MSc

Amaranthus (Amaranthus spp.) is one of the most important leafy vegetables
in Kerala. It is a storehouse of essential phytonutrients and antioxidants. Amaranth
leaves are rich in proteins and higher in fiber content. Among the various cultural
practices that increase crop productivity and yield, nutrient management is involved
in a significant role in enhancing yield per unit area. Microbial strains are used for the
improvement of productivity in sustainable agriculture and are widely accepted
methods in different parts of the world. Drought stress affects agricultural
productivity and yield. It is an important factor, which harms more than 50 percent of
crop yield worldwide. Plant growth-promoting microorganisms like PPFMs supports
plant to survive extreme environmental conditions like severe drought. Among the
various foliar diseases affecting amaranth, the most serious foliar disease affecting
amaranth is leaf blight, which is caused by Rhizoctonia solani. Pink Pigmented
Facultative Methylotrophs, plays an important role in stress tolerance and they can
stimulate induced systemic resistance against plant pathogens. Hence, the current
investigation was carried out on a screening of abiotic stress tolerant PPFMs from
phyllosphere as well as rhizosphere regions of amaranth growing areas of Thrissur
district for their plant growth promoting and foliar disease management under pot
culture studies.
PPFMs were isolated from amaranth leaves and roots from ten significant
locations where amaranth is being cultivated in Thrissur district. Morphological,
cultural and biochemical characters of all PPFM isolates were studied. All bacterial
isolates were rod shaped, motile and Gram negative. All the PPFM isolates were
screened for plant growth promoting activities under in vitro conditions. In the present
study, out of the ten native isolates of PPFM, seven were positive for IAA production.
PPFM isolates produced IAA ranging from 3.15 to 15.03 µg ml-1. IAA production by
Kod-c (15.03 µg ml-1) was significantly higher than other isolates. This was followed
by Nel-c (9.60 µg ml-1), and Kan-a (9.42 µg ml- 1
). Pat-c and Nel-c recorded
significantly superior nitrogen fixation of 0.766 mg/g and 0.756 mg/g, respectively.
Lowest amount of nitrogen fixation was shown by reference strain 0.350 mg/g. The

amount of phosphate solubilization ranging from 5.99% to 11.15%. ACC deaminase,
which plays a significant role in drought mitigation. Out of ten native isolates of
PPFM, eight were positive for ACC deaminase activity. The antagonistic activity of
all PPFM isolates was assessed against Rhizoctonia solani. Three isolates out of ten
inhibited Rhizoctonia solani on potato dextrose medium, Kod-c (62.7 %),Kana(45.7 %) and Nel-c (48.9 %).
PPFM isolates were screened for different mechanisms of antagonism like
ammonia production, siderophore production and HCN production. Out of ten native
isolates, eight were positive for ammonia production. None of the isolates showed the
ability for HCN and siderophore production under in vitro conditions. In vitro
screening of PPFM isolates for acidic pH and water stress tolerance showed that Nel-c
isolate was tolerant to acidic pH upto 3.5 and two isolates namely Nel-c and Kan-a
isolates were water stress tolerant upto 20% PEG. PPFM isolates were identified by
16S rRNA gene sequence analysis. The isolates were ranked and best isolates were
Kod-c and Kan- a identified as Methylobacterium sp and Nel-c as Methylobacterium
populi, which were further evaluated.
Evaluation of the three most promising PPFM isolates (Kod-c, Kan-a and Nelc) that exhibited diverse growth promoting and antagonistic activities against
Rhizoctonia solani in amaranth was carried out. The three most efficient isolates Kana (Methylobacterium sp), Nel-c (Methylobacterium populi) and Kod-c
(Methylobacterium sp) significantly increased plant growth parameters like plant
height, number of leaves, days for first flowering and fresh weight of shoots
compared to uninoculated plants. Disease severity was also found significantly lower
(54.08%) in treatment Nel-c (Methylobacterium populi) at all stages of growth.
Methylobacterium populi (Nel-c) was the most promising PPFM isolate for
growth promotion and disease management in pot culture studies. The present study
proved that native PPFM isolates are more suitable for increased plant growth and
disease suppression. Further evaluation under field conditions will help to confirm the
results.