Plants of the inbred line A632, 51 to
58 days after planting, were used (cool weather early in the season accounts
for the late treatment date). Tassel length at the time of each treatment
was estimated by dissecting a similar plant (range: 7-51 mm, all before
the reduction-division stage). Leaf tips (one or more leaves, usually starting
with the ninth leaf) were cut below the surface of the EMS solution (usually
0.1%) and left for various times (10 minutes to 168 hours). Fresh leaf
cuts were made daily during the course of the treatment due to cell death
near the cut edges. Concurrent studies with methylene blue solution indicated
considerable daily variation in the rate of solution uptake with faster
uptake occurring during warm, sunny days. Pollen from treated plants was
crossed on y su testers and backcrossed to untreated A632.
Unfortunately the testers had poor seed set in many cases, with an average
of only 179 tester kernels per treated plant. In one case (ninth leaf,
0.1% EMS, 144 hours) a single y Su kernel was found out of
415 test kernels. In the other 13 treatments only Y Su kernels
were observed. Samples from the backcrosses will be selfed to obtain a
better estimate of mutation frequency and the y Su will be
selfed to determine if the mutation was premeiotic. Further studies, with
more controlled environmental conditions during the treatment period, are
warranted.
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