A completely male-sterile, female-sterile mutant was derived from tissue culture of cv. Calland. The primary goal was to identify its inheritance, allelism, and cytology. Calland sterile (TC) was nonallelic with st2, st3, st4, and st5 female-sterile and malesterile mutants. In all crosses, except st5, single-gene recessive inheritance was documented. Critical ratios, 15 fertile: 1 sterile (for two loci) and 45 fertile: 19 sterile (for three loci), were observed in the F2 families from the cross of heterozygous Calland TC andSt5st5. F3 segregation data confirmed the duplicate factor inheritance of Calland TC. Calland TC was designated St6st6st7st7 and assigned the genetic type collection number T331H. The mutant was studied for abnormalities during microsporogenesis. The first abnormality was the occurrence of hollow-core nucleoli in sporogenous mass cells. During anaphase I and anaphase II of meiosis, lagging chromosomes and unequal chromosome segregation were observed, resulting in numerically and genetically unbalanced microspore nuclei. This also resulted in four microspores, and in five to eight microspores held together by common callose walls. Dissolution of callose released microspores into locules. Most microspores enlarged and were surrounded by microspore/pollen walls. After microspore mitosis, most young pollen grains degenerated. No viable pollen grains were evident. The sterility in Calland TC can be attributed to desynapsis.
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