Computational Biology and Bioinformatics 2021; 9(2): 31-38 http://www.sciencepublishinggroup.com/j/cbb doi: 10.11648/j.cbb.20210902.11 ISSN: 2330-8265 (Print); ISSN: 2330-8281 (Online) Plant Growth Promoting Actinobacteria from Rhizosphere Soils of Black Pepper in Wayanad Rineesha Backer Alungal * , Devaki Girija, Kulkarni Surendra Gopal, Reshmy Vijayaraghavan, Beena Viswanathan nair Indirabai College of Horticulture, Kerala Agricultural University, Thrissur, Kerala, India Email address: * Corresponding author To cite this article: Rineesha Backer Alungal, Devaki Girija, Kulkarni Surendra Gopal, Reshmy Vijayaraghavan, Beena Viswanathan nair Indirabai. Plant Growth Promoting Actinobacteria from Rhizosphere Soils of Black Pepper in Wayanad. Computational Biology and Bioinformatics. Vol. 9, No. 2, 2021, pp. 31-38. doi: 10.11648/j.cbb.20210902.11 Received: February 27, 2021; Accepted: March 12, 2021; Published: July 16, 2021 Abstract: Actinobacteria isolated from the rhizosphere soils of black pepper comprising both flood affected and non-flood affected areas of Wayanad district. Among different soil samples analysed, Puttad (Ptd) recorded significantly superior actinobacterial population on starch casein aga, Kenknight & Munaier’s agar and actinomycetes isolation agar. Actinobacterial colonies could not be detected in any of the flooded soil samples on any medium, even at a dilution of 10 -1 , except in Meppadi soil, which recorded a low population of 0.3 x 10 1 cfu g -1 soil. Starch casein agar is best media to isolate actinobacteria from soil samples compared to other two media. The cultural, morphological and biochemical characterization of thirty-five isolates was carried out. Further the isolates were evaluated for their plant growth promoting traits such as IAA production, nitrogen fixation, P, K and Zn solubilization. The isolates Ptd-A and Amb-C were found to be significantly superior to all other isolates, with IAA production of 15.9 g ml -1 and 15.38 g ml -1 respectively. The four isolates viz. Ptd-A, Ptd-E, Ptd-B and Ptr-A recorded significantly superior nitrogen fixation and the phosphate solubilized was significantly higher in Ptd-E, Ptd-D, Ptr-E, Ptd-A and Ptr-A, as compared to other isolates. All isolates were negative to K and Zn solubilization. Based on in vitro evaluations, three isolates were shortlisted (Ptd-A, Ptd-E and Ptr-A) and subjected to in vivo evaluation for growth promotion in black pepper (variety Panniyur 1). Rooted plants of black pepper were raised in sterile potting mixture. Bioinoculants applied at the time of planting and 45 days after planting. The PGPR Mix-1 and Organic Package of Practices Recommendations (2017) were used for comparison with the microbial inoculants along with control. In the in-planta experiment, biometric characters were recorded at monthly intervals, up to five months. The actinobacterial treatment, T 1 : Ptd-E, T 2 : Ptd-A and T 3 : Ptr-A showed significant increase in shoot length, number of leaves and internode length throughout the growth period from planting to five MAP. Significantly higher root growth was observed in treatment T 2 : Ptd-A, with significantly higher root volume, fresh and root weight. The potential actinobacteria were identified Ptd-A and Ptr-A as Streptomyces sp. and Ptd-A as Actinobacteria bacterium using 16S r RNA gene sequencing. Keywords: Black Pepper, Actinobacteria, Growth Promotion, PGPR, Rhizosphere 1. Introduction Effective farming practices, now a days, rely on extensive use of chemical fertilizers in order to enhance plant growth and yield. Excessive use of chemical fertilizers to increase production from available land has resulted in deterioration of soil quality. The use of chemical fertilizers is not only costly but also hazardous for both the environment and humans. In addition, manufacturing of such fertilizers depletes non-renewable natural resources. An increasing demand for low-input agriculture has resulted in a greater interest in soil microorganisms which are able to enhance the plant nutrition, health and soil quality [15]. Actinomycetes are one of the major components of rhizosphere microbial populations and are useful in soil nutrient cycling as well as plant growth-promotion (PGP) [21]. Actinomycetes are the most widely distributed group of