A NOTE ON THE CONIDIAL SCAR IN THE XYLARIACEAE

Autor: G. N. Greenhalgh
Rok vydání: 1967
Předmět:
Zdroj: New Phytologist. 66:65-66
ISSN: 1469-8137
0028-646X
DOI: 10.1111/j.1469-8137.1967.tb05987.x
Popis: The conidia produced by species of the Xylariaceae are typically acrogenous blastospores, hyaline to subhyaline, unicellular and elliptical, developed at the apices of conidiophore branches. They are subsequently pushed into a lateral position by further growth of the conidiophores from a new growing point which arises just beneath and lateral to the terminal spore. The slightly thickened base of the detached spore is truncate, tending to be slightly concave; a narrow pore may be visible running through it. Detachment of the conidia produces scars on the conidiophores which, depending on the species, may be clustered together or more or less regularly spaced out along the conidiophore (Chesters and Greenhalgh, I964). Again, they may be conspicuous or inconspicuous. For example, those produced by Rosellinia aquila (Fr.) de Not. and R. buxi Fabre are easily seen, whilst those of Hypoxylon nummularium Bull. ex Fr. are less obvious. It may also be possible to see a channel, corresponding to that in the spore hilum, running through the scar. Indeed in certain species, such as Rosellinia aquila, there appears to be a quite conspicuous pore in the conidiophore wall (Plate 3c). Examination of the conidiophores of several species has only once shown proliferation of an apparent secondary spore through the scar left by the primary conidium. This was in Hypoxylon argillaceum Pers. ex Berk. In the hope that high magnification micrographs of the conidiophore surface would provide more information as to the nature of these scars, conidiophores of Rosellinia buxi, Hypoxylonfuscum Pers. ex Fr. and H. serpens (Pers. ex Fr.) Kickx. were examined using the Stereoscan electron microscope recently developed by the Cambridge Instrument Company. The specimens consisted of small pieces (about IO X 3 mm and about 2 mm deep) of wood, taken from herbarium specimens, bearing immature stromata with conidiophores. These were fixed to standard specimen holders with Durofix and then coated under high vacuum with a very thin film of gold/palladium alloy. Plate 3a and b show the apices of conidiophore branches produced by Rosellinia buxi. In each case the terminal conidium is still attached but has collapsed and become distorted, probably during the coating process. Both conidiophores bear relatively large and conspicuous scars. The conidia have fallen away leaving pores in the conidiophore wall which are plugged at the base. This plugging presumably occurs before spore detachment. The scar has the appearance of a crater and this is accentuated by the slightly raised rim. The conidial scars produced by Hypoxylonfuscum are less conspicuous but have essentially the same form. In this species, the conidia are produced in clusters at the apices of branches, though these clusters may come to occupy a lateral position following renewed extension growth of the conidiophore. A terminal cluster of spores
Databáze: OpenAIRE
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