. Corn smut caused by Ustilago maydis. Corn; Smut diseases. Fig. 19. The haploid progenies of 3 sets of 4 mono- sporidial lines of I'stilago maydis obtained from 3 hybrid chlamydospores F, M, and K, resulting from a cross of a mutant, K.,-1 with line L (Stakman, et al., 319). when injected into corn. In the other group, no in- fection resulted, although the sporidial lines paired in all possible combinations (55). This type of segregation for self-sterility is not uncommon in U. maydis. Christensen (55) obtained no galls by pairing 16 sets of primary sporidial lines when all possible pairings
. Corn smut caused by Ustilago maydis. Corn; Smut diseases. Fig. 19. The haploid progenies of 3 sets of 4 mono- sporidial lines of I'stilago maydis obtained from 3 hybrid chlamydospores F, M, and K, resulting from a cross of a mutant, K.,-1 with line L (Stakman, et al., 319). when injected into corn. In the other group, no in- fection resulted, although the sporidial lines paired in all possible combinations (55). This type of segregation for self-sterility is not uncommon in U. maydis. Christensen (55) obtained no galls by pairing 16 sets of primary sporidial lines when all possible pairings of lines within each set were made. When these sets of lines were paired with those of chlamydospores from another source, how- ever, there was evidence for regular segregation of factors for sex. In general, the pairing of lines of the same promy- celium results in a low proportion of fertile com- binations and the number of sexual groups may be decreased by outbreeding: the progeny from one promycelium may fall into 2 or more sexual groups when paired in all possible combinations, but behave alike sexually when mated with the progeny from an- other chlamydospore (55). All attempts failed to find 4 monosporidial lines from a single chlamydospore each compatible with all those from another chlamydo- spore. Sex ratios obviously depend on whether they are based on inbreeding or outbreeding. This fact has frequently been overlooked in making genetic analysis of factors for compatibility. Inheritance of cultural characters.—Most chlamydo- spores, whether collected in nature or the product of controlled crosses, segregate for cultural charac- ters. Visual observations indicate that the segregates differ in all cultural characters that are possible to observe such as color, consistency, luster, topography, zonation, type of margin, and rate of growth of colonies. Some character differences are very distinc- tive, others virtually imperceptible. Some may be alike on one medium, but
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