Diversity, Host Range and Transmission Efficiency of Bean common mosaic virus by Aphids on Yard Long Beans

Abstract

Bean common mosaic virus (BCMV) is one of the important viruses infecting yard long beans. Severe yellow mosaic symptoms different from common symptoms of BCMV was observed in 2008 in several yard long bean growing areas in West Java and Central Java found. This severe yellow mosaic symptom is caused by Bean common mosaic virus Blackeye Cowpea strain (BCMV-BlC) or double infection of BCMV-BlC and Cucumber mosaic virus (CMV). Information on characters of BCMV-BlC on yard long beans in Indonesia is very limited, despite its importance for the determination of virus control strategy. Therefore this study aims to determine the diversity, host range and transmission efficiency of BCMV-BlC using 3 aphid species . Leaf samples showing yellow mosaic symptoms were taken from yard long bean plants in 3 villages in Dramaga, Bogor, West Java i.e. Bubulak, Cangkurawok, and Situgede and 10 leaf samples from several areas in West Java [Bogor (Bojong), Subang, Indramayu and Cirebon], and Central Java (Tegal, Klaten, Solo, Magelang, Sleman, and Jogjakarta) collection of Plant Virology Laboratory, Department of Plant Protection, Faculty of Agriculture, IPB. Leaf samples were detected by serological using antiserum of BCMV and molecular method using specific primer for BCMV coat protein (CP). Amplified DNA products was then used for nucleotide sequencing followed by sequence allignment and phylogenetic tree analysis. Limited host range study and transmission of BCMV-BlC using three species of aphids was done for BCMV-BlC Cangkurawok isolates. BCMV-BlC isolated by inoculation on indicator plants Chenopodium amaranticolor. Local lesions (LL) were taken and inoculated serially to C. amaranticolor for 3 times to purify the virus. Finally, LL was inoculated on bean cultivar Parade and used as sources of inoculum for further test. A host range study was conducted by inoculating BCMV-BlC mechanically using 18 plant species from 3 families. Transmission efficiency test was done using 3 aphid species i.e. Aphis craccivora Koch, A. gossypii Glover and A. glycines Matsumura with treatment of aphids numbers (1, 3, 5, 7 and 10). Both host range and transmission efficiency studies was conduxted using 15 plants per treatment. Parameter for both studies includes incubation period, type of symptoms and disease incidence. In addition to visual observation, infection of BCMV-BlC on test plants was confirmed by using Dot Immunobinding Assay (DIBA). Based on field observations, the symptoms can be differentiated into 2 groups. The first group consist of those symptoms showing mosaic with light green to bright yellow unevenly (heavy yellow mosaic), vein banding, malformation of leaves (leaf curl like crackers, pucker along the veins), leaf blister, and stunted growth. The second group are those symptoms showing mosaic pattern of light green to yellow (medium yellow mosaic) and vein banding. Molecular detection by RT-PCR are successfully amplified ~861 bp viral DNA from 8 out of 13 BCMV isolates. DNA analysis was able to allign sequence of BCMV collected from Cangkurawok, Cirebon, Subang, Tegal, Solo and Sleman, but was unable to allign the sequence of BCMV isolates from Bubulak and Bojong. Further analysis showed that 4 BCMV isolates (Cangkurawok, Subang, Solo and Sleman) has the highest homology to BCMV-BlC from Taiwan, while 2 isolates (Cirebon and Tegal) has the highest homology to BCMV-NL1 from UK. Phyllogenetic analysis based on nucleotide and amino acid sequences showed that 4 isolates (Cangkurawok, Subang, Solo, and Sleman) were closely related to BCMV-BlC infected yard long bean from Taiwan. Two isolates (Cirebon and Tegal) were closely related to BCMV-NL1 that infects beans from UK based on nucleotide sequences, but they were closely related to BCMV-BlC Y that infects beans from China. Host range study showed that BCMV-BlC was able to infect yard long bean (Vigna sinensis) cultivars Parade, 777, Pangeran, New Jeliteng and Katrina , cowpea (Vigna unguiculata) and mungbean (Vigna radiata). However, BCMV-BlC was unable to infect pea (Pisum sativum), soybean (Glycine max), French bean (Phaseolus vulgaris), peanut (Arachis hypogaea), cucumber (Cucumis sativus), hot pepper (Capsicum annuum), tomato (Lycopersicon esculentum), tobacco (Nicotiana tabacum cv. White Burley, and N. glutinosa). This host range study suggested that BMCV-BlC was limitedly infect Vigna spp. Transmission study using 3 aphid species showed that A. craccivora, A. gossypii and A. glycines were able to transmit BCMV-BlC. Among the three aphid species A. craccivora is considered as the most efficient vector for BCMV-BlC. Single A. craccivora was capable to transmit the virus with the highest incidence (53%) compared to A. gossypii and A. glycines. Transmission efficiency reached 100% using 10 aphids. In general, the more aphids, the higher the efficiency of transmission and the more severe the symptoms. In addition, transmission using different species caused variations of symptoms.