GENETICAL AND CYTOLOGICAL STUDIES OF SEMISTERILITY AND RELATED PHENOMENA IN MAIZE

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Abstract
Two new cases of semisterility in maize are reported. At meiosis in these and in semisterile-1 there are 8 bivalents plus a ring or chain of 4 chromosomes in place of the normal 10 bivalents. The assumption that these strains arose either from segmental interchange or from simple translocation between non-homologous chromosomes fits these results and also the genetic behavior. Crosses of semisteriles-1 and -2 give rise to 75+% sterile plants. In these, 2 separate groups of 4 chromosomes plus 6 bivalents were observed at meiosis. Crossed with standard normals, they throw normal, semi-sterile, and 75+% sterile plants in a 1:2:1 ratio. Both results indicate independence of the 2 steriles. Semi-sterile-2 involves 2 of the smaller chromosome pairs, one of which carries the factors in the sh wx group. Crosses of semisteriles-1 and -3 give rise to 75[long dash]% sterile plants. In these a ring or chain of 6 chromosomes plus 7 bivalents was observed. Crossed with standard normals, they throw all semisteriles with occasional exceptions, which may be crossover types. It is assumed that one of the pairs involved in semisterile-1 also is involved in semisterile-3. This pair is either P br or b lg. Evidence is presented indicating that P br is carried by the longest chromosome in maize. Exceptional plants showing intermediate degrees of sterility had 21 chromosomes. The extra chromosome belongs to the group involved in semi-sterility and thus enables certain deficient combinations to survive. Distorted ratios for factors in the sh wx group were obtained from certain of the 2n X1 plants.

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