The endosperm mutant su3 conditions a sugary-shrunken endosperm and affects debranching enzyme activity in developing maize endosperms (Oliver Nelson, personal communication). su3 shows reduced frequencies of transmission and expression and possible duplicate factor inheritance, but the genetics of su3 have not been completely worked out yet. The only known alleles of su3 (su3-ref; MNL 66:4-5 and su3-89-1303-18; MNL 68:107-108) have arisen from Mutator populations. If su3 is indeed a duplicate factor pair, it is conceivable that at least some Mutator lines are mutant for one of the factors. We report the isolation of a third su3 allele from a Mutator population.
A single ear segregating for a low frequency of sugary-shrunken kernels was found among a group of self-pollinated ears from a Robertson's Mutator population. The sugary-shrunken phenotype of the mutant kernels is similar to that of su3, so mutant kernels from this ear, 94-4079-6@, were planted last summer and the resulting plants were crossed with plants homozygous for su3-ref. The resulting ears had all sugary-shrunken kernels, indicating allelism. This new allele of su3 has been designated su3-94-4079-6.
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