Induction of cytoplasmic male sterility in the seed progeny derived from artificially-synthesized interspecific chimera in Brassica

We produced artificial interspecific chimeras by in vitro grafting, and obtained cytoplasmic male sterile (CMS) variants in the seed progenies derived from backcrossing the chimera with one of the mother plants, B. campestris cv. Komatsuna. The induced CMS has been stably inherited by crossing it with `Komatsuna', not with `Ruby Ball' cabbage. The nuclear component of CMS is complete `Komatsuna' type in morphology, chromosome number (2n = 20) and Southern blot using ribosomal 17S RNA gene as a probe. PCR analysis by using mitochondrial atpA primer showed the complete `Ruby Ball' type, suggesting nuclear-cytoplasmic exchange. However, Southern blot patterns were different among those of the CMS and both parents by using atpA. Recombination or some unknown change is supposed in the mitochondrial genome via the processes of synthesis and propagation of the chimeras.     

Isozyme Analysis of Some Male Sterile Lines in Sorghum bicolor (L.) Moench

A comparative study of peroxidase and acid phosphatase of anthers was carried out on sorghum to characterize five male steriles and their maímainers. Differences in presence/absence and intensity of bands were observed for the isozyme patterns of all the male steriles and their corresponding maintainers. The better expression of enzymes in sterile anthers emphasized the role they play in breaking down various metabolites that are otherwise important for formation of fertile anthers.     

Development of the components of a cytoplasmic male sterility hybrid system in rye through anther culture

Anther culture was applied as a method to develop the essential components of a cytoplasmic male sterility hybrid system in rye (Secale cereale L.). These components are the male sterile seed parent (A line), its isogenic maintainer counterpart (B line) and the restorer pollen parent (R line). Australian rye cultivars were crossed reciprocally to the cultivar ‘Luchs’ which carries the Pampa male sterile cytoplasm (cms-P). Anthers of the F1s in the cms-P cytoplasm (primary cross) and their reciprocals in the normal cytoplasm (reciprocal cross) were cultured in a modified C17 medium. Male sterile and male fertile doubled haploids were obtained from the anther culture of the F1s in the cms-P cytoplasm. Testcrosses indicated that the male sterile doubled haploids were A lines and the male fertile doubled haploids were R lines (restorers). The anther culture of genotypes in the normal cytoplasm (reciprocal cross) gave all male fertile doubled haploids. Testcrosses indicated that the male fertile doubled haploids were R lines (restorers) in the normal cytoplasm. The expected maintainer B lines were not identified because of the limited number of doubled haploids obtained from the anther culture of reciprocal crosses. Experimental single cross hybrids between male sterile and restorer male fertile doubled haploids showed high levels of heterosis. The results of this study have significant economic implications especially in the production of hybrids in several species. This revised version was published online in July 2006 with corrections to the Cover Date.     

Identification of male sterility maintainer lines for Ogura radish (Raphanus sativus L.)

‘Ogura radish’, a cytoplasmic genetic male sterile line, was crossed with four local and three Japanese cultivars to identify maintainer lines. Out of seven F₁ families, one cross involving a local cultivar, Aushi, produced 100% male sterile (MS) progeny. The crosses involving the other two local cultivars, Tangail Local and Kuni, produced about 90% MS progeny, indicating the presence of maintainer gene(s) for male sterility. The fourth local cultivar, Tasaki, produced 100% male fertile (MF) progeny. All three exotic cultivars appeared to possess the chromosomal gene(s) for controlling the male sterility. In BC₁, BC₂ and BC₃ generations, segregation of MS plants were more frequent when ‘Aushi’ was used as recurrent parent. The expression of male sterility was not affected by seasonal influences. Thus the local cultivar ‘Aushi’ may be used as maintainer line for ‘Ogura radish’. To produce hybrid seed, ‘Tasaki’ can be used as pollinator line as it exhibit high heterosis with ‘Aushi’. This revised version was published online in July 2006 with corrections to the Cover Date.     

Identification of two types of differentiation in cultivated rice (Oryza sativa L.) detected by polymorphism of isozymes and hybrid sterility

Magnitudes of genetic variation within each of major varietal groups of cultivated rice were surveyed in terms of isozyme polymorphism and allelic differentiation of hybrid sterility loci, both of which are considered to have litt le selective value. Allelic differences for 20 isozyme loci were examined in a total of 337 accessions, including Indica and Japonica rices. Aus cultivars from India, Javanica cultivars and both landraces and cultivars from China. Eleven out of the 20 isozyme loci were polymorphic. The Aus cultivars contained more alleles per locus than others. The hybrid sterilities in the crosses among Chinese cultivars, Indica and Japonica cultivars were mainly controlled by locus S-5, whereas the hybrid sterilities of Aus cultivars, when they were crossed to Indica, Japonica or Javanica cultivars, were found to be controlled by allelic interaction at hybrid sterility loci S-5, S-7, S-9 and S-15. Also in terms of the number of alleles at S-5 and S-7, Aus cultivars contained more alleles than others. While the Aus group showed an extreme diversity for both hybrid sterility alleles and isozymes, modern cultivars from the south of YangZi River in China were classified into Indica type and those from the north were into Japonica, which were almost the same as those in Japan. On the basis of the measured polymorphism the Indica-Japonica differentiation was explained by founder effects, i.e., through selection and distribution of two original sources each with a unique set of markers. Contrastingly, the continuous and pronounced diversity in the Aus group was attributed to the absence of such a process. The intermediate groups in Yunnan province and Tai-hu Lake region of China are considered to be isolated from such founder effects, retaining an intermediate diversity in terms of isozymes and hybrid sterility genes. Since hybrid sterility hampers the exchange of genes between cultivars of different groups, the understanding of its genetic basis will be important in rice breeding, particularly in hybrid rice breeding. This revised version was published online in July 2006 with corrections to the Cover Date.     

Molecular and biological studies on male-sterile cytoplasm in the Cruciferae. IV. Ogura-type cytoplasm found in the wild radish, Raphanus raphanistrum

The orf138 gene, which is specific to Ogura male-sterile cytoplasm, was analysed in mitochondrial DNA (mtDNA) of the wild radish, Raphanus raphanistrum, by polymerase chain reaction (PCR), Southern hybridization and sequencing. The effect of R. raphanistrum cytoplasm on the expression of male sterility was also examined in progeny with R. sativus. A PCR-aided assay and Southern hybridization revealed that three out of six strains analysed included plants with orf138. The sequence of wild type orf138 was same as that of Ogura, except for one or two nucleotide substitutions. Southern hybridization showed a novel mtDNA configuration in R. raphanistrum, in addition to the normal and Ogura types identical to those in R. sativus. Among interspecific hybrids, all the F₁ had normal pollen fertility. In the F₂ progeny between female wild plants having orf138 and the maintainer of Ogura male sterility, male-sterile plants were segregated, fitting the ratio of 3 fertile: 1 sterile plant. R. raphanistrum has cytoplasm that induces male sterility in radishes, and contains a dominant fertility restorer gene.     

Reproductive Deterioration in Buckwheat (Fagopyrum esculentum) under Summer Conditions

To resolve the problem of low and unstable yield in buckwheat under unsuitable environmental conditions, five varieties were grown and compared in summer and autumn. Vegetative and reproductive growth characteristics were investigated, and embryo development was observed with Nomarski's differential interference contrast (DIG) microscopy. In summer, under high temperatures and longer day-length, autumn-type varieties showed faster vegetative growth and later reproductive development as compared to summer-types. In the autumn, with generally good climatic condition for buckwheat growth in southern part of Japan, the embryo sacs and zygotes of both types developed normally. At 3 days after pollination (DAP), the embryos reached the globular stage. In summer, however, mostly abnormal embryo sacs were observed 3 DAP, leading to incomplete development, failure of fertilization or abortion of embryo. The abnormal embryo sacs were classified into 6 types. Abnormality of either type occurred in 91—100 % of the tetraploids, which is higher than in the diploids (50—77 %). The present study, conducted to clarify the factors causing low seed set in buckwheat under summer conditions, provides detailed information for further breeding of environment-tolerant buckwheat. Di-ploid genotypes which are less sensitive to unfavourable conditions and, thus, show more efficient fertilization in summer, should be considered for use as breeding material in buckwheat.     

Causes of Sterility in Seed Set of Rice under Salinity Stress

The effects of salinity at 50 mM NaCl on floral characteristics, yield components, and biochemical and physiological attributes of the sensitive rice variety IR‐28 were studied under controlled conditions to determine the causes of sterility in seed set under salinity stress. The results showed significant decreases in panicle weight, panicle length, primary branches/panicle, filled seeds/panicle, unfilled seeds/panicle, filled seeds/plant, unfilled seeds/plant, total seeds/panicle, total seed weight/panicle, 1000‐seed weight and total seed weight/plant. The sodium content in different leaves and floral parts increased significantly. In contrast, the potassium content was decreased significantly in leaves and floral parts. A reduction in chlorophyll a and b was also noted in different parts of the leaves. Inhibition of transpiration and photosynthesis was observed in flag leaves at the grain‐filling stage. Soluble carbohydrates in different leaves were reduced significantly in salinized plants but their content in different floral parts was increased, with the exception of primary and secondary branch spikelets. Under salinity stress, total protein concentration in flag, second and third leaves were higher than in control plants. The viability of rice pollen was reduced significantly in salinized plants. It was further observed that starch synthetase activity (α1–4‐glucan glucosyle transferases) in developing rice grains was inhibited very significantly under salinity stress. From these results, it is inferred that sterility and significant reductions in seed set in rice were not merely due to reduction or inhibition of different biochemical constituents and physiological functions, but were mainly due to limitation of soluble carbohydrate translocation in primary and secondary spikelets, accumulation of more sodium and less potassium in all the floral parts, and highly significant inhibition of specific activity of starch synthetase in developing rice grains, thus resulting in failure of seed set.     

Determination of the frequencies of restorer- and maintainer-alleles involved in CMS1 and CMS2 in German chive varieties

There are two cytoplasmic male sterility (CMS)‐systems in chives (Allium schoenoprasum L.), which can be employed in hybrid breeding. However, the probability for selection of maintainer genotypes from German open pollinated varieties is not known. Therefore, the allelic frequencies of the restorer genes X and T involved in CMS¹ were determined in 12 German commercial chive varieties by test crossing single plants to male sterile, temperature‐insensitive genotypes [(S₁)xxT] for segregation analyses of offspring. Temperature sensitive genotypes [(S₁)xxT_] are able to produce pollen at higher temperatures, and should therefore be excluded from hybrid breeding to avoid self‐pollination of the maternal parent. The mean value of the frequency of the non‐restoring allele x in the populations examined was 0.62. The mean value of the allele t, which is responsible for the temperature insensitivity, was 0.9. As a consequence of these allelic frequencies about one‐third of all plants of the chive varieties examined were designated CMS₁ maintainer genotypes, leading to the production of temperature insensitive male sterile lines. The incidence of CMS₂ maintainers in the German varieties examined was nearly four times lower than CMS₁ maintainers. The mean value of the frequency of the non‐restoring allele _st2 involved in the CMS₂‐system was 0.29.     

A new cytoplasmic male sterility source from wild Helianthus annuus

Summary A new cms source, ANN-5, was found in wild Helianthus annuus. This source showed high stability under different conditions in 1991 and 1992. All progenies from crosses of this source with several stable B-lines and restorer lines, which are homozygous for the gene which restores Leclercq's source of male sterility, were completely male sterile. Flower contained pistils and atrophied stamens. The cytological analysis showed that pollen mother cell degeneration took place in a premeiotic stage.