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1.
Summary
Solanum commersonii Dun. is a diploid (2n=2x=24, 1EBN) wild species of potential value for potato breeding. It is a reproductively isolated species and cannot be crossed with Tuberosum haploids (2n=2x=24, 2EBN) or other diploid 2EBNSolanum species. In order to overcome the EBN barriers, triploid hybrids were produced between Phureja-Tuberosum haploid hybrids, which form 2n pollen grains by parallel spindles, and tetraploidS. commersonii. Microsporogenesis analysis of the triploids indicated a trend towards low values of chromosome distribution at Anaphase I; lagging chromosomes were often observed as well. Despite these abnormalities, the percentage of stainable pollen was very high, ranging from 5.0% to 74.3%. A high variation in pollen grain diameter was also evident. Parallel and tripolar orientation of spindles at Metaphase II of microsporogenesis was a common feature of all the triploids analyzed, but dyads and triads were observed at a very low frequency. Therefore, also the frequency of 2n pollen was very low; the different size of stainable pollen appears to represent the ploidy levels which are possible according to the distribution of chromosomes in Anaphase I. The results obtained also suggest thatS. commersonii could have minor genes acting at the end of meiosis in such a way that, despite the presence of parallel/tripolar spindles, dyads/triads are not formed.Contribution no. 124 from the Research Center for Vegetable Breeding. 相似文献
2.
J. G. Th. Hermsen 《Euphytica》1969,18(2):183-189
Summary The species Solanum chacoense BITT. (2n=2x=24) is a tuber-bearing, self-incompatible species which is important both for breeding and for genetic research. It crosses readily with most other tuber-bearing Solanum species including the common potato S. tuberosum (2n=4x=48). Gametophytic incompatibility hampers research in and utilization of this species. Doubling the chromosome number by colchicine makes it a self-compatible autotetraploid. By crossing selfed progeny of 4x-S. chacoense with a number of haploid-inducing diploid Solanum species a high yield of different dihaploid S. chacoense individuals (2n=24) could be obtained from one originally diploid clone: S. chacoense CPC 1153. More than 160 haploids showing a large variability were identified. The average haploid frequency was 53.7 per 100 berries. Most hybrid plants (70–100%) from four 4x × 2x crosses studied were tetraploid. The frequency of triploid hybrids was low (0–10%). Haploid-inducing capacity of fifteen male parents used in this study varied from 0–141 haploids per 100 berries. Careful examination of 156 haploids revealed 15 viable aneuhaploids (2n=25, 26, and 27), i.e. 9.4%. The potential value of these aneuhaploids is discussed.About 50% of the haploids were sufficiently male fertile to use them in crossing. A few of them set berries after selfing. Five aneuhaploids including the one with 27 chromosomes were successfully crossed as females with a diploid hybrid clone. 相似文献
3.
D. Carputo T. Cardi J. P. Palta P. Sirianni S. Vega L. Frusciante 《Plant Breeding》2000,119(2):127-130
The objectives of this study were to evaluate the tolerance to low temperatures and tuber soft rot in hybrids between Solanum commersonii and Solanum tuberosum. The experimental materials consisted of F1 triploid, BC1 pentaploid‐near pentaploid and BC2 tetraploid–near tetraploid hybrids. The F1 triploids had a freezing tolerance and acclimatization capacity closest to S. commersonii. This indicated that the endosperm barriers which prevent the introgression of 1EBN S. commersonii into 4EBN S. tuberosum had been overcome. Indeed, the triploids produced 2n eggs, thus giving a compatible maternal to paternal EBN ratio in the hybrid endosperm generated by the 3x(2EBN) × 4x(3EBN) crosses. The tolerance to low temperatures of BC1 and BC2 hybrids was lower than that of the F1. However, a number of genotypes were identified which were able to withstand temperatures down to ‐5°C. Some BC2 hybrids were also tested for their tolerance to tuber soft rot, and some resistant hybrids were detected. A number of them combined the capacity for cold acclimatization with tolerance to tuber soft rot. These hybrids have an EBN of 4; they are fertile and have been used in backcrosses with 4EBN S. tuberosum. 相似文献
4.
Shelley Jansky 《Euphytica》2011,178(2):273-281
Valuable genetic diversity in diploid wild Solanum species can be accessed through crosses to haploids (2n = 2×) of the tetraploid cultivated potato, Solanum tuberosum. Haploid-wild species hybrids segregate for the ability to tuberize in the field. In addition, they vary in male fertility,
vine size, stolon length, and tuber size. In this study, three haploids were crossed with nine diploid wild Solanum species and 27 hybrid families were evaluated in the field for two years. The proportion of male fertile hybrid clones varied
depending on the wild species parent. A large effect of the female parent was detected for vine size, stolon length, tuber
size, percent tuberization, and percent plants selected for agronomic quality. An exceptional haploid (US-W4) was identified
for the production of agronomically desirable haploid-wild species hybrids. In hybrids derived from US-W4, differences among
wild species parents were observed for agronomic quality. Superior hybrids were produced by S. berthaultii and S. microdontum. Reciprocal crosses were evaluated for a subset of families. When the wild species was used as the female parent, male fertility
was restored, but tuberization and tuber size were reduced. Careful selection of both haploid and wild species parents can
result in a large proportion of fertile, agronomically desirable hybrid offspring. 相似文献
5.
Twenty-one (near) pentaploid hybrids between sexually incompatible Solanum
commersonii [2x(1EBN)] and cultivated S. tuberosum [4x(4EBN)] were characterized for tuber traits and fertility. A number of genotypes resembled the S. tuberosum type in terms of stolon length and eye depth and produced tubers under long day conditions. Tuber yields were not as high
as expected, probably due to lack of adaptation of the S. commersonii genome to the environmental conditions in southern Italy (on average 325 g·pt−1 and 285 g·pt−1 in 2003 and in 2004, respectively). Compared to 2004, in the summer of 2003, characterized by extremely high temperatures,
hybrids gave a higher tuber yield than the S. tuberosum control, suggesting that in our environmental conditions the wild S. commersonii genome, rather than resulting in heterosis for tuber yield, provides better adaptation to harsh environments. Although aneuploidy
has often been associated with reduced fertility, several hybrids were fertile in crosses with S. tuberosum when used as female parents. In particular, the average berry set and number of seeds per berry were 38.2% and 31.8%, respectively.
Based on significant relationships between ploidy levels and all yield and fertility data measured, the presence of extra
chromosome affected the parameters considered: tuber yield in 2003 and 2004, percentage of fruit set, number of seeds per
berry and number of seeds per pollinated flower. Regression analysis also indicated that “Residuals” were significant for
all parameters measured. Therefore, additional factors (e.g. the genetic makeup of hybrids) may be key to fertility and yield. 相似文献
6.
Summary Unidirectional intergeneric crosses using octoploid and hexaploid Fragaria species as a female parent and diploid and tetraploid Potentilla species as a male parent were performed, producing in toto 1345 fruits with an estimated 46089 seeds. The germinating seeds obtained by using P. anserina mostly perished at the cotyledon stage, a few developing into matroclinous octoploid seedlings. The seeds obtained by using P. fruiticosa produced two types of seedlings: matroclinous octoploids and genuine intergeneric hybrids. It is considered that the matroclinous octoploids resulted from contamination during the emasculation process. A great majority of the hybrid seedlings were slow in growth and development and perished before reaching the flowering stage. No haploids have been recovered. Possible reasons for absence of haploid genotypes in the progenies of these intergeneric crosses are considered. Among the seedlings of F. x ananassa cv. Tioga x P. fruiticosa, a seedling of an unusual phenotype was noticed, which upon chromosome determination, proved to be 2n=9x=63. This genotype displayed complete male and female sterility. The implication of the sterility of this seedling for bridging of the two genera is discussed.This research was performed as part of a cooperative project on genetic improvement of cultivated strawberry between the Fruit Laboratory, USDA, Beltsville and NJAES. Paper of the Journal Series, D-12102-16-83. New Jersey Agricultural Experiment Station, Rutgers University, New Brunswick, NJ 08903. 相似文献
7.
Summary In this study, nineteen diploid potato clones (Solanum spp. 2n=2x=24) were identified as 2n egg producers on the basis of fruit set in 2x–4x crosses. The segregation of three genes mapped close to the centromere, Got-1 (1.1 cM), Pgm-2 (2.0 cM), and Sdh-1 (8.3 cM), were analyzed in the tetraploid offspring in these 2x–4x crosses to discriminate between First Division Restitution (FDR) and Second Division Restitution (SDR) modes of 2n egg formation. The co-dominant nature of these markers lead to more precise estimates of the recombinational frequencies as a result of completely classifying the segregating progenies. 2x–4x data revealed a predominance of SDR mechanisms occurring in 20 of the 21 families analyzed. With a SDR mode established, half-tetrad analysis (HTA) of four distal loci, 6-Pgdh-3, Mdh-1, Pgi-1, and Aps-1, revealed two SDR segregation patterns in some of the families. One pattern fit the expectations for the distal arm position. The gene-centromere map distances based upon SDR modes in the families following this pattern, were generally close to 4x–2x (FDR) estimates suggesting similar recombination rates between micro- and mega-sporogenesis. Heterozygosity transmission, on average, was 39.1%. In the other segregation pattern, in which the diploid parents were derived from S. chacoense PI 230580, higher than expected homozygosity levels were found in the female 2n gametophyte populations. A post-meiotic doubling of the reduced megaspore, which generates homozygous 2n eggs, is suggested to operate in three families. The common genetic background of the diploid clones suggested a heritable nature of this mechanism. Pooled data from these three deviant families calculated that 1.8% of the heterozygosity was transmitted to the tetraploid progeny.It is concluded that utilization of seven enzyme-coding loci, with previously established gene-centromere map distances, in 2x–4x crosses improved half-tetrad analysis (HTA) as a means to determine the mode of 2n gamete formation in megasporogenesis and megagametogenesis of diploid Solanum species. 相似文献
8.
Wei Song Hao Xie Qing Liu Chaojie Xie Zhongfu Ni Tsomin Yang Qixin Sun Zhiyong Liu 《Euphytica》2007,156(1-2):95-102
The traditional process of obtaining maize hybrids involves the generation of inbred lines through successive generations
of selfing and subsequent testcrosses in order to identify the best combining ability by allelic complementation. A fast alternative
to obtain inbred lines is to induce the formation of haploids followed by chromosome doubling. However, even with the aid
of haploid-inducing genetic sources, this strategy has not been widely used in maize breeding programs, partly due to difficulties
inherent to haploid generation and identification. In order to evaluate the possibility of using dihaploids to generate homozygous
maize tropical lines, we used the androgenetic haploid inducer line W23 as a female parent in crosses with the tropical single-cross
hybrid BRS1010. Within the progeny of these crosses, 462 seeds were phenotypically selected as putative haploids by the purple-colored
endosperm and colorless embryo conditioned by the R1-nj gene. Among these, only four individuals were confirmed as being haploids using SSR markers, chromosome counting and flow
cytometry, showing that the phenotypic marker was not efficient in detecting haploids in the tropical maize genotype used.
All four haploids as well as some diploid plants presented reduced size, corroborating the difficulties for haploid identification
by phenotypic evaluation. Genetic diversity analysis revealed by SSR markers divided the haploids in two groups represented
by flint and dent maize inbred lines, which could be helpful in identifying complementary dihaploid lines. The present article
demonstrates that a combination of haploid production and SSR fingerprinting is a feasible strategy for maize hybrid development
in tropical germplasm. 相似文献
9.
The possible presence of vertical resistance to late blight conferred by R genes in Argentine wild Solanum species, which presumably have not evolved under the pressure of the fungus, was investigated. Solanum microdontum, S. commersonii and S. chacoense clones were tested in the greenhouse and with detached leaves in the laboratory after inoculation with a complex race and
a non-virulent race of Phytophthora infestans. Two progeny tests were carried out to assess the performance of contrasting parents in regards to their resistance. A varying
frequency of incompatible clones was detected among the species, with S. microdontum having the higher proportion of clones yielding incompatible reactions both in the laboratory and in the greenhouse. S. chacoense and S. commersonii showed a small but still considerable frequency of incompatible clones. The progeny tests confirmed the presence of R genes
in a S. commersonii cross and their absence in a S. chacoense cross. The unexpected presence of R genes, its evolutionary significance and the
consequences on the use of these species in breeding is discussed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
10.
Summary The potato tuber moth, Phthorimaea operculella (Zeller) is an important pest of potatoes in the field and in stores in warm environments throughout the world. In this study genetic resistance to potato tuber moth was identified in clones of Solanum sparsipilum (coded MBN) originally developed for resistance to bacterial wilt and root-knot nematode. Resistance to this pest in S. sucrense and S. tarijense as well as S. sparsipilum was exploited in wide crosses with diploid and tetraploid cultivated potatoes, and haploids derived from S. tuberosum; hybrid progenies were produced. Crosses between resistant S. pinnatisectum or S. commersonii and cultivated potatoes failed completely, although S. commersonii did hybridise with two bridging species S. lignicaule and S. capsicibaccatum which are slightly compatible with cultivated potatoes. Resistance to potato tuber moth was transferred to all progenies except those in which S. tarijense was the resistant parent. The development of potatoes resistant to potato tuber moth is discussed in the context of population breeding for the lowland tropics. 相似文献
11.
Summary Over 2400 pollinations were made to investigate the crossability relationships between cultivated potatoes, and wild diploid species from Series Tuberosa and Circaeifolia, as well as wild polyploid species in Series Tuberosa and Longipedicellata resistant to potato cyst nematode, Globodera pallida pathotypes P4A and P5A. Wild diploids in Series Tuberosa crossed easily with cultivated diploid species, except with Solanum lignicaule where most pollinations failed, and seed set was extremely low (0.2 seeds per pollination or less). It is suggested that this species is 1EBN. S. capsicibaccatum is clearly isolated from Series Tuberosa, but can form hybrids with S. lignicaule, which can act as a bridging species to S. tuberosum haploids. S. gourlayi and S. oplocense can be crossed with both subspecies of S. tuberosum, but S. papita, Series Longipedicellata is reproductively isolated from the tetraploid cultigens. The crossability data are discussed in the light of germplasm utilisation for breeding potato varieties resistant to potato cyst nematode. 相似文献
12.
Summary Endosperm failure is considered the primary reason for the lack of success in intra-and interspecific crosses. The Endosperm Balance Number (EBN) hypothesis is a unifying concept for predicting endosperm function in intraspecific, interploidy, and interspecific crosses. In the EBN system, every species has an effective ploidy (EBN), which must be in a 2:1 maternal to paternal ratio in the endosperm for crosses to succeed. The knowledge of EBN is very useful in the transfer of genes from exotic germplasm, and in the development of new breeding schemes in potato. The paper describes the strategies for introducing 2x(1EBN), 2x(2EBN), 4x(2EBN) and 6x(4EBN) germplasm into the cultivated 4x(4EBN) potato gene pool. A new methodology for producing 4x(4EBN) and 2x(2EBN) chromosome addition lines is also discussed. EBN has evolutionary importance in the origin of tuber-bearing Solanums. The role of the EBN in the origin of diploid and polyploid potato species, and as a barrier for hybridization and speciation of sympatric species within the same ploidy level is demonstrated. The origin of 3x and 5x cultivated tuber-bearing Solanums may also be explained using the EBN concept. EBN has been reported to exist in other plant species: alfalfa, beans, blueberries, rice, soybeans, squashes, tomato, forage legumes, grasses, ornamentals and Datura stramonium. This indicates that EBN may have broad application and could be useful for germplasm transfer and breeding in other crop species. 相似文献
13.
Field experiments were carried out in order to evaluate 4x‐2x families derived from crosses between elite 4x potato cultivars and 2x Tuberosum‐Solanum tarijense and 2x Tuberosum‐Solanum berthaultii clones. Three traits were assessed: total tuber yield (TTY), haulm maturity (HM) and general tuber appearance (GTA). The degree of heterosis of these hybrid families was evaluated by comparison with the respective 2x and 4x parents as well as with seven 4x cultivars. The parental haploid species hybrids derived from S. berthaultii and S. tarijense combined two or more positive horticultural characteristics. Expressed as yield percentage of the 4x parents, the TTY of the families ranged from 53% to 246%. For TTY, the best 4x‐2x hybrid family ranked better than seven out of nine elite 4x cultivars. Some families had GTA scores in the range of the highly selected 4x cultivars. The families, however, were generally later maturing than the 4x parent group. Specific combining ability for TTY and GTA were the only two significant sources of variation observed in this genetic material. Parent‐offspring correlation coefficients were low for all traits, and indicated that parental performance would not be informative at either ploidy level. These results parallel previous investigations with distinct haploid species hybrids where a 4x‐2x breeding scheme was found to be an effective strategy for increasing progeny TTY over the 4x parents. However, the high degree of heterosis for TTY along with good GTA scores observed in certain cross combinations derived from these unadapted 2x species was a somewhat surprising result. Thus far, the importance of these two South American wild potato species, from the potato‐breeding standpoint, has been limited to the fact that they are natural reservoirs of major genes controlling resistance against important diseases and insects. However, the level of performance of some 4x‐2x families in comparative assays with elite cultivars suggests the unanticipated possibility of introgressing genetic factors from S. berthaultii and S. tarijense with positive effects on quantitative traits of horticultural importance along with these major resistance genes. 相似文献
14.
The relative value of haploid Tuberosum-Solanum chacoense (TCH) vs. Solanum phureja-haploid Tuberosum (PTH) hybrids as male parents in 4x–2x crosses was estimated under two distinct crop management systems.
The first experiment (E#1) was carried out with supplementary irrigation (three times a week) at Hancock-Wisconsin (WI) with
27 families derived from a sub-set of crosses involving 11 tetraploid (4x) cultivars and 10 diploid (2x) clones (3 TCH; 6
PTH; and one TCH-PTH hybrid clone). A second experiment (E#2) was conducted at Rhinelander-WI with the same group of families
but it was only rainfed with no supplementary irrigation being provided during the entire course of the assay. For comparison,
a complete set of 4x and 2x clones (used as parents) was also planted in each location. Three traits were evaluated in both
locations: total tuber yield (TTY), haulm maturity (HM), and plant vigor (PV). Altogether, 18 out of 27 and 10 out of 27 families
outyielded the corresponding 4x parents at E#1 and E#2, respectively. Significant differences among all 4x–2x families and
among families of the TCH group were observed for TTY at both locations. No difference was found for TTY among families of
PTH and [TCH–PTH] groups at each location. A total of 75% and 50% of the TCH families outyielded their 4x parents at E#1 and
E#2, respectively. The percentage of families from the PTH group that outyielded their 4x parents at E#1 and E#2 was 83.3%
and 25%, respectively. The TCH group had on average lower HM scores than PTH (at both locations) indicating some segregation
for earliness. However, the HM values of the 4x–2x families were, in general, higher than those observed for the 4x parents.
For PV, the PTH group mean was significantly higher than TCH group only in E#1. The PV values of the 4x–2x families were higher
than the 4x-parent group at both locations. Our results indicated that TCH hybrids might be as good parents as PTH to increase
the TTY of 4x–2x progenies. In addition, the TCH families displayed a slight higher level of performance under more stressful
growing conditions than PTH hybrids as indicated by the assay at Rhinelander. Therefore, selection of genetic materials with
potential broad range of adaptation seems to be feasible with both hybrids via the 4x–2x breeding scheme.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
15.
Summary Results of reciprocal crosses between Solanum verrucosum (2n=2x=24) and S. bulbocastanum (2n=2x=24) are described in terms of pollen tube behaviour in styles, of berry and seed set, of fertility and of meiotic behaviour of the F1 hybrids. Pollen tube growth of S. verrucosum is strongly inhibited in styles of S. bulbocastanum, whereas no inhibition is observed in the reciprocal cross. Therefore S. bulbocastanum x S. verrucosum fails to set berries or seeds, whereas the reciprocal cross produces both berries (54.4% berry set) and seeds (0.3 per berry). Only 14.6% of the seeds germinate. Both the diploid and corresponding tetraploid hybrid plants are vigorous, flower abundantly, have a rather regular meiosis (mainly rod bivalents), but show a high degree of cytoplasmic-genic male sterility. Crossability of the diploid hybrid plants is nil when used as pollen parents and near to zero when used as pistillate parents. The barriers to hybridization of the parent species (unilateral inhibition of pollen tube growth, somatoplastic sterility, cytoplasmic-genic male sterility and structural differences of the parental chromosomes) are discussed and methods are suggested to overcome these barriers. 相似文献
16.
Endosperm balance number (EBN) was used to predict the outcome of crosses among a series of complex polyploid interspecific hybrids between Trifolium repens and T. nigrescens. Normal endosperm development, and hence seed‐set, requires a 2 : 1 maternal : paternal EBN ratio in endosperm. Based on their crossability, T. repens (2n = 4x = 32) and T. nigrescens (2n = 2x = 16) were assigned the same EBN of 4. This number was used to predict the relative success of different backcrosses and intercrosses. The method was further developed to successfully predict which gametes would effect fertilization when complex polyploid hybrids with uneven genomic constitutions (5x, 7x) produced mixtures of euploid and aneuploid gametes. This was achieved by allocating EBNs to all potential gametes of complex polyploids. Allocation of gamete EBNs enabled not only prediction of the success or failure of a cross, but also which gametes would be filtered to effect fertilization in complex crosses. This enhanced ability to understand the potential outcomes of complex crosses will increase the efficiency of plant breeding programmes that integrate secondary gene‐pools into economic species by interspecific hybridization. 相似文献
17.
Summary Verticillium wilt (V. albo-atrum Reinke & Berthold or V. dahliae Kleb) threatens potato (Solanum tuberosum L.) production in most growing areas of the world. Genetic resistance offers the most cost-effective and environmentally-sound control measure. However, there is a dearth of genetic and breeding information on resistance to verticillium wilt in potato, because of obscure parentage of some standard cultivars and the complex segregation at the tetraploid level. The wide range of genetic variability in wild relatives of potatoes can be potentially useful as a source of disease resistance, such as verticillium wilt resistance. Six diploid, wild, interspecific Solanum hybrids involving resistant x resistant and susceptible x resistant crosses, were assayed for verticillium wilt resistance under greenhouse conditions to evaluate their potential as sources of verticillium wilt resistance. The cross between S. gourlayi Oka. and S. chacoense Bitt. and its reciprocal had the most resistant progenies based on mean colony counts. No simple mode of inheritance can be proposed based on the observed segregation ratios. However, the continuous distributions observed on verticillium wilt disease response among hybrid families indicate that inheritance of resistance may be polygenic and complex. In addition, skewness of colony count distributions toward the resistance parents were characteristic of all resistant x susceptible crosses suggesting that resistance may be dominant. By contrast, the susceptible x susceptible cross showed a more normal distribution. Overall, the cross between S. gourlayi and S. chacoense showed the most potential as a source of verticillium wilt resistance. 相似文献
18.
An effective method of incorporating germplasm of wild 2x Solanum species into the cultivated potato is through hybridization with haploids of 4x S. tuberosum Group Tuberosum. This procedure provides for the introduction of desirable traits and genetic diversity from wild species into potato. Haploid and wild species genotypes can be evaluated for parental value based on the presence of good tuberization, desirable traits, fertility, and 2n gametes in their hybrid progeny. Haploid-wild species hybrids may be intercrossed and evaluated at the 2x level to take advantage of diploid genetic ratios. Selected 2x genotypes may then be brought to the 4x level through sexual polyploidization with 2n gametes. 相似文献
19.
Crosses between Hordeum vulgare L. and H. bulbosum L. I. Production,morphology and meiosis of hybrids,haploids and dihaploids 总被引：1，自引：0，他引：1
W. Lange 《Euphytica》1971,20(1):14-29
Summary From crosses between diploid and autotetraploid cytotypes of Hordeum vulgare L. (cultivated barley) and H. bulbosum L. (bulbous barley grass) diploid, triploid and tetraploid interspecific hybrids were produced. Both directly and after vegetative segregation crosses in either direction also gave rise to haploids and dihaploids resembling H. vulgare. The use of embryo culture was necessary. Plant morphology of the hybrids was much like that of H. bulbosum, although the hybrid plants were less vigorous. Meiosis in the hybrids was more or less disturbed, and this seemed to be the main cause of the high level of sterility. 相似文献
20.
Summary A number of crosses were made between diploid and tetraploid Lolium perenne plants in order to determine the degree of cross compatibility between the two different ploidy levels. The range of hybridization undertaken involved diploidxdiploid, and tetraploid x tetraploid control crossings, diploid x tetraploid crosses, tetraploid x diploid crosses and mixed pollinations. The seed set, the germination capacity of resultant hybrid seeds, and the chromosome constitution of derived seedlings was determined. In addition attempts were made to culture 12 day-old hybrid embryos from the diploid x tetraploid and reciprocal crosses.The crossing results obtained indicated no barrier to fertilization between diploids and tetraploids, but the irregular and poor development of the seed accompanied by much reduced germination, indicated unsatisfactory endosperm establishment of large numbers of triploids, as confirmed by the result of culturing embryos dissected from 12-day old seeds.In preliminary studies undertaken to determine the extent to which diploid and tetraploid ryegrass varieties intercross when grown in close proximity for seed production, Griffiths and Pegler (1966) observed a very low incidence of triploids amongst the progenies of diploid plants exposed to the pollen of tetraploid plants and also amongst the progenies of tetraploid material exposed to the pollen of diploid plants.In these and subsequent studies it was noted that only a very small proportion of the so-called fully formed seeds derived from diploid x tetraploid crosses did actually germinate. When, in 1964, propagules of clones of S.24 perennial ryegrass, well separated from one another, were placed in drills of the tetraploid perennial ryegrass variety Reveille, the proportion of florets which formed caryopses, and of caryopses which germinated was as follows (Table 1).The data (Table 1) clearly indicate that a considerable proportion of the S.24 florets had been fertilized by 2n pollen and had formed caryopses, but most of these had proved to be defective. As noted in the previous studies, the frequency of triploid seedlings was low, thus suggesting incompatibility between the n and 2n gametes for the production of viable zygotes.Of the total progenies classed as tetraploids in the early seedling stage, 80% proved to be ryegrass x tall fescue F1 hybrids. These arose as a result of free crossing with 相似文献