Practical 4：Protozoa, Chromista and Lower Fungi : Taxonomy and Pathological Importance

December 20, 2019

Practical 4：Protozoa, Chromista and Lower Fungi : Taxonomy and Pathological Importance

Protozoa (Phylum Plasmodiophoromycota), Chromista (Oomycota), and Lower Fungi (Pyhla Chytridiomycota & Zygomycota).

INTRODUCTION

Protozoa 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.

Chromista is a eukaryotic kingdom, probably polyphyletic. It includes all algae whose chloroplasts contain chlorophylls a and c, as well as various colorless forms that are closely related to them. As it is assumed the last common ancestor already possessed chloroplasts of red algal origin, the non-photosynthetic forms evolved from ancestors able to perform photosynthesis.[3] 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.

OBJECTIVE

To observe morphological features of protozoa, chromista and lower fungi.
To differentiate fungi and fungal-like microorganisms.

Exercise :

A. FUNGAL CULTURE

Pure cultures of Phytophthora sp. and Phythium sp. are grown on CMA (Corn Meal Agar) and Rhizopus sp. on PDA (Potato Dextrose Agar). Examine macroscopic features of the colony (colour : top and reverse), hyphal characteristics, shape of sporangium bearing spores etc.

B. PLANT DISEASE SPECIMENTS

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

I. Downy mildew of cucurbits e.g cucumber

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

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

i. Club root disease

Caused by Plasmodiophora brassicae. Infects cruciferous vegetables such as cabbage groen in Cameron Hihglands. Main symptom of hyperthrophy (enlargement) of roots.

ii. Shoot or flower blight

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

iii. Damping off of seedlings

Caused by Phythium sp. attacks mainly seedlings e.g. vegetables. Damping off during pre-germination caused seed rots. Post germination damping off causes rots on the stem and roots of seedlings usually close to the soil level.

iv. Potato late blight

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

v. Black pod (pod rot) of cocoa

Caused by Phytopthora palmivora. Infects the tapping panel of rubber. 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.

vi. Seedling dieback and patch canker of durian

Caused by Phytopthora 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.

vii. Black stripe of rubber

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

C. Slides

Examine and record fungal structures from slides displayed.

i. Plasmodiophora brassicae

Observe resting spores in root cells.

ii. Synchytrium psophoearpi

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

iii. 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).

iv. Pseudoperonospora cubensis

Observe the dichotomous branching of sporangiophores each bearing the sporangium.Note that the sporangia may be detached during the preparation of slide.