Blind seed, caused by Gloeotinia temulenta, is characterized by reduced seed germination. The fungus colonizes the endosperm, replacing much of the endosperm tissue with a fungal mycelium. Infected seeds are shrunken and pinkish to rusty in color. However, visual detection of infected seed is difficult because grass seeds are typically covered by two glumes-the lemma and the palea-that remain uninfected and appear similar to those of healthy seeds. Infected seeds typically do not germinate, hence the name "blind seed." Gloeotinia temulenta survives and overwinters in infected seed. Infected seeds typically are lightweight, and precleaning seed during combining can return much of the lightweight seed fraction (including infected seed) to the field. The more infected seeds left in the field following harvest, the greater the potential for blind seed development the following spring.
In the spring, about the time of flowering in grasses, apothecia are produced from the infected seed (Fig. 24-2, left). Apothecia produce and release ascospores under moist or rainy conditions. Ascospores are easily dispersed by air currents. Only those ascospores that land on the grass flower will have the potential to infect grass ovaries and developing seeds. No other part of the plant is susceptible to infection by G. temulenta. The fungus proliferates within the endosperm. Within several days after infection of the developing seeds, G. temulenta begins to produce conidia. Within about 7 to 10 d after infection, large numbers of conidia, embedded in a pinkish colored slime layer, appear on the surface of infected seed. Under dry conditions the slime becomes hard or crusty. Under rainy conditions the slime quickly dissolves, with rain splashing as the primary means of secondary spread of the pathogen.
Fig. 24-2. Conidia (left) and apothecia (right) of Gloeotinia temulenta.
Detection of G. temulenta includes soaking the seed in an equal volume of water for about 15 min and examining the effluent at about 200´ magnification for the allantoid, biguttulate conidia typical of G. temulenta (Fig. 24-2, right).
Gloeotinia temulenta has a wide host range (56 species of grasses), including tall fescue (Alderman, 1991; Hardison, 1962b). Control of blind seed is achieved through seed treatments (Rolston and Falloon, 1998), systemic fungicides (Hardison, 1970, 1972; McGee, 1971), and maintaining optimal soil fertility (Hampton and Scott, 1980a, 1980b). Although good blind seed control generally is obtained, blind seed can be a problem in cool, wet seasons. A comprehensive review of blind seed disease is given by Alderman (2001).
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