TY  - BOOK
AU  - Rineesha Backer, A
AU  - Girija, D (Guide)
TI  - Plant growth promoting actinobacteria from rhizosphere soils of Black pepper in Wayanad 
U1  - 660.62 
PY  - 2021///
CY  - Vellanikkara
PB  - Department of Agricultural Microbiology, College of Agriculture 
KW  - Agricultural Microbiology
KW  - Actinobacteria
KW  - Black pepper
N1  - M Sc
N2  - Black pepper (Piper nigrum L.) known as the ‘King of spices’ is one of the 
important export-oriented spice crops that provides major source of income and 
employment for rural households in Kerala. Wayanad is one of the main pepper 
growing tracts in Kerala. However, the production of black pepper in Wayanad has 
been declining over the past many years, mainly due to the poor soil health status, 
improper land management and changes in climatic factors. An increasing demand for 
low-input agriculture has resulted in a greater interest in soil microorganisms which are 
able to enhance plant health and soil quality. However, actinobacteria have not yet been 
exploited for this purpose. Hence the present study focused on isolation, screening and 
characterization of actinobacteria from rhizosphere soils of black pepper in Wayanad 
and evaluation of their plant growth promoting activity.
Rhizosphere soil samples were collected from five different locations of flood 
affected and non-flood affected black pepper growing areas of Wayanad district. 
Enumeration of actinobacteria on three different media revealed that the population of 
actinobacteria ranged from 1.00 x104
cfu to 12.00 x104
cfu g
-1
soil in non-flooded soil. 
Actinobacteria could not be detected in flooded soils, even at a dilution of 10-1
, except 
in Meppadi. Among the different media, starch casein agar recorded higher population
of actinobacteria. A total of 35 isolates were purified and maintained for 
characterization and screening for plant growth promoting activities.
Cultural, morphological and biochemical characters of all 35 isolates of 
actinobacteria were studied. All the isolates were Gram positive, and they varied in the 
colony morphology, colour of aerial mycelium, spore chain morphology and 
pigmentation. Two isolates Vlt-K and Plp-B produced yellow water-soluble pigment 
and Vlt-I produce purple water insoluble pigment. 
Screening of all the 35 isolates under in vitro conditions for plant growth 
promoting (PGP) activities revealed that the isolates were highly variable. Two isolates 
(Ptd-A and Amb-C) were superior to other isolates in IAA production. Significantly 
higher N-fixation was noticed in four isolates (Ptd-A, Ptd-E, Ptd-B and Ptr-A). Six
isolates solubilized insoluble phosphate to available P, and also reduced the pH of the 
medium. Reduction in pH by phosphate solubilizers has been reported earlier and this 
is attributed to the production of organic and inorganic acids. None of the isolates 
solubilized K or Zn. 
Three isolates with multiple PGP activities were selected, based on ranking for 
PGP activities in vitro and identified by 16S rRNA gene sequencing (Ptd-A and Ptr-A
as Streptomyces sp. and Ptd-E as Actinobacteria bacterium). These actinobacterial
isolates evaluated in-planta for PGP activities with black pepper cuttings (variety 
Panniyur-1). Treatments also included PGPR mix-1 (KAU commercial formulation)
and Organic Package of Practices Recommendations (2017). All the three native 
isolates exhibited significant increase in shoot length, number of leaves and internode 
length throughout the growth period from planting to five months. Significantly higher 
root growth was observed in treatment T2: Ptd-A (Streptomyces sp.), with significantly 
higher root volume, fresh and dry root weight. Significantly higher plant fresh weight 
was observed in T2: Ptd-A (Streptomyces sp.) and significantly higher plant dry weight 
was observed in T2: Ptd-A (Streptomyces sp.) and T3: Ptr-A (Streptomyces sp).
The present investigation revealed that native actinobacteria have the potential 
to improve the growth of black pepper. These isolates may further be evaluated under 
field conditions before commercialization. Screening for other beneficial traits like 
disease suppression and drought tolerance may also be carried out. The compatibility 
of the actinobacteria with other PGP microorganisms may also be evaluated. 
Actinobacterial spores survive in soil for longer periods and this may be an added 
advantage. Actinobacterial diversity and the biochemical molecules produced by 
actinobacteria could be exploited to build up sustainable and eco-friendly agriculture
UR  -  https://krishikosh.egranth.ac.in/handle/1/5810198005
ER  -