their transgenic progenitor. If this test was proven, pyramiding novel transgenic and non-transgenic characters in peanut plants by hybridization would probably be a routine procedure in the future. Crosses were made between transgenic peanut plants that were resistant to PStV and non-transgenic peanut line WS. F2 population was evaluated for resistance to PStV and leafspot disease. Number of filled pods, filled pod dry weight per plant, and dry weight of each pod were measured. Result of the experiment showed that some of the plants in F2 population exhibited resistant both to PStV and leafspot disease and produced higher number of filled pods, filled pod dry weight per plant, and dry weight of each pod compared to those produced by their transgenic parent plants.

Occurrence, Prevalence, and Distribution of Viruses Infecting Peanut in Argentina

This is the first survey to determine the occurrence, prevalence, and distribution of peanut (Arachis hypogaea) viral diseases in Argentina. It was conducted in the province of Córdoba, which has 92% of the country's peanut production. It included the main peanut viruses Peanut mottle virus (PeMoV), Peanut stripe virus (PStV), Cucumber mosaic virus (CMV), Peanut stunt virus (PSV), Tomato spotted wilt virus (TSWV), and Groundnut ringspot virus (GRSV). Leaf samples from 1,028 individual peanut plants with virus-like symptoms and 986 samples from asymptomatic plants were collected in six counties of Córdoba over 3 years and serologically tested for the presence of viruses. PeMoV was the most frequently detected virus, found in 58.8, 34.2, and 23.4% of samples from the 2003–04, 2004–05, and 2005–06 growing seasons, respectively, and it was found in all sampled counties. Also, it was the only virus detected in asymptomatic plants. Less than 4% of symptomatic plants were infected with CMV or GRSV; 0.5, 3.6, and 2% of samples were positive for CMV; and 0.5, 3.1, and 1.6% were positive for GRSV in the 2003–04, 2004–05 and 2005–06 seasons, respectively. Some mixed infections were found: CMV-PeMoV and GRSV-PeMoV. During this survey, PSV, PStV, and TSWV were not detected in any peanut samples.