C-m897140 shows reduced frequency of transmission through male

--Vijay R. Thatiparthi and Peter A. Peterson

A sectored kernel identified as C-m897140 was obtained from the cross C Sh Bz Wx/C sh bz X c sh Bz wx/c sh Bz wx (cross 1) as a single seed exception from a TEL (transposable element laden) population carrying Cy, Uq and En transposable elements. The genotype of this kernel was C Sh Bz Wx/c sh Bz wx. The sectored phenotype shows somatic loss of the Wx, Bz and C genes when the appropriate tester is used. The plant from this kernel was selfed and outcrossed to a bz-rcy tester (cross 2). The sectored kernels from cross 2 were backcrossed both as female and male to the bz-rcy tester [(C Sh Bz Wx/C Sh bz-rcy wx X C Sh bz-rcy wx/C Sh bz-rcy wx (cross 3)]. The percentage of sectored kernels (breakage) among the colored class from cross 3 varies from 0% to 7.4% when used as female and 0% to 33.3% when used as a male. This variable rate is likely due to varied expression for causes still to be determined.

The outcross of the sectored kernels in cross 3 also indicated reduced frequency of transmission of chromosome 9. The percentage of colored kernels from cross 3 was close to the expected 50% when crossed as female and only 18-27% when crossed as male. The reduced frequency of transmission also coincided with a reduction in the crossing over frequency between the Bz and Wx loci (2.9% to 15.7% as compared to the normal frequency of 25%) possibly indicating the presence of an inversion (crossover suppressor) in the vicinity of the C-m897140 mutant. Initial screening for the presence of transposable elements indicated the absence of Uq. Further tests are under way to confirm the presence of an inversion in the short arm of chromosome 9.

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