Management of virus disease complex in chilli using the beneficial fungal root Endophyte Piriformospora indica

Abstract

The research work, “Management of virus disease complex in chilli using the beneficial fungal root endophyte Piriformospora indica” was undertaken in the Department of Plant Pathology, College of Agriculture, Padannakkad during 2021- 2023 with the objective to explore the use of the beneficial fungal root endophyte Piriformospora indica for the management of chilli leaf curl virus complex infecting chilli.Infected plant samples were collected from the chilli plots in the Instructional Farm, College of Agriculture, Padannakkad. The chilli variety Anugraha recorded higher disease incidence (D.I.-66 per cent) and vulnerability index (V.I.-15.66) than the local variety (D.I.-64 per cent and V. I. - 14.66 per cent). The major symptoms observed in the fields were leaf curling, puckering and swelling of veins. Molecular detection for the presence of associated viruses was done with begomovirus coat protein specific primers viz., Deng and AV/AC yielded amplicons of 520 bp and 575 bp respectively confirming its association with the disease. RT- PCR with Cucumber mosaic virus (CMV) coat protein specific primers could not detect the presence of CMV. Chilli seeds of variety Vellayani Athulya were sown on P. indica mass-multiplied coir pith-cow dung mixture (1:1) amended with 2 per cent gram flour. Chlamyodspores of P. indica were observed in the root cortical region five days after co-cultivation (DAC). Seeds sown on P. indica mass multiplied medium germinated early (seven days) and completed 50 per cent germination within ten days compared with untreated seeds (ten days for germination and 17 days for 50 per cent germination). Pot culture experiments were conducted with seven treatments and eight replication in a completely randomized design (CRD). The virus was transmitted through wedge grafting at intervals of 2, 5, 10, and 15 days. Pre-colonization of P. indica followed by graft transmission of the virus after 15 days took 28 days for symptom expression while non-colonized, grafted plants took 13 days. Pre-colonized plants expressed low V.I. (25) against noncolonized, grafted plants (64) at 45 DAT. Colonization of P. indica (2 days) after graft transmission of the virus recorded a V.I. (36) at 45 DAT and took 15 days for symptom expression while non-colonized grafted plants recorded a V.I. (65) and took 12 days for symptom expression. PCR amplification using virus specific primers confirmed the transmission of the virus in all grafted treatments. Field study laid out in the Instructional Farm I, College of Agriculture, Padannakkkad with P. indica colonized and non-colonized chilli seedlings of variety Vellayani Athulya recorded per cent D.I. (74) and V.I. (14.66) while the non-primed plants recorded a D.I. (86) and V.I. (32.27) at 90 days after transplanting. Amplicons in agarose gel electrophoresis confirmed that the virus titre in P. indica colonized chilli plants was significantly lower compared to those in control. P. indica colonization recorded improved growth characteristics such as the number of leaves (72.53), leaf area (30.59 cm2) and number of branches (10.78) compared to the non-colonized plants. The days taken for flowering (18.22) was early and the number of fruits per plant increased (68.23) significantly in P. indica colonized plants. P.indica colonized plants recorded a yield of 683 g while non-colonized plants yielded 480.29 g per plant. Mites and mole crickets along with diseases like powdery mildew and fruit rot were also observed. Biochemical basis for P.indica conferred tolerance was estimated based on reactive oxygen species (ROS) and hydrogen peroxide production and the activity of defense related enzymes. The presence of ROS was assessed using nitro blue tetrazolium (NBT) and H2O2 by diaminobenzidine (DAB) staining techniques. Intense colour development was obtained in non-colonized plants inoculated with the virus. Plants pre and post-colonized with P. indica exhibited reduced stain intensity compared to plants containing only the virus with the pre-colonized plants showing better stain reduction than the post-colonized ones. The ROS scavenging enzymes include catalase, peroxidase, superoxide dismutase and phosphatase activity was higher in pre-colonized plants than in post-colonized plants. Plants infected only by the virus expressed a significant reduction in the activities of catalase, peroxidase, superoxide dismutase, phosphatase, and total soluble protein compared to pre-colonized plants at all time intervals. However, at the final harvest, this treatment exhibited an increase in total protein although still lower than pre-colonized plants. The present study revealed that P. indica is effective in managing chilli leaf curl disease both in controlled and open field condition by increasing the production of ROS scavenging enzymes. P. indica was found to improve the germination, growth and development of chilli plants of variety Vellayani Athulya. Gene expression studies in future can unravel the tripartite interaction between plant, virus and the endophyte in rendering tolerance to plants against virus and enhancing plant growth.