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A study was undertaken on “Evaluation of native rhizosphere microflora for
plant growth promotion and management of Fusarium yellows in ginger”. The
main objectives were to enhance the growth and yield of ginger using native
beneficial microorganisms isolated from wayanad district and to manage
Fusarium yellows disease in ginger by using antagonistic microorganisms.
Rhizosphere soils were collected from ten different locations of healthy and
diseased ginger fields of Wayanad district. The predominant beneficial
microorganisms namely nitrogen fixing bacteria, phosphate solubilizing bacteria,
Bacillus sp., Pseudomonas fluorescens, Streptomyces sp., and Trichoderma sp.
were isolated.
The highest population of nitrogen fixers (1.4x104 cfu/g), fluorescent
pseudomonads (9x104 cfu/g), and Trichoderma sp. (6x103 cfu/g) were obtained
from Pulpalli location. Phosphate solubilizing bacteria (9x103 cfu/g) and
Streptomyces sp. (6x104cfu/g) were highest in Kappikunnu and maximum
population of Bacillus sp. (2.3x104 cfu/g) was recorded in Mayilumpadi.
The isolates were screened for plant growth promotion and antagonistic
activity under in vitro condition. Maximum nitrogen fixation was recorded in
NFMh isolate (0.43 mg/g of sucrose utilized) among nitrogen fixers. Highest IAA
(35.02 μg/ ml), HCN and siderophore production were recorded by NFAh
(nitrogen fixer) isolate.
Among the phosphate solubilizers, highest P- solubilization (450.00%) was
by PSBAh isolate where as, IAA (33.07 μg/ ml) and HCN was shown by PSBMh
isolate. Among the isolates of Bacillus sp. The maximum P- solubilization index
(182.99%) was recorded by BsAh isolate and the least (137.43%) by BsKUh
isolate. Highest IAA (14.54 μg/ml) was produced by BsMh isolate (Mayilumpadi)
and the least (12.92 μg/ml) by BsAh isolate (Appade). Out of the ten isolates
tested for HCN production, only three BsMh, BsKuh and BsPTd isolate resulted
moderate level of HCN production. Only one isolates, BsMh positive for
siderophore production.
All the seven isolates of fluorescent pseudomonads the highest (241.57%) psolubilization
was in PfMh isolate and lowest (190.11%) by the isolate PfKh.
Highest IAA production was (16.75 μg/ml) by the isolate PfKh from Kappikunnu
and the lowest (12.13 μg/ml) by PfPh isolate. Hydrogen cyanide production of all
the isolates were tested and that isolates PfPh and PfKUh produced highest HCN
under in vitro screening. Siderophore production was produced only by three
isolates PfKh, PfMh, and PfPh.
Among the eight isolates of Streptomyces sp. the maximum P- solubilization
index (176.99%) was recorded by StrAh isolate and the least (153.76%) by StrPh
isolate. Highest IAA (11.63 μg/ml) was produced by StrMh isolate
(Mayilumpadi) and the least (10.41 μg/ml) by StrKUh isolate (Kurumankotta).
Two isolates StrMh and StrPh resulted moderate level of HCN production. Four
isolates StrMh, StrPh, StrAh and StrAd isolates resulted siderophore production.
StrPh (Pulpalli) isolate resulted excellent siderophore production.
All the isolates of Trichoderma sp. did not solubilized phosphorus and IAA
under in vitro screening Two isolates TrPh and TrKUh produced moderate HCN
under in vitro screening. Siderophore production was produced only by three
isolates TrKh, TrMh, and TrAh.
Selected isolates of Bacillus sp., Pseudomonas fluorescens, Streptomyces
sp., Trichoderma sp., were tested for their antagonistic activity against the major
soil borne pathogens of ginger viz., Fusarium oxysporum, Pythium
aphanidermatum, Rhizoctonia solani and Ralstonia solanacearum under in vitro
condition.
The isolate BsAh showed maximum antagonistic activity against F.
oxysporum (64.08 per cent) and P. aphanidermatum (15. 09 per cent) where as,
BsKh isolate was antagonistic against R. solani (47.09 per cent) and BsMh isolate
showed 43.81per cent inhibition against R. solanacearum.
Among Pseudomonas fluorescens, PfKh showed 59.43 per cent inhibition
against F. oxysporum where as PfAh isolate recorded 33.71 per cent inhibition
against P. aphanidermatum, 27.20 per cent aginst R. solani and PfPh isolate
showed 31.32 per cent inhibition against R. solanacearum.
Among the isolates of Streptomyces sp., StrPh isolate recorded maximum
inhibition (67.78 per cent) against F. oxysporum, 43.11 per cent inhibition against
R. solani and 34.23 per cent against R. solanacearum. TrAh isolate (Trichoderma
sp.,) showed highest (78.93 per cent) inhibition against F. oxysporum, 51.30 per
cent inhibition against P. aphanidermatum and 43.27 per cent against R. solani.
However, TrMh isolate shown 15.96 per cent inhibition against R. solanacearum.
Three most efficient isolates of nitrogen fixers (NFMh, NFPh, NFKh),
phosphate solubilizing bacteria (PSBPh, PSBKh, PSBAh), Bacillus sp., (BSMh,
BSAh, BSKUh), fluorescent pseudomonads (PFKh, PFPh, PFAh), Streptomyces
sp., (StrPh, StrMh, StrKh) and Trichoderma sp., (TrAh, TrKUh, TrPh) obtained
under in vitro studies were further screened under pot culture studies.
Among the isolates PSBPh (T4) was found to be the most efficient in
enhancing the growth and yield of ginger where as the isolate TrKUh (T11) was
the most efficient isolate for the management of Fusarium yellows disease. These
two isolates were identified as Burkholderia cepacia (PSBPh) and Trichoderma
harzianum (TrKUh).
The present study clearly showed that Burkholderia cepacia (PSBPh) and
Trichoderma harzianum (TrKUh) were effective for plant growth promotion and
management of Fusarium yellows in ginger respectively. However, these isolates
have to be evaluated for efficiency under field condition.