There are number of species of genus Phyllactinia. P. dalbergiae is commonest species found growing on the leaves of Dalbergia sissou (shnharn). The specimens can be collected in abundance during the winter on the fallen leaves of shisham. This fungus is an obligate parailte.
Physlactinia guttata is a species of fungus in the Erysiphaceae tautly. It is a plant pathogen distributed in temperate regions, P. gultata causes a powdery mildew on leaves and stems on a broad range of host plants.
Various stages in the life cycle of Phyllactinia . Fig I. Natural size, on chestnut leaf. 2. Cleistothecium enlarged. 3. Two asci. 4.Three sporidia. 5.Coaidia-bearing hyphae. 6.Conidium germinating.
Its mycelium grows on the surface of leaves forming a whitish con ring. The hyphae send their short branches or haustoria through stomata of host in the epidermal or other mesophyll cells. Haustoria are ased to absorb food form the host tissues. Its hyphae are hyaline,
much branched and septate. These form a whitish mat on the surface of leaves.
The fungus reproduces asexually by producing unicellular, hyaline conidia. The wall of conidia is two layered. The outer layer is smooth and thin. But the inner layer is comparatively thic!.. There are ‘toted marking on its surface. These conidia are formed at the tips of short or long conidiophores. These come out of the host stomata. The conidia are elongated, slightly spindle-shaped with blunt ends. The conidium detaches and fall. The sub-terminl cell of com diophores divides again in two daughter cells. The upper cells develop new conidium. Thus conidia are formed singly and no conidia chain is formed. The conidia are produced in abundance. Therefore, the leaf surface appears to be covered by a white )owdery mas., Therefore, this disease is known by the name of Powdery Mildew. The conidia form germ tube after germination. This germ tube infects new leaves of the host.
Sexual reproduction occurs in later summer. The hyphae produce ectophytic mycelium. The conidia production stops during sexual reproduction. Young cleistothecia start developing on the ectophytic mycelium. The colour of cleistothecia changes from white to black. The,;e fruit-bodies are produced as a stimulus of sexual reproduction. Therefore, these cleistothecia represent the perfect stage.
- Sexual reproduction takes place by the usual production of .tntheridia and Ascogonia.
- Plasmogamy occurs in ascogonium. It givers rise to the tscogenous hyphae.
- [hese hyphae ultimately produce asci at their tips. Kai yogamy and meiosis takes place in the asci before ascospores formation.
- [he vegetative hyphae grow around this developim, sexual apparatus. It forms a pseudoparenehymatousl tissue. These tissues ultimately form the wall of the cleistothecium with .tharacteristic appendages on the surface.
- The fruit bodies of another species Phyllactinia corylea are ‘ormed from Leaves of Morns alba. The infected leaves can be easily recognized by examining the thy, fallen leaves under the 3albergiae plants during autumn or the following winter.Fru ling body: Cleistothecia
- The fruit bodies are visible to the naked eye as black do’s on the iurface of the leaves. These fruiting bodies are rounded, ball-like structures without any opening. Such fruit-bodies arc known is cleistothecia. It has globose structure. These are upto I 50p in diameter.
- Ihe characteristic feature of these fruit-bodies is the presence of long, stiff, pointed appendages on the surface called crown. These appendages are swollen at the base to form bulbous part. The type of appendages distinguishes Phyllacania &cm other genera of the Erysiphales.
- The wall of the cleistothecium is pseudoparenchymatous.
- There are many asci within each cleistothecium. Each ascus has 2-4 ascospores instead of the usual 8 ascospores.
Rupturing of cleistothecium
The base of bulbous appendage is thick walled above and thia walled below. The appendages bend downward on drying. Thus thin part buckles inwards. It causes downward pressure of the appendages tips. It frees the cleistothecium from the mycelium. Now cleistothecium attach to leaves.
The ascospores become mature in the asci. Now the inner cells of the cleistothecium absorb water. It swells to rupture the cleistothecium. Asc also burst. Thus ascospores are discharged.