George M. Reed

The Inheritance of Resistance of Oat Hybrids to Loose Smut

The study of the inheritance of disease resistance constitutes a problem of great economic and scientific interest and numerous investigators have contributed towards its elucidation in various groups of diseases. The present paper is concerned with studies on the inheritance of resistance to the loose smut of oats, Ustilago Avenae (Pers.) Jens., in a hybrid between a very susceptible variety, Avena nuda L. var. inermis (S.N. 30), and a very resistant one, A. sativa L. var. Black Mesdag (S.N. 70). Although the results here described relate to a single cross, investigations are in progress on additional ones between the same parents, as well as crosses involving other varieties. A few results on oat smut inheritance have previously been recorded. Wakabayashi (18) has pubiished some data on the behavior of the progeny of a cross between Red Rustproof and Black Tartarian to Ustilago levis (K. & S.) Magn., the former being resistant and the latter susceptible to the smut. No smut was observed among the F1 and F2 plants. In the F3 generation, however, twelve families out of a total of ninety-five were observed to contain a few infected individuals. Barney (1) has recorded more extensive data on three different oat crosses. One cross involved two very resistant varieties, Fulghum and Black Mesdag; a second cross was between the resistant Burt and the susceptible Swedish Select; and the third cross was between two susceptible varieties, Turkish Rustproof and Golden Rain. Barney interpreted his results on the basis that resistance in the first cross depended upon three different factors, in the second upon two, and in the third upon only one. Reed and Stanton (16) have described their results with a cross between

Modes of Infection of Sorghums By Loose Kernel Smut

The various species of cereal smuts differ in certain essential points in the mode of entrance into their respective hosts. The most common method seems to be the penetration of the young seedling by means of germ tubes arising from conidia, which, in turn, originate from the chlamydospores present on the seed or in the soil. Following penetration the fungus develops its mycelium in the embryonic tissue of the host. As the latter reaches its later stages of development the growth of the mycelium becomes particularly vigorous and forms a large mass of chlamy? dospores. We thus have a systemic development of the mycelium of the fungus in the host. This type of seedling infection occurs in several of the cereal smuts: Tilletia laevis Kiihn, T. Tritici (Bjerk.) Wint., and Urocystis Tritici Kcke. on wheat; Urocystis occulta (Wallr.) Rab. on rye; Ustilago Avenae (Pers.) Jens. and U. levis (K. & S.) Magn. on oats; Ustilago Hordei (Peis.) K. & S. on barley; Sphacelotheca cruenta (Kiihn) Potter, S. Sorghi (Link) Clint., and Sorosporium Reilianum (Kiihn) McAlpine on sorghum. In some cases the spores are formed in the stems and later leaves. Wheat plants infected by Urocystis Tritici are very greatly stunted and commonly are prevented from heading, or if an infected plant does head, very Httle seed is produced. The fungus attains its greatest develop? ment in the leaves and to some extent in the stems. Long blackish lines appear between the veins of the leaves, due to the formation of the spores in linear masses. These later rupture and the spores escape. The effects of Urocystis occulta on rye are somewhat similar. The infected plants, however, more fre1 Brooklyn Botanic Garden Contributions No. 44. 51