Effect of level of relative humidity on fungi and germinability of Egyptian peanut seeds

Abstract

The changes in the composition of peanut seed-borne fungal flora at various levels of relative humidity (40–100%) were investigated.

The total count of fungi significantly increased at all levels of relative humidity and the climax was recorded during the last period at 100 %. Aspergillus was the main component of fungal flora, arising in stored seeds. A. fumigatus was the dominant fungal species at 40–80%, but was surpassed by A. flavus at 100 % r.h., A. terreus and A. ochraceus were also good colonizers of peanut seed. A. sydowii, which possessed the highest initial population, could not compete with other fungi and was almost completely lost at all levels of relative humidity.

Penicillium, represented mainly by P. funiculosum, could only markedly increase its population at 100% r.h.; Rhizopus stolonifer was also an active invader of peanut seeds at 100 % r.h.

When the isolation plates were incubated at 45°C, the results were basically similar. Aspergillus fumigatus was the most dominant fungal species, except at 100% r.h. where it was exceeded by A. flavus. Humicola grisea var. thermoidae, Scopulariopsis brevicaulis, Mucor pusillus, Sporo-trichum thermophile, Thermoascus aurantiacus, and Thielavia sepedonium were isolated only when the plates were incubated at 45°C.

At all levels of relative humidity, the germinability of seeds declined slowly or rapidly with the extension of the storage period and the rate of decline was enhanced with the rise of the relative humidity. Complete loss of germinability was recorded after 30 days at 100% and after 180 days at 80% r.h.

Die Untersuchung befaßt sich mit Veränderungen in der Zusammensetzung der auf Erdnußsamen angesiedelten Pilzflora bei unterschiedlicher relativer Luftfeuchtigkeit (40–100%, 28°C).

Die Gesamtzahl der Pilze erhöhte sich bei allen Stufen relativer Luftfeuchtigkeit, der Höchstwert wurde während der 3. Inkubationsperiode (181–240 Tage) bei 100% rel. Luftfeuchte erreicht. Die Aspergillen stellten die Hauptkomponente der Pilzflora dar. A. fumigatus dominierte bei 40 bis 80% rel. Luftfeuchte, wurde jedoch bei einer 100proz. von A. flavus übertroffen. A. terreus und A. ochraceus besiedelten die S amenober fläche gleichfalls gut. A. sydowii hingegen war nur in der Kontrolle zugegen, jedoch in keiner der Feuchtestufen. Die Penicillien sowie Rhizopus stolonifer vermehrten sich vor allem bei 100% rel. Luftfeuchte.

Bei einer Inkubationstemperatur von 45°C waren die Ergebnisse grundsätzlich ähnlich. Einige Pilze — Humicola grisea var. thermoidae, Scopulariopsis brevicaulis, Sporotrichum thermophile, Thermoascus aurantiacus und Thielavia sepedonium konnten nur bei dieser Temperatur nachgewiesen werden.