In this article we will discuss about the asexual and sexual reproductive structure of albugo.
Asexual Reproduction of Albugo:
1. It takes place by conidia or conidiosporangia. They develop on conidiophore or conidiosporan- giophore (Fig. 71).
2. Mycelium below the epidermis gives off many erect, short, unbranched, club-shaped hyphae called conidiophores.
3. Conidiophores lie parallel to one another and perpendicular to the surface of the host, and form a palisade-like layer.
4. On the thin-walled apical end of the thick-walled conidiophore are present four to six or more spherical, smooth and hyaline bodies called conidia.
5. Conidia are arranged in basipetal succession on the conidiophore, i.e., youngest at the base and oldest at the top (Fig. 72).
6. In between two conidia is present a pad or disc of gelatinous material called mucilaginous disc or disjunctor.
7. Each conidium and conidiophore is a multinucleate structure.
8. In the later stages, the epidermis of the host gets ruptured and conidia disseminate. They germinate either directly by forming a germ tube or form biflagellate zoospores.
Sexual Reproduction of Albugo:
1. Sexual reproduction is oogamous and the two sex organs are antheridium and oogonium.
2. Sex organs generally develop in stem.
3. Two sex organs develop near each other but on different male and female hyphae.
4. Antheridium develops in close contact with the oogonium at the side.
5. Oogonium is globular and multinucleate, and contains a large amount of food material. It bears a septum at the base.
6. Mature oogonium (Fig. 73) in C. candidus remains divided into central uninucleate dense ooplasm and peripheral, multinucleate periplasm.
7. Antheridium is elongated, club-shaped and multinucleate structure having a septum at its base.
8. The wall between antheridium and oogonium dissolves at the place of their contact, and a tube is formed by antheridium. This is called fertilization tube.
9. Fertilization tube penetrates into periplasm and ooplasm, and through this tube the male nucleus comes in contact with the female nucleus to form the diploid oospore.
10. Oospore (Fig. 74) is a globular body and remains surrounded by outer thick and sometimes spiny exosporium, and inner thin and smooth endosporium. Sometimes, a third middle layer is also present.
11. Diploid oospore divides first meiotically and then ordinarily into many biflagellate, reniform and haploid zoospores or zoomeiospores.
12. Zoospores, on withdrawing their flagella, germinate and form new mycelial hyphae on the host.
(i) Use of resistant varieties.
(ii) Spraying of fungicides.
(iii) Crop rotation also shows good results.