An analysis of 25 accessions of S-group male-sterile cytoplasms maintained at Cornell showed heterogeneity within the cms-ME cytoplasms (Sisco et al., Theor. Appl. Genet. 71:5, 1985). Those cms-ME cytoplasms descended from cms-ME in inbred N6 were standard in mitochondrial DNA and fertility restoration, whereas those descended from cms-ME in inbred 38-11 were almost fully fertile and had a distinctive mitochondrial DNA restriction pattern. The 38-11(ME) types had not lost the S-1 or S-2 plasmid-like DNAs, however, as is characteristic of many S-group revertants to fertility (Levings et al., Science 209:1021, 1980).

To survey other sources of cms-ME, seed from Beckett's cold storage was grown out. Cms-ME in three other inbred backgrounds--Tr, Wf9, and W23--had the mitochondrial DNA rearrangements and male-fertile phenotype of 38-11 cms-ME and its descendants. Beckett's records show that 38-11(ME), Tr(ME) and W23(ME) all trace back to a single plant that was pollinated by Wf9 (Beckett row 61-304), whereas N6(ME), which has standard S-group mitochondrial DNA and male-sterility, was not pollinated by Wf9. Wf9 is known to cause reversions to fertility of S-group cytoplasms (D. F. Jones, MGCNL 28:19, 1954; 29:14, 1955) and recently Escote, Laughnan, and Gabay-Laughnan have found that these reversions do not involve the loss of the S-1 and S-2 plasmids (Plasmid, in press).

A reasonable hypothesis is that the unusual cms-ME phenotype found in the descendants of Beckett row 61-304 is due to a Wf9-type reversion to fertility.

P. H. Sisco and J. B. Beckett
 
 

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