Instability in the expression of Texas cytoplasmic male-sterility has been observed, particularly when material is passed through tissue culture (B. G. Gengenbach et al., 1977, PNAS 74:5113 and R. I. S. Brettell et al., 1980, TAG 58: 55). Analysis of the newly male-fertile, T-toxin resistant lines has up to now indicated that the reversion is invariably cytoplasmic in origin. Fertility and T-toxin resistance show maternal inheritance and the change in phenotype is correlated with alterations in mitochondrial DNA. However, we have recently found one male-fertile, T-toxin resistant line (32D) derived from an embryo culture of the cross (WF9T/W22 x A188Nrf) x A188Nrf which has shown an exceptional 'restorer' effect when used as pollinator. Preliminary data, yet to be extended or repeated, are as follows:
Nuclear as well as cytoplasmic revertants have been described and well characterized for S cytoplasm (J. R. Laughnan and S. J. Gabay, 1978, in Maize Breeding and Genetics, ed. D. B. Walden). Further experiments will be necessary to confirm that the restorer effect of line 32D may similarly be ascribed to changes in the nuclear genome. Meanwhile I should be interested to hear of any other observations by cooperators pointing to nuclear reversion in Texas cytoplasm, and will supply small amounts of seed from the line 32D on request.
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