Evaluation under long-day conditions of 4x-2x progenies from crosses between potato cultivars and haploid Tuberosum-Solanum chacoense hybrids

Twelve 4x families (obtained from a sub‐set of crosses between seven 4x‐potato cultivars and three 2x haploid Tuberosum‐Solanum chacoense hybrids) were evaluated at Hancock, Wisconsin (USA). The 4x‐parents were elite cultivars selected for adaptation in three continents (Europe, South America, and North America). The 2x male clones were able to produce 2n‐pollen grains by a mechanism akin to first‐division restitution with crossover (FDR‐CO). The estimation of the degree of heterosis for total tuber yield (TTY) was obtained by comparing the field performance of the progenies with their respective 2x and 4x parents. Haulm maturity (HM) and general tuber appearance (GTA) were also evaluated. For TTY, the 4x‐2x families (as a group) outyielded both the 4x and 2x parental groups by 10.6% and 42.5%, respectively. In addition, 5 out of 12 families outyielded their corresponding 4x‐parents. These best five families outyielded the group of 4x‐parents by 40.6%. A considerable variability was observed for HM but, in general, the families were later maturing than the 4x cultivars. The identification of 4x‐2x families with GTA within the range of the 4x commercial cultivars was another important observation. An overall lack of parent‐offspring correlation was detected indicating that performance of the parents per se cannot provide a reliable prediction about the performance of the families. Therefore, progeny testing would be an imperative step for selection of parental clones at both ploidy levels. Our study indicated that haploid Tuberosum‐S. chacoense hybrids are able to generate heterotic 4x‐2x families for TTY in combination with good GTA. These results reinforce the view that selection of superior clones for the Northern Hemisphere can be feasible using germplasm with ～25% genomic contribution of this wild South American species.     

Direct estimation of the effects of meiotic recombination on potato traits via analysis of 4x-2x progenies from synaptic mutants with 2n-pollen formation by FDR without crossing-over

Diploid potato clones with 2n-pollen formation by first-division restitution without crossing-over (FDR-NCO) are ideal testers to estimate the breeding value of elite 4x cultivars by virtue of transmitting their genotypes practically intact to their progenies. This characteristic facilitates genetic analysis, since meiotic recombination would take place only in the 4x parent and not in the diploid parent. We evaluated (under short-day conditions) families from complete factorial crosses between four 4x cultivars and five 2x(FDR-NCO) clones. Families were compared with two standard 4x cultivars (’Bintje’ and ’Delta’) for total tuber yield (TTY), commercial yield (CY), haulm maturity (HM), plant vigor (PV), plant-top uniformity (PU), eye depth (ED), number of tubers per hill (NTH), and the CY/TTY index (CTI). For TTY, the contrasts family group (310 g/ hill) vs ’Delta’ (430 g/hill) and the family group vs ’Bintje’ (210 g/hill) were significant. Only 25% of the families were different from ’Delta’ and 20% of them outyielded ’Bintje’. For CY, differences were observed between families (240 g/hill) vs ’Delta’ (340 g/hill) and families vs ’Bintje’ (150 g/hill). The two best families had 53% CY over ’Bintje’. Surprisingly, only one family had a higher NTH than ’Bintje’. No differences were observed for HM. Seventy five and 30% of the families had an ED similar to ’Delta’ (ED = 2) and ’Bintje’ (ED = 1), respectively. A multivariate analysis indicated that 63% of the data variability could be explained by two factors. TTY, CY, and PV had high loading on the first factor, whereas ED, PU and HM had high loading on the second factor; CTI and NTH had equal sizes on both factors. High TTY and PV were associated with high NTH and CTI. Deep eye, PU, and late maturity were associated with high NTH and reduced CTI. The distributions of factor scores of the entries indicated that some 2x parents had strong influences (irrespective of the direction of their effects) on the crosses. Six crosses due to two 2x males were in the ’Bintje’ quarter with negative scores for both factors (implying low TTY, poor vigor, and low NTH). Also three crosses due to another 2x clone were distributed in the quarter of positive factor 1 and negative factor 2. These crosses plus another one were in the same quarter of ’Delta’ (implying high yields, low ED, low PU, and early maturity). The FDR-NCO clones provide a homogeneous sample of heterozygous 2n-gametes allowing the unique opportunity to estimate the relative contribution of the random meiotic products (from the 4x parents) and the ’somatic’ 2x genome for the phenotypic expression of quantitative traits. The interesting result was that measurable effects (favorable or not) on the data variability were mainly determined by the genomic contribution of the haploid-species hybrids. Three out of five 2x-male parents showed rather strong effects on progenies. No such effects were observed on the four 4x-female parents. Received: 3 September 1999 / Accepted: 24 November 1999     

Genetic diversity in kiwifruit polyploid complexes: insights into cultivar evaluation,conservation, and utilization

Understanding the extent and partitioning of crop genetic diversity is necessary for conserving and utilizing their genetic potentials for breeding. In the present study, fluorescence-labeled amplified fragment length polymorphism markers were used to characterize the genetic diversity and relationships of 79 cultivars and also of 122 F1 hybrids which resulted from six kiwifruit interploid crosses. A high level of mean genetic diversity was detected (Hj > 0.22) for all cultivars investigated, without significant differences among diploids (2x), tetraploids (4x), and hexaploids (6x). This suggested that no significant genetic erosion occurred in these cultivars, which were directly selected from natural resources or created from crosses. The Unweighted Pair Group Method with Arithmetic Mean analysis of the genetic dissimilarity between cultivars showed three main groups mostly based on their three ploidy levels. Among these, the red-fleshed cultivars which were originally derived from ‘Hongyang’ clustered into one subgroup of group I, suggesting their unique genetic background despite they were marked as different cultivars used in the current kiwifruit industry. By analyzing the genetic variation of hybrids with variable ploidy levels, our genetic analyses further revealed that interploid crosses can increase the genetic diversity of F1 offsprings, especially from the parental combinations of 6x–2x and 6x–4x, in which both parents showed significant differences in morphology and genetic backgrounds. Based on these findings, strategies were proposed for the conservation and utilization of the current kiwifruit genetic resources for future breeding programs.     

Determination of heterotic groups for tropical Indica hybrid rice germplasm

Key message

Two heterotic groups and four heterotic patterns were identified for IRRI hybrid rice germplasm to develop hybrid rice in the tropics based on SSR molecular data and field trials.

Abstract

Information on heterotic groups and patterns is a fundamental prerequisite for hybrid crop breeding; however, no such clear information is available for tropical hybrid rice breeding after more than 30 years of hybrid rice commercialization. Based on a study of genetic diversity using molecular markers, 18 parents representing hybrid rice populations historically developed at the International Rice Research Institute (IRRI) were selected to form diallel crosses of hybrids and were evaluated in tropical environments. Yield, yield heterosis and combining ability were investigated with the main objectives of (1) evaluating the magnitude of yield heterosis among marker-based parental groups, (2) examining the consistency between marker-based group and heterotic performance of hybrids, and (3) identifying foundational hybrid parents in discrete germplasm pools to provide a reference for tropical indica hybrid rice breeding. Significant differences in yield, yield heterosis and combining ability were detected among parents and among hybrids. On average, the hybrids yielded 14.8 % higher than the parents. Results revealed that inter-group hybrids yielded higher, with higher yield heterosis than intra-group hybrids. Four heterotic patterns within two heterotic groups based on current IRRI B- and R-line germplasm were identified. Parents in two marker-based groups were identified with limited breeding value among current IRRI hybrid rice germplasm because of their lowest contribution to heterotic hybrids. Heterotic hybrids are significantly correlated with high-yielding parents. The efficiency of breeding heterotic hybrids could be enhanced using selected parents within identified marker-based heterotic groups. This information is useful for exploiting those widely distributed IRRI hybrid rice parents.     

Effects of 2n-pollen formation by first meiotic division restitution with and without crossover on eight quantitative traits in 4x-2x potato progenies

 The 2n-pollen grains formed by first-division restitution without crossover (FDR-NCO) are unique breeding tools, since they can transmit almost 100% of non-additive genetic effects from the parent to the progeny. FDR-NCO gametes are considered superior to those formed by FDR with crossing over (FDR-CO), which can pass on to the progenies approximately 80% of the heterozygosity and a large fraction of the epistasis. However, 2n-pollen formation by FDR-NCO mechanism requires the incorporation (in homozygous condition) of at least two recessive alleles. In the present work, 40 tetraploid families derived from complete 4x-2x factorial crosses were evaluated under short-day conditions to verify whether or not the postulated genetic superiority of FDR-NCO over FDR-CO gametes holds true for eight quantitative traits in potato. Families were derived from crosses between four 4x commercial cultivars, and a random sample of ten diploid Solanum phureja-haploid S. tuberosum hybrids producing 2n-pollen by either FDR-CO or FDR-NCO. The results indicated no significant superiority of FDR-NCO over FDR-CO families for total tuber yield (TTY) and six other traits (haulm maturity – HM; plant vigor – PV; plant uniformity – PU; eye depth – ED; number of tubers per hill – NTH; and commercial over total yield index – CTI). Based upon cytological observations, the FDR-CO and FDR-NCO gametes are expected to be genetically equivalent for all loci between the centromeres and the chromosomal site of maximum recombination. In our experiment, differences between FDR-CO- and FDR-NCO-derived progenies were not observed for TTY. Therefore, our results can be interpreted as additional evidence for the hypothesis that genes with major effect on TTY expression might have a physical location between centromeres and proximal crossovers in the potato chromosomes. In addition, a similar trend was observed for HM, PV, and ED but apparently not for commercial yield – CY (i.e., tubers with more than 33 mm in diameter). Received: 21 September 1998 / Accepted: 26 October 1998     

Breeding of Brassica rapa for Biogas Production: Heterosis and Combining Ability of Biomass Yield

The use of plant biomass as substrate for biogas production has recently become of major interest in Europe. Winter Brassica rapa produces high early biomass and could be grown as a pre-crop harvested early in the year followed by a second crop such as maize. The objectives of this study were to estimate heterosis and combining ability of 15 European winter B. rapa cultivars for biomass yield at end of flowering. A half-diallel without reciprocals was conducted among cultivars to produce 105 crosses. These crosses and their parents were evaluated in two years at two locations in Northern Germany. Data collected were days to flowering (DTF), fresh biomass yield (FBY), dry matter content (DMC) and dry biomass yield (DBY). The mean DBY was 5.3 t/ha for the parental cultivars and 5.6 t/ha for their crosses. The crosses surpassed on average their parents by 7.6% for FBY and 5.9% for DBY whereas DMC was 1.4% higher in the parents. Maximum mid parent heterosis was 21.0% for FBY and 30.4% for DBY. Analysis of variance showed that genetic variance was mainly due to specific combining ability (SCA). The correlation between parental performance and general combining ability (GCA) was 0.42** for FBY and 0.53** for DBY. In conclusion, the amount of heterosis in crosses between European winter B. rapa cultivars is not very high on average, but can be up to 30% in the best crosses. Selection of parental combinations with high specific combining ability to produce synthetic cultivars can rapidly improve biomass yield.     

Activities of photosystem II and antioxidant enzymes in chickpea (<Emphasis Type="Italic">Cicer arietinum</Emphasis> L<Emphasis Type="Italic">.</Emphasis>) cultivars exposed to chilling temperatures

This study was carried out to determine the effect of chilling on both cold-acclimated and non-acclimated chickpea (Cicer arietinum L.) cultivars (Gökçe and Can?tez 87). Chickpea seedlings grown in soil culture for 12 days were subjected to chilling temperatures (2 and 4°C for 12 days) after maintaining in cold-acclimation (10°C, 7 days) or non-acclimation (25°C, 7 days) periods. The lowest values of growth parameters were obtained with cold-acclimated plants, whereas non-acclimated plants exhibited the lowest water content values, especially at 2°C. There was no effect of cold-acclimation period on chlorophyll fluorescence parameters. Plants subjected to chilling temperatures after cold-acclimation were more tolerant with respect to chlorophyll fluorescence parameters, and Gökçe had better photosystem II (PSII) photochemical activity. In the chilling treatments, total chlorophyll (a + b) content reduced, especially at 2°C, while anthocyanin and flavonoid contents increased to a greater extent in Gökçe and carotenoid content of the cultivars did not change. Malondialdehyde (MDA) content was higher for Can?tez 87, mostly at 2°C, while proline accumulation was greater for Gökçe. The cold-acclimation period led to a remarkable increase in antioxidant enzyme activities of both cultivars. The superoxide dismutase (SOD) activity was much higher in Gökçe for both chilling temperatures and the ascorbate peroxidase (APX) activity increased only in the cold-acclimated 4°C treatments. Similarly, with APX activity, the glutathione reductase (GR) and peroxidase (POD) activities of cultivars were higher in cold-acclimated plants at both the chilling temperatures, mostly in Gökçe. The results of this study indicate that cold-acclimation increased the cultivars ability to withstand the chilling temperatures. The lower MDA content and higher antioxidant and photochemical activities in Gökçe indicated an enhanced chilling tolerance capacity of this cultivar to protect the plant from oxidative damage.     

Population-based diallel analyses among nine historically recognized alfalfa germplasms

Identification of heterotic groups and patterns among breeding populations provides fundamental information to help plant breeders more knowledgeably manipulate heterosis. A diallel analysis was conducted among nine alfalfa (Medicago sativa L.) germplasms, commonly referred to as African, Chilean, Flemish, Indian, Ladak, M. falcata, M. varia, Peruvian, and Turkistan, which represent a significant proportion of the genetic diversity present in US cultivars. Heterotic responses were determined by evaluating forage yield of the germplasms and their 36 half-diallel hybrids in seeded plots that were harvested five times in each of 2 years. Commercially acceptable yields were obtained from some hybrids of unimproved parents, where at least one parent was adapted to the study environment. Variation among crosses was attributed primarily to general combining ability (GCA) effects; however, specific combining ability effects were also significant. GCA estimates for African, Chilean and Peruvian were positive, while those for Ladak, M. falcata, and M. varia were negative. Estimates for variety heterosis effects were positive for Peruvian and M. falcata and negative for Indian and M. varia. Significant mid-parent heterosis [(MPH) range of –21% to 55%] and high-parent heterosis [(HPH) range of –33% to 23%] was detected. M. falcata hybrids exhibited the highest MPH values. However, this likely reflects the poor yield of M. falcata per se in the study environment and consequently, low MPH values. Peruvian hybrids demonstrated the highest cross mean performance, significant positive MPH in all crosses, and positive HPH in five out of eight crosses. The results indicate that Peruvian should be recognized as a heterotic group. Alfalfa breeders may wish to explore opportunities for heterotic yield gains that are likely to exist in hybrids between the Peruvian germplasm and elite breeding populations, in particular, those adapted to the southwestern United States. MPH results suggest that alfalfa breeders may have capitalized on the heterotic response between Flemish and M. varia during past development of alfalfa synthetics adapted to the central and northern latitudes of the United States.     

Nature of 'Pollinator' Effect in Potato (Solanum tuberosum L.) Haploid Production

Haploids (2n =24) of the common tetraploid (2n=48) potato (SolanumtuberosumL.) provide promising material for attacking many problemsconcerned with the genetics, cytogenetics and breeding of thisspecies. Interspecific 4xx2xcrosses betweenSolanum tuberosumgp.Andigenaorgp.Tuberosumcultivars as pistillate parents andSolanum tuberosumgp.Phurejaassource of pollen (hereafter ‘pollinator’) have beenused to produce maternally derived haploids through parthenogenesis.This paper discusses the nature of the ‘pollinator’effect in haploid extraction. The ‘pollinator’ hada significant effect on haploid frequencies following 4xx2xcrosses.The ‘pollinator’ effect seems to operate via theendosperm, in which haploid (n=2x) embryos are associated withhexaploid endosperm. A superior ‘pollinator’ appearsto have its effect by contributing two haploid (n) gametes tothe central cell. 2n pollen; double fertilization; endosperm; ploidy manipulations; Solanum tuberosum     

Characterization of <Emphasis Type="Italic">Brassica napus</Emphasis> L. genotypes utilizing sequence-related amplified polymorphism and genotyping by sequencing in association with cluster analysis

Identifying parental combinations that exhibit high heterosis is a constant target for commercial Brassica napus L. hybrid development programs. Finding high heterotic parental combinations can require hundreds of test crosses and years of yield evaluation. Heterotic pool development could be used to divide breeding material into specific breeding pools and focus the number of parental combinations created. Here, we report the genotypic characterization of 79 B. napus genotypes by calculating genetic distance based on sequence-related amplified polymorphism (SRAP) and genotyping by sequencing (GBS) in association with a neighbour-joining clustering algorithm. Despite the different genotypic analyses, neighbour-joining cluster analysis based on genetic distance of SRAP and GBS produced similar clusters. Homology between SRAP and GBS clusters was approximately 77 % when manually comparing clusters and 68 % when comparing clusters using Compare2Trees. This research demonstrates that SRAP can have similar efficacy when compared to next-generation sequencing technology for heterotic pool classification. This information may provide an important breeding scaffold for the development of hybrid cultivars based upon genetic distance and cluster analysis.     

Genetics of Heading Time in Wheat (TRITICUM AESTIVUM L.). II. the Inheritance of Vernalization Response

The inheritance of vernalization response was studied in crosses involving four spring wheats (Sonora 64 (S), Pitic 62 (P), Justin (J) and Thatcher (T)) and three winter wheats (Blackhull (B), Early Blackhull (E) and Extra Early Blackhull (EE)).—All winter cultivars were highly responsive to vernalization, and Pitic 62 was the only spring cultivar whose time to heading was significantly accelerated following cold treatments. When vernalized and grown under long days, spring and winter cultivars became comparable in their heading response, indicating that cold requirement is the major attribute differentiating the heading behavior of true spring and true winter wheats.—Inheritance of growth habit in the F₁ generation of a five-parent diallel cross showed dominance of the spring character in all spring x winter crosses. Depending on the cross, one or two duplicate major genes governing growth habit were detected in F₂, F₃ and backcross generations grown in the field under long days in the absence of vernalizing temperatures. In some spring x winter crosses most of the variation in heading time among spring segregates could be attributed to the effects of major genes conditioning growth habit. In other crosses the heading patterns appeared more complex, indicating that genes with smaller effects are also involved in the control of heading response under spring or summer environments.—Evidence was presented supporting the hypothesis that the cultivar Pitic 62 carries a different allele at one of the two major loci governing its spring habit. This allele was associated with some response to vernalization and acted as a dominant gene determining earliness under low temperature vernalization, but as a partially recessive gene determining lateness in the absence of vernalizing temperatures. Genotypes were assigned to five cultivars as follows: S, CC DD; P, CC D'D'; J, cc DD; B and EE, cc dd.—The presence of major and minor genes and of multiple alleles governing response to photoperiod and vernalization was discussed in relation to the genetic manipulation of the heading response and to breeding wheat cultivars with specific or broad adaptation.     

Breeding of nodulated red clover (Trifolium pratense) for high yield

The symbiotic effectiveness of four cultivars of red clover were compared and breeding programmes undertaken to increase nitrogen fixation and yield of agar- and pot-grown plants. Programme I used the moderately effective Rhizobium trifolii strain 0403 and Programme II the highly effective strain 5. Aggregate scores of plant size (leaf area) were chosen as the criterion of selection. All cultivars, inoculated with strain 0403, differed in time of initial nodulation and in dry matter yield and three differed in leaf area. None differed in nodule number or N-content. Dry matter and leaf area were highly correlated. Diallel crosses among highly effective selections in Programme 1 gave progeny yields that exceeded those of crosses between modal selections by averages of 6% in the first generation, 5% in the second generation and 23% in the third generation. Yields of the high cross category exceeded those of the original cultivar by an average of 9% in the second generation and by 25–101% in the third generation. Effects on leaf area were similar. Highly effective progeny tended to nodulate earlier and have more nodules than the remainder but differences were very small. Crosses between cultivars were generally more effective than those within cultivars, indicating heterotic effects. Similar results for yield were obtained in Programme II. The average increase in yield of crosses of third-generation material between highly effective selections compared with cv. S123 was 63%. The modal crosses were intermediate. In each Programme and generation there were large differences between parents within each cross category.     

Genomic mating in outbred species: predicting cross usefulness with additive and total genetic covariance matrices

Diverse crops are both outbred and clonally propagated. Breeders typically use truncation selection of parents and invest significant time, land, and money evaluating the progeny of crosses to find exceptional genotypes. We developed and tested genomic mate selection criteria suitable for organisms of arbitrary homozygosity level where the full-sibling progeny are of direct interest as future parents and/or cultivars. We extended cross variance and covariance variance prediction to include dominance effects and predicted the multivariate selection index genetic variance of crosses based on haplotypes of proposed parents, marker effects, and recombination frequencies. We combined the predicted mean and variance into usefulness criteria for parent and variety development. We present an empirical study of cassava (Manihot esculenta), a staple tropical root crop. We assessed the potential to predict the multivariate genetic distribution (means, variances, and trait covariances) of 462 cassava families in terms of additive and total value using cross-validation. Most variance (89%) and covariance (70%) prediction accuracy estimates were greater than zero. The usefulness of crosses was accurately predicted with good correspondence between the predicted and the actual mean performance of family members breeders selected for advancement as new parents and candidate varieties. We also used a directional dominance model to quantify significant inbreeding depression for most traits. We predicted 47,083 possible crosses of 306 parents and contrasted them to those previously tested to show how mate selection can reveal the new potential within the germplasm. We enable breeders to consider the potential of crosses to produce future parents (progeny with top breeding values) and varieties (progeny with top own performance).     

Microsatellite and flow cytometry analysis to help understand the origin of Dioscorea alata polyploids

Background and Aims Dioscorea alata

is a polyploid species with a ploidy level ranging from diploid (2n = 2x = 40) to tetraploid (2n = 4x = 80). Ploidy increase is correlated with better agronomic performance. The lack of knowledge about the origin of D. alata spontaneous polyploids (triploids and tetraploids) limits the efficiency of polyploid breeding. The objective of the present study was to use flow cytometry and microsatellite markers to understand the origin of D. alata polyploids.

Methods

Different progeny generated by intracytotype crosses (2x × 2x) and intercytotype crosses (2x × 4x and 3x × 2x) were analysed in order to understand endosperm incompatibility phenomena and gamete origins via the heterozygosity rate transmitted to progeny.

Results

This work shows that in a 2x × 2x cross, triploids with viable seeds are obtained only via a phenomenon of diploid female non-gametic reduction. The study of the transmission of heterozygosity made it possible to exclude polyspermy and polyembryony as the mechanisms at the origin of triploids. The fact that no seedlings were obtained by a 3x × 2x cross made it possible to confirm the sterility of triploid females. Flow cytometry analyses carried out on the endosperm of seeds resulting from 2x × 4x crosses revealed endosperm incompatibility phenomena.

Conclusions

The major conclusion is that the polyploids of D. alata would have appeared through the formation of unreduced gametes. The triploid pool would have been built and diversified through the formation of 2n gametes in diploid females as the result of the non-viability of seeds resulting from the formation of 2n sperm and of the non-viability of intercytotype crosses. The tetraploids would have appeared through bilateral sexual polyploidization via the union of two unreduced gametes due to the sterility of triploids.     

Influence of grapevine cultivars on the leafhopper <Emphasis Type="Italic">Empoasca vitis</Emphasis> and its egg parasitoids

The leafhopper Empoasca vitis (Göthe) (Homoptera: Cicadellidae) can cause economic damage in European vineyards. Egg parasitoids, in particular Anagrus atomus (Linnaeus) (Hymenoptera: Mymaridae), are the most important natural enemies of the leafhopper. In four different years, leaves of ten grapevine cultivars, which were grown in a vineyard of north-eastern Italy, were collected at the end of the leafhopper 2nd generation to determine the total number of E. vitis eggs per leaf and the percentage of the E. vitis eggs parasitized. These data were analysed for correlation with leaf density and foliar pubescence. The E. vitis eggs per leaf and the percentage of eggs parasitized by Anagrus spp. were significantly influenced by the cultivar. The number of E. vitis eggs per leaf was positively correlated to leaf density, but it was not influenced by leaf hair density. The parasitization rate by Anagrus spp. was affected by foliar pubescence, especially by erect hairs on the veins. These findings could be used for integrated pest management. In particular, (1) the more susceptible cultivars can be used as early indicators of leafhopper infestation, (2) agronomic practices, that reduce leaf density, could decrease the E. vitis population level and (3) clones with glabrous leaves would favour egg parasitoid activity.     

Obtaining sexual genotypes for breeding in buffel grass

Buffel grass (Cenchrus ciliaris L. syn. Pennisetum ciliare (L.) Link) is a species that is highly tolerant to drought and is used primarily as forage in drier regions throughout the subtropics and tropics. It reproduces mainly by apomixis and the acquisition of obligate sexual genotypes or facultative apomicts with high levels of sexuality is required for performing crosses and plant improvement. The aim of this study was to obtain sexual genotypes from controlled crosses using obligate apomictic cultivars and a sexual line. Twelve putative hybrid F1 plants were selected morphologically and two of them were identified as sexual genotypes by PCR using specific primers for reproductive mechanism. Cytoembryological analysis showed 65.5 and 71.3% meiotic embryo sacs in these plants and their hybrid nature was corroborated by AFLP. Both highly sexual genotypes could be used as female parents in crosses for obtaining improved cultivars of buffel grass.     

Prediction of progeny variation in oat from parental genetic relationships

Summary The ability to predict agronomic performance of progeny from a cross would be a great benefit to plant breeders in selecting parents. The predictive value of parental genetic relationships estimating F₁ progeny means and F₄ family variances of nine argronomic traits was tested in 76 oat crosses, using genetic distance measures based on coefficients-of-parentage, quantitatively inherited morphological characters, and discretely inherited biochemical and morphological characters. Coefficients-of-parentage were better predictors of F₁ performance than similarity measures derived from plant morphology or discretely inherited characters. Combined distance measures were better estimators of F₁ specific combining ability (SCA) effects than any single measure. Among cultivars of similar adaptation and quantitative morphology, crosses between parents with high coefficients-of-parentage gave higher SCA effect values than crosses of distantly related parents for grain yield and total biomass. The opposite was found for crosses among cultivars of different adaptation or quantitative morphology. The best predictor of trait variances among F₄ families was coefficients-of-parentage. Crosses between more distantly related parents produced larger variances among families than crosses between closely related parents for plant biomass. For grain yield, test weight, heading date, grain filling period, and maturity date, crosses between more closely related parents produced larger among-family variances than crosses of distantly related parents. Crosses between more distantly related parents involved at least one parent unadapted to central New York, and resulted in most of the progeny being generally unadapted. This, in part, may account for the low genetic variances for heading date, test weight, and grain yield in crosses of distantly related parents.     

Comparison of FDR- and SDR-derived tetraploid progeny from 2x×4x crosses using haploids of Solanum tuberosum L. that produce mixed modes of 2n eggs

 The relationship between heterozygosity and heterosis in tetraploid potato (Solanum tuberosum subsp. tuberosum L., 2n=4x=48) was examined in a series of first-division restitution (FDR)- and second-division restitution (SDR)-derived tetraploid subpopulations. The subpopulations were constructed using two 2n egg-producing, mixed-mode haploids (2n=2x=24) crossed to three tetraploid (2x= 4x=48) potato clones. Half-tetrad analysis using a co-dominant electrophoretic marker (Pgm-2), which is closely linked to the centromere, discriminated between FDR- and SDR-derived 4x progeny. The FDR:SDR ratio of the 4x progeny observed was dependent upon the haploid parent used in the 2x×4x cross. Field studies were conducted between 1992 and 1996 to compare the yield and specific gravity of the two subpopulations and their parents from three crosses. There was no difference in the total tuber yield or specific gravity between the FDR- and SDR-subpopulations based upon family means, despite the expectation that FDR-derived progeny would transmit a greater portion of the genome’s heterozygosity intact than SDR-derived progeny. The 4x parent in each family had a higher yield than either 4x progeny subpopulation. Inbreeding, as a consequence of the haploidization process and a lack of genetic diversity, may have negated any advantage of the FDR-derived progenies over the SDR-derived progenies. Received: 14 April 1998 / Accepted: 12 May 1998     

Heterosis,transmission genetics,and selection for increased growth rate in a <Emphasis Type="Italic">N. tabacum</Emphasis> × synthetic tobacco cross

Cultivated tobacco (Nicotiana tabacum L.) is a classic amphidiploid, and hybrids between this cultivated species and closely related diploid Nicotiana relatives often exhibit heterotic effects for growth rate and yield. Crosses between N. tabacum and synthetic tobaccos, 4x(Nicotiana sylvestris × Nicotiana otophora) or 4x(N. sylvestris × Nicotiana tomentosiformis), may provide superior routes for genome-wide introgression from diploid relatives and allow increased potential to capitalize on heterotic effects in tobacco. Significant levels of mid-parent heterosis were observed for yield and growth rate in F₁ hybrids between synthetic tobaccos and a standard tobacco cultivar. Microsatellite marker genotyping of an F₂ population derived from a K326 × [4x(N. sylvestris × N. otophora)] cross was carried out to preliminarily investigate the relative importance of different types of gene action on observed heterosis in the original interspecific cross. Results suggested a role for both partial dominance and overdominance. Marker genotyping also indicated an overall reduced level of recombination in the N. tabacum × synthetic tobacco cross relative to a N. tabacum × N. tabacum cross but no evidence of genomic regions with severely restricted levels of recombination. Results suggest that populations derived from N. tabacum × synthetic tobacco crosses may be more efficient for introgressing germplasm from diploid relatives, as compared to populations derived from crosses between N. tabacum and diploid forms where preferential pairing between N. tabacum homologues can reduce the potential for introgression of alien chromatin. Such materials may be useful as sources of favorable alleles influencing quantitative characters in tobacco.     

Production of somatic hybrids between frost-tolerant Solanum commersonii and S. tuberosum: characterization of hybrid plants

Somatic fusion of mesophyll protoplasts was used to produce hybrids between the frost-tolerant species Solanum commersonii (2n=2x=24) and dihaploid S. tuberosum (2n=2x=24). This is a sexually incompatible combination due to the difference in EBN (Endosperm Balance Number, Johnston et al. 1980). Species with different EBNs as a rule are sexually incompatible. Fifty-seven hybrids were analysed for variation in chromosome number, morphological traits, fertility and frost tolerance. About 70% of the hybrids were tetraploid, and 30% hexaploid. Chloroplast counts in stomatal guard cells revealed a low frequency of cytochimeras. The frequency of aneuploids was relatively higher at the hexaploid level (hypohexaploids) than at the tetraploid level (hypotetraploids). The somatic hybrids were much more vigorous than the parents, and showed an intermediate phenotype for several morphological traits and moderate to profuse flowering. Hexaploid hybrid clones were less vigorous and had a lower degree of flowering than the tetraploid hybrid clones. All of the hybrids were female fertile but male sterile except for one, which was fully fertile and self-compatible. Many seeds were produced on the latter clone by selfing and on the male-sterile clones by crossing. The somatic hybrid plants showed an introgression of genes for frost tolerance and an adaptability to cold from S. commersonii. Therefore, the use of these somatic hybrids in breeding for and in genetic esearch on frost tolerance and cold-hardening is suggested.