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Black pepper has been reported to be the most vulnerable spice crop to
climate change. The beneficial microorganisms in the rhizosphere of black pepper
can reduce the impact of abiotic stress due to changes in the weather variables.
However, the soil microbial community are also influenced by changes in weather
and microclimatic parameters.
A study was undertaken on the “Impact of weather variables on the
functional efficiency of beneficial microflora in the rhizosphere of black pepper”.
The main objectives were to study the effect of weather and microclimatic
parameters on the population and functional efficiency of beneficial microflora
namely; Azospirillum, phosphate solubilizing bacteria (PSB), Pseudomonas
fluorescens and Trichoderma sp.
The rhizosphere soil samples from black pepper were collected at monthly
interval for a period of one year from Pepper Unit, Kerala Agricultural University
(KAU), Vellanikkara. The selected beneficial microorganisms were enumerated
and in vitro screening was done at monthly interval for IAA, ammonia, HCN,
siderophore production, phosphate solubilization and antagonistic activity against
Phytophthora capsici. Simultaneously, the weather and microclimatic parameters
were also recorded.
The Azospirillum and PSB were not obtained throughout the study period
from July, 2015 to June, 2016. The population of fluorescent pseudomonads was
highest in September, 2015 and was absent in March, 2016 and April, 2016.
Trichoderma sp. recorded the highest population in July, 2015 and lowest in June,
2016. A total of 31 isolates of fluorescent pseudomonads and 3 isolates of
Trichoderma sp. were obtained during the entire study period.
Out of 31 isolates of fluorescent pseudomonads, 29 isolates produced
ammonia with different concentrations. Fifteen isolates produced HCN and only
ten isolates showed siderophore production as their antagonistic mechanism. Only
5 isolates were phosphate solubilizers and 4 isolates were antagonistic to
Phytophthora capsici. However, in the case of Trichoderma sp. two isolates
produced ammonia, one isolate was HCN producer, two produced siderophore and
two isolates showed antagonistic activity against Phytophthora capsici.
Considering the correlation studies between weather, microclimatic
parameters and population of isolates obtained, it was found that the population of
fluorescent pseudomonads were positively correlated with rainfall and soil moisture
whereas negatively correlated with air temperature, sunshine hours and soil
temperature. However, the population of Trichoderma sp. was positively correlated
with rainfall, relative humidity and soil moisture whereas it was negatively
correlated with air temperature, sunshine hours and soil temperature. The study
indicated that rainfall (200 to 500 mm) and soil moisture (15 to 20%) favoured
fluorescent pseudomonads and Trichoderma population.
The functional efficiency of the isolates were also correlated with the
weather and microclimatic parameters. In case of fluorescent pseudomonads, the
weather and microclimatic parameters had no significant effect on its ammonia and
HCN production. However, significant effect on the siderophore production was
noticed. In the case of Trichoderma, weather and microclimatic parameters had no
significant effect on ammonia, HCN and siderophore production.
The present studies clearly indicated that the weather and microclimatic
parameters affected the siderophore production in the case of fluorescent
pseudomonads but, there was no effect on functional efficiency of Trichoderma sp.
However, mitigation strategies have to be studied in the case of fluorescent
pseudomonads to overcome the effect of weather and microclimatic variables on
functional efficiency.