UNIVERSITY OF THE PHILIPPINES – LOS BAÑOS
COLLEGE OF FORESTRY AND NATURAL RESOURCES

In partial fulfilment of the requirements of
FBS 45

EXERCISE 5: DIAGNOSIS OF SEEDLING DISEASES IN THE SILVICULTURAL
FOREST INFLUENCES NURSERY OF THE COLLEGE OF FORESTRY AND
NATURAL RESOURCES

Submitted by:
Mary Angela H. Magno
Y – 2L

Submitted to:
Mutya Ma. Q. Manalo

INTRODUCTION

Diagnosis of forest plant diseases requires a thorough understanding of the nature of disease, whether it is infectious or non-infectious. Systematic and careful observations of the plant, its environment, and other plants in the area are a vital step in determining what factors have damaged the plant (Green, 2011). The accuracy of diagnosis is dependent on the available information about the causal agent and its host plant such as history of previous disease occurrence, conditions of the plants in the forest, and knowledge about symptoms and signs occurring within the plants. On the other hand, consulting a plant pathologist or comparing the existing symptoms with those given in books and other literatures about forest pathology may also be done. Proper control of forest diseases is important to avoid ecological and economic loss
(Militante & Manalo).

In this exercise, symptoms and signs of diseases of seedlings in the nursery were observed. Specifically, the objectives of this exercise is to (1) identify the symptoms occurring within the seedlings, (2) gather information about the prevailing growing conditions of the host plant, and (3) compute for percent disease incidence, average rating, and index of infection of the extent of disease in affected seedlings.

METHODOLOGY

The following information were taken from a person in charge in the nursery:
1. Name of the host plant (common name and scientific name)
2. Age of seedlings
3. Frequency of watering
4. Type of fertilizer and other chemicals applied
5. Soil characteristics

50 seedlings of Hopea plagata (saplungan) were observed empirically and were measured according to amount of infection occurring in each of the seedlings with rating and numerical rating classified in table 1.

Table 1. Amount of infection and its corresponding rating and numerical rating.
Amount of Infection

Rating

Numerical Rating

0% infection (healthy)

1

0

1% to 25% infection

2

0.75

26% to 50% infection

3

1

51% to 75% infection

4

2

76% to 100% infection

5

3

Data were summarized using Microsoft Excel and percent disease incidence, average rating of disease severity, and index of infection were computed.

RESULTS

According to the information gathered by the researcher, it has now been 7 years since the saplungan seedlings were planted in the nursery by BS Forestry students. Garden soil was used in planting the seeds and watering is done 3 times a week depending on the weather. No fertilizer and other chemicals were applied to the plants.

Thirty four percent of the seedlings occur within 26% to 50% (Rating = 3; Numerical
Rating = 1) amount of infection. On the other hand, seedlings with 51% to 75% (Rating = 4;
Numerical Rating = 2) amount of infection comprise only 8% of the total population.
Additionally, 20% of the seedlings were remarked as dead plants.

20%

14%
0%
1%-25%

8%

24%

26%-50%
51%-75%
76%-100%

34%

Figure 1. Percent distribution of the amount of infection of Saplungan seedlings in the nursery.

Percent disease incidence, average rating of disease severity, and index of infection were computed using the following formula:

% Disease Incidence =

Average Rating =

Number of diseased seedlings
Total number of seedlings

Sum of all ratings

x 100

Total number of seedlings

Index of infection =

Sum of all numerical ratings x 100
Total number of seedlings x 3

From the data, it can be inferred that 86% of all saplungan seedlings are diseased, while disease severity following the ratings and numerical ratings are 2.96 and 1.28 respectively.
Common symptoms found in the seedlings were leaf spots, shot holes, leaf blight, and yellowing of leaves. Others were eaten by leaf insects and catterpillars.

DISCUSSION

Diagnosis is a process of gathering information about the disease of a host plant and its causal agent. Determining the causes of the plant problem is a vital step in recommending a possible solution or remedy to the problem (Mohan, 1996). These causes may either be due to a pathogen (fungi, bacteria, viruses, nematodes, and pests) or a physiopath (environmental conditions and chemicals).

Eighty six percent of the total population of saplungan seedlings are infected with disease with an average rating of disease severity of 2.96 and index of infection of 1.28. These values mean that the plants have an average amount of infection ranging from 51% to 75%. Most of the plants exhibit chlorosis or yellowing of leaves which means that there may be a nutrient deficiency in the soil, drought stress, or that soil pH was not favourable for the plant (Small,
2011). The use of garden soil in planting the seedlings probably induced the symptom. Another observed symptom among the seedlings was the leaf spot. These lesions in the leaf are caused by different kinds of fungi, bacteria, and viruses. Shot holes, another symptom observed, are circular holes which results from dropping out of the central dead areas of spots in the leaves
(Mohan, 1996).

Table 2. Symptoms and signs of fungal and bacterial leaf spots (Green, 2011).
Abnormality

Fungal

Watersoaking

Not common

Texture

Usually dry; may be papery

Odor

Usually none

Pattern
Disintegration
Color changes
Pathogen structures

Irregular to circular; may have concentric rings
Uncommon
Common: red, yellow, purple halos Common: mycelia, spores, spore structures

Bacterial
Common with rots of thick and succulent leaves and with initial appearance of angular leaf spots
Some dry, some slimy to sticky; may be papery when dry
Foul (putrid to earthy, acrid) odor usually associated with rots of fleshy plant parts
Irregular to angular; often restricted by large veins
Common with rots
Less common, but may have irregular, yellow halos
Wet or dried slime at edge of canker or leaf spot

Blight, a sudden death of foliage, starts from rapid, extensive discoloration, and wilting of leaves. One of the major causes of this symptom is the occurrence of the bacteria called
Erwinia (Erwinia blight) which induces water-soaking appearance. This occurs when the bacteria dissolve the material that holds plant cells together, resulting to destruction of leaf and stem integrity to decrease (Green, 2011). Sometimes, blight may also be caused by fungal diseases.

Spread of disease in plants may be controlled with proper diagnosis. Plant diseases can be managed through an integrated approach. This includes cultural, mechanical, biological, and chemical practices combined. Cultural management considers what type of plant to use according to local climate and favourable environment. It also includes preparation and cultivation of the soil, and application of fertilizer when needed. Mechanical management applies different silvicultural practices such as pruning, rotation cropping, weeding, etc. in order to reduce the source of inoculum in the area. In this exercise, it was observed that dead seedlings were next to each other and it was also inferred these dead seedlings may infect other plants near them that is why cleaning and sanitation cutting should be done. Introduction of beneficial microbes through the use of compost, compost teas, and hyperparasite products is the main concern of the biological control. Lastly, chemical practices such as the use of herbicides, fungicides, and insecticides may also be done. However, it is very important to identify the cause of the problem first before applying any of these (Small, 2011).

CONCLUSION

Proper diagnosis cannot be done without knowledge of the nature of disease. Diagnosis is important to decrease rapid spread of disease occurring in plants, and to avoid economic and ecological loss.

REFERENCES

Green, J. L. (2011). Diagnosing Plant Problems. Retrieved May 4, 2016, from University of
Kentucky Cooperative Extension: www2.ca.uky.edu/agcomm/pubs/id/id194/id194.pdf
Militante, E. P., & Manalo, M. M. (n.d.). Syllabus on Forest Tree Diseases. Los Banos, Laguna.
Mohan, S. K. (1996). Idaho Master Gardener Program Handbook.
Small, M. (2011, December). Plant Pathology. Retrieved May 4, 2016, from Colorado State
University Extension: www.ext.colostate.edu/mg/Gardennotes/331.pdf

APPENDIX

Table 3. Seedling number and corresponding rating, numerical rating, and remarks.
Seedling

Rating

Numerical Remarks

Seedling Rating Numerical Remarks

Rating

Rating

1

2

0.75

26

3

1

2

3

1

27

1

0

3

3

1

28

1

0

4

5

3

dead

29

3

1

5

5

3

dead

30

2

0.75

6

5

3

dead

31

3

1

7

2

0.75

32

3

1

8

1

0

33

3

1

9

2

0.75

34

4

2

10

3

1

35

4

2

11

2

0.75

36

5

3

dead

12

4

2

37

5

3

dead

13

5

3

dead

38

4

2

14

5

3

dead

39

3

1

15

5

3

dead

40

3

1

16

2

0.75

41

2

0.75

17

2

0.75

42

2

0.75

18

2

0.75

43

2

0.75

19

1

0

44

1

0

20

1

0

45

1

0

21

3

1

46

3

1

22

3

1

47

3

1

23

3

1

48

3

1

24

3

1

49

5

3

dead

25

2

0.75

50

5

3

dead