Exercise No.
1 | CP 1
PLANT DISEASE DIAGNOSIS
INTRODUCTION
Diagnosis of plant disease is the process of identifying the disease through its
characteristics symptoms and signs including factors related to disease development.
Familiarity with the symptoms and knowledge of the different causes of plant disease is
essential in diagnosis. Control measures depend on proper identification of diseases and of
the causal agents. Therefore, diagnosis is one of the most important aspects of a plant
pathologist's training. Without proper identification of the disease and the disease-causing
agent, disease control measures can be a waste of time and money and can lead to further
plant losses. Proper disease diagnosis is therefore vital.
Diagnostic techniques employed for the detection of pathogens may vary depending
on the nature of the pathogen and host plant infected. Commonly followed for all kinds of
pathogen is a preliminary examination with the aid of a microscope or a laboratory test to
demonstrate presence of the pathogen. Visual inspection of symptoms, examination of
associated pathogen structures (signs) and culturing of pathogen on appropriate culture
media are traditional routine methods of diagnosing infectious plant diseases.
Nowadays, several modern methods for the detection and identification of diseases
in crops are available via both direct and indirect methods. Direct detection of diseases
includes molecular such as Polymerase Chain Reaction (PCR) and serological methods
such as enzyme-linked immunosorbent assay, that could be used for high-throughput
analysis when large numbers of samples need to be analyzed. In these methods, the
disease-causing pathogens such as bacteria, fungi and viruses are directly detected to
provide accurate identification of the disease/pathogen. On the other hand, indirect methods
identify the plant diseases through various parameters such as morphological change,
temperature change, transpiration rate change, and volatile organic compounds released by
infected plants.
Knowledge of the characteristics of the different plant pathogens and the symptoms
and signs they produce on their host is essential to attain correct disease diagnosis.
OBJECTIVES
At the end of the exercise, the student should be able to:
1. Diagnose plant diseases caused by pathogenic microorganisms, primarily fungi,
bacteria, and viruses using visual assessment of symptoms and signs.
2. Recognize the different diseases of plants, the characteristics of associated plant
pathogens, and symptoms and signs they produce.
PROCEDURE
Part I (50 points)
1. Look for a farm near in your vicinity and observe the occurrence of plant diseases on
different crops.
2. Examine five (5) different kinds of diseaseand describe its characteristic symptoms.
Take photo for documentation and indicate it in your report. (Take note that the hole
on the leaf is not a symptom). All data must be recorded in the worksheet.
Part II (50 points)
1. Look for the symptoms and signs of the following diseases in the net (2.5 points each
item).
2. Sharing of lab report is not allowed. No points will be given if reports are similar with
your classmate.
Name of the Disease Causal Organism
Bacterial Diseases
1. Potato scab Streptomyces scabies
2. Rice bacterial blight Xanthomonasoryzaepv. oryzae
3. Soft rot of carrots Pectobacteriumcarotovorum subsp.
carotovorum
4. Cassava phytoplasma disease Candidatusphytoplasmaluffae
5. Aster yellows Candidatusphytoplasmaasteris
Fungal Diseases
1. Mango Anthracnose Colletotrichumgloeosporioides
2. Southern blight of tomato Sclerotiumrolfsii
3. Corn rust Puccinia maydis
4. Corn smut Ustilagomaydis
5. Panama wilt of banana Fusariumoxysporumf.sp. cubense
Virus Diseases
1. Abaca bunchy top Abaca bunchy top virus
2. Banana Bunchy top Banana Bunchy top virus
3. Papaya ringspot Papaya ringspot virus
4. Tobacco mosaic Tobacco mosaic virus
5. Cucumber mosaic Cucumber mosaic virus
Nematode Diseases
1. Rice white tip of rice Aphelencoidesbesseyi
2. Root knot of okra Meloidogyne incognita
3. Toppling disease of banana Radopholussimilis
4. Slow decline of citrus Tylenchulussemipenetrans
5. Rice root knot (mentek) Hirschmanniellaoryza
REFERENCES
ILAG, L.L. & L.L. ILAG. 2002. Learning the Principles of Plant Pathology. Second Edition.
267 p. UPCA, College, Laguna.
TUITE, J.F.1969. Plant Pathological Methods. Fungi and Bacteria. Burgess Publ.
Minneapolis, Minnesota.
Crop Protection Laboratory Worksheet
Name: Daniel David T. Faelnar_____________________ Section:
________________________
Date Conducted: ______________________ Date Submitted: __________________
Exercise No. 1
PLANT DISEASE DIAGNOSIS
Part I.
Symptoms Documentation/ Photo
(Describe the symptoms observed)
1. The cabbage is water-
soaked and has brown
and mushy leaves that
easily spread to other
parts of the plant.
2. This tomato is soft and
mushy and it also has
watery rot.
3. This carrot has soft
and watery rot with
fluffy white mycelia.
4. The eggplant has black
spots and brown rot and
it is also water-soaked.
5. This mango has black
spots and it is also soft
and mushy.
Part II.
Symptoms Signs
Bacterial Diseases
Potato scab Streptomyces scabies
Rice bacterial blight Xanthomonas oryzae pv. oryzae
Soft rot of vegetables Pectobacterium carotovorum subsp.
carotovorum
Cassava phytoplasma disease Candidatus phytoplasma luffae
Aster yellows Candidatus phytoplasma asteris
Fungal Diseases
Mango Anthracnose Colletotrichum gloeosporioides
Southern blight of tomato Sclerotium rolfsii
Corn rust Puccinia maydis
‘
Corn smut Ustilago maydis
Panama wilt of banana Fusariumoxysporumf.sp. cubense
Virus Diseases
Abaca bunchy top Abaca bunchy top virus
Banana Bunchy top Banana Bunchy top virus
Papaya ringspot Papaya ringspot virus
Tobacco mosaic Tobacco mosaic virus
Cucumber mosaic Cucumber mosaic virus
Nematode Diseases
Rice white tip of rice Aphelenchoides besseyi
Root knot of okra Meloidogyne incognita
Toppling disease of banana Radopholus similis
Slow decline of citrus Tylenchulus semipenetrans
Rice root knot (mentek) Hirschmanniella oryzae
