Continued study of a defective WF9 cytoplasm, "wsp"

The wsp and related progenies described in MNL 60:69-70 were regrown in 1986. Nuclear/cytoplasmic interactions and segregation ratios were essentially the same as in 1985. Thus it appears that expression of the wsp phenotype, the result of a cytoplasmic/nuclear genetic interaction, is reasonably stable. Tables 1 and 2 summarize the two-year results among families (Table 1), and within those families that showed segregation (Table 2).

Additionally, ear-rows were grown and observed of seed from open-pollinated ears borne on plants classified as wsp in the 1985 observation planting. Each ear-row generally contained several plants of wsp phenotype when its pedigree indicated wsp cytoplasm, but not when the pedigree indicated SK2 cytoplasm. When pedigrees indicated WF9 cytoplasm (all such ear-rows came from open-pollinated ears of WF9) about half the ear-rows contained plants of wsp phenotype.

These results agree with the hypotheses that: (1) wsp is stably inherited through the seed parent, even after being hidden for many generations by a "repressor" nuclear genotype, (2) the small number of plants with SK2 cytoplasm that were classified as wsp in 1985 were probably misclassified, and (3) WF9 (in at least some progenies) is capable of producing new cytoplasmic defectives of wsp phenotype. Appropriate backcrosses have been initiated to facilitate study of the persistence and inheritance of the recovered wsp selections.

Work also continues to investigate the possibility that the wsp cytoplasmic genotype may be lost as well as created. To date, evidence indicates that once created, it persists, although its expression in uniform nuclear "expressor" genotypes is highly variable from plant to plant. One WF9 backcross ear-row (82-A8 in Table 2) has not yet shown any wsp plants in observations of about 40 plants; progeny from that ear-row will be further tested to see if the wsp cytoplasmic genotype is indeed gone, or only not yet expressed.

Tables 1 and 2.

Donald N. Duvick

Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors.

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