Treatment of zygospores of Choanephora cucurbitarum with KMnO4, NaClO or HjO, effectively activated the spores and induced their germitiation. The optimum concentration of KMnO4 for activation of zygospores was 0.25 to 0.5%. Zygospores were not able to germinate in darkness even after activation by K!VlnO4. When zygospores from 40 to 50-day-old cultures were treated with 0.5% KMnO4 solution for 60 min before incubation on water agar at 24% under light, about 50% germinated in 10 days. KMnO4 treatment killed more than 99% of residual mycelial fragments, sporangiospores and sporangiola in the zygospore suspension. During germination disappearance of oil droplets in zygospores occurred prior to the cracking on zygospore wall. Both sporangial germination and mycelial germination were found. Moreover, sporangiole germination was observed for the first time. Zusammenfassung Faktoren, die die Keimung uod die Art der Keimung Ton Choanephora cttcurbitaram-Zygosforen beeinflussen Eine Behandlung von Choanephora eucurbitarum-Zygosporen mit KMnO4 NaClO bzw. H^O, aktivierte die Sporen und induzierte deren Keimung. Die optimale KMnO4-Konzentration ftlr die Zygosporenaktivierung lag zwischen 0,25 und 0,5%. In Dunkelheit fand eine Keimung der Zygosporen nicht statt, auch nicht nach einer KMnO4-Aktivierung. Wenn Zygosporen von 40 bis 50 Tage alten Kulturen mit einer 0,5%igen KMnO4-Losung fur 60 Minuten behandelt wurden und anschlieUend auf Wasseragar bei 24°C und mit Licht zur Keimung inkubiert wurden, keimten circa 50% der Sporen nach 10 Tagen. Die KMnHO4-Behandiung totete mehr als 99% der zurflckgebliebenden Myzelfragmente, Sporangiosporen und Sporangiolen in der Zygosporensuspension ab. Wahrend der Keimung verschwanden die in den Zygosporen vorhandenen Oltropfchen bevor die Zygosporenwand sich spaltete. Sowohi eine Sporangienals auch eine Myzelkeimung wurde beobachtet. AuBerdem wurde eine Sporangiolenkeimung zum ersten Mai nachgewiesen.

Zygospore progeny from the cross between + and − isolates of Choanephora cucurbitarum consisted of +, −, and ± types. The + and − zygospore isolates were stable, giving rise to hyphal fragment cultures and sporangiospores with the same mating type as their respective parent. However, the ± zygospore isolates were unstable, segregating to +, −, and ± types during asexual propagations. During long-term storage, the + and − isolates were also very stable, but ± isolates were not. All the ± isolates originating from single zygospores, hyphal fragments, or sporangiospores produced azygospores, suggesting that azygospores of this fungus are produced by mating-type heterokaryotic mycelia. Keywords: azygospore, Choanephora cucurbitarum, germsporangiospore, germsporangium, zygospore germination.

When oospores of Phytophthora caetorum from 30‐day‐old culture were treated with 0.25% KMnO4 for 20 min and incubated at 24°C under light for 10 days, 65–75% germinated on water agar and water agarose but only 1–21% germinated on V‐8 agar and S+L agar. Water agarose was selected because germinated oospores formed restrieted colonies on this medium that could be isolated easily. KMnO4 treatment killed sporangia, chlamydospores and mycelial fragments present in oospore suspensions. Under the above conditions, approximately 44% of oospores from 10‐day‐old culture germinated and the optimum germination rate of about 75% was obtained when oospores reached about 20 days old.

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