Routine screening for the presence of the S bands in our cytoplasm bank (Kemble and Bedbrook, Maydica 24:175, 1980) showed that one cytoplasm/inbred combination, W182BN(L), has two additional nucleic acid species found neither in any other member of the S group in a W182BN background nor in L cytoplasm in any other inbred in our cytoplasm bank. We do not know when these bands first appeared in W182BN(L), since all seed prior to the ninth backcross of that line has been discarded. Analysis of these nucleic acid species has shown them to be double-stranded RNA's. We have named these unique RNA bands LBN1 and LBN2. If they are linear in conformation, we can estimate their size to be 2.9 and 0.84kbp, respectively. The cytoplasm in which these two bands are found should be differentiated from others called "L," and we have therefore designated it "LBN" for "L cytoplasm in inbred W182BN."
The only unique characteristic of W182BN(LBN) which we have been able to detect, other than the presence of these RNA species, is an extra degree of male sterility apparent in crosses. In 1975 most of the S group in W182BN was pollinated with CO192, an inbred which partially restores S-types. The F1's resulting from these crosses were rated in 1975 and again in 1981 for fertility.
W182BN(B and D) x CO192: plants rated 5 (fully fertile)
W182BN(most S types) x CO192: plants rated 3 (anthers exserted, but little normal pollen)
W182BN(LBN) x CO192: plants rated 1 (no anthers exserted)
Because of its high degree of sterility, W182BN(LBN) was used after 1975 as a source of S-type cytoplasm for several new inbreds. Again using Kemble and Bedbrook's "Rapid Assay," we have analyzed LBN cytoplasm in the ten inbreds in which at least three backcrosses to the inbred have been completed. This analysis has shown:
1) The dsRNA's characteristic of LBN cytoplasm are present in all ten inbreds through all the backcrosses. These RNA's would therefore seem to be 100% seed transmissible.
2) The amount of these RNA's present is influenced by the nuclear background. In nine of the inbreds, the intensity of the two LBN bands decreased during the backcrossing process. In one of the inbreds, 2132, the LBN bands have been maintained in full intensity through 5 backcrosses. To determine whether the band intensity could be recovered, W182BN and 2132 were crossed as males onto each of the nine inbreds in which the band intensity had been reduced. In each case, the amount of the LBN1 and LBN2 bands was increased in the F1 hybrids.
P. H. Sisco, M. Zaitlin and V. E. Gracen
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