On the morphology and taxonomy of some species of the genus Pythium which cause crop diseases

Abstract

In the present paper the writer has treated the taxonomical studies of seven species of Pythium causing damping-off disease of various crop seedlings. The fungi tested are as follows: Pythium aphanidermatum isolated from rotten fruits and from water of the drainage; Pythium deBaryanum isolated from diseased cucumber seedlings; P. vexans isolated from diseased tomato seedlings; P. ultimum isolated from wilted Hibiscus seedlings; P. monospermum isolated from water; P. zingiberum sp. nov. isolated from rotten roots of ginger; and P. Hemmianum sp. nov. isolated from wilted sponge-gourd seedlings (Luffa cylindrica).The sporangium formation is found abundantly in Pythium aphanidermatum and P. monospermum, but not in P. ultimum, P. deBaryanum and P. vexans. It is difficult to make clear the difference between P. ultimum and P. deBaryanum by the characters of sexual organs. In Pythium ultimum, however, one antheridium arising usually from oogonial stalk immediately below the oogonium, attaches to an oogonium, and in Pythium deBaryanum one to three androgenus antheridia attach usually to an oogonium.Butler described that antheridium of Pythium vexans was attached to an oogonium with its broad base. In my observations of P. vexans, such figures were not found, and no sporangium and few conidia were obtained.A new species of Pythium attacking roots of ginger was described as a new species under the name of Pythium zingiberum. It forms numerous oogonia and few conidia on agar culture. Sporangia are filamentous or irregularly inflated and are rarely formed. The oospore wall is smooth and usually filling the oogonium. Antheridia are usually diclinous, and wrap around the oogonium with antheridial branches.A Pythium isolated from wilted sponge-gourd seedlings was also studied. It forms no sporangia and only a few sexual organs, but numerous conidia are formed. The writer gave the name of Pythium Hemmianum to the present fungus as a new species in memory of the sixty first birthday of Dr. Takewo HEMMI.