Phytophthora Blight
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| Phytophthora infestans in potato causes Late blight |
The most common species is p.infestans (the casual organisms of late blight of potato)
important species of phytophthora are p. Colocasine on colocasia(kachalu) p. Areca on arica nuts, p. Parasitica on castor seedlings(supaari), p. Cinnamoni(on conifers), p.citrophthor (causing brown rot on lemons).
How to know that water is infested with phytophthora fungus:-
Phytophthora fungus loves hemp seed so for knowing that the water have part of the fungus, we use sterilized hemp seeds as host to catch phytophthora capsici zoospores.
When phytophthora Fungus attached from hemp seeds then we tested it in lab, for knowing their presence.
Symptoms Of phytophthora blight :-
Phytophthora infestans is responsible for causing late blight and root rot of potatoes.
it is one of the most serious and most common disease of potatoes.
the symptoms can be seen on any part of the plant.
On The leaves symptoms appear in the form of dark brown or olive green, oval or irregular water shoaked areas.
first of all symptoms developed at the tips and margins of old leaves,
the infection spread by vigorously particularly when temperature is low and humidity is high.
After destroying the leaves, the disease attacks whole of the aerial parts of the plant and is reduced to damp, shrivelled and blackish mass of plant debris with a peculiar and characteristic foul order.
Infections on the underground tubers is first seen in the form of dry rot and brown disloration of the tissues.
In the letter stages the infection spread inwards, the entire tube becomes brown and ultimately gets destroyed.
Reproduction :-
vegetative
a sexual
sexual
Vegetative Reproduction :-
By chlamydospores.
Thick Walled, spherical and hyaline or non papillate and straw coloured.
They are either terminal or intercalary in position and germinate by producing 3 - 11 germ tubes.
Each germ tube bears sporangium at its tip.
Sometimes( in p. Parastica) sporangium may form secondary sporangia on germinated germ tubes.
Asexual reproduction:-
By sporangia.
During damp weather, the mycelium gives rise to branched hyphae, which make their exit mainly through stomata on leaves.
The internal mycelium which comes out in tuft forms sporangiospores.
They may also come out by piercing through epidermis or tenticles of tubes or even through injured parts of plant.
A sporangium develops at the tip of each branch of sporangiospohores.
Developing sporangiosphores branch may push the terminal sporangium to one side (lateral side) and forms further sporangia.
At each point where growth is renewed, nodular swelling is formed, making the place where sporangia are born the spring is highline avoid or lemon shaped with epiculate tip having a baby detached easily and are carried away by air currents and rain splashes.
Sporangium is a multinucleate structure and remains separated from sporangiospohores by thickening of wall material which develops into basal plug this easily detachable.
Two types of germination :-
Indirect
Direct
Indirect germination :-
The sporangium show this type of germination when temperature is low below (15°c) and conditions are wet.
In such conditions, sporangium behaves as zoosporangium.
The protoplasmic content becomes segmented into 5 - 10 uninucleate pieces each forming biflagellite zoospore.
The zoospores all released either by breakdown of papilla, or by the first formation of a visicle from the papilla and then passing of zoospores into it before release.
They escape when papilla bursts and swim about in rain or dew drops.
Zoospores withdraw their flagella, come to rest, get encysted and produce a fine germ tube.
This may penetrate through the stomata.
It may come in contact with epidermal cell.
At the point of contact a small swelling or apprisorium is formed which provides the way the germ tube into host epidermis.
Direct germination :-
If the atmosphere is dry and temperature is high (20 - 28°c) the sporangium does not produce zoospores.
Now it behaves as conidium.
It germinates directly into germ tube.
This germ tube may be branched or unbranched and causes further infections in plants.
Sexual Reproduction:-
Involvement of male and female gametes.
Male and female gametes are totally differ.
It is of oogamous type.
Male sex organ :- antheridia.
Female sex organ :- oogania.
Control of phytophthora blight fungus :-
Water management is necessary because the fungus is transmitted through water very vigorously.
Standing water due to uneven fillds or fields with poor drainage, will promote disease by facilitating zoospores spread.
Culls left in the field can become source of inoculum and infest surface.
Heavy rain events and/or overhead irrigation splash infested soil to above ground plant parts infecting fruits (and leaves of squashes and peppers).
Plastic munch and drip irrigation reduce soil splashing.
Surface irrigation through pathogen infested water can devastate a field.
Crop rotation is must.