EFFECT OF ANTAGONISTIC BACTERIA IN SORGHUM TURCICUM LEAF BLIGHT MANAGEMENT
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Date
2023-12-07
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Acharya N G Ranga Agricultural University
Abstract
The present research on “Effect of antagonistic bacteria in sorghum Turcicum leaf blight management”, using eight methylotrophic bacteria isolated from the sorghum phyllosphere, four endophytes and three phylloplane bacterial isolates available in the Department of Plant Pathology, Agricultural College, Bapatla were used to test their antagonistic potential against E. turcicum in vitro.
In vitro dual culture studies revealed that, among 15 bacterial isolates tested, six bacterial isolates were found to be the most promising isolates with maximum antagonistic potential in restricting the growth of E. turcicum viz., two endophytes SLSE-05 (60.73%), SLSE-04 (54.97%), two phylloplane bacteria HMP A 1902 (54.45%), HMP Bc 1903 (27.27%) and two methylotrophs PPFMH-5 (30.89%), PPFMH-8 (22.51%). Hyphal morphological alterations like hyphal thinning, shortening of hyphal septa, swelling, wrinkling, protoplasm disintegration, clustering of hyphae and hyphal tip shearing were noticed in the fungal mycelium when interacted with endophytes SLSE-05, SLSE-04 and phylloplane HMP A 1902 bacterial isolate.
Volatiles produced by six antagonistic bacterial isolates significantly inhibited the mycelial growth and completely prevented pigment production in E. turcicum. Among them, the endophytes SLSE-05 (25.18%) and SLSE-04 (22.18%) were found to be superior over phylloplane and methylotroph isolates in inhibiting the growth of E. turcicum up to 120 h of incubation.
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In vitro studies on effect of culture filtrate of bacterial antagonists at different concentrations revealed that the endophytic isolate SLSE-05 at 15% concentration significantly inhibited E. turcicum mycelial growth up to 100%.
Intra and inter compatibility studies of six antagonistic bacterial isolates, (SLSE-05, SLSE-04, HMP A 1902, HMP Bc 1903, PPFMH-05 and PPFMH-08) revealed that all the isolates were compatible with each other under in vitro conditions which was tested through cross streak method and were further used for testing their combined impact in plant growth promotion and disease reduction under green house conditions.
Plant growth promotional ability of antagonistic bacteria was evaluated under green house conditions. The phylloplane isolate HMP A 1902 was found to be superior over all other isolates in terms of increasing shoot (14.43 cm) and root length (16.00 cm), while the endophyte SLSE-05 treated seeds had the highest vigour index (2370.00) compared to untreated control (1397.50) at 15 DAS.
Seed treatment followed by two foliar sprays with antagonistic bacteria, resulted in significant increment in sorghum growth parameters over untreated pathogen check where 11.42 to 47.14% increase in shoot length, 40.10 to 68.75% in root length, 9.26 to 40.57% in leaf length and 9.46-72.97% in leaf width was noticed. Combination treatment involving seed treatment with both the endophytes SLSE04, SLSE05 and foliar spray with both phylloplane bacteria HMP A 1902, HMP Bc 1903 was found most effective in controlling the disease even two weeks after second spray (64 DAS) under green house conditions with the lowest PDI of (19.63%) and with minimum area under disease progress curve of 496.86 as against untreated pathogen check (708.57). Biochemical studies revealed that all antagonistic bacterial isolates except the phylloplane isolate HMP A 1902 to be positive for catalase activity, and only three isolates have amylase activity, while all the isolates were tested positive for urease and indole production and negative for HCN activity.
Based on 16S rRNA gene sequencing the endophytic isolate SLSE-05 was found closely related with Janthinobacterium sp., while SLSE-04 with Ochrobactrum sp. However the phylloplane bacteria HMP A 1902 clustered separately with Pseudomonas fluorescens isolates and methylotroph PPFMH-5 grouped with Methylobacterium extorquens indicating their relatedness. Similarly, under field conditions combination treatment T6, where endophyte SLSE-05 was used for seed treatment @ 108 CFU ml-1 as well as its foliar spray in combination with phylloplane bacteria HMP A 1902 @ 108 CFU ml-1 was found most effective with the lowest PDI (22.63%) and with minimum area under disease progress curve of 538.82. Treatment T6 where the endophyte SLSE-05 was used for seed treatment followed by foliar spray along with phylloplane bacteria HMP A 1902 was found with significant increase in weight of filled grains per panicle (43.33 g) with the highest test weight of 28.64 g, yield of 1918 kg ha-1. However, the benefit cost ratio (BCR) of the different treatments varied from 1.06 to 1.40 with the highest BC ratio was recorded with Treatment T6 (SLSE-05 (ST) and SLSE-05 + HMP A 1902 (FS)) (1.40) representing a potential alternative to fungicide treatments.