INTER-THALLIC SEXUAL REACTIONS IN ACHLYA,A GENUS OF THE AQUATIC FUNGI

Barksdale , Alma Whiffen . (New York Botanical Garden, New York.) Inter-thallic sexual reactions in Achlya, a genus of the aquatic fungi . Amer. Jour. Bot. 47(1): 14—23. Illus. 1960.– Inter-thallic sexual reactions, involving the coöperative induction of sexual organs, have been found to occur between members of homothallic, as well as heterothallic species of the sub-genus Achlya. The induction of sexual organs, both on single thalli and on paired thalli, is temperature-dependent. Sexual organs were initiated at 15°—20°C. in 14 of 27 heterothallic strains that were usually sterile at 25°. The hermaphroditic sexual organs were like those of either A. ambisexualis or A. bisexualis in 19 strains; like those of A. prolifera in 3 strains; like those of A. inflata in 1 strain; and like those of A. americana in 1 strain. In some instances, the sexual reaction between paired thalli was complete at 20°C. but incomplete (i.e., oospores were not formed) at 25°C. The heterothallic and homothallic strains studied could be assigned to 1 of 12 (6 female and 6 male) inter-action types, on the basis of their sexual responses. These sexual types are characterized and their possible usefulness in indicating kinship among species of Achlya is assessed. The possible origin of heterothallic from homothallic forms of Achlya is discussed.