This presentation deals with the detection and diagnosis of plant pathogens. Plant diseases caused by fungi, bacteria, viruses, nematodes, and other microbes are a major threat to global agriculture. For effective management, early and accurate diagnosis is the first and most important step

1. Detection and Diagnosis of Plant Pathogens
PRESENTED BY:
RAVINDRA KUMAR
DEPERTMANT OF PLANT PATHOLOGY
K.D COLLEGE SIMBHAOLI
MSc 4th SEM

2.  Detection
In plant pathology, detection is the process of
identifying the presence of a disease, pathogen, or its
specific signs and symptoms on a plant, often through
visual inspection or advanced techniques like nucleic
acid amplification or biosensors. It's a critical step for
early intervention, distinguishing it from diagnosis,
which involves identifying the specific pathogen and
understanding the disease's nature and cause.
Introduction

3.  Diagnosis
In plant pathology, diagnosis refers to the
process of identifying the cause of a plant disease. It
involves recognizing the symptoms (visible effects on
plants) and signs (physical presence of the pathogen)
to determine whether the disease is caused by fungi,
bacteria, viruses, nematodes, phytoplasmas, or abiotic
factors (like nutrient deficiency, pollution, or stress).
 Importance of early detection
 Role in disease management and crop

4.  Symptoms: visible changes in host (chlorosis, necrosis, wilting, galls)
Leaf symptoms – yellowing (chlorosis), spots, blights, mosaic patterns.
Stem symptoms – wilting, cankers,
galls, rotting
.Root symptoms – root knots, necrosis,
stunted growth
.Fruit/flower symptoms – rots, malformations,
premature drop
.Whole plant symptoms – stunting, wilting,
death.
 Signs: presence of pathogen
structures (mycelium, spores
, bacterial ooze)
Symptoms vs Signs
Alternaria
Rust

5.  Koch’s postulates
Koch's postulates are a four-step scientific process
developed by Robert Koch in the 19th century to establish a
causal relationship between a microbe and a disease.
Traditional Methods

6.  ELISA (Enzyme-Linked
Immunosorbent Assay)
The ELISA test was
developed by Swedish
scientists Eva Engvall
and Peter Perlmann in 1971.
This method uses
antibodies to detect
substances such as
hormones or viruses
and was a safe and
effective alternativ
e to radioimmunoassay
(RIA) .
Serological Techniques

7.  PCR (Polymerase Chain
Reaction)
Polymerase Chain Reaction (PCR) is a
laboratory technique that creates millions
of copies of a specific DNA or RNA
segment,enabling detailed study and
analysis.
Developed by Kary Mullis in the 1980s,
PCRutilizes a thermostable DNA
polymerase, primers, and
deoxynucleotide triphosphates (dNTPs) to
replicate a targeted DNA sequence
through repeated cycles of denaturation,
annealing, and extension
 qPCR (quantitative PCR)
 DNA barcoding & sequencing
 LAMP (Loop-mediated isothermal
Molecular Techniques

8.  Next-Generation
Sequencing (NGS
. Next-Generation Sequencing (NGS) in
plant pathology was not "discovered" by a
single person but emerged from the
cumulative work of the scientific
community, with key early developments
including Adams et al. (2009) and Al
Rwahnih et al. (2009), who first described
sequencing plant viruses using total RNA.
These pioneering studies applied the
high-throughput capabilities of NGS to
plant virology, rapidly establishing it as a
powerful, low-cost, and efficient tool for
discovering and characterizing plant
pathogens.
 Biosensors & nanotechnology
 Remote sensing & imaging
Advanced Diagnostic Tools

9.  Traditional: cost-effective, simple, but less precise
Traditional methods for diagnosing plant diseases, while cost-
effective and simple, lack precision due to their reliance on visual
observation and subjective human interpretation, which can lead
to diagnostic errors, inability to detect early or low-level
infections, and are often time-consuming.
I. Visual Inspection
II. Manual Sampling and Laboratory Tests
Molecular: highly sensitive, specific, but requires expertise
Molecular diagnostics are highly sensitive and specific tools for
pathogen identification, with Polymerase Chain Reaction (PCR) and
DNA sequencing being prominent examples.
III. Amplification of Genetic Material
IV. DNA Sequencing
V. Specific Targets
Advantages of Molecular vs
Traditional

10.  Virus detection using ELISA
Detection of potato virus Y (PVY) using DAS-ELISA
Potato virus Y (PVY) is one of the most significant and
prevalent viruses in potatoes worldwide, causing major yield
loss. It is transmitted by aphids and can infect other
solanaceous crops like tomatoes and peppers.
 Fungal pathogen detection with PCR
Colletotrichum lupini in Lupin
A PCR-based case study for detecting a plant fungal pathogen
involves extracting pathogen DNA from infected tissue,
amplifying a specific DNA region using species-specific
primers, and analyzing the amplified product for the presence
of the pathogen.
Case Studies

11. The high cost of advanced diagnostic methods (e.g.,
biosensors, high-throughput sequencing) and the need
for skilled personnel create significant barriers to
implementing and accessing these techniques,
particularly in resource-limited settings. Furthermore,
pathogen variability (e.g., mutation, loss of virulence) and
the presence of mixed infections complicate detection
and identification, requiring robust, adaptable, and often
complex diagnostic solutions.
 High cost of advanced methods
 Need for skilled personnel
 Pathogen variability & mixed infections
Challenges

12.  Early & accurate detection = key to disease
management
Early and accurate disease detection is crucial for effective
disease management, and the best approach combines the
strengths of traditional and molecular tools, as modern
molecular techniques offer rapid, sensitive, and specific
identification of pathogens and genetic markers, which are
sometimes beyond the capabilities of older, more time-
consuming methods. By integrating these technologies,
healthcare can achieve faster diagnosis, better treatment
planning, and improved disease control.
 Combination of traditional & molecular tools
recommended
Conclusion

13.  Agrios, G.N. Plant Pathology
 ICAR publications
 FAO reports
 Recent research papers
References

14. Thank
You