Telium formation and teliospore germination in Melampsora lini

Abstract

Teliospore formation occurred 10–15 days following inoculation with urediniospores of Melampsora lini on stems of Linum usitatissimum cv. Bison. Seedlings supported extensive uredinial development followed by little telial production, whereas older stems exhibited progressively less uredinial development and generally more abundant telial production. Teliospores of M. lini were conditioned to germinate by treating telia with either alternate periods of (i) freeze–thaw and wet–dry or (ii) wet–dry. The minimum time required for the induction of germination was ca. 25 and 15 days for the two methods, respectively. Under constant conditions of temperature, humidity, and continuous light, teliospores germinated rhythmically with a periodicity of ca. 24 h and daily maxima between 1200 and 1800 for a period of 5 weeks, after which the cultures had decomposed. Quantitative estimation of germination was based on the ability of telial cultures, held over susceptible plants for a defined period, to cast infectious basidiospores that initiated the pycnial stage. After 6–10 freeze–thaw and (or) wet–dry cycles, the stem epidermis was severely disrupted and sloughed off from the fissured telial surface. Concurrently, the level of teliospore germination increased rapidly to its maximum. Metabasidia and basidiospores were observed only on telial surfaces stripped of epidermis. Following 21 cycles, no further germination was detected from the cultures then void of all telial remnants.