Note on EMS pre-meiotic mutagenesis --Allen D. Wright Reports of success using chemicals for gametophytic screening for traits such as alcohol dehydrogenase activity (Cheng and Freeling, MNL 50:11, 1976) and herbicide tolerance (Sari Gorla et al., MNL 63:98,1989) no doubt are due to pollen tube gene expression. For this reason, it may be desirable to mutagenize prior to meiosis, thus enabling subsequent chemical selection from a population of gametophytes having the mutation of the tube nucleus reflected in the sperm. The following study was an attempt to determine the treatment conditions required for optimal mutation frequency with pre-meiotic EMS treatment.

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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