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Study of phialea mucosa N.SP., and other fungi associated with species of lolium

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Date
1942
Author
Gray, Elizabeth Gillam
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Abstract
 
 
Caryopses of Lolium perenne infected by Phialea mucosa, the blind -seed fungus, bear conidia on the surface of the pericarp, but are not readily distinguishable, macroscopically, from healthy seeds, and are sown with them, in spring. Heavily infected seeds fail to germinate and are described as "blinds' seeds. The fungus in the grain gives rise to microconidia, which are developed endogenously in the conidiophores in pink sporodochia on the surface of the caryopses, in early spring, and to apothecia, in summer, during the flowering period of L. perenne. The ascospores, which are ejected in clouds, reach the flowers and infect the ovary. Conidia, developed on the surface in large numbers, form an amber- brown slime and may spread the infection. The extent to which hyphae penetrate the tissues of the grain depends on its stage of differentiation at infection. Infection at pollination prevents further development of the grain. Blind seeds result from infection when differentiation of the embryo is almost complete. Infection, of mature grains causes the production of conidia on the surface but does not result in injury to the tissues.
 
The fungus has been distinguished in culture from Pullularia, with which other workers have associated it.
 
In gross morphological structure, the perfec stage resembles Ciboria, Sclerotinia, Helotium and Phialea, and the blind -seed fungus is similar in many respects to Sclerotinia temulenta, a parasite of Secale Cereale. A study of the anatomy of apothecia of representative species of these genera shows that it differs markedly in this feature, which appears to be taxonomically reliable, from all save Phialea, to whit it is assigned, with the specific name mucosa, chosen on account of the macroconidial slime. Phialea mucos occurs on L. perenne and L. multiflorum and is widely distributed throughout the British Isles. The macro - conidial stage has been obtained by inoculation on L. temulentum and S. Cereale.
 
The time at which apothecia are produced and the duration of their activity are governed by tempera ure, humidity and light. Development is delayed by protracted low temperatures, and by poor illumination, and the period of production is shortest in dry conditions. Treatment with organic mercurial dusts is not effective as a control measure.
 
Infection, with consequent low germination, is heaviest in cool wet conditions. The best seed crops are obtained when conditions are warm and dry from glowering to harvest.
 
Cultures derived from single conidia are either conidial or m rcelial in character and remain true to type in successive single spore isolations. Niicr.oconidia and structures of a sclerotial nature appear in both forms. In multispore and single spore cultures of ascospores, it has been found that all isolations from an individual apothecium are of the same type, either conidial or mycelial. It is not proposed to elaborate on this point until it has been further investigated.
 
In forming coils of hyphae and producing microconidia, the mycelial strains of P. mucosa resemble the second endophyte described on a few plants of L. perenne and Festulolium loliaceum by Sampson, but a few macroconidia are almost always present even on extreme mycelial forms of P. mucosa, while they have not been described by Sampson for the endophyte. No evidence of systemic infection of Lolium by P. mucosa has been obtained. Sampson's second endophyte has not beenlobserved, but the more widely distributed first endophyte has been isolated and grown on various culture media.
 
Anatomical studies of caryopses of L. perenn infected with P. mucosa have shown that germination is prevented only when hyphae are present in the scut - ellum. In a few instances, severely infected caryops -s including some which bore apothecia, have germinated. In some of these, hyphae of P. mucosa were found in th scutellum, but they had not entered the plumule. The first endophyte as observed in plumules developed fror seeds of this type and :Jas isolated from one of them.
 
Germination in the presence of severe infection by P. mucosa may result from the interaction of temperature, humidity and the degree of development of the caryopsis at infection, or may imply a form of resistance to the fungus. This will be tested at flowering -time, in a number of plants developed from heavily infected caryopses.
 
Helminthosporium siccans, a fungus which causes a foot -rot of seedlings, lesions on the foliage and a partial failure in the development of reproductive parts, is commonly present on L. perenne in Central Scotland. Seed -borne infection can be controlled by treatment with organic mercurial dusts.
 
URI
http://hdl.handle.net/1842/32350
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