Jiangsu Agricultural College

Character and inheritance of a new Y-type cytoplasmic male-sterile line --Zin Tai-chen, Dan De-xiang, Xu Ming-liang and Liu Da-wen The breeding process. The maintainer lines were selected as males to cross with restorer lines, which may bear sterile cytoplasms, and backcrossed to the same lines repeatedly. New sterile lines may be obtained in this way. The concrete methods are as follows: In 1978 some restorer lines such as Wa 8 were selected as females to cross with inbred lines including B37. No sterile offspring have been detected in the F1 progeny. But in following F2 populations, 6 sterile individuals came to light in 1 cross of Wai-si 137xB37. In 1982 we duplicated the same experiment, and other restorer lines involving A170 were selected as females to cross with maintainer lines such as L107 to obtain 19 combinations. Male-sterile individuals came out in 3 F2 populations and appear to have normal male spikes, no anthers exserted, and fewer and anomalous pollen grains in anthers. The sterile lines bred later showed stable sterility and could readily be applied in hybrid production. The variable fertility restoration responses have been shown to correspond to the different sources of male-sterile cytoplasms, which in turn were derived from the respective restorer lines. Therefore, the former (derived from the cross of Wa 8 x Wei-si 137) and the latter (derived from the cross of A170 x L107) were named YI and YII type, respectively.

Research on their resistant reactions against HmT (Helminthosporium maydis race T), fertility restoration patterns, hereditary traits, light microscopy, electron microscopic ultrastructure and biochemical character have been conducted rather systematically for several years. According to the results, it has been fundamentally considered that the Y-type sterile lines are new in maize and differ from the C, T and S groups.

The explanation may be illustrated as follows: The induced assay was done for the resistance of Y type male-sterile lines against H. maydis (Helminthosporium maydis) and H. turcicum (Helminthosporium turcicum) in 1982 and 1984. The results indicated that YI and YII type male-sterile lines showed some resistance to H. maydis and H. turcicum.

Since 1981, 62 combinations have been obtained by crossing 46 inbred lines with the T group male sterile line, 26 combinations by crossing 20 inbred lines with the S group sterile line, 172 combinations by crossing 82 inbred lines with the C group sterile line, 372 combinations by crossing 126 inbred lines with YI type sterile line and 632 combinations by crossing 191 inbred lines with the YII type sterile line. According to Duvick's standard for classification, the male fertility of the F1 generation was investigated with the finding that the relationship between restoration and maintenance for the Y type sterile line was different from that of the other 3 groups of sterile lines.

There was a distinct difference in the pollen abortion between C group and Y type sterile lines; the pollen abortion in the C group sterile line occurred at the early mononucleate stage after the division of the tetrad, while in the Y type sterile line it occurred at the late microspore stage.

The analysis of esterase isozyme was done by disc polyacrylamide gel electrophoresis for materials from C group, T group, S group and Y type sterile lines, for which C group and Y type sterile lines belong to a genetic background with the same genotype but different cytoplasms. The results revealed that these 4 groups (types) of sterile lines and their maintainer lines had different zymograms of esterase isozyme with their own specific character; they also differed in the number and order of the bands and the stained degree for each band varied with different groups (types) of sterile lines.

Four maintainer lines which bear a pair of restorer genes for the Y type sterile cytoplasm were selected as recurrent parents to cross with Wu 15, and then backcrossed repeatedly to transform Y type restorer lines with the recurrent parental backgrounds. The major gene's restoring capacity was assayed for each transforming restorer line at every backcross pedigree. The simple linear regression equation with replication was postulated to describe the correlation between the changes of nuclear ratios of a given recurrent parent and the corresponding changes of the major gene's restoring capacity. According to this equation, the expectation of the major gene's restoring capacity in various recurrent parental nuclear backgrounds or their differences may be possible when the nonrecurrent parent nuclei were completely replaced by recurrent ones. The results are as follows: The more the backcrosses, the higher the restoring capacity for those transforming restorer lines, assigned RYms330 and RYms632. In reverse, the restoring capacity decreased as the backcross pedigrees went up for RYms Santuan. No significant difference was detected for RYms02. The expected major gene's restoring capacity showed significant differences among various transformed restorer lines when Wu 15's nucleus was absolutely substituted by the recurrent parental nucleus. These differences of the restoring capacity between nonrecurrent and recurrent parent or among various recurrent parents may be attributed to the variable number or functions of the minor or modifying genes in different nuclear backgrounds, which influence the major gene's fertility expression quantitatively.

Finally, we believe that further testing is needed before it can be assigned to a group. Y type sterile lines have shown some favorable characters, such as the stable inheritance of pollen abortion, ready application in hybrid production, possessing many restorer lines in multitudinous inbred lines, and strong resistance against HmT and so on. They are regarded as a valuable germplasm source and have important applied value in seed production.

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