The effect of four isogenic cytoplasmic types, normal, Salvador, Texas, and Charrua (the latter three causing male sterility), on the process of chiasma formation has been studied using two different maize hybrids. The cytoplasmic male sterility determinants have been shown to reduce the rate of interstitial exchanges per nucleus and per bivalent and the frequency of univalents. Increased variation between plants and relative stability of the intercellular variation within a plant have been observed for the parameters studied. It is concluded that the determinants of cytoplasmic sterility lower the probability of additional exchanges (relative to the obligate one) and reduce the frequency of premature disruption of one-exchange chromosome associations.Key words: maize, chiasma frequency, male sterile cytoplasm, univalent formation, genotype × cytoplasm interaction.
ABSTRACT
Analysis by a progeny test system has permitted the selection for different cytoplasmic sterility factors in two strains of mosquitoes derived from the progeny of a single female. Reciprocal interstrain crosses show full fertility and viability. However, testcrosses to a third cytoplasmic type show highly significant, reproducible differences in the cytoplasmic systems of the selected strains. A direct relationship between teratological growth patterns and the degree of heterozygosity of cytoplasmic factors was observed. In testcrosses, cytoplasmic sterility factors, when selected to homozygosity, produce non-teratological inviable haploid, or exceptional viable gynogenetic diploid larvae. Heterozygosity in the cytoplasmic system in testcrosses produced a broad spectrum of teratological growth patterns related to the degree of heterozygosity of the multiple factors present in the cytoplasm. Formal genetic crosses involving the selected strains show that teratological growth and cytoplasmic sterility, both partial and complete, are inherited through the germ plasm of the maternal parent. This work suggests that the interactions of cytoplasmic factors that result in teratological growth and cytoplasmic sterility may not be restricted to Culex pipiens, where in some cases it is prominent and obvious, but may be a much more general hereditary mechanism of major significance in other eukaryotic animals.
ABSTRACT
Tissues of cytoplasmic male sterile, maintainer, restorer, and restored lines, and sterile plants which reverted to fertility in Vicia faba were examined in ultrathin sections. Cytoplasmic spherical bodies (CSB), ca. 70 nm in diameter, were observed in tissues of all sterile plants but not in tissues of maintainer, restorer or restored sterile plants. No CSB were observed in a reverted fertile branch of a tiller-sterile plant, nor in 5 of 6 reverted fertile plants. One reverted fertile plant contained CSB in ovules. It is proposed that the CSB are the sites of, or possibly, products of, sterility factors in Vicia faba.
Stress immunity of CMS lines of Sorghum bicolor (L.) Moench at the basis of different cytoplasmic sterility types
