Cytological analysis of tetraploid hybrids between sweet potato and diploid Ipomoea trifida (H. B. K.) Don.

Summary Tetraploid F₁ hybrids between Ipomoea batatas, sweet potato (2n = 6x = ca. 90), and diploid (2n = 2x = 30) I. trifida (H. B. K.) Don. showed various degrees of fertility reduction. The present study aimed to clarify its causes by cytological analysis of meiotic chromosome behavior in the diploid and sweet potato parents and their tetraploid hybrids. The diploid parents showed exclusively 15 bivalents, and the sweet potato parents exhibited almost perfect chromosome pairing along with predominant multivalent formation. Their hybrids (2n = 4x= 57–63) formed 2.6–5.0 quadrivalents per cell, supporting the autotetraploid nature. The meiotic aberratios of the hybrids were characterized by the formation of univalents, micronuclei, and abnormal sporads (monad, dyad, triad, and polyad). The causes underlying these aberrations were attributed in part to the multivalent formation, and in part to a disturbance in the spindle function. Three hybrids showing serious meiotic aberrations were very low in fertility. The utilization of the sweet potato-diploid I. trifida hybrids for sweet potato improvement is described and, further, the role of interploidy hybridization in the study of the sweet potato evolution is discussed.     

Abortion and determination of stages for embryo rescue in crosses between sweet-potato,Ipomoea batatas Lam. (2n=6x=90) and its wild relative,I. trifida (H. B. K.) G. Don. (2n=2x=30)

Summary The frequency of aborted fruits and the changes and abnormalities that occur during the embryo development in intraspecific crosses of sweet-potato Ipomoea batatas (2n=6x=90) and interspecific crosses between I. batatas and I. trifida (2n=2x=30) were investigated in order to study the causes of the low seed production. Three genotypes of I. batatas and 18 genotypes of I. trifida were intermated. The frequency of aborted fruits was below 25% in the intraspecific crosses and over 90% in the interspecific crosses. Paraffin sections were used to examine the developmental stages of fruits and seeds. Embryos in different developmental stages were observed to determine the stage of abortion. These observations permitted the identification of developmental stages of embryo rescue in interspecific crosses. There were no significant differences in the frequency of embryo abortion before the early globular stage among female sweet-potato progenitors for the intraspecific and interspecific crosses. The frequency of the late occurrence of embryo abortion (when embryo abortion occurs after the pre-globular stage) was higher in interspecific crosses (19.1%) than in intraspecific crosses (5.5%). The frequency of the late occurrence of embryo abortion in interspecific crosses was higher at the globular stage (9.6%) than at the heart stage (4.3%). Providing that embryo rescue is conducted in interspecific crosses, the estimated number of potentially viable embryos could be increased: 30 times with embryos at the globular stage; 20 times with embryos at the heart stage; and 11 times if embryos at the torpedo stage were used for the rescue with respect to the seed set. The results suggested that the appropriate time for embryo rescue in interspecific crosses is at the globular stage. If embryos could be rescued at the globular stage, it would be possible to increase the number of surviving embryos up to 30 times in interspecific crosses and 0.02 times in intraspecific crosses with respect to natural conditions without embryo rescue.This research was initiated during sabbatical of M.I. at the Asian Vegetable Research and Development Center (AVRDC) in Taiwan     

Characterisation of progeny from backcrosses of triploid hybrids between Hordeum vulgare L. (2x) and H. bulbosum L (4x) to H. vulgare

Interspecific hybridisations between Hordeum vulgare L. (cultivated barley) and H. bulbosum L. (bulbous barley grass) have been carried out to transfer desirable traits, such as disease resistance, from the wild species into barley. In this paper we report the results of an extensive backcrossing programme of triploid hybrids (H. vulgare 2x x H. bulbosum 4x) to two cultivars of H. vulgare. Progenies were characterised cytologically and by restriction fragment length polymorphism analysis and comprised (1) haploid and diploid H. vulgare plants, (2) hybrids and aneuploids, (3) single and double monosomic substitutions of H. bulbosum chromosomes into H. vulgare and (4) chromosomal rearrangements and recombinants. Five out of the seven possible single monosomic chromosome substitutions have now been identified amongst backcross progeny and will be valuable for directed gene introgression and genome homoeology studies. The presence amongst progeny of 1 plant with an H. vulgare-H. bulbosum translocated chromosome and one recombinant indicates the value of fertile triploid hybrids for interspecific gene introgression.     

Interspecific hybridization between the cultivated potato Solanum tuberosum subspecies tuberosum L. and the wild species S. circaeifolium subsp. circaeifolium Bitter exhibiting resistance to Phytophthora infestans (Mont.) de Bary and Globodera pallida (Stone) Behrens

Summary Somatic fusions between the cultivated potato Solanum tuberosum and the wild species S. circaeifolium subsp. circaeifolium Bitter were produced in order to incorporate desirable traits into the potato gene pool. Selection of the putative hybrids was based on a difference in callus morphology between the hybrids and their parents, with the hybrids showing typical purple-colored cells in otherwise green calli. In all, 17 individual calli regenerated to plants. Of the nine plants that could be transferred to the greenhouse, eight showed a hybrid and one a parental morphology. Restriction fragment length polymorphism (RFLP) analysis confirmed the hybrid character in the former group. Chloroplast counts in stomatal guard cells and flow cytometric determination of nuclear DNA content showed that four hybrid plants were tetraploid (4x), one was mixoploid (5x–8x), and the others were polyploid (6x; 8x). Three out of four tetraploid hybrids were found to be fully resistant to Phytophthora infestans, and all four hybrids were resistant to Globodera pallida pathotypes Pa2 and Pa3. It was further observed that the type and amount of steroidal glycoalkaloids varied among the tubers of the parents and the hybrids. Using the hybrids as female parents in crosses with S. tuberosum, viable seeds could be obtained. This demonstrates the potential of these hybrids in practical plant breeding.     

Use of 2n pollen-producing triploid hybrids to introduce tetraploid Mexican wild species germ plasm to cultivated tetraploid potato gene pool

Summary Tetraploid (2n=4x=48) 2EBN Mexican wild species in the series Longipedicellata, which consists of Solanum fendleri, S. hjertingii, S. papita, S. polytrichon, and S. stoloniferum, were crossed with two 2EBN cultivated diploid (2n=2x=24) clones. The resulting triploid hybrids (2n=3x=36) produced 2n pollen (triplandroids) by the mechanism of parallel orientation of anaphase II spindles. The percentage of stainable pollen in 520 triploids ranged between 0 and 23.5%, with a mean of 2.7%. Triploids producing between 13.0 and 23.5% stainable pollen were crossed as staminate parents to the tetraploid cultivars, resulting in abundant pentaploid (2n=5x=60) and near-pentaploid hybrid progeny. Crosses of triploids with lower percentage of stainable pollen as pollen parent to the tetraploid cultivars did not yield fruit, unless rescue pollen from a tetraploid cultivar was added 2 days later. Pentaploid hybrids were selected among selfed tetraploid progenies using morphological and isoxyme markers transmitted from their cultivated diploid parents. These pentaploid hybrids were vigorous and had uniformly sterile pollen. They were female fertile and were crossed with tetraploid cultivars, yielding an average of 19 seeds per fruit. Triplandroids provide the opportunity of transferring 2EBN tetraploid Mexican wild species in the series Longipedicellata germ plasm into the 4EBN cultivated potatoes.Cooperative investigations of the ARS, USDA, and the Washington State University Agricultural Research Center, Prosser, WA 99350, USA. H/LA Paper No. 90-03, College of Agriculture and Home Economies Research Center, Washington State University, Pullman, WA 99164, USA     

送春与多花兰种间杂交后代的ISSR分析

该文使用简单重复序列间( ISSR)分子标记,对送春与多花兰种间杂交后代进行了研究。结果表明：从80个ISSR引物中筛选出14个扩增效果稳定的ISSR引物,对两亲本和59个F1代个体进行了ISSR扩增,得到107个扩增位点,扩增的片段大小位于90~2100 bp之间,平均每个引物扩增7.64条条带,得到11种类型的带。 ISSR标记在送春×多花兰的F1代中表现出一定的多态性,分离频率为44.86％,分离位点有83.33％符合孟德尔1︰1或3︰1的分离规律,产生偏孟德尔分离的位点占12.50％,余下的4.17％属于特殊分离带型。可能导致后代变异的位点为偏孟德尔分离的6条带、缺失的8条带或新生成的2条带。聚类图中父本和母本与F1代个体间的遗传距离较远,59个杂交后代先聚集成一组,再同母本相聚为一组,最后才同父本聚在一起,59个杂种均偏母本型。送春与多花兰的杂交后代在植株形态、染色体、遗传物质方面都具备双亲特点,61个个体间的ISSR分子量标记结果和植株形态学特征都说明,59个F1代杂种包含送春和多花兰的遗传特性是真杂种;F1代杂种既有双亲的互补特征带,又有双亲的重组片断即产生新的特异带,这说明送春与多花兰的杂交后代具有遗传变异的特点。该研究结果可以有效地对杂交后代进行定向选择,为兰花的杂交育种提供了分子依据。     

Production of potato monohaploids (2n=x=12) through prickle pollination

Summary Data are presented on the potential of gynogenesis for the production of monohaploids and on factors affecting their frequency and relative vigour. Diploid Solanum tuberosum L. and S. tuberosumxS. phureja Juz et Buk hybrids were used as maternal parents and selected S. phureja clones as prickle pollinators with embryo-spot and nodal band as dominant seed and plant marker. About 2 million seeds were screened for absence of embryo-spot. After raising plants from phenotypically spotless seeds, further screening for absence of nodal bands and for ploidy level was carried out. Finally more than 500 monohaploid plants from three genetically different groups of maternal parents were obtained. Frequency and vigour of the monohaploids were clearly dependent on their maternal genotypes. The data also indicated an effect of the pollinator genotype, the physiological stage of the maternal plant and the environment on monohaploid frequency. On the basis of these results the possibility of breeding for a higher monohaploid production rate and for more stable and vigorous monohaploids is discussed. Furthermore, gynogenesis and androgenesis are compared. It is suggested that both should be used in order to obtain monohaploids from sufficiently various diploid breeding material.     

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.     

C-banding variation in the Moroccan oat species Avena agadiriana (2n=4x=28)

The C-banding technique was used to describe the chromosomes of a relatively recently-discovered Moroccan oat species, Avena agadiriana (2n=4x=28). A substantial amount of polymorphism for arm ratios and C-banding patterns was observed among five accessions of this species. However a common set of ten putatively homologous chromosomes was identifiable among the five accessions. The chromosomes of A. Agadiriana do not closely match those of any of the previously described diploid or tetraploid oat species in terms of their arm ratios and C-banding patterns. However, their overall C-banded appearance generally resembles the A/B/D groups of chromosomes of Avena species, rather than the more hetrochromatic C genomes. Implications of these findings in terms of chromosome evolution in the genus Avena are discussed.Contribution no. 95-490-J of the Kansas Agricultural Experiment Station, Kansas State University, Manhattan, KS, USA     

Chromosome doubling of 2x Solanum species by oryzalin: method development and comparison with spontaneous chromosome doubling in vitro

A potato breeding scheme implies the possibility of ploidy level manipulation either by reducing the chromosome number of cultivars from 48 to 24 to be able to cross them with diploid related species or by doubling diploid material to reach the generally optimal tetraploid level. In vitro spontaneous chromosome doubling is widely used but can lead to somaclonal variation. Since oryzalin has proven to be efficient as a chromosome doubling agent on potato cell suspension cultures, we tried this herbicide on various Solanum species and interspecific diploid hybrids. A 24 h dip in a 28.8 M aqueous oryzalin solution applied on apical buds was the most efficient treatment in terms of tetraploid plant production (mean = 4.1 tetraploid plants for 10 treated buds over 4 genotypes). However 50–100% of the regenerated tetraploid plants acclimatized after in vitro treatment proved to be chimaeric. Consequently, a selection procedure in the progeny was necessary to obtain real and stable doubled clones and final yields were low. This technique is easy to apply and could be a good alternative to chromosome doubling by spontaneous in vitro regeneration in the case of refractory genotypes especially where somaclonal variation is problematic. Percentage of tetraploids among the regenerated plants varied from 6 to 29% with the oryzalin doubling technique while it varied from 20 to 78% by in vitro spontaneous doubling for five diploid genotypes. An observation of the progeny indicated that chimaeras were more frequent using oryzalin (50–100% of the initially supposed tetraploid plants) than when chromosomes doubled spontaneously (4–67% of the initially supposed tetraploid plants).     

Features of recombination of nuclear genome in back crossed offspring of barley-wheat hybrids Hordeum vulgare L. (2n=14) x Triticum aestivum L. (2n+42) with the use of SSR-analysis

The backcross progenies of the barley-wheat hybrids Hordeum vulgare L. (2n = 14) x Triticum aestivum L. (2n = 42) and two alloplasmic lines derived from them were studied using microsatellite markers of barley and wheat. The F1 hybrids and first backcross plants BC1 contained the genetic material of both cultivated barley and the cultivars of common wheat involved in developing of these hybrid genotypes. The genomes of BC3, BC4, and alloplasmic lines contained no microsatellite markers of the cultivated barley, whereas chromosomes of each homeologous group of common wheat were identified. In chromosomes of backcross progenies BC3, BC4, and alloplasmic lines yielded by backcrosses of hybrids and various common wheat cultivars, microsatellite markers of the parental wheat cultivars were shown to undergo recombination.     

Fertilization fitness and offspring ploidy in 3x × 2x matings in potato

Abstract

The main objective of the current research was to study the reproductive behaviour of artificial triploid potato hybrids between wild Solanum commersonii and the cultivated potato Solanum tuberosum. When used in 3x × 2x crosses, triploids gave aneuploid progenies with somatic chromosome number ranging from 29 to 36. Fertilization fitness data suggested that the survival rate of gametes produced by the triploid parents may be related to their chromosome number. In addition, consistent with molecular data, our results indicated that fitness of gametes and chromosome number of progenies are influenced by the genome dosage of interspecific triploids. Since a main route to polyploidy formation is via 2n gametes and triploids, our study may contribute to a better understanding of polyploid plant reproduction, evolution and breeding.     

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.     

Plant regeneration from stem and petiole protoplasts of sweet potato (Ipomoea batatas) and its wild relative,I. lacunosa

A protoplast-to-plant regeneration system has been established for sweet potato (Ipomoea batatas (L.) Lam.) and its wild relative, I. lacunosa L. Viable protoplasts, isolated from preplasmolyzed stems and petioles of in vitro-grown plants, were cultured on liquid MS (Murashige & Skoog 1962) medium that supported cell division and colony formation. Embryogenic calli of sweet potato were induced on agar-solidified MS medium supplemented with 3% (w/v) sucrose, 50 mg l^-1 casamino acids, 0.2–0.5 mg l^-1 2,4-d, 1.0 mg l^-1 kinetin and 1.0 mg l^-1 ABA. On average, 3 plants were regenerated from a single sweet potato callus subcultured on semi-solid MS medium containing 3% (w/v) sucrose, 800 mg l^-1 glutamine, 2.0 mg l^-1 BA or 1.0 mg l^-1 kinetin and 1.0 mg l^-1 GA₃. Embryogenic calli of I. lacunosa L. were initiated on semi-solid MS medium containing 0.2–0.5 mg l^-1 IAA and 1.0–2.0 mg l^-1 BA. An average of 5 plants was regenerated from a single sweet potato callus subcultured on semi-solid MS medium containing 0.5 or 1.0 mg l^-1 GA₃.Abbreviations ABA abscisic acid - BA benzyladenine - 2,4-d 2,4-dichlorophenoxyacetic acid - GA₃ gibberellic acid - IAA indole acetic acid - MES 2-(N-morpholino)-ethane sulfonic acid - NAA -naphthaleneacetic acid     

Assessing hybrid sterility in <Emphasis Type="Italic">Oryza glaberrima</Emphasis> × <Emphasis Type="Italic">O. sativa</Emphasis> hybrid progenies by PCR marker analysis and crossing with wide compatibility varieties

Interspecific crossing of the African indigenous rice Oryza glaberrima with Oryza sativa cultivars is hindered by crossing barriers causing 100% spikelet sterility in F₁ hybrids. Since hybrids are partially female fertile, fertility can be restored by back crossing (BC) to a recurrent male parent. Distinct genetic models on spikelet sterility have been developed predicting, e.g., the existence of a gamete eliminator and/or a pollen killer. Linkage of sterility to the waxy starch synthase gene and the chromogen gene C, both located on chromosome 6, have been demonstrated. We selected a segregating BC₂F₃ population of semi-sterile O. glaberrima × O. sativa indica hybrid progenies for analyses with PCR markers located at the respective chromosome-6 region. These analyses revealed that semi-sterile plants were heterozygous for a marker (OSR25) located in the waxy promoter, whereas fertile progenies were homozygous for the O. glaberrima allele. Adjacent markers showed no linkage to spikelet sterility. Semi-sterility of hybrid progenies was maintained at least until the F₄ progeny generation, suggesting the existence of a pollen killer in this plant material. Monitoring of reproductive plant development showed that spikelet sterility was at least partially due to an arrest of pollen development at the microspore stage. In order to address the question whether genes responsible for F₁ sterility in intraspecific hybrids (O. sativa indica × japonica) also cause spikelet sterility in interspecific hybrids, crossings with wide compatibility varieties (WCV) were performed. WCV accessions possess "neutral" S-loci (Sⁿ) improving fertility in intraspecific hybrids. This experiment showed that the tested Sⁿ-loci had no fertility restoring effect in F₁ interspecific hybrids. Pollen development was completely arrested at the microspore stage and grains were never obtained after selfing. This suggests that distinct or additional S-loci are responsible for sterility of O. glaberrima × O. sativa hybrids.Communicated by H.C. Becker     

Monosomic and double monosomic substitutions of Hordeum bulbosum L. chromosomes into H. vulgare L.

Summary One of the aims of the interspecific crossing programme between Hordeum vulgare L. and H. bulbosum L. has been to introgress desirable genes into barley from the wild species. However, despite their close taxonomic relationship there have been few reports of achieving this objective using amphidiploid hybrids. In order to broaden the range of available hybrids, partially fertile triploids between H. vulgare (2n = 2x = 14) and H. bulbosum (2n = 4x = 28) were developed and crossed with H. vulgare as female parent. From 580 progeny which were screened, eight putative single monosomic chromosome substitution lines and one double monosomic substitution were identified by cytological analysis. These involved the substitution of H. vulgare chromosome 1 (two lines), 6 (four lines), 6L (one line), 7 (one line) and 1 + 4 (one line) by their respective H. bulbosum homoeologues. The H. bulbosum chromosome was frequently eliminated during plant development, but it was observed regularly in pollen mother cells of two lines. However, pairing between the H. bulbosum chromosome and its H. vulgare homoeologue was low. Several of the lines were more resistant than their H. vulgare parents to powdery mildew (Erysiphe graminis DC. f.sp. hordei Em. Marchai), net blotch (Drechslera teres Sacc.) and scald (Rhynchosporium secalis (Oudem.) Davis). Apart from their use in studying genome relationships, their value to plant breeders will depend on the ease of inducing translocations between the parental chromosomes.     

Cytological and molecular characterization of oat x maize partial hybrids

In cereals, interspecific and intergeneric hybridizations (wide crosses) which yield karyotypically stable hybrid plants have been used as starting points to widen the genetic base of a crop and to construct stocks for genetic analysis. Also, uniparental genome elimination in karyotypically unstable hybrids has been utilized for cereal haploid production. We have crossed hexaploid oat (2n=6x=42, Avena sativa L.) and maize (2n=2x=20, Zea mays L.) and recovered 90 progenies through embryo rescue. Fifty-two plants (58%) produced from oatxmaize hybridization were oat haploids (2n=3x=21) following maize chromosome elimination. Twenty-eight plants (31%) were found to be stable partial hybrids with 1–4 maize chromosomes in addition to a haploid set of 21 oat chromosomes (2n=21+1 to 2n=21+4). Ten of the ninety plants produced were found to be apparent chromosomal chimeras, where some tissues in a given plant contained maize chromosomes while other tissues did not, or else different tissues contained a different number of maize chromosomes. DNA restriction fragment length polymorphisms (RFLPs) were used to identify the maize chromosome(s) present in the various oat-maize progenies. Maize chromosomes 2, 3, 4, 5, 6, 7, 8, and 9 were detected in partial hybrids and chromosomal chimeras. Maize chromosomes 1 and 10 were not detected in the plants analyzed to-date. Furthermore, partial self-fertility, which is common in oat haploids, was also observed in some oat-maize hybrids. Upon selfing, partial hybrids with one or two maize chromosomes showed nearly complete transmission of the maize chromosome to give self-fertile maize-chromosome-addition oat plants. Fertile lines were recovered that contained an added maize chromosome or chromosome pair representing six of the ten maize chromosomes. Four independently derived disomic maize chromosome addition lines contained chromosome 4, one line carried chromosome 7, two lines had chromosome 9, one had chromosome 2, and one had chromosome 3. One maize chromosome-8 monosomic addition line was also identified. We also identified a double disomic addition line containing both maize chromosomes 4 and 7. This constitutes the first report of the production of karyotypically stable partial hybrids involving highly unrelated species from two subfamilies of the Gramineae (Pooideae — oat, and Panicoideae — maize) and the subsequent recovery of fertile oat-maize chromosome addition lines. These represent novel material for gene/ marker mapping, maize chromosome manipulation, the study of maize gene expression in oat, and the transfer of maize DNA, genes, or active transposons to oat.Joint contribution of the Minnesota Agricultural Experiment Station and USDA-ARS. Scientific journal series paper No. 21 859 of the Minnesota Agricultural Experiment Station. Mention of a trademark or proprietary product does not constitute a guarantee or warranty by the USDA-ARS or the University of Minnesota and does not imply approval over other products that also may be suitable     

Cytogenetics of double cross hybrids between Pennisetum americanum — P. purpureum amphiploids and P. americanum x Pennisetum squamulatum interspecific hybrids

Summary Pearl millet, Pennisetum americanum L. Leeke-napiergrass, Pennisetum purpureum Schum. amphiploids (2n=42) were crossed with pearl millet X Pennisetum squamulatum Fresen. interspecific hybrids (2n=41) to study the potential of germplasm transfer from wild Pennisetum species to pearl millet. These two interspecific hybrids were highly cross-compatible and more than two thousand trispecific progenies were produced from 17 double crosses. All doublecross hybrids were perennial and showed a wide range of morphological variations intermediate to both parents in vegetative and inflorescence characteristics. Some crosses resulted in sublethal progenies. Chromosomes paired mainly as bivalents (¯x15.88) or remained as univalents. At metaphase I, trivalents, quadrivalents, an occasional hexavalent and a high frequency of bivalents indicated some homeology among the genomes of the three species. Delayed separation of bivalents, unequal segregation of multivalents, lagging chromosomes, and chromatin bridges were observed at anaphase I. Although approximately 93% of the double-cross hybrids were male-sterile, pollen stainability in male-fertile plants ranged up to 94%. Seed set ranged from 0 to 37 seed per inflorescence in 71 plants under open-pollinated conditions. Apomictic embryo sac development was observed in double-cross progenies when crosses involved a pearl millet x P. squamulatum apomictic hybrid as pollen parent. These new double-cross hybrids may serve as bridging hybrids to transfer genes controlling apomixis and other plant characteristics from the wild Pennisetum species to pearl millet.     

The development of bridge lines for interspecific gene transfer between Lycopersicon esculentum and L. peruvianum

Summary Using a modified embryo callus culture technique, hybrids between Lycopersicon esculentum and L. peruvianum were developed and their usefulness as bridge lines for facilitating interspecific gene transfer was evaluated. Four of these lines showed a high level of sexual compatibility with several other L. peruvianum var. typicum accessions, as well as with accessions of L. peruvianum var. humifusum and L. peruvianum var. glandulosum and L. esculentum. These bridge line x L. peruvianum hybrids could be crossed with L. esculentum to introgress genes from L. peruvianum into L. esculentum.     

An analysis of the B genome speciesArachis batizocoi (Fabaceae)

Arachis batizocoi Krap. & Greg. is a suggested B genome donor to the cultivated peanut,A. hypogaea L. Until recently, only one accession of this species was available in U.S.A. germplasm collections for analyses and species variability had not been documented. The objective of this study was to determine the intraspecific variability ofA. batizocoi to better understand phylogenetic relationships in sect.Arachis. Five accessions of the species were used for morphological and cytological studies and then F₁ intraspecific hybrids analyzed. Some variation was observed among accessions—for example, differences in seed size, plant height and branch length. The somatic chromosomes of accessions 9484, 30079, and 30082 were nearly identical, whereas, the karyotypes of accessions 30081 and 30097 have several distinct differences. For example, 30081 had significantly more asymmetrical chromosomes 2 and 6 and more median chromosomes 7 and 10, and 30097 had significantly more asymmetrical chromosomes 3 and 10 and more median chromosomes 1 and 5 than accessions 9484, 30079, and 30082. All F₁ hybrids among accessions were highly fertile. Meiotic observations indicated that hybrids among accessions 9484, 30079, or 30082 had mostly bivalents. However, quadrivalents were observed when either 30081 or 30097 was crossed with the above three accessions and 30081 × 30097 had quadrivalents, hexavalents and octavalents. The presence of translocations is the most likely cause of multivalent formation inA. batizocoi hybrids. Cytological evolution via translocations has apparently been an important mechanism for differentiation in the species.Paper No. 12382 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, NC 27695-7643.