Modes of Infection of Sorghums by Loose Kernel Smut

Abstract

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