B-chromosomes in Iseilema laxum Hack. I. Cytology

Upto 6 B-chromosomes occurred in natural populations of the fodder grass Iseilema laxum Hack. They were smaller than the A-chromosomes and stained darker. Although the number of B's varied in different PMC's of even the same anther presumably due to the phenomena of nondisjunction and precocious divisions, it was possible to assign a definite number to a particular plant. As seen from pachytene morphology, three types of B's were seen. More than one type can also occur in the same plant. Pairing can take place between homo-as well as heteromorphic B's resulting in bivalents. B-chromosomes in Iseilema laxum appear to have a common origin.     

Hybrid maize breeding with doubled haploids. IV. Number versus size of crosses and importance of parental selection in two-stage selection for testcross performance

Parental selection influences the gain from selection and the optimum allocation of test resources in breeding programs. We compared two hybrid maize (Zea mays L.) breeding schemes with evaluation of testcross progenies: (a) doubled haploid (DH) lines in both stages (DHTC) and (b) S₁ families in the first stage and DH lines within S₁ families in the second stage (S₁TC-DHTC). Our objectives were to (1) determine the optimum allocation regarding the number of crosses, S₁ families, DH lines, and test locations, (2) investigate the impact of parental selection on the optimum allocation and selection gain (ΔG), and (3) compare the maximum ΔG achievable with each breeding scheme. Selection gain was calculated by numerical integration. Different assumptions were made regarding the budget, variance components, correlation between the mean phenotypic performance of the parents and the mean genotypic value of the testcross performance of their progenies (ρ _P ), and the composition of the finally selected test candidates. In comparison with randomly chosen crosses, maximum ΔG was largely increased with parental selection in both breeding schemes. With an increasing correlation ρ _P , this superiority increased strongly, while the optimum number of crosses decreased in favor of an increased number of test candidates within crosses. Thus, concentration on few crosses among the best parental lines might be a promising approach for short-term success in advanced cycle breeding. Breeding scheme S₁TC-DHTC led to a larger ΔG but had a longer cycle length than DHTC. However, with further improvements in the DH technique and the realization of more than two generations per year, early testing of S₁ families prior to production of DH lines would become very attractive in hybrid maize breeding. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. T. Wegenast and C. F. H. Longin contributed equally to this work.     

Variable transmission rates of a B-chromosome in Myrmeleotettix maculatus (Thunb.) (Acrididae: Orthoptera)

Karyotype comparisons of both parents and progeny from single pair matings in the grasshopper Myrmeleotettix maculatus have shown that there is an accumulation of the large mitotically stable B-chromosome when transmitted through the female. This is presumed to result from a preferential segregation of univalent B-chromosomes at the first division of female meiosis and occurs irrespective of whether the B's are odd or even in number. In the male there is a loss of B-chromosomes. This loss does not appear to be due simply to the lagging and elimination of B-chromosomes in meiosis but probably involves sperm formation or function. When the balance of the gain and loss after one generation is calculated, it shows large overall accumulation in crosses involving individuals from a population in Wales, and a slight loss in individuals from a population in East Anglia. Such differences in transmission rates may be responsible for differences in B-frequency between populations. Since the B-chromosome frequency of these two populations has remained stable over five years, possible forces in the maintenance of the equilibria are examined. Females with B-chromosomes produce more aneuploid embryos than 0B females, but neither this cause of inviability nor general embryo mortality seem sufficient to produce an equilibrium situation. It is necessary to postulate that progeny with more than 2B chromosomes are inviable in order to approach equilibria. The presence of B-chromosomes in females has also led to the formation of polyploid embryos. The possible involvement of repetitive DNA in the formation of unreduced egg nuclei and preferential segregation is discussed.     

INTERSPECIFIC INCOMPATIBILITY IN SOLANUM SPECIES

Pandey , K.K. (Crop Res. Div., D.S. & I.R., Lincoln, Christchurch, New Zealand.) Interspecific incompatibility in Solanum species. Amer. Jour. Bot. 49(8): 874–882. Illus. 1962.—A diallel cross involving 11 self-incompatible and 3 self-compatible species of Solanum was made to study the genetic basis of interspecific incompatibility. Interspecific incompatibility was not limited to crosses in which a self-compatible species was used as the male parent onto a self-incompatible species (unilateral incompatibility). A number of crosses between self-incompatible species were incompatible. In one cross, Q vernei X verrucosum, a self-compatible species was successful as a pollen parent with a self-incompatible species. Unlike other hybrids between self-compatible and self-incompatible species, which are self-incompatible, these F₁ hybrids were self-fertile, and cross-fertile among themselves and with both parents. The self-fertile S. polyadenium was cross-incompatible as a female as well as a male parent with all other species. It is suggested that the unilateral incompatibility is a property of the allele S_C which originated as a consequence of one kind of breakdown of the S_I gene; the S_C allele produces “bare” pollen growth substances which are inactivated in an incompatible style. It is proposed that the failure of the principle of unilateral interspecific incompatibility in solanaceous species may be due to the action of alleles at the second incompatibility locus revealed in certain Mexican species. It is assumed that the South American species are selected intraspecifically only for the action of S alleles but that in certain interspecific crosses and rarely in intraspecific crosses the alleles at the second locus may be expressed, thus interfering with the usual action of S alleles. The F₁ hybrids Q verrucosum (self-fertile) X simplicifolium (self-sterile) were self-incompatible at the tetraploid as well as the diploid level, and their cross-compatibility behavior was consistent with the expected activity of the S_C and S_I alleles of the 2 parents respectively.     

The B-chromosomes of Locusta migratoria I. Detection of negative correlation between mean chiasma frequency and the rate of accumulation of the B's; a reanalysis of the available data about the transmission of these B-chromosomes

B-chromosomes were studied in two Spanish populations of Locusta migratoria. Both exhibit a high frequency of B-carrying individuals (75% and 94%). In both the B-chromosomes are mitotically unstable and they accumulate in the male germ line. The mean rate of accumulation is 28.5% in Baños de la Encina and 31.9% in Carboneras. There are no significant differences in mean cell chiasma frequency and between-cell variance of chiasmata between follicles with different number of B's within individual males. Likewise, there are no significant differences in mean cell chiasma frequency and between-cell variance between males with and without supernumeraries. However, a significant negative correlation exists between mean chiasma frequency and the rate of accumulation.     

Mitotic instability leading to an accumulation of B-chromosomes in grasshoppers

The study of mitotically unstable B-chromosomes (supernumeraries) of two grasshopper species confirmed a suggestion made earlier (Nur, 1963) that the instability should always be associated with a tendency of the B's to increase in frequency. Among 780 Camnula pellucida (Scudder) males from California, 105 had B's. In the testes of these males the number of B's varied from follicle to follicle and ranged between 0 and 4. Because of this variation, the number with which each male started to develop could not be determined. However, the relatively low frequency of males with B's and the regular meiotic behavior of the latter suggested that most of the 105 males started with a single B. Cytological analysis of the cells of the gastric caeca of 31 males whose testes contained B's confirmed this suggestion by showing that only one male had two B's in these cells; all the rest had one. In the testes of the 74 other males the mean number of B's ranged from 0.89–2.50, but only two males had means higher than 2.00. The observed ratio of one male with two B's to 30 with one, suggested that only the two males with the highest means started to develop with two B's and that the other 72 males all started with one. Since the mean for the 72 males was 1.37 B's per male, it was concluded that during the development of the testes of these males the mean increased by 37%. The males with B's had fewer follicles in their testes and apparently had also a lower frequency of normal sperm. — The analysis of the testes of Locusta migratoria L. males from Japan gave results which agreed with those from C. pellucida.Supported by grants GB 1585 and GB 6745 from the National Science Foundation, Washington, D.C.     

Heritability of bulb shape in some north European onion varieties

Heritabilities for shape index (the ratio of bulb height to diameter), based on parent—offspring regressions, were calculated for north European onion cultivars and inbred lines derived from them. Heritability estimates of 0·46 and 0·47 respectively were obtained for the two groups, S₀ parent bulbs giving S₁ progenies, and S₁ parent bulbs giving S₂ progenies. Within each offspring progeny, the regression of bulb shape index on log_e bulb weight was significant. The regressions were used to estimate the mean shape indices of the progenies at the same mean bulb weight as their parents, and a series of ‘corrected’ progeny shape means thus obtained. Recalculation of the heritabilities using these ‘corrected’ progeny means gave increased estimates (0·78 and 0·84). By using this regression approach, the breeder can achieve high heritabilities when selecting for a specific mean shape index.     

Genotype-dependent effect of B-chromosomes on chiasma frequency in Eyprepocnemis plorans (Acrididae: Orthoptera)

In order to analyze the effect of B-chromosomes on chiasma frequency, the offspring of different females of the grasshopper Eyprepocnemis plorans have been studied. From the comparison between individuals of the different families having a given number of B's and between individuals with different numbers of B-chromosomes within the same family, it can be concluded that the effect of the genetic background on chiasma frequency is greater than that produced by the presence of B's, and that there is a between-families variation in the effect of B-chromosomes which, in addition, is negatively correlated with the chiasma frequency of related individuals without B's. This genotype-dependent effect of B-chromosomes is discussed.     

An isoenzyme marker linked to the incompatibility locus in cherry

Analysis of two cherry progenies from semi-compatible crosses for the esterase enzyme system showed extremely distorted segregation ratios for Est-5. Analysis of two progenies from compatible crosses for esterase and for stylar ribonuclease proved that Est-5 is linked with the incompatibility locus S. The recombination fraction is 4%. About a fifth of some 50 cultivars or selections genotyped for Est-5 were heterozygous. The various heterozygotes could provide ’testers’ for the presence in cultivars of unknown genotype of 8 of the 11 known S alleles. A seedling suitable for testing S ₉ has been identified and crosses have been made to raise testers for S ₁₀ and S ₁₁ . Isoenzyme analysis of the four progenies for glutamate oxaloacetate transaminase, and of one of them for isocitrate dehydrogenase, showed no evidence for the linkage of Got-1 or Idh-2 with S, contrary to a previous report. Estimation of linkage with S in semi-compatible crosses is discussed. Received: 16 April 1999 / Accepted: 22 June 1999     

Pollen tube expression of pseudo-self-compatibility (PSC) inPetunia hybrida

Summary AnS _1.1 self-incompatible (SI) petunia plant which showed atypical seed set was found in an I₇ population. This plant showed a strong SI reaction when selfed but produced varying amounts of seed when used as the seed parent in crosses with unrelated individuals homozygous for the sameS allele. Reciprocal crosses yielded no seed indicating that the reaction was a stylar response. Self seed obtained by high temperature treatments produced 18 plants, all of which exhibited the parental characteristics, the ability to reject self pollen but accept, to varying degrees, pollen bearing the sameS allele from unrelated plants. Several petunias homozygous forS ₁, and exhibiting various levels of PSC as determined by self seed set, progeny tests and temperature treatments, were used as pollen parents. The mean seed set of these crosses produced a ranking of the pollen parents which reflected the PSC levels obtained by other methods. The behavior of the F₁ and F₂ populations suggests that the pollen discriminating ability may be a simply inherited, dominant character in these plants. The styles of these unusual petunias illustrate the participation of the pollen tube in determining PSC.Scientific Journal Series Paper Number 10.479 of the Minnesota Agricultural Experiment Station     

Selection for increased nodule number in common bean (Phaseolus vulgaris L.)

Common bean (Phaseolus vulgaris L.) plants were grown for 21–28 days in plastic container-modified Leonard jar assemblies and placed in a controlled-environment room. The nodules on each plant were removed, counted; selected plants were repotted, grown and intercrossed to produce progenies for the next cycle of recurrent selection. Among the ten parent lines, Puebla 152 and WBR 22–34 produced the most nodules and Rio Tibagi and Negro Argel the fewest, when averaged over five experiments. An analysis of number of nodules on F₁ plants resulting from crosses made in a partial diallel design among the ten parents revealed highly significants variation for general combining ability (GCA) but not for specific combining ability (SCA). After three cycles of recurrent selection for nodule number per plant, the mean nodule number was 211% of the mean for the 10 parents control. Total nodule weight on selected plants also increased, but individual nodule weight decreased. Nineteen C₁ and 18 C₂ lines resulting from the individual plants selected for greater nodule number, along with the ten parents and two non-nodulating soybean lines included as non-fixing check plants were grown in a single experiment in a low-N field. C₂ lines on average accumulated significantly more N per plant than either the parents or C₁ lines, providing evidence for increased N₂ fixation measured by the N difference method. These data show that more nodules, possibly resulting from greater susceptibility to nodulation, are an important, heritable component of symbiosis and that selection for increased nodule number resulted in lines capable of fixing more atmospheric N₂.     

Inheritance of resistance to leaf and glume blotch caused by Septoria nodorum Berk. in winter wheat

Sixteen crosses between eight winter wheat cultivars were screened for resistance to Septoria nodorum leaf and glume blotch in the F₁ and F₄ generations using artificial inoculation in the field. The F₁ of most crosses showed dominance for susceptibility on both ear and leaf. The effects of general combining ability were of similar magnitude as the effects for specific combining ability. On the basis of the phenotypic difference of the parents, no prediction was possible about the amount and the direction of genetic variance in the segregating populations. The variation observed in this study both within and among the segregating populations suggests a quantitative inheritance pattern influencing the expression of the two traits. The components of variance between F₂ families within a population were as high as (for S. nodorum blotch on the ear) or higher (for S. nodorum blotch on the leaf) than those between populations. Therefore, strong selection within a few populations may be as effective to obtain new resistant genotypes as selection in a large number of populations. In almost all crosses, progenies were found that were more resistant than the better parent. Thus transgression breeding may be a tool to breed for higher levels of resistance to S. nodorum blotch. Highly resistant genotypes were found even in combination with two susceptible parents. The genetic source for Septoria resistance is probably broader than is generally assumed and could be used to improve S. nodorum resistance by combination breeding followed by strong selection in large populations. Received: 18 January / Accepted: 30 April 1999     

Hybrid maize breeding with doubled haploids: V. Selection strategies for testcross performance with variable sizes of crosses and S1 families

In hybrid maize (Zea mays L.) breeding, doubled haploids (DH) are increasingly replacing inbreds developed by recurrent selfing. Doubled haploids may be developed directly from S₀ plants in the parental cross or via S₁ families. In both these breeding schemes, we examined 2 two-stage selecting strategies, i.e., considering or ignoring cross and family structure while selection among and within parental crosses and S₁ families. We examined the optimum allocation of resources to maximize the selection gain ΔG and the probability P(q) of identifying the q% best genotypes. Our specific objectives were to (1) determine the optimum number and size of crosses and S₁ families, as well as the optimum number of test environments and (2) identify the superior selection strategy. Selection was based on the evaluation of testcross progenies of (1) DH lines in both stages (DHTC) and (2) S₁ families in the first stage and of DH lines within S₁ families in the second stage (S₁TC-DHTC) with uniform and variable sizes of crosses and S₁ families. We developed and employed simulation programs for selection with variable sizes of crosses and S₁ families within crosses. The breeding schemes and selection strategies showed similar relative efficiency for both optimization criteria ΔG and P (0.1%). As compared with DHTC, S₁TC-DHTC had larger ΔG and P (0.1%), but a higher standard deviation of ΔG. The superiority of S₁TC-DHTC was increased when the selection was done among all DH lines ignoring their cross and family structure and using variable sizes of crosses and S₁ families. In DHTC, the best selection strategy was to ignore cross structures and use uniform size of crosses.     

Partial resistance to late blight (Phytophthora infestans) in hybrid progenies of four South American Solanum species crossed with diploid S. tuberosum

Resistant genotypes of the diploid tuber-bearing South American species Solarium arnezii x hondelmannii, S. berthaultii, S. leptophyes and S. microdontum were crossed with three diploid genotypes of S. tuberosum that varied in resistance and maturity type. The progenies were field tested for 2 years for resistance to a complex race of Phytophthora infestans. A wealth of genetic variation for resistance was found in most of the progenies. At least two susceptibility groups could be distinguished in some progenies of S. microdontum. This could be explained by the presence of several major resistance genes in the wild parent and, unexpectedly, in the susceptible parent SH 82-44-111. In most of the wild parents and in the susceptible parent SH 77-114-2988 there appeared to be minor resistance genes. General combining ability effects were predominant; small specific combining ability effects were detected in some crosses of S. microdontum. Gene action appeared dominant in some crosses.     

B-chromosomes in some Himalayan hardwoods

B-chromosomes are reported for the first time for woody angiosperms. Out of six species from the eastern Himalayas in which B-chromosomes were observed, two are polyploid. The number of B-chromosomes varied from 0–5 in the different species. In Sambucus canadensis, Glerodendrum colebrookianum and Neolitsea zeylanica B's were found to pair with each other at Metaphase-I.The financial support for this work was provided by the U. S. Government from PL 480 funds in India (Grant: A7-FS-12).     

Genetic analysis of incompatibility in the diploid Ipomoea species closely related to the sweet potato

Summary In order to identify the genotypic constitutions of incompatibility in the diploid species, Ipomoea leucantha Jacq. (K221), which is most closely related to the sweet potato, the progenies derived from the reciprocal crosses, backcrosses and testcrosses were analysed. All the plants examined were self-incompatible, and pollen germination was inhibited on the stigma after incompatible pollinations. No reciprocal differences were found in the incompatibility reactions. In the progenies three incompatibility groups were observed which showed the rather simple segregation ratios. The homozygous plants for incompatibility alleles were obtained in the progenies. The experimental results demonstrated a sporophytic type of incompatibility controlled by a single locus with multiple S-alleles exhibiting a dominance relationship in both the pollen and the stigma. The plants obtained in the progenies had the following genotypes: S ₁ S ₂, S ₁ S ₃, S ₂ S ₂, S ₂ S ₃ and S ₃ S ₃.     

桉树及其杂交种叶片形态的遗传变异特征

为了解桉树重要性状在杂交种亲本、子代间的遗传变异规律,以尾叶桉(Eucalyptus urophylla)为母本、粗皮桉(E. pellita)和细叶桉(E. tereticornis)为父本、8个全同胞杂交子代为材料,对亲本和子代的叶片形态性状进行了分析。结果表明,亲缘关系近的尾叶桉和粗皮桉的叶片性状大多无显著差异;但他们与亲缘关系远的细叶桉间的差异显著;尾粗桉与父母本间的性状无显著差异或仅与母本差异显著,属偏父本型;尾细桉与双亲间的多数性状都差异显著,且多偏向于母本。在树种内的家系间或个体间,叶片数量性状差异显著,而质量性状仅叶面革质厚度、叶面朝向差异显著;杂交种家系部分性状有超亲现象,且尾细桉家系超亲频率显著高于尾粗桉。叶长、叶长宽比、形状因子、叶色、叶面革质是区别叶片形态特征的决定性状。     

Inheritance of a dwarf seed stalk character in onion

Results are reported of crossing a dwarf seed stalk line (mean height 44.8 cm) from Israel with five inbred lines of the Rijnsburger type each having normal tall seed stalks (mean heights 83.1–105.9 cm). The seed stalk height of F₁ generations from these crosses was slightly greater than that of the Rijnsburger parents but segregation occurred in the F₂ giving plants which could be considered ‘dwarf’ and ‘normal’ with respect to seed stalk height. Selfing individual F₂‘dwarf’ plants produced F₃ progenies whose mean heights were in the dwarf range, and were significantly correlated with those of their F₂ parent. The results obtained in the F₂ and F₃ families suggest that although a major recessive gene for dwarfness may be present, substantial minor gene and environmental variation is also involved.     

Evaluation of circulant partial diallel crosses in maize

Summary The present study was conducted in maize (Zea mays L.) on crosses among 20 diverse parents. The materials were evaluated in four different environments for eight characters. Combining ability analysis was carried out following diallel and partial diallel crosses. The number of crosses per parent (s) varied from 3 to 19 and the results were studied to identify the critical value of s that would provide an adequate information with minimum resources. The S₅ partial diallel was as good as the S₁₉ for the detection of differences among general combining ability (GCA) effects. Even the S₃ gave adequate information in the case of characters with high heritability. However, partial diallel analysis was less efficient in detecting the differences due to specific combining ability (SCA) effects. These results varied with environments, and characters with low heritability were more prone to misinterpretation. GCA effects showed fluctuations in partial diallel analysis which were more pronounced in S₅ and S₃, particularly for characters with low heritability. The average standard error of difference between GCA effects increased with a decrease in s, with a steep slope for s < 7. The partial diallel analysis was more efficient for the estimation of the variance component of GCA than for SCA, as the estimate of SCA was biased upwards. Estimates of broad sense heritability obtained from the partial diallels agreed with the full diallel analysis better than the narrow sense estimates. Smaller partial diallels gave erratic estimates of heritability, particularly for the characters with low heritability.     

Chloroplast DNA inheritance in Populus

Summary The inheritance of chloroplast (cp) DNA was examined in F₁ hybrid progenies of two Populus deltoides intraspecific controlled crosses and three P. deltoides × P. nigra and two P. deltoides × P. maximowiczii interspecific controlled crosses by restriction fragment analysis. Southern blots of restriction digests of parental and progeny DNAs were hybridized to cloned cpDNA fragments of Petunia hybrida. Sixteen enzymes and five heterologous cpDNA probes were used to screen restriction fragment polymorphisms among the parents. The mode of cpDNA inheritance was demonstrated in progenies of P. deltoides × P. nigra crosses with 26 restriction fragment polymorphisms of cpDNA differentiating P. deltoides from P. nigra, as revealed by 12 enzyme-probe combinations, and in progenies of P. deltoides × P. maximowiczii crosses with 12 restriction fragment polymorphisms separating P. deltoides from P. maximowiczii, as revealed by 7 restriction enzyme-probe combinations. In all cases, F₁ offspring of P. deltoides × P. nigra and P. deltoides × P. maximowiczii crosses had cpDNA restriction fragments of only their maternal P. deltoides parent. The results clearly demonstrated uniparental-maternal inheritance of the chloroplast genome in interspecific hybrids of P. deltoides with P. nigra and P. maximowiczii. Intraspecific P. deltoides hybrids also had the same cpDNA restriction fragments as their maternal parent. Maternal inheritance of the chloroplast genome in Populus is in agreement with what has been observed for most other angiosperms.