Allelism tests for recessive lethal mutants (either kernel or seedling) are made difficult by the fact that the homozygotes do not survive to produce gametes for testing. The best individuals that can be obtained for testing are the heterozygotes resulting from the self of a known heterozygote. The normal kernels (in the case of a lethal kernel mutant) or the normal seedlings (in the case of a lethal seedling mutant) from such a heterozygote will be randomly 2/3 right. According to Coe (MNL 51:61) the most efficient method for such a test is to "self a plant in source A and cross onto two plants in source B; test each of the two plants in B by crossing each onto one ear of a sib (set consists of 5 pollinations; failure of heterozygosity in source A is 1/3 and failure of showing heterozygosity in one or both plants of source B is 25/81; three such sets, totalling 15 plants, will have about 75% certainty of including an ideal test; 6 sets will have about 93% certainty).
However, we have determined that a better way is to bulk the pollen from 3-5 tester plants and cross on 3 ears of the mutant family to be tested. The male plants may be selfed for insurance and may be used on as many target sets as there are mutants to be tested. Our experience with this procedure is that it is practically foolproof in obtaining positive allelism tests, and statistically very reliable as a negative test. The negative test may be made more secure by either selfing a second ear on the target plants or by performing a split double pollination self of the target ears.
M.G. Neuffer and Dan J. England
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