MSc

The research entitled ‘Biochemical response of okra to Bhendi Yellow Vein Mosaic Virus and production of virus free plants’ was undertaken at the College of Agriculture, Vellayani, Thiruvananthapuram during the years 2021 to 2023 with the objective of host pathogen interaction of Bhendi yellow vein mosaic virus (BYVMV)infecting okra, screening of different genotypes of okra cultivars for disease resistance and production of virus free plants using meristem culture.
Purposive sampling survey was done and samples were collected from AEU8 and AEU 10. The disease incidence of virus infected okra plants in surveyed locations ranged from 37 to 100 %. And vulnerability index varied from 23.40 to 85.20. Highest V. I. was observed in Arka Anamika (85.2) followed by varieties, Varsha Uphar(80) and Anakomban (83.53). The okra variety, Anjitha, recorded lowest disease incidence of 37.20 per cent and vulnerability index of 23.40. Disease incidence was observed to be high at the flowering and fruiting stage.
The virus causing BYVMD was serologically detected using ELISA and DIBA and found that BYVMV isolate have close relationship with tomato leaf curl New Delhi virus. The molecular detection of virus was done using PCR and an expected amplicon of size 520 bp was obtained using Deng primer. The BLAST analysis of the sequence of amplicon from okra with vein clearing symptom and enation symptom showed 96.27 % and 96.67 % similarity with DNA-A segment of bhendi yellow vein mosaic virus isolate.
Out of 286seeds collected from infected plants seeds sown, only 57.14 % germination was observed. None of the seedlings established symptoms till flowering stage. Molecular analysis of random samples taken from asymptomatic leaves of grow out plants also showed negative reaction to the virus. ELISA also showed negative results confirming absence of seed transmission. But, presence of virus was detected molecularly on whole seeds taken randomly from the seeds collected from infected plants. Out of 20 seeds examined only four seeds showed positive reaction. The presence of virus was also not detected on any of the seed parts examined. Hence it can be inferred that the virus is present on seed samples but there is no seed transmission.
On screening of 15varieties, Phule Vimukta variety (V.I.-13.34) was found to be moderately resistant to BYVMD and Anjitha variety (V. I.- 38.30) was moderately susceptible to BYVMD. Arka Anamika, Anakomban, Arka Nikitha and ten NBPGR accessions studied were found to be highly susceptible to BYVMD.(IC 052303, IC 00780, IC 588166, IC 002134, IC 006101,IC 002024, IC 043279, IC 093771, IC 093688, IC 045820)Defense-related enzymes activities varied with genotypes and also with the growth stages of the crop. Tolerant varieties were found to possess the highest content of defence enzymes compared to susceptible varieties. PO activity of moderately resistant variety Phule Vimukta was observed with 270.29 % and 35.02 % more enzyme activity than the susceptible variety, Anakomban at 90 days after sowing and 45 days after graft inoculation respectively. PO and PPO activity showed an increasing trend on inoculation with virus while PAL showed a decreasing trend.
Standardisation of production of virus free plants using meristem culture was done. Meristem culture can be successfully done using MS media with BAP (0.5µM), NAA(0.1 µM) and GA3(0.1µM). Virus indexing of meristem cultured plants by PCR confirmed the absence of virus in regenerated plants.
Based on the present study, the virus causing BYMD showing symptoms of vein clearing and enation was found to be BYVMV. Presence of virus was detected on seed (20 %) but seed transmission was not observed in grow out test. Breakdown of resistance was observed in Varsha Uphar and Arka Anamika which were earlier reported as resistant. The variety Phule Vimukta, with disease resistance and high defense related enzyme activity can be used for breeding purposes for the development of disease resistant varieties. Meristem culture can be successfully used for the production of disease-free planting materials and production of quality seeds.

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