In order to understand whether the phenomenon of Uq activation (85 sectored) (MNL 60:5-6) was a random event or whether there was a specific factor in the genomes of sectored kernels that stimulated Uq activation, the following crosses were tested.
The F1 and BF1 progenies of the 4 inbreds that had been tested previously by the a-ruq tester for Uq activity were crossed both by 85 sectored genotypes (homozygous for R) and onto a-ruq tester. In addition, 187 plants from 85 sectored and 67 plants from 85 colorless sib kernels were crossed by a -ruq tester. If the activation of Uq is not a random event, we would expect a higher frequency of generating sectored kernels in crosses involving the 85 sectored than involving a-ruq tester due to the enhancement effect of the factor selected. On the other hand, if the process of Uq activation is random, no difference would be found between the two types of crosses.
Results from this study have indicated the following: a) The Uq activity seen in sectors of spotting in the aleurone layer of the 187 kernels was not transmitted; b) Apparently lower frequency of sectored kernels was seen in (F1 or BF1 of B70, C103, C123) X 85 sectored than onto a-ruq tester. Frequency of sectored kernels in F1 or BF1 of 187-2 by 85 sectored was slightly higher or the same than onto a-ruq tester; and c) Similar frequencies of sectored kernels were observed in progenies derived from crosses by a-ruq tester of 85 sectored and of 85 colorless sibs. All these suggest that the activation of Uq transposable element is likely a random event.
This hypothesis is supported by the following observations. First, colorless kernels with very large area of sectoring did not produce a higher frequency of sectored kernels when crossed with a-ruq tester. Second, 3 sectored kernels were found in a population of 2,458 colorless kernels from crosses between a-ruq and a sh (no Uq) testers. Third, sectors of spotting in an otherwise colorless aleurone were very often encountered in the development of an a-ruq tester with sh and bz markers.
Yong-Bao Pan and Peter A. Peterson
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