Soil biotic and abiotic factors influencing plant diseases in rice based cropping system with different regimes of conservation agricultural practices
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Date
2023-12-20
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Plant Pathology, Bidhan Chandra Krishi Viswavidyalaya, Mohanpur, Nadia – 741252
Abstract
Conservation agriculture (CA) aims to conserve, improve and make more
efficient use of natural resources through integrated management of soil, water and
biological resources combined with external fertilizer inputs. At early stage of CA there
appear some serious issues related to supplying sufficient nutrients to the crops to achieve
economically viable yields. These issues can be addressed by strengthening microbial
interaction and optimizing soil biological activity through self-sustaining biological
systems rather than reliance on external inputs or synthetic fertilizers. Modern agriculture
is input and energy intensive and highly torturous in nature thus, becoming threats not
only to microbial world but to whole ecology and environment. Thus, it is high time for
the farmers and agriculturists to address the issues of environmental sustainability along
with eco-friendly management practices for harnessing sustained crop productivity to
ensure the future food security goal. Conservation agriculture (CA), offers low
mechanical disturbance, crop rotation, retention of diverse crop residues and release of
diversified chemical compounds as rhizo-depositions to soil and maintaining a protected,
cozy habitat for microbes is well ahead biodynamic technology for sustainable crop
production. Practices of CA are capable of regenerating and conserving top soil by
restoring microbes, and ecosystem services and manage the disease dynamics in field
crops under natural conditions. Scanty of literature has been available on the details of
microbial population dynamics along with vis –a-vis plant disease dynamics under
intensification of CA practices. In the current experiment, microbial dynamics, disease
dynamics and yield was assessed and some of the important disease prediction models
were developed under rice-wheat-green gram (R-W-G) and rice-mustard-black gram (R-
M-B) cropping system under different degrees of CA practices.
In the present study, it was observed that zero tillage was found to significantly increase
the total bacterial, total fungal, total Actinomycetes and total Bacillus population,
whereas, reduced tillage favoured the total phosphate solubilizing bacteria (PSB), total
Pseudomonads population and nitrogen fixing bacterial (NFB) population. Real time
(RT) PCR was performed to evaluate the population dynamics of Alphaproteobacteria,
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Betaproteobacteria and Gammaproteobacteria under three tillage different systems and it
was found that intensification of CA practices favoured the Proteobacterial population
dynamics, when compared to conventional tillage system. In the current study,
dehydrogenase enzyme activity was also performed for better understanding of microbial
enzyme activity under different tillage systems in combination with different nutrient-
residues level. Zero tillage along with NR2 (100% residue + 50% RDF) performed the
best, with highest enzyme activity in both the cropping system, proving effects of tillage
systems and residue retention on microbial activity. Thus, a hypothesis that keystone
microbial clads were well conserved in CA under microclimate created due to less soil
disturbance, habitat restoration, cover cropping, crop rotation etc. ,is put forward.
Population dynamics of Sclerotium rolfsii was evaluated along with the suppressiveness
and conducivenesss of the soil under different regime of CA practices. In both the
cropping systems (R-W-G & R-M-B), the maximum sclerotial population of Sclerotium
rolfsii was observed in conventional tillage system as compared with CA practices. A
meta-analysis was performed to assess the changes in microbial abundance under varying
degrees of CA. Different tillage practices were the most important factors in defining the
structure of bacterial communities and β-diversity matrix showed that reduced tillage
(RT) and zero tillage (ZT) are closely related to each other whereas conventional tillage
(CT) is distantly related to them, which is the reflection of management followed in these
scenarios. Abundance at genus level showed that zero tillage and reduced tillage
exhibited higher abundance of Bacillus when compared to conventional tillage.
Streptomyces and Spingomonas showed similar kind of result, with maximum abundance
in reduced tillage, followed by conventional tillage and zero tillage. Pseudomonas, on
the other hand, showed maximum abundance in reduce tillage, followed by zero tillage
and conventional tillage. The present study clearly demonstrated that the structure and
diversity of soil bacteria in reduced tillage were significantly different compared with
other tillage practices.
Also the dynamics of naturally occurring plant diseases of rice (blast, brown spot,
bacterial blight and sheath blight), wheat (leaf blight disease), green gram (Cercospora
leaf spot disease), mustard (Alternaria blight and downy mildew) and black gram
(Cercospora leaf spot disease) under rice-wheat-green gram and rice-mustard-blackgram
cropping system were evaluated and it was observed that severity of some of the diseases
are comparatively less with increasing intensity of CA practices and it was also observed
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that severity of the majority of rice diseases were less in reduced tillage system. Studies
were also conducted for understanding the influence of different weather factors, micro-
climatic variables and soil temperature on important diseases in R-W-G and R-M-B
cropping system under varying degrees of CA practices. Disease prediction equations
were developed based on 2 years data (2019-20 & 2020-2021) for few important diseases
to understand the significant disease predicting weather and micro-climatic variables
under different rgime off CA practices. In case of Cercospora leaf spot disease of green
gram, different prediction models (multiple regression model, logistic regression model
and canonical discriminant function model) had been compared and it was observed that
canonical discriminant analysis model performed better in predicting the disease risk in
comparison to other two models. Outcome of this study will be helpful to the farmers for
adopting CA, particularly, in tropic and subtropical countries where agriculture is greatly
relying on the benefits derived from plant–microbe interactions.