Loading...
![Thumbnail Image](assets/images/Collection.png)
Theses
Browse
1 results
Search Results
ThesisItem Open Access Interaction of Beauveria bassiana (Bals.) Vuill. with Leptocorisa oratorius Fab. (Hemiptera: Alydidae) with special reference to chitinase(2021) Das,Karishma; Das, PurnimaRice earhead bug, Leptocorisa oratorius Fab. and Leptocorisa acuta Thun. (Hemiptera: Alydidae) are the most important sucking pests of rice. The insect cause significant yield losses to the rice crop in the field condition. Therefore, the present investigation was carried out with a view to study the seasonal incidence of L. oratorius in relation to the meteorological parameters, their damage potential, biology, pathogenicity of Beauveria bassiana (Bals.) Vuill. against different stages of L. oratorius and to characterize the B. bassiana-chitinase that secreted during insect fungus interaction. To study the seasonal incidence of L. oratorius, an experiment was conducted at Instructional Cum Research (ICR) Farm, Assam Agricultural University, Jorhat during Ahu, 2018 & 2019 and Sali (Kharif), 2018 & 2019. During Ahu, 2018 & 2019, the population of L. oratorius was first appeared on 2nd week of May i.e. 20th standard meteorological week (SMW) with an average of 0.33 and 0.30 adult per hill, respectively. The population was gradually increased with a peak of 2.66 and 1.56 adult per hill on 24th SMW (2nd & 3rd week of June), respectively. During Sali (Kharif) 2018 & 2019, the population of L. oratorius was first appeared on 41st standard (SMW) with an average of 0.30 and 0.36 adult per hill, respectively. The population was found to be highest at 1st week of November i.e. 44th SMW with an average of 1.20 and 1.13 adult per hill, respectively. The correlation studies between incidences of L. oratorius with meteorological parameters showed non significant correlation with all the meteorological parameters during Ahu, 2018 and Sali (Kharif), 2018 and 2019. However, during Ahu 2019, it showed significant positive correlation with maximum (r = 0.802) & minimum (r = 0.711) temperature and BSSH (r = 0.631) whereas, significant negative correlation with morning (r = -0.849) & evening (r = -0.750) relative humidity and non significant negative correlation with rainfall (r = -0.255). Multiple regression analysis during Ahu 2019, revealed that only morning relative humidity determined the incidence of L. oratorius in concert with R2 =0.721 (72.10%) and adjusted R2= 0.691 (69.10 %). The „best fit model‟ Y= 12.82531-0.13115*Mor. RH (%) expressed the magnitude of the relationship. The percent grain infestation due to rice earhead bug were recorded as 39.34 and 37.11 during Ahu, 2018 & 2019 and 35.43 & 36.28 during Sali (Kharif), 2018 & 2019, respectively. The biology of L. oratorius and L. acuta were studied under laboratory condition. The preoviposition and oviposition period of L. oratorius were found to be 12.00±7.17 and 11.60±4.35 days whereas, 7.40±3.50 and 10.20±5.71 days were recorded incase of L. acuta, respectively. A gravid female of L. oratorius laid on an average 99.20±22.01 number of eggs during her life span whereas, 76.80±21.79 number of eggs was laid by L. acuta. The incubation period of L. oratorius and L. acuta were 5.80±1.09 and 5.00±1.00 days, respectively. Both the species have five nymphal instars. The duration of each instar of L. oratorius were 3.80±0.84, 2.20±0.45, 3.60±0.89, 6.80±0.84 and 4.80±0.84 days whereas, 4.40±1.14, 4.80±1.09, 3.40±1.14, 3.80±1.48 and 6.00±1.22 days incase of L. acuta. The total nymphal period and total developmental period of L. oratorius were found to be 21.20±1.09 and 27.00±1.58 days whereas, 22.40±1.14 and 27.40±2.02 days were found incase of L. acuta, respectively. Adult male of L. oratorius lived for 28.60±2.40 days and female lived for 57.60±7.06 days. The longevity of both male and female of L. acuta were 28.40±5.81 and 51.80±6.37 days, respectively. The morphometric study of L. oratorius revealed that the average length of eggs, first, second, third, fourth and fifth instar were 1.02±0.06, 1.49±0.06, 2.82±0.05, 5.05±0.06, 10.61±0.09 and 14.03±0.15 mm whereas, width were found as 0.75±0.05, 0.28±0.04, 0.40±0.05, 0.48±0.05, 1.07±0.07 and 1.39±0.06 mm, respectively. The female L. oratorius was slightly shorter than the male and measured 17.08±0.16 mm in length and 1.98±0.09 mm in width while the male bug was slightly longer than female measured 18.01±0.16 mm in length and 2.11±0.11 mm in width. In case of L. acuta the average length of eggs, first, second, third, fourth and fifth instar were recorded to be 1.27±0.04, 1.39±0.05, 2.41±0.08, 3.75±0.07, 5.46±0.11 and 6.68±0.12 mm whereas, width were found to be 0.52±0.03, 0.55±0.07, 0.59±0.05, 1.38±0.08, 1.75±0.05 and 2.29±0.04 mm, respectively. The average length and width of male bug were 10.23±0.12 and 2.31±0.04 mm whereas, female bug were 9.85±0.12 and 2.39±0.44 mm, respectively. The head length and width of L. oratorius varied as 2.35±0.07 and 0.82±0.07 mm whereas, incase of L. acuta 1.29±0.02 and 0.53±0.02 mm, respectively. Likewise thorax length, thorax width, abdomen length, abdomen width, distance between two compound eyes, length of compound eyes, width of compound eyes, antennal length, stylet length, fore wing length, fore wing width, hind wing length, hind wing width, fore leg length, middle leg length and hind leg length of L. oratorius were also measured as 3.16±0.15, 2.05±0.07, 12.65±0.13, 2.23±0.14, 1.03±0.13, 0.89±0.10, 0.73±0.08, 14.74±0.12, 5.60±0.05, 12.20±0.19, 2.00±0.14, 8.51±0.16, 2.02±0.09, 9.07±0.25, 9.85±0.27 and 14.22±0.20 mm whereas, 1.60±0.02, 1.94±0.04, 6.00±0.07, 2.61±0.05, 1.8±0.08, 0.41±0.03, 0.29±0.02, 5.20±0.04, 4.85±0.06, 6.38±0.07, 1.87±0.08, 4.64±0.07, 1.79±0.05, 3.43±0.16, 4.11±0.21 and 5.37±0.16 mm were found incase of L. acuta, respectively. The pathogenicity test of B. bassiana against different stages of L. oratorius was carried out under laboratory condition and found to be effective against all the stages of this pest. The B. bassiana treated eggs showed 72.00±3.74 percent egg hatchability as compared to the untreated control (100±0.00). The mean percent mortality of first, second, third, fourth, fifth instar and adult were recorded as 84.00, 80.00, 66.00, 70.00 and 62.00 and 58.00, respectively at 9 days after treatment (DAT). However, significant differences (P ≤ 0.05) were found among the mean percent mortality of nymphal and adult stages at different DAT. Infection process of B. bassiana in insects is mainly triggered by the chitinase which is secreted during insect fungus interaction. Therefore, an experiment was conducted in the Department of Agricultural Biotechnology, Assam Agricultural University, Jorhat during the period 2016-2021 to optimize the growing condition of B. bassiana for chitinase production, reaction condition for chitinase activity assay and to purify the enzyme. For the production of B. bassiana-chitinase, different growth parameters viz., growth period, media composition (peptone concentrations, colloidal chitin concentrations and ferrous sulphate concentrations), media-pH and growth temperature were optimized. Along with the different growth parameters, reaction parameters viz., temperature and pH were also optimized for the estimation of B. bassiana–chitinase activity. The optimum incubation time required for chitinase production by B. bassiana was found to be 5 days, peptone concentration as 0.07%, colloidal chitin concentration as 0.4% and ferrous sulphate (FeSO4.7H2O) concentration as 0.015%, media pH as 5.0 and growth temperature as 28°C, whereas, for B. bassianachitinase activity the optimum reaction temperature and reaction pH were found to be 37°C and 5.0, respectively. Chitinase was purified by ammonium sulphate precipitation method by using different salt fractions, 55%, 65%, 75%, 85% and 95%. Chitinase activity and protein were estimated in crude enzyme as well as in its different salt fractions after proper dialysis. From the estimated chitinase activity and protein, the specific activity, fold purification and yield were calculated. Among the different fractions, with 75% ammonium salt saturation showed the best result as it purified the enzyme to the maximum fold of 2.68 with a yield of 14.34% and specific activity of 2.60 U/mg. The purity of the enzyme was examined by SDS-PAGE and determined the molecular weight at the highest purified fraction i.e. 75% ammonium salt saturation. The molecular weight of purified chitinase was estimated to be around 60 kDa.