Lab Practical 4：Protozoa Chromista and Lower Fungi

Practical 4

PROTOZOA (PHYLUM PLASMODIOPHOROMYCOTA) CHROMISTA (OOMYCOTA) AND LOWER FUNGI (PHYLA CHYTRIDIOMYCOTA & ZYGOMYCOTA) -TAXONOMY AND PATHOLOGICAL IMPORTANCE

Introduction：

Protozoa (also protozoan, plural protozoans) is an informal term for single-celled eukaryotes, either free-living or parasitic, which feed on organic matter such as other microorganisms or organic tissues and debris.

The Chromista is an eukaryotic kingdom, probably polyphyletic. They include all algae whose chloroplasts contain chlorophylls a and c, as well as various colorless forms that are closely related to them. These chloroplasts are surrounded by four membranes, and are believed to have been acquired from some red algae.

The lower fungi comprise the simplest and the primitive group of true fungi represented by about 1,500 species. The majority of these are aquatic (Saprolegnia), some are amphibious (Phytophthora) and some terrestrial (Rhizopus).

They live either as strict parasites or saprophytes. Strictly parasitic species live on algae, ferns and seed plants. A number of them cause diseases of economic plants.

Exercise：

s   A：FUNGAL CULTURE

Pure culture of Phytophthora sp. and Pythium sp. are grown on CMA (Com Meal agar）and rhizopus sp. on PDA (Potato dextrose agar). Examine macroscopic features of the colony (color: top and reverse), hyphal characteristics, shape of sporangium bearing spores etc.

s   B: PLANT DISEASE SPECIMEN

The following live specimens (if available) will be provided:

1)        Downy mildew of cucurbits e.g. cucumber.

2)        False rust of four-angled bean ( kacang botor).

Examine and record the following disease symptoms ( either live , preserved or pictures) ,

1)        Club root disease

Caused by Plasmodiophora brassicae. Infects cruciferous vegetables such as cabbage grown in the Cameron Highlands. Main symptom of hypertrophy (enlargement) of roots.

2)        Shoot or flower blight

Caused by Choanephora cucurbitarum . Infects chili and various solanaceous crops such as brinjal and okra. Symptoms include leaf defoliation, fruit and shoot rot.

3)        Damping off of seedling

Caused by Pythium sp. Atacks mainly seedlings e.g. vegetables, Damping off during pre-germination causes and roots. Post germination damping off causes rots on the stems and roots of seedlings usually close to the soil level.

4)        Potato late blight

Caused by Phytophthora infestans. Infects potato leaves, stems and tubers. Symptoms of black lesions. Disease also occurs in tomato cultivated in the Cameron Highlands.

5)        Black pod ( pod rot ) of cocoa

Caused by Phytophthora palmivora. Infects cocoa pods during wet weather. Symptoms of black lesions causing pods to rot within days. Fungus can also infect the cocoa main stem and causing stem canker.

6)        Black stripe of rubber

Caused by Phythophthora palmivora. Infects the tapping panel of rubber. Black stripes in stems and causing vertical splits of the bark.

7)        Seedling dieback and patch canker of durian

Caused by Phytophthora palmivora. Death of durian seedlings. It also causes death of mature durian trees with symptoms of brownish to reddish patches on the bark infected by stem canker.

8)        White rust of kangkong

Caused by Albugo ipomoea-panduranae. White patches observed on the lower surfaces of leaves and stems of kangkong.

s   C. SLIDES

Examine and record fungal structures from slides displayed.

1)      Plasmodiophora brassicae
Observe resting spores in root cells.

2)      Synchytrium psophoearpi

Observe slides of sporangia produced from sorus ( yellowish in colour )

3)      Phythophthora , Pythium sp

Observe the shape of sporangium (lemon shaped and rounded respectively). Differentiate shape of sporangia (asexual reproductive stage) from the slides of oospores (sexual stage).

4)      Pseudoperonospora cubensis

Observe the dichotomous xbranching of sporangiophores each bearing the sporangium.

Note that the sporangia may be detached during the preparation of slide.

5)      Albugo ipomoea-pandaranae

Observe the squarish shaped sporangium borne in chains on a club shapedsporangiophore.

6)      Choanephora cucurbitarum

Observe the rounded sporangium bearing sporangiospores. The fungus can also produce conidium (sporangiolum) that is formed on heads.

7)      Rhizopus sp .

Observe the slides of sporangium bearing sporangiospores (asexual stage) and zygospores (sexual stage).

s   D. DISEASE CYCLES

Observe the disease cycles of various fungal-like organisms and fungi as shown in

1)      Plasmodiophora brassicae

2)      Pythium sp. 

3)      Phytophthora infestans

4)      Plasmopara citicola

5)      Rhizopus sp.