IDENTIFICATION AND MOLECULAR CHARACTERIZATION OF THRIPS COMPLEX TRANSMITTING THE Groundnut bud necrosis virus IN BLACKGRAM AND THEIR MANAGEMENT
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Date
2023-12-01
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Acharya N G Ranga Agricultural University
Abstract
Thrips species were collected from 35 major blackgram cultivating areas in Andhra Pradesh. Based on the morphological identification, major species of thrips species on black gram in Andhra Pradesh state was Thrips palmi (63.12), Megalurothrips usitatus (30.05) and Scirtothrips dorsalis (6.83). Out of thirty five locations surveyed, no record of S. dorsalis was observed in 19 mandals and highest mean per cent of S. dorsalis i.e., 52.38 was recorded in Mentada mandal of Vizianagaram district. In Chittoor district Megalurothrips typicus (Bagnall), Ayyaria chaetophora (Karny), Phibalothrips peringueyi (Faure) and some Tubuliferan thrips were also observed in meager number.
Molecular characterization of thrips samples revealed that T. palmi produced an amplicon size of 570 bp with ITS2 marker, M. usitatus with mtCOI marker at 655 bp and S. dorsalis amplified with mtCOIII marker at 713 bp. This study contributed a total of 21 gene sequences (seven samples for each thrips species ) to NCBI website Tajimas d statistic revealed the existence of low genetic polymorphism among the, ITS2 sequences of T. palmi, COI sequences of M. usitatus, COIII sequences of S. dorsalis.
The thrips population was observed in the field approximately after 14 DAS during rabi 2019-2020 where as during kharif 2020-2021 in third week of August (21 DAS) Highly fluctuating thrips population incidence was noticed during the kharif season as population has increased gradually and reached peak at 35 DAS with 17.35 mean number of thrips per plant and after 35 DAS, thrips population started declining to 5.2 and 4.6, 4.55, 3.33 (thrips per plant) at 42, 49, 56, 63 DAS respectively. At 70 DAS slight increase in thrips population was noticed i.e. 7.1 thrips per plant during first week of October (40th SMW). Similarly thrips population was observed initially at 21 DAS during fourth week of December i.e. during 52nd SMW with 2.15 mean number of thrips per plant and reached peak at 63 DAS during second week of
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February i.e. during 6th SMW (Standard meteorological week) with 10.10 mean number of thrips per plant. The thrips population started declining towards maturity and lowest incidence was recorded at 77 DAS during fourth week of February i.e. during 8th SMW with 1.10 mean number of thrips per plant during rabi 2020-21.
Overall view of GBNV incidence in blackgram in the present study revealed that the per cent disease incidence was more during kharif 2020-2021 (26.05 %) compared to rabi 2019-2020 (25.90 %) and rabi 2020-2021 (10.22 %).
During rabi 2019-20, rabi 2020- 2021 the number of thrips per plant showed a highly significant positive correlation with maximum temperature i.e. 0.74, 0.726 respectively where as during kharif 2020-2021 positive correlation with out any significance i.e. 0.151 was observed. Similarly minimum temperature (0.75, 0.55), mean temperature (0.819, 0.435) showed highly significant positive correlation during rabi 2019-20, rabi 2020- 2021 respectively where as during kharif 2020-2021 positive correlation with out any significance i.e. 0.158, 0.172 was observed with number of thrips per plant.
Rainfall showed non significant negative correlation with thrips population i.e. -0.256, -0.289, -0.319 during rabi 2019-20 and kharif 2020-2021, rabi 2020-2021 respectively. Number of rainy days (-0.156, -0.319) showed non significant negative correlation during rabi 2019-20 and rabi 2020-2021, respectively where as significant negative correlation -0.657 was observed during kharif 2020-2021. Wind speed (0.802) showed highly significant and positive correlation with thrips population was observed during rabi 2019-20. But during kharif 2020-2021, rabi 2020-2021 wind speed showed non significant negative correlation i.e. -0.346, -0.463 respectively.
The number of thrips per plant showed a highly significant positive correlation with per cent disease incidence (0.889) where as mean number of thrips per square meter showed non significant positive correlation with disease incidence (0.57) during rabi 2019-2020 whereas the number of thrips per plant (0.279), mean number of thrips per square meter (0.179) showed a positive correlation with per cent disease incidence during kharif 2020-2021. Similarly during rabi 2020-2021, the number of thrips per plant (0.466) and mean number of thrips per square meter (0.508) showed a non significant positive correlation with per cent disease incidence.
Multiple linear regression equation showed that all the weather variables together could influence the incidence of thrips by 77.0 (R2 = 0.77), 70.0 (R2 = 0.70) per cent, 83.0 (R2 = 0.83) per cent during rabi 2019-2020; kharif 2020-2021; rabi 2020-2021 respectively whereas weather variables together contributed to the incidence of bud necrosis disease incidence by 95.0 (R2 = 0.95) per cent, 94.0 (R2 = 0.94) per cent, 92.0 (R2 = 0.92) per cent during rabi 2019-2020; kharif 2020-2021; rabi 2020-2021 respectively.
Out of the two species tested for transmission of GBNV, only T. palmi could able to transmit the GBNV from diseased to healthy plants where in the inoculated plants exhibited symptoms viz. chlorotic local lesions. Whereas M. usitatus failed to transmit the virus and the inoculated plants remained healthy. Hence Thrips palmi was identified as vector of Groundnut bud necrosis virus in blackgram. A minimum of 2 h acquisition access period (48 IAP), 4 h inoculation access period (24 h AAP) was required to transmit the bud necrosis disease in case of first instar larvae of T. palmi and a minimum of 2 larvae were required to transmit the bud necrosis disease
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at 24 AAP, 48 h IAP; 48 AAP, 48 h IAP. A minimum of 2 h acquisition access period (with 48 h IAP), 8 h inoculation access period (24 h AAP) was observed in case of second instar larvae and a minimum of 10 larvae required to transmit the disease at 24 AAP and 48 h IAP, and 2 larvae required to transmit the disease at 48 AAP and 48 h IAP.
There was no disease transmission was observed at 30 min, 1 h, 2 h, 4 h, 6 h, and 8 h of acquisition access period and inoculation access periods in case of adults. Surprisingly a minimum of 24 h AAP (48 h IAP), 24 h IAP (24 h AAP) was observed with 8.33 per cent of disease transmission and there is no further increase of disease with increasing AAP (48 h IAP) and IAP (24 h AAP). A minimum of 10 adults were required to transmit the disease at 24 h AAP, 48 h IAP; 48 AAP and 48 h IAP.
Among the all evaluated insecticides imidacloprid 70 WG seed treatment + fipronil 5 SC spray @ 50 g a.i ha-1 followed by thiamethoxam seed treatment + fipronil 5 SC spray @ 50 g a.i were proved best in reducing the thrips population with highest blackgram grain yield i.e. 1414 kg ha-1 with incremental cost benefit ratio 1:4.80 followed by thiamethoxam 70 WS seed treatment + fipronil 5 SC spray @ 50 g a.i ha-1 (1:4.47) during rabi 2019-2020. Similarly imidacloprid 70 WG seed treatment + fipronil 5 SC spray @ 50 g a.i ha-1 recorded least bud necrosis disease incidence among the all other tested insecticides.
During Kharif 2020-2021, highest per cent population reduction over untreated control was found in treatment imidacloprid 70 WG seed treatment + spinosad 45 SC spray @ 72 g a.i ha-1 (86.67 per cent) followed by imidacloprid 70 WG seed treatment + fipronil 5 SC spray @ 50 g a.i ha-1(86.62). Whereas among the treatments tested, imidacloprid 70 WG seed treatment + fipronil 5 SC spray @ 50 g a.i ha-1 recorded highest grain yield i.e. 1372 kg ha-1 with incremental cost benefit ratio 1:3.73 followed by thiamethoxam 70 WS seed treatment + fipronil 5 SC spray @ 50 g a.i ha-1 (1:2.93).
Similarly, among the tested treatments imidacloprid 70 WG seed treatment + fipronil 5 SC spray @ 50 g a.i ha-1 recorded least mean bud necrosis disease incidence in blackgram i.e. 5.19 per cent and it was at par with thiamethoxam 70 WS seed treatment + fipronil 5 SC spray @ 50 g a.i ha-1 (5.64 per cent), imidacloprid 70 WG seed treatment + flonicamid 50 WG spray @ 75 g a.i ha-1 (5.94 per cent) thiamethoxam 70 WS seed treatment + spinosad 45 SC spray @ 72 g a.i ha-1(6.13 per cent), thiamethoxam 70 WS seed treatment + flonicamid 50 WG spray @ 75 g a.i ha-1 (6.39 per cent), imidacloprid 70 WG seed treatment + spinosad 45 SC spray @ 72 g a.i ha-1 (6.64 per cent) during kharif 2020-2021.
During rabi 2020-2021, thiamethoxam 70 WS seed treatment + fipronil 5 SC spray @ 50 g a.i ha-1, imidacloprid 70 WG seed treatment + fipronil 5 SC spray @ 50 g a.i ha-1, imidacloprid 70 WG seed treatment + spinosad 45 SC spray @ 72 g a.i ha-1 proved best in reducing the thrips population. Thiamethoxam 70 WS seed treatment + fipronil 5 SC spray @ 50 g a.i ha-1 recorded least mean disease incidence. Among the treatments imidacloprid 70 WG seed treatment + fipronil 5 SC spray @ 50 g a.i ha-1 recorded highest grain yield i.e. 1439 kg ha-1 with incremental cost benefit ratio 1:4.45 followed by thiamethoxam 70 WS seed treatment + fipronil 5 SC spray @ 50 g a.i ha-1 (1:3.97).