MSc

Pokkali rice farming is a time-honoured, environmentally beneficial,
traditional and organic method of growing rice. Neither chemical fertilizers nor plant
protection agents are used on the crop in this conventional rice farming technique.
The present study was undertaken to evaluate a native plant growth promoting
rhizobacteria (PGPR) consortia with an objective to screen PGPR for functional
efficiency under in vitro and evaluate for plant growth promotion in Pokkali rice.
Isolation, characterization and screening of plant growth promoting rhizobacteria such
as nitrogen fixers, phosphate solubilizers, potassium solubilizers, fluorescent
pseudomonads and Bacillus sp. were carried out from three Pokkali rice growing
regions of Ernakulam district (Vytilla, Varapuzha and Kadamakudy).
Maximum population of 4 x 103
, 4.66 x 103
and 16.67 x 103 cfu per g of soil
were recorded for nitrogen fixers, phosphate solubilizers and Bacillus sp. respectively
and fluorescent pseudomonads and potassium solubilizers were absent. A total of 25
predominant isolates were obtained of which 17 isolates belonged to Bacillus sp. and
remaining 4 isolates each were nitrogen fixers and phosphate solubilizers. Cultural,
morphological and biochemical characters of all the 25 isolates of rhizobacteria
showed varied colony morphology and Gram reaction.
These isolates were evaluated under in vitro for plant growth promotion
activities (production of indole acetic acid, nitrogen fixation, phosphate and potassium
solubilization), antagonistic mechanisms (NH3, HCN and siderophore production) and
its activities against Xanthomonas oryzae. Quantity of IAA produced by
rhizobacterial isolates ranged from 0.46 to 31.27 μg ml-1. Quantity of nitrogen fixed
and phosphate solubilized by rhizobacterial isolates varied from 5.72 to 25.21 mg of
N g-1 sucrose utilized and 1.98 to 53.19 μg ml-1, respectively. There was no significant
difference between potassium solubilized by isolates. Among the rhizobacterial
isolates all Bacillus sp. isolates and two isolates each of nitrogen fixers and phosphate
solubilizers were found positive for ammonia production. In case of screening of
isolates for siderophore production, isolate VYP1 produced moderate orange halo
zone on CAS agar media. Isolates VYN1, VYN2, VRB1 and VRB3 recorded poor
siderophore activity. Remaining all isolates in the study screened negative for
siderophore production. All isolates in the study were found negative for HCN
production. Antagonistic activities of isolates to inhibit the rice pathogen
Xanthomonas oryzae was evaluated and twenty one isolates screened exhibited
antagonistic response against pathogen in which Bacillus isolates KDB4 and KDB5
exhibited excellent antagonism against pathogen. Based on the plant growth
promotion activities and antagonistic activities, four most efficient isolates each of
nitrogen fixers, phosphate solubilizers and Bacillus sp. were selected for salinity
tolerance studies. Among the isolates, nitrogen fixers and Bacillus sp. exhibited
maximum salinity tolerance of 12% whereas, phosphate solubilizers exhibited salinity
tolerance up to 4% salt concentration. After salinity tolerance studies, three most
tolerant nitrogen fixers (VYN2, KDN1 and KDN2), phosphate solubilizers (VYP1,
VRP1 and KDP1), and Bacillus sp. (VYB3, VYB6 and KDB1) were selected for
compatibility studies. Three most promising PGPR based consortia, PGPR consortia1 (KDN2 + KDP1 + VYB6), PGPR consortia-2 (KDN1 + KDP1 + VYB6) and PGPR
consortia-3 (KDN2 + VYP1 + KDB1) were formulated. The three most promising
consortia were evaluated under pot culture experiment, along with KAU commercial
formulation (PGPR Mix-1) and Organic Package of Practices Recommendations of
KAU (2017), at RRS, Vytilla, with Pokkali rice (variety Vytilla-6) as the test crop.
All the three native PGPR consortia (T1, T2 and T3) exhibited significant
increase in plant height and plants treated with T1 (PGPR consortia 1- KDN2 + KDP1
+ VYB6) and T2 (PGPR consortia 2 - KDN1 + KDP1 + VYB6) recorded significantly
higher results. Higher number of grains per panicle, grain yield (g per pot) and
theoretical grain yield (kg ha-1) were observed in PGPR consortia 1 consisting of
isolates KDN2 (N-fixer) + KDP1 (P- solubilizer) + VYB6 (Bacillus sp.). Significantly
higher test weight of seeds were observed in T1, T2 and T3 inoculated with native
PGPR consortia compared to other treatments. However, the treatments did not have
any significant effect on number of tillers, number of panicles per plant and the
percentage of chaffy grains produced.
The present study indicated that saline tolerant PGPR consortia-1 consisting of
Enterobacter cloacae strain KDN2 (N-fixer) + Bacillus subtilis strain KDP1 (Psolubilizer) + Bacillus altitudinis strain VYB1 (Bacillus sp.) was the most promising
biofertilizer in enhancing the production of Pokkali rice of Kerala. However, further
evaluation of the most promising consortia needs to be done under field conditions to
confirm the results.