Two Cases of Haplo-Lethal Deficiency In Ustilago Bullata Operative Against Saprophytism

SUMMARY

Five collections of Ustilago bullata on Agropyron, Bromus, Elymus, and Festuca spp. were found to possess a haplo-lethal deficiency preventing saprophytic development. Approximately half of the sporidia isolated from any promycelium would develop, when isolated, into typical sporidial colonies. The other sporidia would bud several times and then gradually undergo complete lysis.

In four of the five collections this lethal appears to be definitely sex-linked. Forty-two pedigreed monosporidial isolates of these four collections proved to be all of the same sex phase. The fifth collection possesses a lethal which is segregated independently of sex factors, since both sexes were represented in the isolates not possessing the character.

Twenty-nine pedigreed monosporidial isolates of the five collections exhibiting the lethal were paired with 22 such isolates from Ustilago nigra, U. Hordei, U. levis, U. Avenae and of collections of U. bullata not possessing it. Both sexes were equally represented in these 22 isolates, and when paired with these, the 29 isolates from collections exhibiting the character gave the same reaction as when paired with each other. Thus, in the four collections in which the lethal factor is sex-linked, the 23 isolates representing these collections were all of the same sex, not only with reference to each other, but with reference to the 22 isolates of other collections and other species.

These haplo-lethal deficiencies operate only against saprophytic development. When chlamydospores of two of the collections were used as inoculum high percentages of infection were easily obtained, showing that both sexes operate toward parasitic development, since both are necessary to infection.

Since the lethals are exhibited by approximately half of the sporidia borne on any promycelium, it is considered that they are probably borne on odd chromosomes, in one case sex-linked and in the other independent of sex.