The mutant dex4d was selected from a M2 population of the cultivar 'Betzes' that had been treated with the chemical mutagen, 'diethyl sulfate'. All of the defective endosperm mutants are zygotic lethals that express xenia and are maintained in heterozygous condition. Seed that are homozygous recessive for the mutations grow normally for a few days after fertilization. Then, growth stops and the seed begin to shrivel. At maturity, shrunken endosperm seed are so reduced in size that they are barely visible within the lemma and palea.
Defective endosperm prevents stand establishment under normal field conditions.
The mutants express xenia and behave as zygotic lethals. Since the defective endosperm mutants are zygotic lethals, allele tests among them are accomplished by crossing heterozygous stocks. The F2 allows us to confirm nonallelic crosses. The results of allele crosses tested to date are shown in Table 1. Based on these results, dexla , dex2b , dex3c , and dex4d are all non-allelic and have been assigned to loci.