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.
