Please use this identifier to cite or link to this item: http://krishikosh.egranth.ac.in/handle/1/5810102193
Authors: RAGHAVENDRA, BACHU
Advisor: SRINIVAS, T
Title: STUDIES ON THE Sclerotium rolfsii Sacc. INCITANT OF STEM ROT OF GROUNDNUT (Arachis hypogaea L.)
Publisher: Acharya N.G. Ranga Agricultural University
Language: en_US
Type: Thesis
Pages: 147
Agrotags: null
Keywords: Sclerotium rolfsii Sacc., INCITANT, STEM ROT, GROUNDNUT, Arachis hypogaea L.
Abstract: The present investigation was carried out to study the groundnut stem rot causing pathogen Sclerotium rolfsii Sacc. The causal organism was isolated from the infected portion of the stem collected from the fields of S.V. Agricultural College, Tirupati. Pathogenicity of the fungus was tested by soil infestation method. Effect of different inoculum densities of S. rolfsii on the development of stem rot of groundnut was assessed using soil infestation method in pot culture under green house. At 14 days after sowing, highest germination (45.83%), root length (12.37 cm) and shoot length (15.16 cm) was observed at 1 per cent inoculum density. Least germination (16.66%), root length (7.50 cm), shoot length (8.33 cm) was observed at 5 per cent inoculum density. Germination percentage, root length and shoot length of groundnut was gradually decreased with increase of inoculum densities from 1 to 5 per cent. Disease symptoms were not observed in any of the treatments, however development of sclerotial bodies were observed at 4 and 5 per cent inoculum. Influence of soil temperature, soil pH and soil moisture levels were observed on the viability of sclerotia. Maximum sclerotial germination (100%) was observed at soil temperature of 27o and 30oC and lowest at 20oC. From the study it was observed that optimum soil temperature for survival of sclerotia is 27-30oC and the germination is affected if temperature is decreased below 25oC and also above 35oC. Soil pH 7.2 and 7.5 was found to be best (100%) for sclerotial germination and pH 9.0 was found to be less favourable showing least (76.66%) sclerotial germination. Soil moisture levels of 50% (control) and 40% were found to be best for sclerotial germination (100%). Least germination (76.67%) was observed at 100% moisture, indicating that increase in soil moisture decreases the sclerotial viability. xv The antagonistic effect of three Trichoderma viride isolates (Tr-DM, Tr-SNG and Tr-RGP) and three Pseudomonas fluorescens isolates (Pf-DM, Pf-SNG and Pf-RGP) were assessed against S. rolfsii by dual culture technique. Among the T. viride isolates, maximum inhibition (87.19%) was observed with the DM-Tr and among P. fluorescens isolates maximum inhibition (28.25%) was observed with the Pf-DM isolate and they were significantly different from each other. Efficacy of ten fungicides belonging to systemic and non-systemic groups were observed at various concentrations against mycelial growth of S. rolfsii by using poison food technique. Among different fungicides tested, fungus was most sensitive to systemic fungicides azoxystrobin, tebuconazole, hexaconazole, carboxin and non-systemic fungicide mancozeb showing complete mycelial growth inhibition (100%) at all the concentrations tested. Among systemic fungicides, carbendazim and among non-systemic fungicides, copper oxychloride was found to be less effective in inhibiting the mycelial growth of S. rolfsii. Efficacy of different herbicides viz., pendimethalin, quizalofop ethyl, imazethapyr were observed at various concentrations against mycelial growth of S. rolfsii by using poison food technique. Among them, quizalofop ethyl showed maximum inhibition of mycelial growth (100%) at higher concentration (1000 ppm) and imazethapyr was found to be less effective in inhibiting the fungus. Studies conducted to identify the effective dosage of T. viride (Tr-DM) isolate on germination of sclerotial bodies of S. rolfsii and observed that at higher concentration (1 x 108) maximum sclerotial inhibition was observed i.e., 66.66% inhibition over control and least sclerotial inhibition (43.33%) was observed at 1 x 104 concentration, this indicates that increase in spore concentration increases sclerotial inhibition. Similarly, sclerotial germination was tested against effective P. fluorescens isolate (Pf-DM) suspension at the concentrations from 10-4 to 10-8 CFU/ml and the inhibition of sclerotial germination was 66.66 per cent at 10-4 and 10-5 concentrations, 46.66 per cent at 10-6 and 10-7 concentrations. Lower sclerotial germination (36.66%) was observed at concentration of 10-8 (lower concentration). There was a significant increase in per cent inhibition of sclerotial germination with increase in concentration of the bacterial suspension. All the above mentioned fungicides were tested at recommended dosage against the sclerotial germination in soil. Among different fungicides tested, highest inhibition (100%) was observed with the fungicides mancozeb, tebuconazole, hexaconazole and carboxin and least inhibition (16.66%) was observed with validamycin. Similarly, different herbicides were tested and quizalofop ethyl was highly effective in inhibiting the germination of sclerotia recording 36.66 per cent inhibition. xvi Compatibility among effective fungicides, herbicide and their combinations on the effective T. viride isolate (Tr-DM) has revealed that mancozeb was highly compatable with effective T. viride isolate (Tr-DM) and did not show mycelial growth inhibition, hence this fungicide was used for further pot culture study. Efficacy of effective herbicide, fungicide and bioagent was tested against S. rolfsii through pot culture under greenhouse conditions. Among different treatments, T6 (T. viride @ 10 g/kg soil+ mancozeb @ 0.3% a.i/kg soil + quizalofop ethyl @ 0.3% ml a.i./kg soil) did not show disease incidence upto 30 DAS with highest groundnut seed germination (91.67%), root length (22.33 cm) and shoot length (32.67 cm). In addition, disease incidence was not observed with T8 (control), T6 (T. viride @ 10 g/kg soil+ mancozeb @ 0.3% a.i/kg soil + quizalofop ethyl @ 0.3% ml a.i. /kg soil), T4 (mancozeb @ 0.3% a.i/kg soil + quizalofop ethyl @ 0.3% ml a.i. /kg soil), T3 (mancozeb @ 0.3% a.i/kg soil) and T1 (quizalofop ethyl @ 0.3% ml a.i./kg soil). Highest dry weight of the plant was recorded at T8 (control) (3.66 gm) followed by T4 (mancozeb @ 0.3% a.i/kg soil + quizalofop ethyl @ 0.3% ml a.i./kg soil), and T6 (T. viride @ 10 g/kg soil+ mancozeb @ 0.3% a.i/kg soil + quizalofop ethyl @ 0.3% ml a.i./kg soil) (3.26 gm). From the study it was clear that integrated treatment T6 (T. viride @ 10 g/kg soil+ mancozeb @ 0.3% a.i/kg soil + quizalofop ethyl @ 0.3% ml a.i. /kg soil) is highly effective with high groundnut seed germination, root length, shoot length, dry weight of the plant and least disease incidence.
Description: D5726
Subject: Plant Pathology
Theme: STUDIES ON THE Sclerotium rolfsii Sacc. INCITANT OF STEM ROT OF GROUNDNUT (Arachis hypogaea L.)
Research Problem: STUDIES ON THE Sclerotium rolfsii Sacc. INCITANT OF STEM ROT OF GROUNDNUT (Arachis hypogaea L.)
These Type: M.Sc
Issue Date: 2018
Appears in Collections:Thesis

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