Karakterisasi chili veinal mottle virus strain lemah dan potensinya sebagai agens proteksi silang

Abstract

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 to 7.33 per plant with average weight of 0.53 to 13.01 g per fruit). Inoculation only with severe isolate ChiVMV-CKB caused disease severity 0% to 98.61% at 28 days and increased to 55.55% to 100% at 112 days. Inoculation with weak isolate prior severe isolate was able to protect the plants from severe isolate, showed by no infection at 28 days and disease severity reached only 1.38% to 8.33% at 112 days. Inoculation with weak isolates 14 days prior inoculation with severe isolate showed no significant effect on yield, except weak isolate ChiVMV-KAR. Molecular characterization of ChiVMV isolates was conducted based on analysis of their coat protein gene. Fragment of coat protein gene (900 bp) was successfully amplified using universal primers ChiVMV F Ind and ChiVMV R Ind. Sequence analysis of the coat protein gene showed high homology between 5 weak isolates with nucleotide and amino acid identity varied from 92.8% to 99.6% and 90.5% to 99.6% respectively. Similarly, the weak isolates have high percent similarity of their nucleotide and amino acid with severe isolate ChiVMV-CKB i.e. 92.6% to 98.1% and 90.8% to 97.5%, respectively. Further more phylogenetic tree analysis showed that the weak isolates were in the same group with severe isolate ChiVMV-CKB. As conclusion, 5 weak isolates of ChiVMV (KAR, SPR, SKT, CSR, and PGL) were identified as potential agents for cross protection due to their ability to protect the plant from infection of severe isolate ChiVMV-CKB. The selected weak isolates were also capable to maintain yield, showed no evidence to cause diseases on other plants and showed a close genetic relationship with severe isolate.

Chili veinal mottle virus (ChiVMV) merupakan salah satu penyebab penyakit yang penting pada tanaman cabai. Infeksi ChiMVM menyebabkan tanaman mengalami perubahan antara lain daun menjadi belang hijau tua, malformasi, ujung daun meruncing, lamina menyempit, dan tanaman kerdil. Hingga saat ini belum ada teknik pengendalian yang efektif, sehingga perlu dilakukan evaluasi pengendalian penyakit melalui proteksi silang. Proteksi silang merupakan teknik pengendalian secara biologi dengan menggunakan virus strain lemah sekerabat dengan virus penyebab penyakit (strain kuat)