Polygon of crossability between eleven species of Ipomoea: section Batatas (Convolvulaceae)

Summary Crossability within Ipomoea section Batatas is complex because of genetic, cytogenetic and physiological interactions. This complexity is responsible for the fact that knowledge about phylogenetic relationships within this section remains preliminary. Between 1988 and 1991, studies of planting, pollination and evaluation of progenies were carried out at the facilities of CIP in La Molina and San Ramon, Peru. Self-compatibility was found in nine diploid species. Self-incompatibility was found in diploid I. trifida, tetraploid I. tiliacea and both tetraploid and hexaploid I. batatas. Sexual compatibility is though to be related to a multiallelic sporophytic incompatibility system which is expressed in the stigmatic papillae. Altogether, 4,162 cross pollinations were made between 11 species and 76 interspecific combinations of 110 possible combinations in a diallel 11×11 design. From these 76 interspecific combinations only 38 survived, and in these crossability (= proportion between number of fruits harvested/pollinations made) ranged from 0.01 to 1.00 at La Molina. At San Ramon, 11 out of 17 cross combinations were successful, and in these crossability ranged from 0.01 to 0.71. Crossability appeared to be influenced by latitude which is related to flowering synchrony. The early death of seedlings is hypothesized to be related to a genomic imbalance between embryo and endosperm. Maternal effects were found in crosses between diploids and tetraploids which produced triploid and diploid offspring, and in crosses between hexaploids and diploids which gave rise to hexaploid offspring. This study shows that I. trifida and I. x leucantha may act as bridge species for gene flow from wild Ipomoea species to the genepool of the sweetpotato.     

Progenies of allotriploids of Oriental × Asiatic lilies (Lilium) examined by GISH analysis

With the aim of utilizing allotriploid (2n = 3x = 36) lily hybrids (Lilium) in introgression breeding, different types of crosses were made. First, using diploid Asiatic lilies (2n = 2x = 24), reciprocal crosses (3x − 2x and 2x − 3x) were made with allotriploid hybrids (AOA) obtained by backcrosses of F₁ Oriental × Asiatic hybrids (OA) to Asiatic cultivars (A). Secondly, the AOA allotriploids were crossed with allotetraploid (OAOA, 2n = 4x = 48), in 3x − 4x combination. Finally, the AOA allotriploids where crossed to 2n gamete producer F₁ OA hybrids (3x − 2x (2n)). Two types of triploids were used as parents in the different types of crosses, derived from: (a) mitotic polyploidization and (b) sexual polyploidization. Ploidy level of the progeny was determined by estimating the DNA values through flowcytometry as well as chromosome counting. The aneuploid progeny plants from 3x − 2x and reciprocal crosses had approximate diploid levels and in 3x − 4x crosses and 3x − 2x (2n) the progeny had approximate tetraploid levels. Balanced euploid gametes (x, 2x and 3x) were formed in the AOA genotypes. Recombinant chromosomes were found in the progenies of all crosses, except in the case of 2x − 3x crosses through genomic in situ hybridization (GISH) analyses. Recombinant chromosomes occurred in the F₁ OA hybrid when the triploid AOA hybrid was derived through sexual polyploidization, but not through mitotic polyploidization with two exceptions. Those recombinant chromosomes were transmitted to the progenies in variable frequencies.     

Heterosis in crisphead lettuce (Lactuca sativa L.) hybrids

Summary Six of 16 F₁ hybrids from diverse crosses of crisphead lettuce with butterhead, cos or other crispheads significantly outyielded their respective better parent. Four were crosses between crisphead and cos parents, one was a butterhead × crisphead cross and one, a winter crisphead × winter crisphead cross. This latter hybrid plus one other also proved heterotic in a subsequent trial of ten crosses involving five winter crisphead parents, with yield excesses over better parent of 16 and 19%. It appeared significant that the heterotic crosses were given by parents of dissimilar origin. Trials of F₂ segregants from one of these heterotic hybrids enabled predictions to be made for 10.2 to 24.1% yield increases over better parent by the retention and clonal multiplication of the 10% highest yielding selections. Heterosis demonstrated in these trials may constitute the first reported cases in lettuce.     

Interspecific hybrids of Cyclamen persicum Mill. and C. purpurascens Mill. produced by ovule culture

Summary Interspecific crosses were made to introduce the scent of flowers of C. purpurascens into C. persicum cultivars and ovule culture was used to rescue the abortive hybrid embryos. Cultivars of C. persicum diploid (CPD, 2n=2×=48) and C. persicum tetraploid (CPT, 2n=4×=96) were the pistillate parents and wild species of C. purpurascens (CP, 2n=34) were staminate parents. After pollination, crossed ovaries were collected periodically and examined using paraffin sections. Histological observations suggested that both hybrid ovules of CPD x CP and CPT x CP should be transferred to culture medium 35 days after pollination. Based up on this observation, crossed ovaries were collected 28 days after pollination and ovules with placenta were transferred to MS (1962) medium containing 3% sucrose. These ovules were cultured in the dark at 25° C. The hybrids (2n=41) derived from CPD x CP had the scent of C. purpurascens, whereas the hybrids (2n=65) derived from CPT x CP had the scent of C. persicum. Although both hybrids had complete genomes from the parents and produced a few viable pollen grains, they failed to yield viable seeds by self- and cross-pollination with fertile pollen grains of C. persicum cultivars.Abbreviations CPD C. persicum diploid - CPT C. persicum tetraploid - CP C. purpurascens     

Heterosis and heritability in crosses among Asian and Ethiopian parents of hot pepper genotypes

Hot pepper is the most important worldwide grown and consumed spice and vegetable crop. Though hybrid breeding has been proposed for genetic improvement in the crop, but there is lack of information on heterosis in crosses among crop genotypes in Ethiopia. Twelve genotypes (nine Asian and three Ethiopian parents) of hot pepper were crossed in 2003 cropping season in a half-diallel fashion to fit Griffing’s fixed effect model analysis. An open field experiment was conducted in 2004/2005 to investigate heterosis for fourteen traits in 66 F₁ hybrids grown together with their 12 selfed parents. Highly significant genotypic differences were observed for all the traits except for leaf area. Variance component due to specific combining ability (dominance) were larger than that due to general combining ability (additive) for each of the studied traits with few exceptions. Broad sense heritability (H _b²) for fruit traits were more than 60% and with wide gap from narrow sense heritability (h _n²) for most of the important traits like number of fruit per plant (H _b² = 88.3% and h _n² = 46.0%), days to maturity (H _b² = 87.2% and h _n² = 23.1%) and dry fruit yield per plant (H _b² = 72.6% and h _n² = 14.6%). Maximum heterosis over mid-parent and better-parent, and economic superiority of hybrid over standard check were recorded, respectively for dry fruit yield per plant (163.8, 161.8 and 92.1%), number of fruits per plant (104.4, 79.6 and 136.4%) and days to maturity (−29.8, −31.5 and −23.6%). These observations suggested a possibility of utilizing dominance genetic potentiality available in diverse genotypes of the crop by heterosis breeding for improving hot pepper to the extent of better economic return compared to the current commercial cultivar under production in the country. Low narrow sense versus very high broad sense heritability for days to maturity and dry fruit yield per plant could be a sign for achievability of earliness and high fruit yield using heterosis in hot pepper. The maximum heterobeltiosis were recorded either from F₁s obtained from Ethiopian and Asian crosses or from within Asian crosses, suggesting the possibility of maximizing heterosis by considering genetically diverse parental genotypes. The manifestation of highest heterosis in hybrids from among Asian lines indicated existence of genetic diversity among Asian genotypes and the potentiality for improvement of hot pepper using genotypes from different regions of the world along with elite inbred lines from local cultivars.     

Novel interspecific hybridization between sweetpotato (<Emphasis Type="Italic">Ipomoea batatas</Emphasis> (L.) Lam.) and its two diploid wild relatives

Interspecific hybridization is an important approach to broaden the genetic base and create novel plant forms in breeding programs. However, interspecific hybridization in Ipomoea is very difficult due to the cross incompatibility. Here we report two novel interspecific F₁ hybrids between I. batatas (L.) Lam. (2n = 6x = 90) and two wild species, I. grandifolia (2n = 2x = 30) and I. purpurea (2n = 2x = 30). Hybridization was stimulated by applying plant growth hormones. Morphological, molecular and cytological tests were conducted to confirm their hybridity. We found that the two hybrids were quite distinctive in leaf color and morphology, and yielded intermediate sizes of storage roots compared to their respective parents. Inter-simple sequence repeat analysis showed that the unique DNA bands from the wild parents could be detected in these two hybrids. The cluster analysis also showed that the two F₁ hybrids were closer to I. batatas in phylogeny relationship. The number of chromosomes of the two hybrids was both 60, indicating that the hybrids were tetraploid. The meiotic configuration analysis of the H₁ of I. batatas × I. grandifolia revealed the occurrence of 17.58I + 14.28II + 1.36III + 2.48IV at metaphase I in average chromosome association per pollen mother cells (PMCs), 4.26I + 18.32II + 2.56III + 3.12IV was average meiotic configuration in the H₂ of I. batatas × I. purpurea. Both hybrids appeared to be polyads and multi-microcytes at tetrad phase and differed in their pollen fertility.     

The inheritance of a basal branching type in guar

Summary Eight different genotypes of the F₁ hybrids between Oriental × Asiatic lily (Lilium) hybrids (2n = 2x = 24) were treated with nitrous oxide (N₂O) gas under pressure for 24 and 48 hours. At the time of treatment, all plants possessed early meiotic stages in the anthers of the oldest flower buds. The mature flowers from treated plants were monitored for fertility through pollen germination in vitro as well as by using them in crosses with diploid Asiatic hybrids (2n = 2x = 24) both as male and female parents. In five out of the eight genotypes of OA hybrids there was evidence for the production of 2n pollen which germinated in vitro from either one or both treatments. The 2n pollen from three genotypes was successfully used in crosses. In two cases, the treated plants were successfully used as female parents which indicated the formation of 2n (or 2x) egg cells. From an analysis of 41 sexual polyploid progenies obtained from N₂O treated plants it was shown that they were all euploids consisting of 34 triploids (2n = 3x = 36) and seven tetraploids (2n = 4x = 48). A detailed cytological analysis of 12 progeny plants through genomic in situ hybridization (GISH) proved that N₂O had induced first division restitution gametes in most cases and in two cases they produced gametes through indeterminate meiotic restitution. There was evidence for intergenomic recombination in three cases.     

The transfer of triazine resistance from Brassica napus L. to B. oleracea L. III. First backcross to parental species

Summary Atrazine resistant Brassica napus × B. oleracea F₁ hybrids were backcrossed to both parental species. The backcrosses to B. napus produced seeds in both directions but results were much better when the F₁ hybrid was the pollen parent. Backcrosses to B. oleracea failed completely but BC₁s were rescued by embryo culture both from a tetraploid hybrid (2n = 4x = 37; A₁C₁CC) and sesquidiploid hybrids (2n = 3x = 8; A₁C₁C). Progeny of crosses between the tetraploid hybrid and B. oleracea had between 25 and 28 chromosomes. That of crosses between the sesquidiploid hybrid and B. oleracea had between 21 and 27. A few plants that had chromosome counts outside the expected range may have originated from either diploid parthenogenesis, unreduced gametes or spontaneous chromosome doubling during in vitro culture. Pollen stainability of the BC₁s ranged from 0% to 91.5%. All the BC₁s to B. oleracea were resistant to atrazine.     

Interspecific hybrids of Cyclamen persicum and C. graecum

Summary Interspecific crosses were made to introduce the disease resistance of Cyclamen graecum into C. persicum cultivars and the abortive hybrid embryos were rescued by ovule culture. Diploid and tetraploid cultivars of C. persicum (CPD, 2n=2x=48; CPT, 2n=4x=96) were the pistillate parents and wild form of C. graecum (CG, 2n=84) were the staminate parents. After pollination, crossed ovaries were periodically collected and examined using paraffin sections. Histological observations suggested that both hybrid ovules of CPD × CG and CPT × CG should be transferred to the culture medium 35 days after pollination. Based upon this observation, crossed ovaries were collected 35 days after pollination, then ovules with placenta were explanted on culture medium and cultured in the dark at 25°C. Plantlets were induced from ovules cultured in MS medium containing 3% sucrose and 10% coconut milk. The hybrids (2n=66) derived from CPD × CG failed to yield viable seeds by self-pollination, although they showed some pollen fertility. In contrast, the hybrids (2n=90) derived from CPT × CG showed high pollen fertility and yielded viable seeds by self-pollination. Furthermore, they were resistant to disease caused by Fusarium oxysporum f. sp. cyclaminis, Erwinia herbicola pv. cyclamenae and Pseudomonas marginalis pv. marginalis.Abbreviations CPD C. persicum diploid - CPT C. persicum tetraploid - CG C. graecum     

Chromosome associations and crossability with Iris ensata Thunb. in induced amphidiploids of I. laevigata Fisch. × I. ensata

Summary The chromosome associations of amphidiploids of I. laevigata × I. ensata were analysed and compared with those of the parental species and F₁ hybrids of I. laevigata × I. ensata. The F₁ hybrids showed partial chromosome associations. Their mean chromosome association per cell was 20.73I+3.63II, although the mean chromosome association per cell in the parental species was 0.09I+15.96II for I. laevigata and 0.03I+11.98II for I. ensata, respecively. In contrast, the normal association (28II) was partially restored in the amphidiploids. Their mean chromosome association per cell was 1.93I+26.48II+0.28III+0.03IV+0.03V. In this study, moreover, the crossability between I. ensata (2X and 4X) and the amphidiploids and between I. laevigata and the amphiliploids was examined. No hybrid plants were obtained from both reciprocal crosses between I. ensata (2X) and the amphidiploids and between I. laevigata and the amphidiploids. Only the cross of I. ensata (4X) × the amphidiploids in the reciprocal crosses produced hybrid plants. The observation of their somatic chromosome numbers indicates that these are true hybrid plants between autotetraploid I. ensata and the amphidiploids, and such plants can be called autoallotetraploids between I. ensata and I. laevigata. The interspecific cross-breeding of I. ensata using the autoallotetraploids is discussed.     

Effect of Zinnia angustifolia HBK genotype on morphology and flowering of Z. angustifolia × Z. elegans Jacq. hybrids

Summary Interspecific hybrids were generated from crosses between 4 Zinnia angustifolia clones (maternal parents) and an inbred line of Z. elegans Orange King (paternal parent) to investigate the influence of Z. angustifolia genotype on morphology and flowering of hybrids. Leaf length, leaf width, flower diameter, number of ray petals, and days to flowering of interspecific hybrids were significantly influenced by Z. angustifolia clonal genotype. Genetic analysis of hybrid morphology and development was performed using 2 parental Z. angustifolia clones and 18 F₁ (9 seedlings from each of 2 populations generated from reciprocal crosses between parental clones) as maternal parents in crosses with Z. elegans Orange King. Genotype of Z. angustifolia significantly affected plant height, fresh weight, number of nodes, and days to flowering of interspecific hybrids. Control of these traits was through the Z. angustifolia nuclear genome. Improvement in interspecific hybrid morphology or development, i.e., shorter stature, earlier flowering, or larger flowers, may be possible by selection of superior-performing Z. angustifolia clones as parents.     

Structural hybridity in the series Etuberosa of the genus Solanum and its bearing on crossability

Summary Three non-tuberous Solanum species of series Etuberosa-S. brevidens (brd), S. etuberosum (etb) and S. fernandezianum (frn)-upon selfing displayed compatible berry set but seed set varied and on an average was below normal. Also in crosses between species berry set was unhampered (apart from the crosses with short-styled frn as pollen plant), but the interspecific hybrid plants showed various degrees of sterility and a low average seed set upon selfing. Cytological investigations revealed that in pure species-plants semi-sterility regularly occurred and was invariably associated with multivalent associations (up to decavalents). This may account for the decreased seed set found after selfing and intercrossing. Meiosis in F₁-hybrids was even more irregular, 75% of the pmc's showing multivalents involving from 4 to as many as 22 chromosomes in various complicated configurations in which even numbers of chromosomes were predominant. However, anaphase I separation was numerically balanced in more than 75% of the cells. Pollen stainability was very low in the hybrids.It is concluded that heterozygous translocations occur within each species and that the genomes of the species are differentiated by means of gross structural changes. In view of this and of the high chromosome pairing affinity the genome symbols E ₁, E ₂ and E ₃ are proposed for etb, brd and frn, respectively.Crossability of the Etuberosa species with tuberous S. pinnatisectum (pnt) was slightly more successful (average 2.7 seeds/berry) than that of Etuberosa species hybrids with S. pinnatisectum (average 1.7 seed/berry). In the hybrids studied-etb × pnt, frn × pnt and (brd × etb) × pnt-a high frequency of univalents was the rule (range 6–16 per cell). In addition rod bivalents (4–8 per cell) and a low frequency of trivalents occurred (0–3 in the biparental hybrids and 1–4 in the trispecific hybrid).Utilization of the valuable characters of Etuberosa for potato breeding is dependent on the degree of gene exchange between Etuberosa chromosomes and chromosomes of tuberous species. In the diploid hybrids such exchange, though limited, may take place through bivalents and trivalents. As shown in this article such diploid hybrids are non-crossable because of complete male and female sterility. Only after doubling the number of chromosomes the hybrids are fertile and can be used for further crosses.     

Fertility improvement in tetraploid pearl millet

Summary Autotetraploid (2n=4x=28) pearl millet inbred lines, Tift 23BE and Tift 239DB, have been developed for use in crosses with other polyploid Pennisetum species. Each line set less than 1% and 3% selfed and open-pollinated seed, respectively. Seed germination was usually less than 17%. First generation (F₁) hybrids between the two inbreds set up to 61% seed while up to 40% of the seed from hybrids germinated.Seed weight per inflorescence for two planting dates averaged 0.32 g and 3.06 g for the two inbreds and the second generation F₂ progeny, respectively. One hundred seed weight was also significantly higher (0.78 g vs 0.48 g) in the F₂ progeny, probably due better endosperm development. Chromosome behavior and pollen stainability were similar in the inbred parents and hybrids. However, the hybrids shed more pollen than the inbred parents.Heterosis was evident in the F₁ hybrids and F₂ progeny which showed significant increases in plant height, leaf length, leaf width, and inflorescence length in addition to fertility improvement.     

Identification of somatic hybrids of dihaploid Solanum tuberosum lines and S. brevidens by species specific RAPD patterns and assessment of disease resistance of the hybrids

Summary Symmetric somatic hybrids were produced by electrofusion of protoplasts of two dihaploid tuber-bearing potato (Solanum tuberosum L.) lines and Solanum brevidens Phil., a diploid non-tuber-bearing wild potato species. A total of 985 plants was obtained. Verification of nuclear hybridity of putative hybrids was based on additive RAPD patterns, general morphological characteristics and chromosome counts. 53 (90%) calli regenerated into plants which were identified as somatic hybrids. Most of the hybrids were aneuploids at the tetraploid (4×) or hexaploid (6×) level. The 20 hybrids tested expressed a high level of resistance to potato virus Y (PVY ^N ) characteristic of the S. brevidens parent. Resistance to late blight (Phytophthora infestans (Mont.) de Bary) varied between hybrids, but was on average better than that of the fusion parents. Resistance of hybrids to bacterial stem rot (Erwinia carotovora subsp. atroseptica (van Hall) Dye) was not superior to that of commercial potato cultivars.     

Heterosis of interspecific soybean hybrids for traits related to N2 fixation

Summary Three greenhouse experiments were conducted to compare the performance of soybean (Glycine max (L.) Merr.), wild soybean (G. soja Sieb. et Zucc.), and soybean x wild soybean hybrids for traits relating to N₂ fixation including nodulation, acetylene reduction, nodule leghemoglobin concentration, and nitrogen (N) accumulation and dry matter (DM) accumulation. In all three experiments G. max generally exceeded G. soja in nodulation, acetylene reduction, and N and DM accumulation while the soybean possessed higher nodule leghemoglobin concentration. In Experiment I, the mean of the hybrids did not differ significantly from the G. max parent in nodule mass, acetylene reduction activity, nodule leghemoglobin concentration, or DM accumulation. The hybrids did exceed the soybean parent in N accumulation, thus demonstrating high parent heterosis. In Experiments IIA and IIB with a more carefully chosen set of G. soja parents, high parent heterosis of individual crosses was common. Across the three experiments average high parent heterosis was 34, 28, and 28%, respectively, for nodule mass, N accumulation, and DM accumulation. If one accepts the assumption that hybrid vigor results from the accumulation of dominant alleles, then these alleles could theoretically be accumulated via selection in a homozygous genotype. If this is true than the results of the experiments reported here suggest that interspecific soybean x wild soybean crosses could serve as sources of homozygous lines which would exceed currently available soybean cultivars in nodule mass, and N and DM accumulation.This work was supported in part by the USDA Competitive Grants Program, Grant 82-CRCR-1-1039 and Cooperative Agreement 58-32U4-2-370 between the U.S. Department of Agriculture and the Agronomy Department, University of Maryland, Scientific Article No. A-4648, Contribution No. 7644 of the Maryland Agricultural Experiment Station.     

Inheritance of downy mildew resistance in Indian cauliflower (group III)

Summary Inheritance of downy mildew (Peronospora parasitica) resistance in three resistant x susceptible crosses, one susceptible x susceptible and one resistant x resistant cross were studied in Indian cauliflower (Group III) over the two years (1990 and 1991). No significant difference was observed between the years for various estimates and hence pooled data are presented. Downy mildew resistance in crosses cc×HR 5-4 and 3-5-1-1×244 (R×S) is governed by single dominant gene PPA3 but in cross cc×244 (R×S), recessive epistasis was observed. The resistance level was not improved in both the cc×3-5-1-1 (R×R) and 244×267-6-9 (S×S) crosses. Exploitation of downy mildew resistance from cc and 3-5-1-1 in F₁ hybrid is explained in detail.     

Comparison of diploid and tetraploid potato families derived from Solanum phureja x dihaploid S. tuberosum hybrids and their vegetatively doubled counterparts

Summary To determine whether in potatoes the tetraploid level is preferable to the diploid level, especially regarding tuber yield, four diploid (2n=2×=24) Solanum phureja x dihaploid S. tuberosum hybrid parents and their vegetatively doubled, tetraploid (2n=4×=48) counterparts were intermated, which resulted in two F₁ hybrid families at both levels of ploidy. The parents and clones of the F₁ families and their offspring were used in crosses in such a way that in addition Sib₁, Sib₂, F₁×Sib₁, BC₁ and Sib₁×Sib₁ families were produced. Of the first clonal generation of the 12 2 x families and their 12 counterpart 4 x families two tubers per clone were planted in three replications in a field experiment at Sturgeon Bay in 1969; of the parents six tubers were planted in each replication. Data were recorded on 16 characters, including plant height at four different times.The ANOVA's showed significant clone effects within each family for all characters. Computed from all family means as well as from the family means per ploidy level, differences due to family were also significant for all characters except one.As at the 2 x level and at the 4 x level of ploidy the mean phenotypic correlations between characters were of similar magnitude, it is concluded that they are independent of ploidy level.With the exception of eye depth, the mean coefficient of variation was greater at the 2 x than at the 4 x level of ploidy, indicating the greatest response to selection for those characters at the 2 x level. From the differences in family means between the 4 x and the 2 x level of ploidy it was apparent that the 4 x families generally had significantly taller plants, later maturity, fewer tubers, higher mean tuber weight, more tuber yield and more dry matter yield than their counterpart 2 x families. In contrast, the 4 x parents had on the average shorter plants, lower mean tuber weight, much lower tuber yield and lower dry matter yield than their 2 x counterparts.The phenotypic correlation and Spearman's rank correlation between the family means of the 2 x and the 4 x level of ploidy were positive for almost all characters and significant for nearly half of them.From the results it is concluded that 1. in potatoes the 4 x level of ploidy is preferable to the 2 x level, and 2. the performance of 4 x families is predictable from the performance of their counterpart 2 x families.Based on results mentioned in the literature and on the present results, a continued use of S. tuberosum dihaploids in potato breeding needs to be dissuaded.     

Inheritance of pseudo-self compatibility in self-incompatible garden and greenhouse chrysanthemums, Dendranthema grandiflora Tzvelv

Summary Self incompatibility (SI) can be used to alleviate costly hand emasculation and pollination in F₁ hybrid chrysanthemum seed production. SI, however, disrupts the progression of inbreedig (selfing or full-sib mating). Consequently, inbreds are selected for breakdown of the SI system or the presence of pseudo-self compatibility (PSC). PSC inbreds, recombinant inbreds, and noninbred cultivars were selfed and/or intercrossed to determine PSC expression across environments and generate 1–3 inbred generations (I₁–I₃). Percent PSC ranged from 0–68.8% for inbred parents, 0.2–99.7% for recombinant inbreds, and 0.6–25.7% for noninbred cultivars. There was no indication of end-of-season PSC. The majority of parents (78%) were classified as low PSC and this trend continued in the I₁ (70.1%), I₂ (65.6%), and I₃ (83.6%) generations; mid PSC was rarer (11.9–18.8%) and high PSC the least common (4.5–15.6%). PSC distributions were primarily continuous, rather than discrete, indicating quantitative inheritance. In several inbred families, 100% of the I₁ individuals were SI; this was not correlated with parental PSC level. Inbred families derived from selfing low and mid PSC parents were the most likely to reach extinction due to inbreeding depression. High PSC was not highly heritable, since I₁ progeny were predominantly SI or had low to mid PSC levels. Most 153-1 values for PSC:SI segregations (1:1, 1:3, 3:1) were not significant at the 5% level. Realized heritability (H _R ) estimates for PSC ranged from a low of 0.05% to 10.19%, although increased H _R values did not account for inbreeding depression or genetic mechanisms preventing selection for high PSC. The highest individual %PSC increased over the high parent with SI × low PSC or SI × mid PSC parents in all cases; progeny means did so only in SI × low PSC. Low × low crosses were split evenly between an increase and decrease in progeny or highest individual mean. Since all low × low crosses and low selfs produced 43–50% of the progeny with PSC levels higher than the parents, it appears that most low parents possess some unexpressed PSC genes. Mid PSC parents responded similarly to low PSC genotypes. An increase in PSC was found when crossing SI × PSC parents, illustrating a threshold effect. PSC × PSC crosses (high × low, low × low) produced SI, low, and mid PSC I₁ individuals but did not show a heterotic effect, since the PSC parents had already surpassed the PSC threshold. Selfing high PSC parents, however, suggested different genetic control. Progeny and highest individual means behaved the same; 83% decreased and 17% remained the same for PSC levels. The drop in PSC indicated non-additive gene action. Thus, the PSC threshold with additive gene action holds when selection for higher PSC levels is being done from low and mid PSC parents, but once high PSC levels are obtained, non-additive gene action prevails.Abbreviations self pollinated - H _R Realized Heritability - PSC Pseudo-Self Compatibility - SC Self Compatibility - SI Self Incompatibility     

甘薯近缘野生种Ipomoea trifida(4x) GISH分析

以甘薯近缘野生种I. trifida (2x)为探针, 与I. trifida (4x) 2个株系“695104”和“697288”的体细胞染色体进行基因组荧光原位杂交, 结果显示, 2株系都与I. trifida (2x)有很近的亲缘关系, 但2株系的信号存在差异。“695104”几乎所有染色体整条都有均匀明亮的信号, 应为I. trifida (2x)基因组直接加倍而来;而 “697288”与“695104”不同, 虽然各条染色体也均有杂交信号, 但信号的区域与亮度有差异, 较为复杂, 可分为三种情况。第1种是整条染色体有均匀明亮的信号, 亮度与分布区域同“695104” , 有41条;第2种是几乎整条染色体有信号, 但亮度较第一种暗, 有14条;第3种为染色体部分区域有信号, 亮度较前二者更暗, 有5条。推测 “697288”是在加倍同时或之后又发生了基因组重组与部分变异。     

Interspecific cross of Brassica oleracea var. alboglabra and B. napus : effects of growth condition and silique age on the efficiency of hybrid production, and inheritance of erucic acid in the self-pollinated backcross generation

Interspecific hybrids were produced from reciprocal crosses between Brassica napus (2n = 38, AACC) and B. oleracea var. alboglabra (2n = 18, CC) to introgress the zero-erucic acid alleles from B. napus into B. oleracea. The ovule culture embryo rescue technique was applied for production of F₁ plants. The effects of silique age, as measured by days after pollination (DAP), and growth condition (temperature) on the efficiency of this technique was investigated. The greatest numbers of hybrids per pollination were produced under 20°/15°C (day/night) at 16 DAP for B. oleracea (♀) × B. napus crosses, while under 15°/10°C at 14 DAP for B. napus (♀) × B. oleracea crosses. Application of the ovule culture technique also increased the efficiency of BC₁ (F₁ × B. oleracea) hybrid production by 10-fold over in vivo seed set. The segregation of erucic acid alleles in the self-pollinated backcross generation, i.e. in BC₁S₁ seeds, revealed that the gametes of the F₁ and BC₁ plants carrying a greater number of A-genome chromosomes were more viable. This resulted in a significantly greater number of intermediate and a smaller number of high-erucic acid BC₁S₁ seeds.