Fertility in Crosses Involving Diploid and Autotetraploid Raspberries: II. Fruit and Seed Development

Variation in fruit and seed development following crosses betweendiploid and autotetraploid forms of raspberry cultivars is described. Drupelet set was sensitive to a large number of influences,and varieties differed in their response to such crosses but,once set, fruit growth was largely independent of seed development.Mailing Jewel had a high drupelet set as a seed parent. Chromosomedoubling reduced the fertility of both male and female gametes,but the effect was greater in the pollen where the ability toinduce set was impaired. This is ascribed to physiological ratherthan chromosomal causes. It is suggested that seed size in infertile crosses betweenplants of different ploidy depended on a balance between earlygrowth following the stimulus of fertilization and later slowergrowth due to a weakness in the endosperm. The rate of fruit maturation was more rapid on tetraploid seedparents, but otherwise showed few consistent features.     

Segregation for sexual seed production in Paspalum as directed by male gametes of apomictic triploid plants

BACKGROUND AND AIMS: Gametophytic apomixis is regularly associated with polyploidy. It has been hypothesized that apomixis is not present in diploid plants because of a pleiotropic lethal effect associated with monoploid gametes. Rare apomictic triploid plants for Paspalum notatum and P. simplex, which usually have sexual diploid and apomictic tetraploid races, were acquired. These triploids normally produce male gametes through meiosis with a range of chromosome numbers from monoploid (n = 10) to diploid (n = 20). The patterns of apomixis transmission in Paspalum were investigated in relation to the ploidy levels of gametes. METHODS: Intraspecific crosses were made between sexual diploid, triploid and tetraploid plants as female parents and apomictic triploid plants as male parents. Apomictic progeny were identified by using molecular markers completely linked to apomixis and the analysis of mature embryo sacs. The chromosome number of the male gamete was inferred from chromosome counts of each progeny. KEY RESULTS: The chromosome numbers of the progeny indicated that the chromosome input of male gametes depended on the chromosome number of the female gamete. The apomictic trait was not transmitted through monoploid gametes, at least when the progeny was diploid. Diploid or near-diploid gametes transmitted apomixis at very low rates. CONCLUSIONS: Since male monoploid gametes usually failed to form polyploid progenies, for example triploids after 4x x 3x crosses, it was not possible to determine whether apomixis could segregate in polyploid progenies by means of monoploid gametes.     

ANEUPLOIDY IN CITRUS

Analyses of ploidy levels in progenies from 2x x 2x, 2x x 4x, 4x x 2x, 4x X 4x, and 4x x OP crosses during embryogenesis and seed germination indicate that the progenies include an array of aneuploids. The occurrence of some of the aneuploids was previously unreported. Most of the aneuploids were from 2x x 4x crosses, which yielded the largest number of progeny. Chromosome counts from embryos and endosperms of sectioned young seeds provide evidence that aneuploids originate in progenies of 2x x 4x crosses from the functioning of male gametes with more or fewer chromosomes than 2x = 18 in syngamy with reduced and unreduced female gametes. The origins of aneuploids in progenies from other crosses are problematical at this writing.     

Factors Influencing Seed Set in Triploid Musa spp. L. and Production of Euploid Hybrids

Seed set in triploid Musa spp. L. is very low due to high levelsof sterility. This makes cross breeding of plantain and bananadifficult. Nonetheless, several triploid plantain and bananacultivars produce seeds after hand pollination with diploidparents. This paper reports results about the pattern of seedvariation, success of in vitro germination and hybrid productionafter triploid-diploid crosses. Between-and within-clones differencesin seed set were observed. ABB cooking bananas had the highestrates of seed production followed by AAB French plantains. Plantainsproduced more diploid than tetraploid offsprings after triploid-diploidcrosses, which suggests that meiosis resulted in the productionof balanced haploid gametes (n = x) due to normal chromosomebehaviour between homologous genomes. Seed set variation withinclones was influenced by both the production of 2n (= 3x) gametesin the triploid parent and climatic factors. Indeed, seed production,embryo and seed germination success, and euploid and tetraploidhybrid production followed a pattern of seasonal variation reachinga peak in September. High frequency of seed with tetraploidembryos was obtained in the period from January to mid-March.The results demonstrate that production of desirable tetraploidswould be more efficient when hand pollinations are done underhigh temperature, high solar radiation and low relative humidity.These seem to be the most convenient conditions for relativelyhigh production of 2n eggs as compared to haploid gametes.Copyright1995, 1999 Academic Press Banana, fertility, embryo culture, Musa spp. AAA group, Musa spp. AAB group, Musa spp. ABB group, plantain, ploidy, seed set, 2n gametes     

Evaluation of BC2 progenies derived from 3x-2x and 3x-4x crosses of Lilium hybrids: a GISH analysis

An allotriploid (ALA, 2n=3 x=36) BC(1) plant was obtained by backcrossing a diploid F(1) interspecific hybrid (LA, 2n=2 x=24), derived from a Lilium longiflorum (L genome) and an Asiatic hybrid (A genome), to the latter parent. This allotriploid was backcrossed to a diploid Asiatic hybrid (2n=2 x=24) and to an allotetraploid (LLAA, 2n=4 x=48) LA hybrid. A total of 25 plants of these crosses were examined for ploidy level, and 12 individuals were analyzed for their genome constitution through genomic in situ hybridization (GISH). In most cases the progenies from the triploid-diploid (3 x-2 x) crosses consisted of aneuploids. Further more, there was evidence for the formation of near-haploid (x=12+2) to triploid (3 x=36) gametes in the allotriploid BC(1) plant. The progenies of triploid-tetraploid (3 x-4 x) cross also consisted of mostly aneuploids but in this case the triploid female parent had contributed predominantly near-triploid (2n) gametes for the origin of BC(2) progenies. The different ploidy levels observed between 3 x-2 x and 3 x-4 x crosses are possibly caused by preferential fertilization or survival resulting in a different ratio of chromosome numbers between the embryo and endosperm. Though Lilium has a tetrasporic, eight-nucleate type of embryo sac formation (Fritillaria type), the observed difference between the progeny types in 3 x-2 x and 3 x-4 x crosses is comparable to that of observed in monosporic eight nucleate types (Polygonum type) that predominate in most genera of Angiosperms. An important feature of the genome constitution of the progenies was that the homoeologous recombinant chromosomes were transmitted intact from BC(1) to BC(2) progenies in variable numbers. In addition, there was evidence for the occurrence of new homoeologous recombinations in the triploid BC(1). Of the two euploid BC(2) plants one had originated through the parthenogenetic development of a 2n egg and the other had originated through indeterminate meiotic restitution (IMR).     

The effect of 2n gametes on sex ratios in Actinidia

Sex can sometimes lead to complications. In some crops, 2n gametes have been exploited by plant breeders to transfer genetic variation between taxa of different ploidy levels. However, their role and use in dioecious genera have received relatively little attention. In the dioecious genus Actinidia (kiwifruit), seedling populations usually segregate equally for females and males as sex is determined by an XX female/XY male system. While fertilization involving 2n egg cells is not expected to affect the sex ratios of progenies, fertilization involving 2n pollen is likely to produce progenies with excess males. The extent of sex ratio distortion will depend on the relative contributions of first and second division restitution, and the frequency and location of cross-overs in meiosis. In this study, seedlings recovered from crosses between females of hexaploid Actinidia deliciosa and males of two diploid species, Actinidia chinensis and Actinidia eriantha, included a proportion of pentaploid hybrids presumably derived from fertilization involving 2n pollen. Most of these pentaploids were male, and a proportion of them were likely to be carrying two Y chromosomes. If used as parents in further crosses, males with multiple Y chromosomes are likely to cause distorted sex ratios in their immediate progenies. In dioecious genera such as Actinidia, the effects on sex ratios of different mechanisms of ploidy change need to be taken into account when considering the evolution of polyploidy and the design of breeding strategies involving ploidy manipulation.     

Unreduced gametes in diploid Medicago and their importance in alfalfa breeding

Summary In the genus Medicago, it is known that 2n gametes have been important in the evolution and breeding of cultivated alfalfa, which is a natural polysomic polyploid (2n=4x=32), however little is known on the frequency of male and female 2n gametes in diploid relatives of alfalfa. To obtain data on the frequency of 2n gametes, more than 12,000 2x–4x and 4x–2x crosses were made in 1982 at Madison (USA). Diploid parents in crosses were from four populations of M. coerulea, two of M. falcata and one diploid population of cultivated M. sativa which was derived by haploidy. The tetraploid seed parent in the crosses was a male-sterile M. sativa clone and vigorous tetraploid M. sativa plants were used as pollen parents. Each of 274 diploid plants was utilized both as male and as female. Of the 548 cross combinations, 266 crosses produced variable quantities of seeds which were sown in 1983 in a greenhouse at Perugia (Italy); the plants were subsequently space transplanted in the field in 1984. The identification of ploidy level of these genotypes was made on the basis of morphological characters, plant fertility, pollen stainability and chromosome counts.Of the 515 plants analyzed, the majority behaved as normal tetraploids indicating that many diploid plants produced 2n gametes. Diplogynous and diplandrous gamete production was not correlated with each other, which indicated a different genetic control of 2n sporogenesis in the 2 sexes. Only 4 F₁ triploid plants confirmed the presence of a very effective triploid block in alfalfa. In consequence, bilateral sexual polyploidization is a more likely alternative for the origin of tetraploid alfalfa than triploid bridges. The present study showed that it is possible to efficiently identify genotypes able to produce high frequencies of 2n gametes within natural populations of diploids Medicago that are useful in alfalfa breeding.Part of this study was conducted at the Agronomy Department, University of Wisconsin, Madison, Wis, USA, while one of us (F. Veronesi) was in receipt of financial assistance provided by the National Research Council of Italy; part was conducted at Centro di Studio per il Miglioramento Genetico delie Piante Foraggere, C.N.R., Perugia, Italy. The paper was presented at the Eucarpia Fodder Crops Section Meeting, Svalöv, Sweden, 16–19th September 1985     

SEED DEVELOPMENT IN CITRUS WITH SPECIAL REFERENCE TO 2X X 4X CROSSES

Comparative cytological and histological studies during embryogenesis of seeds from 2x X 2x and 2x x 4x crosses indicate that the ratio of ploidy level between embryo and endosperm is the most important factor affecting the course of seed development. The crosses produced seeds with the expected ploidy relationships between embryo, endosperm, and maternal tissue of 2:3:2 and 3:4:2 as well as the anomalous relationships 3:5:2, 4:6:2, and 6:10:2. All but 3:4:2 resulted in normal, germinable seeds. The ploidy level of the maternal tissue in relation to that of the embryo or endosperm did not appear to have any effect on seed development. About 92–99 % of seeds from 2x x 4x crosses containing triploid embryos with tetraploid endosperm aborted at different stages of embryogenesis. The abortion in all cases was preceded by abnormalities in the tetraploid endosperm. It is postulated that the unbalance of chromosome number between embryo and endosperm disturbs physiological relationships between these two tissues, leading first to the abortion of the endosperm and then of the embryo.     

Evidence for the existence of 2n gametes in Lotus tenuis Wald. et Kit. (2n=2x=12): their relevance in evolution and breeding of Lotus corniculatus L. (2n=4x=24)

Summary Crosses between male sterile L. corniculatus (2n=4x=24) and L. tenuis (2n=2x=12) plants were performed in order to verify the presence of 2n gametes in L. tenuis. All but one of the plants from these crosses had 2n=4x=24 and the L. corniculatus phenotype; this plant had 2n=2x=12 and the L. tenuis phenotype. The plants also showed good quantity of pollen at tripping, good pollen fertility and good percentage of seed setting in the backcross to L. corniculatus. On the whole, both cytological and morphological observations, showing that all but one of the plants from L. corniculatus x L. tenuis were normal tetraploids, suggest the existence of diploandrous gametes in L. tenuis. On the other hand, haploid parthenogenesis probably gave origin to the dihaploid plant 2n=2x=12.     

Production of 2n Gametes in Diploid Subspecies of Dactylis glomerata L. 2. Occurrence and Frequency of 2n Eggs

Whereas polyploidy has been found in more than half the Gramineae,the occurrence of 2n gametes, a potentially major mechanismof polyploid production, has been rarely studied. In the presentwork, the frequency of 2n egg production in nine diploid (n= 2x = 14) subspecies of the polyploid complex Dactylis glomeratahas been estimated by determining the ploidy level of the progenyin 98 2X-4X crosses. The 2n egg origin of the 4X offspring wasverified using enzyme markers. The frequency of 2n egg productionin each subspecies was estimated from the number of 4X offspring,the number of florets in the seed plant and the fertility ofthe subspecies. The ploidy level of the progeny was determinedby chromosome counts or nuclear DNA quantification using flowcytometry. Plants producing 2n eggs were detected in 47% ofthe fertile crosses, involving eight subspecies. Variabilitywas related to individuals and not to subspecies. Average 2negg frequency was 0·49% for all crosses, and 1·53%for crosses where 2n egg production was detected. Individualfrequencies did not exceed 3·5%, with the exception of26% in one plant. Triploid block was higher and fertility, frequencyof high 2n gamete producers and average 2n gamete frequencywere lower in the 2X-4X crosses than in the opposite 4X-2X crossesinvolving the same plants, previously studied. Diplogynous anddiplandrous gamete production were not correlated with eachother. However, the widespread occurrence of plants producingboth kinds of 2n gametes in almost all the studied subspecies,as well as the presence of several individuals able to producehigh rates of 2n eggs or 2n pollen, support the hypothesis thattetraploids can be formed anywhere and anytime by sexual polyploidizationin diploid populations of Dactylis glomerata L. 2n eggs, polyploidy, Dactylis glomerata L., flow cytometry, sexual polyploidization     

Ploidy level manipulations in potato through sexual hybridisation

There is no better use of sexual reproduction in regard to breeding and genetic research than the ploidy level manipulations possible in the potato and its relatives. Unique reproductive characteristics of tuber‐bearing Solanum species make possible: the production of gametes with unreduced chromosome number; the presence of an endosperm dosage system that regulates success of interploidy/interspecific crosses; the possibility to easily extract maternal haploids following crosses with S. phureja. This paper reviews results obtained in scaling genomic multiples up and down in potato, and relates these manipulations to breeding strategies for the genetic improvement of the cultivated potato. Several ploidy series have been developed, ranging from the monoploid to the hexaploid level. Cultivated tetraploids were scaled down to the diploid and monoploid level by haploidy. Scaling upward was achieved by sexual polyploidisation via 2n gametes that resulted in triploid, tetraploid, pentaploid, and hexaploid genotypes with a broad genetic base. Altogether, the success of ploidy level manipulations constitutes further proof that sexual polyploidisation played an important role in the polyploid evolution of Solanum species, and supports the idea that gene flow can be relatively easily accomplished through interploid and bridge crosses.     

Inter-embryo competition in the progeny of autotriploid Aloineae (Liliaceae)

In reciprocal crosses between diploid and triploid Aloineae the progeny are largely diploid or diploid plus one or two chromosomes, but in reciprocal crosses between triploids and tetraploids they are tetraploid or nearly so. Thus the triploids contribute circa haploid gametes to the progeny when crossed with diploids but circa diploid gametes when crossed with tetraploids. These results are compared with those of a number of earlier workers. It is concluded that the bias in the frequency of progeny types towards diploidy or tetraploidy, depending on the ploidy level of the plant which is crossed with the triploid, is caused by inter-embryo competition. Those embryos with an endosperm/embryo factor of 1.5, the value found in normal diploid/diploid crosses having triploid endosperms, are selected in preference to those with factors higher or lower than 1.5.Inter-gamete competition also occurs among the euploid and aneuploid gametes produced by the triploids. This is more pronounced on the male side, because the degree of survival of aneuploid pollen from the triploids into the next generation is much lower than that of aneuploid egg nuclei.Non-reduction in the triploids gives rise to occasional pentaploid progeny in crosses with tetraploids, but it is more probable that in diploid/triploid crosses tetraploid progeny are the products of non-reduction in the diploid.     

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     

Cytological and breeding behavior of pentaploids derived from 3x × 4x crosses in potato

Cytology and breeding behavior of Solanum commersonii - S. tuberosum hybrids derived from 3 x x 4 x crosses was examined. The chromosome number of hybrids ranged from hypo-pentaploid (2 n=5 x - 8=52), to hyper-pentaploid (2 n=5 x + 7=67), with the euploid pentaploid 2 n=5 x=60 class predominant. The high variability in chromosome number of the 3 x x 4 x hybrids was attributed to the fact that meiotic restitution during megasporogenesis of the 3 x female may have involved poles with various chromosome numbers, resulting in 2 n eggs with 24-48 chromosomes. Microsporogenesis analyses provided evidence that chromosome pairing between S. commersonii and S. tuberosum genomes occurred. In addition, chromosome distribution at anaphase I and anaphase II revealed an average chromosome number of 29.5 and 29.1 per pole, respectively. To further study the extent of transmission of extra genome chromosomes from pentaploids, 5 x x 4 x and 4 x x 5 x crosses were performed, and the chromosome number of resulting progeny was determined. Ploidy ranged from 2 n=4 x=48 to 2 n=5 x=60 following 5 x x 4 x crosses, and from 2 n=4 x + 1=49 to 2 n=5 x=60 following 4 x x 5 x crosses. These results provided indirect evidence that the pentaploid hybrids produced viable aneuploid gametes with a chromosome number ranging from 24 to 36. They also demonstrated that gametes with large numbers of extra chromosomes can be functional, resulting in sporophytes between the 4 x and 5 x ploidy level. Fertility parameters of crosses involving various (aneuploid) pentaploid genotypes were not influenced by chromosome number, suggesting a buffering effect of polyploidy on aneuploidy. The possibility of successfully using (aneuploid) pentaploid genotypes for further breeding efforts is discussed.     

Microsporogenesis in Brachiaria brizantha (Poaceae) as a selection tool for breeding

The genus Brachiaria comprises more than 100 species and is the single most important genus of forage grass in the tropics. Brachiaria brizantha, widely used in Brazilian pastures for beef and dairy production, is native to tropical Africa. As a subsidy to the breeding program underway in Brazil, cytological studies were employed to determine the chromosome number and to evaluate microsporogenesis in 46 accessions of this species available at Embrapa Beef Cattle (Brazil). Thirty-four accessions presented 2n = 36; seven had 2n = 45, and five had 2n = 54 chromosomes. Based on the higher level of chromosome association observed in diakinesis, in tetra-, penta-, and hexavalents, respectively, it was concluded that they are derived from x = 9; consequently, these accessions are tetra- (2n = 4x = 36), penta- (2n = 5x = 45), and hexaploids (2n = 6x = 54). The most common meiotic abnormalities were irregular chromosome segregation due to polyploidy. Chromosome stickiness, abnormal cytokinesis, non-congressed bivalents in metaphase I and chromosomes in metaphase II, and chromosome elimination were recorded at varying frequencies in several accessions. The mean percentage of meiotic abnormalities ranged from 0.36 to 95.76%. All the abnormalities had the potential to affect pollen viability by generating unbalanced gametes. Among the accessions, only the tetraploid ones with less than 40% of abnormalities are suitable as pollen donors in intra- and interspecific crosses. Currently, accessions with a high level of ploidy (5 and 6n) cannot be used as male genitors in crosses because of the lack of sexual female genitors with the same levels of ploidy.     

Components of Selection in X Chromosome Lines of DROSOPHILA MELANOGASTER: Sex Ratio Modification by Meiotic Drive and Viability Selection

Selection coefficients and segregation parameters have been estimated in 18 randomly chosen lines carrying wild X chromosomes on the cn bw genetic background. Each line was studied in replicated crosses of four types, with approximately 100 replications per line per cross. Crosses in which male X chromosomes differed exhibited significant sex ratio heterogeneity. Maximum likelihood estimation of segregation parameters revealed two lines in which the proportion of X-bearing gametes produced by males was significantly different from Mendelian expectations. These observations suggest that segregation distortion is a common feature of naturally occurring genetic variation. Non-Mendelian segregation has important evolutionary implications.     

The Genetic Control of Time to Germination in Tomato

The time to germination of seeds derived from crosses betweenLycopersicon pimpinellifolium and five varieties of L. esculentumwas analysed in the F₁ and F₂2 generations and in seeds derivedfrom inter-crossing the F₁ hybrids. Inheritance of time to germinationwas largely additive and closely related to seed size. Therewere marked maternal and paternal effects particularly whereL. pimpinellifolium was involved. Variation in time to germinationcould easily be modified by selection but probably at the expenseof seed size and embryo size at emergence. Seed characteristicsare a compromise between the contending advantages of size atemergence, rapidity of germination, and the number of seedsproduced.     

The significance of genic balance to endosperm development in interspecific crosses

Summary The endosperm has played a significant role in the evolution of angiosperms because of its physiological and genetic relationships to the embryo. One manifestation of this evolutionary role is its abnormal development in interploidy crosses. It is now established that the endosperm develops abnormally in interploidy-intraspecific crosses when the maternal: paternal genome ratio deviates from 21 in the endosperm itself. We propose an Endosperm Balance Number (EBN) hypothesis to explain endosperm development in both interploidy-intraspecific and interspecific crosses. Each species is assigned an EBN on the basis of its crossing behavior to a standard species. It is the EBN which determines the effective ploidy in the endosperm of each species, and it is the EBNs which must be in a 21, maternal:paternal ratio. The EBN of a species may be determined by a few genes rather than the whole genome. This hypothesis brings most intraspecific-interploidy and interspecific crossing data under a single concept with respect to endosperm function. The implications of this hypothesis to isolating mechanisms, 2n gametes, the evolution of disomic polyploids, and reciprocal differences in seed development are discussed.     

Genetic relationships among Hylocereus and Selenicereus vine cacti (Cactaceae): evidence from hybridization and cytological studies

BACKGROUND AND AIMS: Hylocereus and Selenicereus are native to tropical and sub-tropical America. Based on its taxonomic status and crossability relations it was postulated that H. megalanthus (syn. S. megalanthus) is an allotetraploid (2n = 4x = 44) derived from natural hybridization between two closely related diploid taxa. The present work aimed at elucidating the genetic relationships between species of the two genera. METHODS: Crosses were performed and the putative hybrids were analysed by chromosome counts and morphological traits. The ploidy level of hybrids was confirmed by fluorescent in situ hybridization (FISH) of rDNA sites. Genomic in situ hybridization (GISH) was used in an attempt to identify the putative diploid genome donors of H. megalanthus and an artificial interploid hybrid. KEY RESULTS: Reciprocal crosses among four diploid Hylocereus species (H. costaricensis, H. monacanthus (syn. H. polyrhizus), H. undatus and Hylocereus sp.) yielded viable diploid hybrids, with regular chromosome pairing. Reciprocal crosses between these Hylocereus spp. and H. megalanthus yielded viable triploid, pentaploid, hexaploid and aneuploid hybrids. Morphological and phenological traits confirm the hybrid origin. In situ detection of rDNA sites was in accord with the ploidy status of the species and hybrid studied. GISH results indicated that overall sequence composition of H. megalanthus is similar to that of H. ocamponis and S. grandiflorus. High sequence similarity was also found between the parental genomes of H. monacanthus and H. megalanthus in one triploid hybrid. CONCLUSIONS: The ease of obtaining partially fertile F1 hybrids and the relative sequence similarity (in GISH study) suggest close genetic relationships among the taxa analysed.     

High frequncies of fertilization and embryo formation in hexaploid wheat x Tripsacum dactyloides crosses

The Hexaploid wheat variety Fukuho was crossed with Tripsacum dactyloides (2n=4x=72). The total fertilization frequencies for the egg cell, polar nuclei, and both, were 58.3%, 26.8% and 58.9% of the 168 ovaries examined. However, the fertilization frequency of single polar nuclei was much lower at only 0.6%. The total frequency of fertilization was higher than that in wheat x maize crosses. A total of 49 hexaploid wheat varieties, including Hope carrying the dominant genes Kr1 and Kr2, were crossed with T. dactyloides, and most gave embryos. The embryoformation frequencies ranged from 0.5% to 59.0%. A higher frequency of 32.0% embryo formation was obtained following pollination of the variety Hope. In comparison with embryo formation in wheat x maize crosses the difference of embryo-formation frequencies between the two crosses was significant. The results of high frequencies of fertilization and embryo formation in wheat x T. dactyloides crosses indicated that the Kr genes are as inactive in wheat x T. dactyloides, as they are in wheat x maize crosses, and also that the efficiency of fertilization and embryo formation is higher in wheat x T. dactyloides than in what x maize crosses. The potential of wheat x T. dactyloides crosses for wheat haploid production and wheat improvement is discussed.