At the University of Georgia, seeds of the long-time maize inbred CI21(Athens) were prepared with the genotype of CI21(A) and the normal cytoplasms of inbreds GA199, GT112 and CI21(A) separately in backcross programs. Similarly, GT112 inbred seeds were also prepared in simultaneous backcross programs. At the end of the backcross programs, each inbred was selfed for several generations. Thus, each lot of seed had either the CI21(A) or the GT112 nuclear genotype in a homozygous condition with a different cytoplasm. A pedigree analysis of each of these long-time inbreds clearly shows that these inbreds are unrelated either nuclearly or cytoplasmically.

Seeds from several selfed plants within each cytoplasmic source were harvested in 1978 at the University of Georgia and were planted on Texas Tech University research farm for seed increase. During the month of August, tassels with silks were observed for the first time in these cytoplasmic stocks. The tassel silks were terminal in position and present only on the tillers. The percentages of plants with tassel silks were as follows:
 

Cytoplasmic Source	%
GT112 x C121(A)8	54
GA199 x CI21(A)8	61
CI21(A) selfed	29.6

The data indicate that the CI21(A) nuclear genotype in its own cytoplasm produced fewer tassel silks than in GA199 or GT112 cytoplasms. The latter cytoplasms provided more favorable environment for 'ts' gene to express most. Apparently, the 'ts' gene is under the control of CI21(A) nuclear genotype and environment in these inbreds. Presumably, differences in auxin concentration levels, particularly during the later part of growth period, might be the basis for production of tassel seeds on the tillers alone but not on the main stalks. Other cytoplasmic sources with GT112 nuclear genotype did not produce any tassel silks.

Arelli P. Rao, John C. Bickel and A. A. Fleming

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