Evaluation of biocontrol potential of Beauveria bassiana (Balsamo) Vuillemin against major rice pathogens
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Date
2021-12
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College of Post Graduate Studies in Agricultural Sciences, CAU-Imphal, Umiam
Abstract
Beauveria bassiana (Ascomycota: Hypocreales: Cordycipitaceae), a widely studied entomopathogenic fungus recently drawn attention worldwide as potential biocontrol agent not only against insect-pests but also against several plant pathogens. As potential alternative to injudicious chemicals uses in crop protection, B. bassiana plays multifarious roles as plant disease antagonist, endophytes, plant growth promoter as well as beneficial rhizosphere colonizers providing an excellent opportunity as biocontrol agent in plant disease management. The present study was conducted with an aim to evaluate biocontrol potential of native B. bassiana isolates against major rice pathogens by studying its antimicrobial, growth promoting and colonizing ability in rice. A total of fifty-three (53) native isolates of B. bassiana were obtained from six major districts of Meghalaya, identified based on morphological and microscopic characteristics further confirmed by PCR-based detection by using universal ITS (ITS1, ITS4) primers at 550 bp amplicon size. Under in vitro assay, out of 53 tested isolates, only 15 isolates of B. bassiana were screened based on their efficient antagonistic potential against three (3) fungal viz., Rhizoctonia solani, Pyricularia oryzae, Bipolaris oryzae and one (1) bacterial pathogen viz., Xanthomonas oryzae pv. oryzae of rice with per cent inhibition recorded maximum up to 71.15%, 63.33%, 62.59% and 84.00% respectively. Under antimicrobial studies, screened B. bassiana isolates (15) showed ability to release volatile inhibitory metabolites delimiting the growth of R. solani (86.48%), P. oryzae (67.78%), B. oryzae (90.18%) and X. oryzae pv. oryzae, respectively. Majority of the isolates showed ability to produce cell wall degrading enzymes (CWDEs) viz., caesinases (68.41%), cellulase (77.26%), lipase (61.66%), xylanase (81.54%), α-amylase (77.78%), protease (72.22%) and pectinase (76.46%) in addition to iron-chelating siderophore compounds (74.74%). Presence of virulent genes viz., Bbchit1, Cdep1, Bbhog1 and Bbjen1 were detected in majority of B. bassiana isolates by performing PCR amplification using gene-specific primers at 198 bp, 249 bp, 193 bp and 198 bp, respectively. However, under plant growth promotion (PGP) studies, majority of B. bassiana isolates showed ability to produce ammonia (NH3) and inole-3-acetic acid (IAA) of concentration maximum up to 3.49 μg/ml and 6.16 μg/ml respectively. In addition to that, B. bassiana isolates also qualified as potential phosphorus (P), potassium (K) and zinc (Zn) solubilizers with per cent solubilization efficiency recorded maximum up to 68.68%, 81.74% and 64.36%, respectively. Based on potential antimicrobial and PGP traits, only five (5) isolates viz., Bb4, Bb16, bb25, Bb44 and Bb53 were selected for further studies. Potential B. bassiana isolates showed ability to tolerate aluminium (Al) and iron (Fe) stress conditions with maximum tolerance limit up to 100 ppm and 275 ppm, respectively under different acid (pH) condition to the lowest up to pH 3.0, respectively. Further, potential B. bassiana isolates viz., Bb4, Bb16, Bb25, Bb44 and Bb53 were found compatible among each other and developed into liquid-based microbial consortium (Bb-MC). Biopriming of rice seeds with Bb-MC showed considerable increase in seedling growth parameters as compared to seed treatment with single isolates and control at 10th DAS and 25th DAS. Per cent colonization (%) of B. bassiana was recorded maximum in stems (96.00%) followed by leaves (92.00%) and roots (28.00%) on 14th dpi through combined application of seed, root and foliar spray techniques. However, association of B. bassiana isolates viz., Bb4, Bb16 and Bb44 as potential colonizer in rice was further confirmed by light microscopy studies and PCR-based detection assay. In addition to that, application of Bb-MC also performed better under pot and field conditions against sheath blight disease R. solani of rice by combined treatment of seed, seedling and four (4) foliar sprays of 10 ml Bb-MC in 1 litre water at 15 days interval after transplanting. Reduced disease incidence and severity of 22.87% and 37.07% was recorded against maximum yield of 2.83 tonne/ha as compared to inoculated control with 74.23% and 94.27%, respectively with yield of 1.36 tonne/ ha. With these findings, the multifaceted role played by B. bassiana as biocontrol agent as investigated in the present study paved substantial evidence that B. bassiana in addition to its entomopathogenic behaviour also act as potential plant disease antagonist, thus, providing a new dimension in crop protection by introducing newer concept in Integrated plant disease management programmes along with overall health of plant.
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Keywords
Biological control, Beauveria bassiana