PHYLLACTINIA

CLASSIFICATION OF PHYLLACTINIA

Kingdom :- Mycota

Division :- Eumycota

Sub-division :- Ascomycotina

Class :- Plectomycetes

Order :- Erysiphales

Family :- Erysiphaceae

Genus :- Phyllactinia

Phyllactinia dalbergiae is very common on the leaves of shisham and shahtoot. The leaves show white powdery mass on the lower surface.

STUDY OF HOSTS, DISEASES AND SYMPTOMS

COMMENTS :-

The fungus is a hemiendophytic parasite and commonly causes powdery mildew. Phyllactinia parasitizes leaves of over hundred species of plants, chiefly the deciduous trees. Some of the important species are listed below. 

• P. guttata (= P. corylea) is a very common species parasitizing Corylus, Betula (vern. bhojpatra; fam. Betulaceae), Cassia fistula (vern. amaltass; fam. Caesalpiniaceae), etc.
• P. dalbergiae is very common in northern India and attacks Dalbergia sissoo (vern. shisham; fam. Papilionaceae). 
• P. moricola is found on leaves of Morus alba (vern. shahtoot; fam. Moraceae). 
• P. acaciae attacks some species of Acacia (fam. Mimosaceae).
• P. yarwoodii is found on the leaves of Dalbergia volubilis and D. lanceolaria.

The disease caused by species of Phyllactinia is known as ‘powdery mildew’ , owing to the presence of white powder on the host surface. It is the result of profuse extramatrical mycelium spreading on the host surface. The disease is air borne.

STUDY OF VEGETATIVE STRUCTURE

COMMENTS :-

• • The mycelium which spreads over the surface of the host possesses septate hyphae with uninucleate cells.
  • The saccate haustoria are formed in the mesophyll cells bordering the sub-stomatal chamber by 6-7 celled hyphal branches of limited growth. The mycelium is thus hemiendophytic.

ASEXUAL REPRODUCTIVE​ STRUCTURES​

COMMENTS :-

• Conidia are the asexual reproductive structures formed on conidiophores; the latter develop from the superficial mycelium.
• The conidiophores are abundant, first on both the surfaces of the leaves but later become restricted only to the lower surface.
• Each conidiophore is 3-4 celled erect branch terminating into a single conidium.
• The conidia are disseminated by wind. These germinate into a new mycelium under favourable conditions.
• Each conidium is clavate, thin-walled and uninucleate.

ASCOCARP, ASCI AND ASCOSPORES​

COMMENTS :– 

• The ascocarp or the fruiting body is cleistothecium provided with long, unbranched, setiform and rigid appendages. 
• The appendage has bulbous base which helps in release of ascospores after freeing the cleistothecium from hyphal mat.
• Besides the appendages, there is an apical crown of penicillately branched hyphae over the cleistothecium. These hyphae give out a slimy substance which helps fruiting body to get attached to the host surface. 
• The asci get exposed and the ascospores are liberated, only after the rupture of the cleistothecial wall. 
• Asci are clavate, arranged more or less in parallel manner on the floor of the ascocarp. 
• Each ascus contains two ascospores. Each is ovate to elliptical and uninucleate.

IDENTIFICATION

• Kingdom – Mycota
  1. Chlorophyll absent
  2. Reserve food glycogen
  3. Cell wall of fungal cellulose.
• Division – Eumycota
  1. A definite cell wall present.
• Sub-division :- Ascomycotina
  1. Mycelium septate.
  2. Spores borne endogenously in the ascus.
  3. Spores in definite numbers, in multiples of two, usually eight.
• Class :- Plectomycetes
  1. Ascocarp, a cleistothecium.
• Order – Erysiphales
  1. Ectoparasites
• Family – Erysiphaceae
  1. Aerial mycelium hyaline
  2. Enormous production of conidia on host surface gives it a white powdery appearance.
• Genus – Phyllactinia
  1. Hemiendophyte.
  2. Cleistothecial appendages with bulbous base.
  3. Ascospores two per ascus.

REFERENCES

• https://en.wikipedia.org/wiki/Phyllactinia
• https://www.shutterstock.com/search/phyllactinia