Judul: Characterization of weak isolates of Chili veinal mottle virus and its potency as agents for cross protection
Abstrak: Chili veinal mottle virus (ChiVMV) is considered as an important factors for production of chili pepper in Indonesia. Disease control strategies have been evaluated previously involving resistant cultivars, insecticide application, and several cultural practices. Cross protection approach has been implemented for many plant viruses, therefore it is interesting to evaluate its effectiveness for controlling ChiVMV. Cross protection in plant viral disease is known as the phenomenon where the plants systematically infected with one strain of a virus are protected from infection by a second related strain of the same virus. The objectives of this research are: (i) to obtain weak isolates of ChiVMV; (ii) to study host range of weak isolates of ChiVMV; (iii) to study interaction between weak isolates and severe isolate of ChiVMV; (iv) to study ability of weak isolates in cross protection; (v) to determine molecular character of potential weak isolates of ChiVMV. Weak isolates of ChiVMV was obtained from chili pepper fields in West Sumatera, Jambi, and West Java. Field isolates were selected using biological assays : (1) Isolates of ChiVMV were transmitted mechanically to chili pepper genotipe IPB C13 to screen isolates that could infect the plants without showing any symptoms. (2) The selected isolates were used in next experiment, i.e. to evaluate their host range involving 8 chili pepper genotipes and 11 plant species in the family Solanaceae. (3) Based on the second experiment the selected isolates were used in further experiments, i.e. to evaluate the interaction between weak isolates and severe isolate of ChiVMV. The presence of ChiVMV was confirmed through DAS-ELISA, DIBA, or TBIA. Finally, molecular characterization of weak isolates was done by sequencing the coat protein gene . Out of 223 field samples, 30 samples were positively reacted in DASELISA with only ChiVMV antibody. Based on the response on chili pepper genotype IPB C13, ChiVMV isolates can be differentiated into weak isolates (16 samples), mild isolates (2 samples), and severe isolates (3 samples). Based on host range study, 8 isolates out of 16 weak isolates were selected for further evaluation. These isolates were able to cause systemic infection without showing visible symptom in Capsicum annuum (IPB C2, IPB C13, IPB C120, Laris, IPB C8, Bara, California Wonder, and Yolo Wonder), C. frutescens, Datura metel, D. stramonium, Lycopersicon esculentum, Physalis floridana, Solanum melongena, and S. nigrum. Strong interference interaction was obtained between severe isolate ChiVMV-CKB and 5 weak isolates. Inoculation of weak isolates one week prior inoculation of severe isolate were able to reduce disease severity up to 97.23%, weak isolates could delay symptoms development and reduce symptom intensity of severe isolate. Five weak isolates of ChiVMV (KAR, SPR, SKT, CSR, dan PGL) were effectively protected chili pepper from severe isolate ChiVMV-CKB. Plants inoculated with weak isolates before inoculated with severe isolates, showed no symptoms up to 110 days after inoculation with severe isolate and had no detrimental effects on yield and quality of chili pepper On the other hand, all plants inoculated with only severe isolate ChiVMV-CKB showed severe symptoms, i.e. dark green mottle, malformation, shoestring, stunting, and low yield (average fruit 0.32
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