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In this article we will discuss about the life cycle of melampsora with the help of suitable diagrams.
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Mycelium of Melampsora:
The mycelium is intercellular, septate, branched, dikaryotic, subepidermal and usually found within the parenchymatous tissues of the host.
Life-Cycle of Melampsora:
M. lini infecting several species of Linum is an autoecious rust. Although uredinial and telial stages are very common, the pycnidial and aecidial stages are not commonly recorded in nature. However, these stages have been produced in experimental plants by Prasada (1940).
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The initial infection is due to urediniospores blown down from Hills or produced locally on collateral hosts. These spores imitiate infection in freshly grown flax plants and by December-January, bright orange or reddish brown pustules appear on leaves, stems and petioles.
While on leaves the pustules are formed in circles, on stems the pustules are elongated. These pustules are uredia which are small scattered or in groups and contain urediniospores (uredospores).
The uredospores are globose and echinulate and formed at the tips of long multicellular sporophores.
These sporophores remain intermingled with capitate paraphyses. The pressure of the uredospores and paraphyses breaks open the epidermis and the uredospores are released, disseminated by wind and cause infection upon reaching a suitable host.
Usually these uredospores serve to spread the disease and the fungus until the end of the host season. Since the uredospores cannot tolerate the high temperature of the plains, they die or they are blown away to hills where they survive on flax or collateral host.
At the end of the season, black or reddish brown crust like telia are formed on the stems. These telia consists of a palisade layer of black to brown coloured, sessile, cylindrical, unicellular, binucleate teleutospores.
These can withstand the adverse environmental conditions for a long period of time and they also have a long dormant period.
The teleutospores are released during harvesting of the crop and remain buried in the soil of the field. According to Prasada (1948), the teleutospores cannot tolerate the scorching heat of India and die.
When exposed to freezing temperatures, the teleutospores germinate to produce four uninucleate basidiospores on a promycelium. In India the basidiospores do not play any role in the recurrence of the disease and die.
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In places, where environmental conditions are favourable and in green house experiments the basidiospores germinate to produce small, rounded or oval yellow pycnia on both the surfaces of the leaf.
The pycnia contain paraphyses and pycniosporophores producing pycniospores at their apical ends. After about fifteen days of the formation of pycnia, aecia develop on the lower surface of the leaf.
The aecia are small, orange coloured and scattered and contain polygonal, binucleate aeciospores. But the aecia do not contain paraphyses and peridia. On gemmation the aeciuspores produce dikaryotic mycelium and ultimately uredia. Linum mysorens usually acts as a collateral host for the fungus.
