Sources of Resistance to Net Blotch of Barley 1

N ET blotch of barley, Pyrenophora teres (Died.) Drechsl. (Helminthosporium teres Sacc.), is widely distributed in California, especially on early-sown fields. While the disease is generally considered of less importance than stripe, scald, or powdery mildew, complete necrosis of the leaves may occur in years favorable for its development. Recent investigations with mildew and scald, both foliar diseases, suggest that losses in yield may be greater than have been suspected (5). Since all of the important varieties grown in California are highly susceptible to net blotch, emphasis has been placed on finding suitable sources of resistance for use in a breeding program as outlined by Briggs (1). Companionate backcrossing programs involving the transfer of resistance to stripe, scald, and powdery mildew are now underway. Eventually resistance to the four diseases mentioned above will be incorporated into the important varieties grown in California. In a .survey of available germ plasm for potential sources of resistance, the major part of the barley varieties in the world collection assembled by the Division of Plant Exploration and Introduction and maintained by the Division of Cereal Crops and Diseases were tested for reaction to net blotch. The most promising sources of resistance found are discussed in this paper. While available evidence suggests physiologic specialization of the causal organism, nevertheless many of the varieties enumerated in this paper may be suitable parental material in other areas.