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The Formation of Elongating Secondary Hyphae of Erysiphe graminis and the Segregation of Ml Genes in Barley. S. L. Yang, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48823; J. G. Moseman(2), and A. H. Ellingboe(3). (2)Plant Science Research Division, ARS, USDA, Beltsville, Maryland 20705; and (3)Department of Botany and Plant Pathology, Michigan State University, East Lansing 48823. Phytopathology 62:1219-1223. Accepted for publication 3 May 1972. DOI: 10.1094/Phyto-62-1219.

Barley plants grown from seed derived from heterozygous parent plants with genotypes Mla mla, Mlg mlg, Mlp mlp, or Mlk mlk were inoculated with culture CR3 of Ersiphe graminis f. sp. hordei. Barley plants from homozygous-recessive and homozygous-dominant parents were also inoculated and used as controls. Inoculated plants were held under environmental conditions known to favor parasite development. The percentages of conidia that produced elongating secondary hyphae (ESH) on individual plants were recorded 26 to 28 hr after inoculation. The genotype of each progeny plant was determined by the segregation of disease reaction of its progenies. The range of the per cent ESH was greater on homozygous progeny derived from plants heterozygous for an Ml, gene than on homozygous progeny derived from homozygous plants. The per cent ESH ranged from 45 to 85 on homozygous-recessive progenies derived from heterozygous parent plants. The per cent ESH ranged from 70 to 85 on homozygous-recessive progenies derived from homozygous parent plants. The per cent ESH on plants homozygous-dominant for an Ml gene was also dependent on the genotype of the parent plant. For example, the per cent ESH formed on Mla Mla plants ranged from 0 to 15 when the parent plants were homozygous Mla Mla, and 0 to 40 when the parent plants were Mla mla. The results suggested a carry-over effect from heterozygous parent plants to homozygous progenies.