DEVELOPMENTAL CYTOLOGY OF 13 GENETIC MALE STERILE LOCI IN MAIZE

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Abstract
Thirteen nonallelic genetic-male sterile loci of maize (Z mays L.) were investigated cytologically to determine the microsporogenesis breakdown characteristics for each mutant. These male-sterile mutants included ms1, ms2, ms5, ms6, ms7, ms8, ms9, ms10, ms11, ms12, ms13, ms14 and ms17 in A632 and 0h43 inbred backgrounds. Male-sterile mutants ms8 and ms9 resulted in abnormal microspore (pollen) mother cells that exhibited nearly normal nuclear development but abnormal cellular development. These mutants had the earliest effect on microsporogenesis. Male-sterile mutants ms5, ms11, and ms14 had the latest effect on microsporogenesis in that microspores developed until the microspore mitosis stage. Other male-sterile mutants seemed to have similar expressions when compared with each other. Mutants ms2 and ms7 both lacked significant microspore wall formation at the time of microspore collapse. Mutants ms10 and ms13 were similar in that the microspore wall developed to approximately 1/2 the normal thickness before microspore collapse. A unique feature of ms1 was the occurrence of an abnormally thickened microspore wall. Almost complete microspore wall development occurred in ms12 plants despite nuclear degradation. Mutant ms6 was cytologically and genetically similar to polymitotic (po). Mutant ms17 had variable expression that most notably affected spindle formation. These observations may be useful in utilizing genetic male sterility in maize hybrid seed production schemes.