Germination of teliospores and basidium formation in Ustilago

Abstract

This note describes a method for obser ving and reco rding the germination of telio spores, wit h the formation of basidi a, in species of UstiJago and its allie s. Telio spores of man y smut fun gi germi na te readily on 0.2% malt ag a r at ro o m temp erature. In most no preliminar y per iod of rest is necessa ry. Thi s is tru e, for exa mple, in such abunda nt spe cies as Ustilago avenae (Pers.] Rostrup on oat-grass , U. violacea (Pers.) Roussel on members of Caryophyllaceae and Uitritici (Pers .) Rostrup on barl ey. The initial germ-tubes from the teliospores, together with the resulting basidia and any spo ridia they produce, are on the surface of the agar; there is no aerial development. Further , if th e agar is covered with a cov erglass, growth seems unaffected, at leas t for many hours. My pr oced ure is to spread telio sp or es sp arsely on agar in a Petri dis h in wh ich th e depth of medium is ar ound 1.5 mm. At th e first sign of germination, often after only a few hours, a squa re (ca 1.5 mm side) with a suitable spread of spores is cut out, transferred to a slide and, without added water. covered with a coverglass. Then on e or more tuliospores. with germ-tubes jus t emerg ing, ore selected and drawn with the aid of a camera lucida (or altern atively photographed), the pro cess being repeated at appropr iate intervals. Between observations, the preparation on the stage of the microscope is kept covered wit h half a Petri dish lined with wet filter paper to minimize evapora tio n from the agar un der the coverglass . This technique has been used in the study of many sp ecies of UstiJago and closely related genera (summary in Ingold, 1989). In the great majority, the result of teliospore germination is the production of a structure th at is either obviously a 4-celled ba sid ium or can reasonably be inte rpre ted as a mod ification thereof. Modifications may involve a number of processes: fragmentation of th e axis of th e basidium; branching of that axis; omi ssion of septation following the final division of meiosis; and failure to form basidiospores. In a particular species more than one of these may occur. This note is illustrated (Fig. 1) by the pattern of development in Ustilego scabiosae (Sow.) Winter on Knauti a arvensis (1.) Coult. (collected by John Web ster in Spain) and U. phrygica P. Magnus on Taeniantherum caput-medusae (1.) Nevski (provided by Kalmus Vanky from Iran) neither of which has featured in my published papers. The situation in the former is the on e usually to be seen in text-books, that in the latter being more frequ ent. In it th e lowermost of the four cells of the basidium is entirely wi thin the teliospore, and the ba sidiospore buds through its thick wall. It is to be noted that the technique here described cannot be used for smuts belonging to Tilletiaceae, for in that famil y the ba sidium is an aer ial structure.