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.     

An apomictic polyhaploid obtained from a pearl millet x Pennisetum squamulatum apomictic interspecific hybrid

Summary In a research program to transfer apomixis from Pennisetum squamulatum Fresen to pearl millet, P. americanum L. Leeke, a polyhaploid plant (2n=21) was discovered in the uniform open-pollinated progeny of an apomictic interspecific hybrid (2n = 41) between pearl millet and P. squamulatum. The polyhaploid was shorter, less vigorous and was smaller morphologically than its maternal parent. It probably originated by parthenogenetic development of a reduced gametophyte in the apomictic interspecific hybrid. The most common metaphase I chromosome association in the polyhaploid was 4 bivalents plus 13 univalents. Irregular chromosome distribution, tripolar spindles, bridges and fragments were observed at anaphase I and telophase I. The polyhaploid was male-sterile and partially female- fertile having multiple aposporous embryo sacs in 95% of the ovules. Seed set was 3% when open-pollinated and 33% when pollinated with pearl millet pollen. Low seed set was due to competition among multiple embryos developing in the same ovule. Seventeen progeny from seed produced under open-pollination on the polyhaploid each had 2n=21 chromosomes and were morphologically uniform and identical to the female parent. The expression of obligate apomixis in the polyhaploid conditioned by the P. squamulatum genome between the simplex and duplex condition indicates that apomictic reproduction is possible in nonpolyploid plants.     

Single cross alfalfa (Medicago sativa L.) hybrids produced via 2n gametes and somatic chromosome doubling: experimental and theoretical comparisons

Summary The potential breeding value of 2n gametes from diploid alfalfa (2n = 2x = 16) was tested by comparing single cross alfalfa hybrids produced via 2n = 2x gametes from diploids versus n = 2x gametes from somatic-chromosome-doubled, tetraploid counterparts. Three diploid clones, designated 2x-(rprp), homozygous for the gene rp (conditions 2n gamete formation by a first division restitution mechanism) were colchicine-doubled to produce their tetraploid counterparts, designated 4x-(SCD). These six clones were crossed as males to the same cytoplasmic male sterile clone. Yield comparisons of progeny from the six clones demonstrated a significant yield increase of the hybrid progeny from 2n = 2x gametes from the diploids over the hybrid progeny from n = 2x gametes from the chromosome doubled tetraploid counterparts. The yield gain ranged from a 12% increase to a 32% increase. Theoretical comparisons indicated the 2n = 2x gametes from diploids would have 12.5 to 50% more heterozygous loci, on average, than the n = 2x gametes derived from somatic doubling. These results confirm the importance of heterozygosity on alfalfa yield, and the results demonstrate that 2n gametes formed by first division restitution offer a unique method for producing highly heterotic alfalfa hybrids.     

Cytological studies on diploid and polyploid taxa of the genus Pennisetum Rich

The cytology of thirteen taxa and two hybrids in the genus Pennisetum indicated the distribution of the taxa among the four basic chromosome numbers 5, 7, 8 and 9. The diploid nature of P. ramosum and P. typhoides and the genomic allotetraploid status of P. purpureum was further confirmed. P. massaicum (2n=32), P. orientale (2n=36) and P. subangustum (2n=36) suggested probable autotetraploid nature and the three hexaploids (2n=54) investigated (P. polystachyon, P. longistylis and P. squamulatum) revealed allohexaploid constitution. The natural triploid, P. ruppellii (2n=27) and pentaploid P. villosum (2n=45) were found to be apomicts and they were allotriploid and allopentaploid respectively. The tetraploid-hexaploid complex of P. pedicellatum showed them to be cytotypes only. The cytogenetical behaviour of the hybrid, P. typhoides x P. purpureum with 2n=21 and the trispecies hybrid (P. typhoides x P. purpureum) x P. squamulatum with 2n=48 brought out the homology within the genomes of x=7 and x=9 and also between the genomes with x=7 and x=9. The significance of the inter- and intragenomic chromosome pairing had been brought out from the interspecific hybrids and the natural allotriploid and allopentaploid species having one genome in the haploid condition.The morphological sections of this genus did not correspond with the cytological groups. A high degree of evolutionary specialization was evident in species of the section Gymnothrix. A complete series of polyploids and high degree of heterogeneity from the morphological point of view was brought out in species with x=9.     

A dynamic evolution of chromosome in subgenus Potamogeton revealed by physical mapping of rDNA loci detection

In this study, we analyzed 12 species in the subgenus Potamogeton (8 tetraploids and 2 diploids, 2 putative tetraploid hybrids) at the chromosomal level, including counting the chromosome number and physically mapping the rDNA. The extent of variation in the chromosome number and rDNA loci was determined in the Potamogeton species on both the inter- and intra-specific level. Moreover, one of the hybrid sets (P. perfoliatus ♂?×?P. wrightii ♀) was picked for performing artificial pollination for producing F1 generation adults and for sequential morphological character analysis and FISH detection. After comparing the parental species and natural hybrids from three different geographic locations, the intraspecific variations of rDNA loci were revealed in sampled plants; in addition, comparisons between artificial F1 and natural hybrids (P.?×?intortusifolius) showed a rapid change of 45S rDNA loci in response to the interspecific hybridization. We also compared our results concerning rDNA patterns with phylogenetic documents to derive complementary clues to karoytype evolution and interspecific relationships. Based on frequent hybridizations and active clonal reproduction with weak genetic selection, the rDNA chromosomal repatterning, such as the gain or loss of rDNA loci together with rDNA movements, might be one trend of chromosome evolution in this genus.     

Gametes with somatic chromosome number and their significance in interspecific hybridization in Fuchsia

Sexual polyploidization has both a theoretical as well as an applied significance. Morphological screening for large pollen grains and shape of pollen produced by the individual, cytological investigation of hybrid progeny, and unbalanced separation of chromosomes at anaphase I in pollen mother cells were used to detect the gametes with somatic chromosome number in Fuchsia. The interspecific hybrids of F. fulgens (sect. Ellobium) × F. magellanica (sect. Quelusia), F. fulgens (sect. Ellobium) × F. splendens (sect. Ellobium), and F. triphylla (sect. Fuchsia) × F. splendens (sect. Ellobium) produced at the University of Auckland, New Zealand, showed both large and normal pollen grains in the same anther indicating the presence of unreduced gametes. Cytological investigation carried out on the hybrid progeny of F. fulgens (diploid, 2n=22, sect. Ellobium) × F. magellanica (tetraploid, 2n=44, sect. Quelusia) and F. triphylla (diploid, sect. Fuchsia) × F. arborescens (diploid, sect. Schufia) revealed unexpected chromosome numbers of 2n=44 and 2n=33, respectively. In general, the hybrids showed low fertility caused by genetically unbalanced gametes resulted from random disjunction of chromosomes at anaphase I. Studies on meiosis together with the presence of different shapes and sizes of pollen grains in Fuchsia proved indirectly that unreduced gametes are the products of first division meiotic nuclear restitution. These unreduced gametes were viable irrespective of pollen shape, their predominance in the hybrids, nuclear DNA amount and species phylogenetic position.     

Reproductive interactions between hybridizing irises: analyses of pollen-tube growth and fertilization success

Pollen-tube growth and seed siring ability were measured in crosses between the Louisiana iris species Iris fulva and Iris hexagona and their F₁ and F₂ hybrids. Flowers of the parental species were pollinated with self, outcross intraspecific, and interspecific pollen. Pollen-tube lengths were similar for all three pollen types in I. fulva, but in I. hexagona interspecific pollen tubes were longer than intraspecific pollen tubes. Pollen-tube lengths also differed for F₁ and F₂ flowers pollinated with I. fulva, I. hexagona, and hybrid pollen. For both hybrid classes I. fulva pollen tubes were the shortest while pollen tubes from I. hexagona and hybrids grew the furthest. Mixtures of genetically marked pollen were used to assess the seed siring ability of intra- and interspecific pollen in the parental species by varying the proportion of each pollen type in a replacement series design. For both species, the observed proportions of hybrid seeds were lower than the expected based on the frequency of each pollen type in the mixtures across all treatments. Flowers of I. fulva produced less than 10% hybrid progeny even when 75% of the pollen applied to stigmas was derived from interspecific flowers. The frequency of hybrid seed formation was somewhat greater in I. hexagona, but was still significantly lower than expected across all mixture treatments. Seed set per fruit remained constant across the mixture treatments for both species, but in I. fulva fruit set decreased with an increase in the proportion of interspecific pollen. The data indicate that both pre- and postfertilization processes contribute to discrimination against hybrid seed formation.     

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     

Introgressive hybridization between a native and an introduced species:Viola lutea subsp.Sudetica versusV. Tricolor

A hybrid swarm betweenViola lutea subsp.sudetica (2n=50, native species) andViola tricolor (2n=26, introduced species) originated in the 1970’s in the Krkono?e Mts. Analyses of chromosome numbers, reproductive biology, morphology, and ecology gave the following results: (1) Compared to the plants found in the 1970’s, the number of colour morphs have decreased and the types now prevailing in the field are morphologically closer toV. lutea subsp.sudetica, forming a continuum. (2) In the field, hybrids having approximately the same chromosome number as the primary hybrids are most common. Some plants of the hybrid swarm have certain characters unknown to their parents. (3) In the field, autogamous types similar toV. tricolor were found. (4) A limited number of plants from the field and culture have higher somatic chromosome numbers thanV. lutea subsp.sudetica; there was a tendency towards increasing chromosome numbers in their progeny (up to 2n=62). These plants have some new morphological characters (a small proportion of hexacolpate pollen) not found in the parents (nor in the other hybrids with prevailing tetracolpate and pentacolpate pollen grains) and higher pollen fertility in comparison to the other hybrids. These plants also have the highest germination rate. (5) There is a tendency for chromosome numbers to decline in the progeny of open pollinated hybrid plants in the lowland experimental graden. (6) The phenology of the plants in the mountain grasslands and the lowland garden is different; the parents behave in a totally contrasting manner. (7) In the field at least some hybrids extend outside the geographical and ecological ranges of the parental species, invading new communities. (8) Seeds ofV. tricolor do not show any dormancy and germinate in the year of production; most of theV. lutea subsp.sudetica seeds germinate during the spring of the following year. Hybrids with intermediate chromosome numbers had both types of germination strategy. The germination rate of intermediates with high chromosome numbers was even higher than that ofV. tricolor.     

Intergeneric hybridization between Diplotaxis siettiana and crop brassicas for the production of alloplasmic lines

Summary Intergeneric hybrids were produced between Diplotaxis siettiana and Brassica campestris through embryo rescue. The hybrids were completely pollen sterile and backcrosses with pollen of B. campestris did not yield any seeds. Induction of colchiploidy restored pollen fertility and backcross pollinations yielded viable seeds. Cytological details of the hybrid, amphidiploid and backcross progenies were studied. Both pollen-sterile and pollen-fertile plants have been obtained in backcross 2 progeny. This hybrid (D. siettiana x B. campestris) was used as a bridge cross to transfer the cytoplasm of D. Siettiana to two other incompatible cultivars of Brassica — B. juncea and B. napus. Pollinations of the amphidiploid (D. siettiana x B. campestris, 2n = 36) with pollen of B. juncea/B. napus readily produced seeds without embryo rescue. These hybrids were grown to flowering and their cytological details were studied. Seeds have been produced from backcross pollinations of both these hybrids with the pollen of the respective cultivars. The results clearly show the feasibility of producing alloplasmic lines in all the three oilseed brassicas.     

Cytogenetic studies in Cyclamen persicum, C. graecum (Primulaceae) and their hybrids

Haploids, diploids and tetraploids of Cyclamen persicum (2n=x=24, 2x=48 and 4x=96), C. graecum (2n=84) and their interspecific hybrids (2n=45, 3x=66, 4x=90) were analyzed cytologically. The mean chromosome association per PMC at diakinesis or at metaphase I in meiosis was 23.29–23.39 I + 0.31–0.36 II in C. persicum (x), 0.17–0.23 I + 23.88–23.92 II in C. persicum (2x), 0.52–1.18 I + 46.39–46.78 II + 0.03–0.09 III + 0.41–0.48IV in C. persicum (4x) and 0.40–0.46I + 41.34–41.63 II + 0.02 III + 0.07–0.21IV in C. graecum. The mean chromosome association per PMC at diakinesis or at metaphase I was 0.47–0.62 I + 44.69–44.76 II in the hybrid (2n=90) of C. persicum (4x) × C. graecum, 38.48–42.50 I + 1.27–3.26 II in microspore-derived plants (2n=45) from the hybrid (2n=90) by anther culture and 26.22–26.67 I + 19.67–19.89 II in the hybrid (2n=66) of C. persicum (2x) × C. graecum. The results indicate that C. graecum is an autotetraploid, the hybrid (2n=4x=90) is an amphidiploid, the microspore-derived plant (2n=45) is a polyhaploid and the hybrid (2n=3x=66) is a sesquidiploid. Based on studies of meiosis, the ploidy levels and the origin of C. graecum and C. persicum are discussed in comparison with several species in the genus Cyclamen.     

Uniparental chromosome elimination at mitosis and interphase in wheat and pearl millet crosses involves micronucleus formation, progressive heterochromatinization, and DNA fragmentation

Complete uniparental chromosome elimination occurs in several interspecific hybrids of plants. We studied the mechanisms underlying selective elimination of the paternal chromosomes during the development of wheat (Triticum aestivum) x pearl millet (Pennisetum glaucum) hybrid embryos. All pearl millet chromosomes were eliminated in a random sequence between 6 and 23 d after pollination. Parental genomes were spatially separated within the hybrid nucleus, and pearl millet chromatin destined for elimination occupied peripheral interphase positions. Structural reorganization of the paternal chromosomes occurred, and mitotic behavior differed between the parental chromosomes. We provide evidence for a novel chromosome elimination pathway that involves the formation of nuclear extrusions during interphase in addition to postmitotically formed micronuclei. The chromatin structure of nuclei and micronuclei is different, and heterochromatinization and DNA fragmentation of micronucleated pearl millet chromatin is the final step during haploidization.     

Fertile allotetraploid from the cross betweenPhaseolus coccineus L. andPhaseolus acutifolius A. Gray

Summary As somatic hybridization and genetic transformation are not yet applicable to beans, a programme of hybridization between a male sterile line ofP. coccineus and a wild genotype ofP. acutifolius var.tenuifolius was carried out in order to introduce useful characters from the wild parent into the genome of the cultivated species. This interspecific cross is of particular interest sinceP. acutifolius is a source of resistance to many diseases, drought and high temperature. The difficulties in producing these hybrids were overcome by repeated pollinations and with the help of embryo culture. The F₁ hybrid shows a high sterility which may be explained by the poor pollen quality and the presence of a chromosomic asynapsis at meiosis. Fertile allotetraploids (Co) were successfully produced in progeny from colchicine treated cuttings of F₁ hybrids. Several (C₂) mature seeds were harvested from selfed allotetraploid plants.Abbreviations Co initial allotetraploid plants - C₁, C₂ first and second allotetraploid generation - PMC pollen mother cell     

Cytogenetics of pearl millet

Summary The somatic karyotype of pearl millet Pennisetum americanum (L.) Leeke. (2n = 14) has been studied in several cultivars, but few cytological markers have been discovered which could help in the easy identification of the chromosomes. Analysis of pachytene bivalents permits such identification but is feasible only in a few cultivars. Recently, several lines having telocentric chromosomes have been produced and classified but their potentialities as cytogenetic tools have yet to be explored. Some African populations of pearl millet carry B-chromosomes in their karyotype. Cytogenetics of B-chromosomes has been reported in great detail. Bs undergo spontaneous changes to produce deficient- and iso-chromosomes. The main effect of B-chromosomes is on chiasma frequency which is exerted by the relative amounts of chiasma promoting euchromatin and the chiasma depressing heterochromatin in the Bs. Haploid plants occur occasionally and sometimes show a low degree of seed set, offering a possibility of establishing homozygous inbred lines. Cytogenetics of several spontaneous and induced autotetraploids have been reported. In general quadrivalent formation between the seven sets of four homologues was random. Seed set of the autotetraploids could be improved by selection; improved seed fertility was found to be associated with increased chiasma frequency, increased quadrivalent frequency and regular distribution of chromosomes at anaphase I. Genes controlling morphological characters of plant phenotype segregate independent of those controlling fertility and in pearl millet polyploidy per se is not limiting to plant vigour. Primary trisomics represent the best studied among the aneuploids of pearl millet. All the seven primary trisomics have been identified and described. Some were used in assigning genes to specific chromosomes but in general trisomies have poor vigour and fertility, and show low frequency of transmission. Apart from B-chromosomes, cytogenetics of interchanges has been the best studied aspect of pearl millet. The frequency of co-orientation of an interchange complex at metaphase I, which determines the fertility or sterility of the interchange heterozygote, is influenced by the genetic background and thus is theoretically amenable for selection leading to improved fertility of the heterozygote. Interchange tester-stocks have been assembled which can be used to identify the chromosomes involved in any newly obtained interchange. A complex interchange line involving all the chromosomes of the complement has also been produced, but the ring-of-fourteen produces total male and female sterility.Genotypic control of mitosis and meiosis has been reported, with reference to chromosome numerical mosaicism, multiploid sporocytes, desynapsis and chromosome fragmentation, and male sterility. Pearl millet being a largely outbreeding species, forced inbreeding was mainly found to result in loss of morphological vigour and reduction in mean chiasma frequency per PMC. Interspecific hybrids between pearl millet and several related species have been cytologically investigated and homology of the seven chromosomes of pearl millet with seven of the fourteen chromosomes of P. purpureum has been demonstrated. Cytogenetic evidence from haploids, autopolyploids and interspecific hybrids has indications to suggest that the haploid number of x = 7 is derived from x = 5, but the evidence is inconclusive and needs critical evaluation.     

Chromosomal inheritance of parental rDNAs distribution pattern detected by FISH in diploid F1 hybrid progeny of Cobitis (Teleostei,Cobitidae) species has non-Mendelian character

This study was conducted to describe the major and the minor rDNA chromosome distribution in the spined loach Cobitis taenia (2n = 48) and the Danubian loach Cobitis elongatoides (2n = 50), and their laboratory-produced diploid reciprocal F₁ hybrid progeny. It was tested by fluorescence in situ hybridisation (FISH) whether the number of 28s and 5s rDNA sites in the karyotypes of diploid hybrids corresponds to the expectations resulting from Mendelian ratio and if nucleolar organiser regions (NOR)were inherited from both parents or nucleolar dominance can be observed in the induced F₁ hybrid progeny. Ten (females) or twelve (males) 28s rDNA loci were located in nine uniarm chromosomes of C. taenia. Two of such loci terminally bounded on one acrocentric chromosome were unique and indicated as specific for this species. Large 5s rDNA clusters were located on two acrocentric chromosomes. In C. elongatoides of both sexes, six NOR sites in terminal regions on six meta-submetacentric chromosomes and two 5s rDNA sites on large submetacentrics were detected. The F₁ hybrid progeny (2n = 49) was characterised by the intermediate karyotype with the sites of ribosome synthesis on chromosomes inherited from both parents without showing nucleolar dominance. 5s rDNA sites were detected on large submetacentric and two acrocentric chromosomes. The observed number of both 28s and 5s rDNAs signals in F₁ diploid Cobitis hybrids was disproportionally inherited from the two parental species, showing inconsistency with the Mendelian ratios. The presented rDNA patterns indicate some marker chromosomes that allow the species of the parental male and female to be recognised in hybrid progeny. The 5s rDNA was found to be a particularly effective diagnostic marker of C. elongatoides to partially discern genomic composition of diploid Cobitis hybrids and presumably allopolyploids resulting from their backcrossing with one of the parental species. Thus, the current study provides insight into the extent of rDNA heredity in Cobitis chromosomes and their cytotaxonomic character.     

Experimental analyses of the evolutionary processes inTrillium

In the Japanese species ofTrillium examined here, every interspecific cross produced healthy F₁ progeny at the rate of about 50 to 60 per cent of the total inborn ovules except forT. hagae. These figures were not appreciably different from those of self-pollinated or sib-mated examples of these species.Trillium hagae, a putative natural hybrid betweenT. kamtschaticum (2n=10) andT. tschonoskii (2n=20), accepted all foreign sources of pollen grains in manual pollination. These and other crossing experiments suggest that no appreciable barrier has developed that might cause interspecific crossability and that they are habitual inbreeders. Despite theri crossability, a very low rate of actual pollen flow was detected by examining electrophoretic phenotypes of seeds taken from sympatric populations of these species.     

Reproduction of Belonolaimus longicaudatus,Meloidogyne javanica,Paratrichodorus minor,and Pratylenchus brachyurus on Pearl Millet (Pennisetum glaucum)

Pearl millet (Pennisetum glaucum) has potential as a grain crop for dryland crop production in the southeastern United States. Whether or not pearl millet will be compatible in rotation with cotton (Gossypium hirsutum), corn (Zea mays), and peanut (Arachis hypogaea) will depend, in part, on its host status for important plant-parasitic nematodes of these crops. The pearl millet hybrid ''TifGrain 102'' is resistant to both Meloidogyne incognita race 3 and M. arenaria race 1; however, its host status for other plant-parasitic nematodes was unknown. In this study, the reproduction of Belonolaimus longicaudatus, Paratrichodorus minor, Pratylenchus brachyurus, and Meloidogyne javanica race 3 on pearl millet (''HGM-100'' and TifGrain 102) was compared relative to cotton, corn, and peanut. Separate greenhouse experiments were conducted for each nematode species. Reproduction of B. longicaudatus was lower on peanut and the two millet hybrids than on cotton and corn. Reproduction of P. minor was lower on peanut and TifGrain 102 than on cotton, corn, and HGM-100. Reproduction of P. brachyurus was lower on both millet hybrids than on cotton, corn, and peanut. Reproduction of M. javanica race 3 was greater on peanut than on the two millet hybrids and corn. Cotton was a nonhost. TifGrain 102 was more resistant than HGM-100 to reproduction of B. longicaudatus, P. minor, and M. javanica. Our results demonstrated that TifGrain 102 was a poor host for B. longicaudatus and P. brachyurus (Rf < 1) and, relative to other crops tested, was less likely to increase densities of P. minor and M. javanica.     

Interspecific hybridization of perennial Medicago species using ovule-embryo culture

Summary New interspecific hybrids between alfalfa (Medicago sativa L.) and several perennial Medicago species were obtained by embryo rescue techniques. The methodology, designated ovule-embryo culture, involved preculturing the fertilized ovule (10 to 20 days post-pollination) for a period of six to 12 days followed by excision and direct culture of the embryo. Placement of the hybrid embryo directly onto culture medium without the interim ovule culture was unsuccessful. Ovule culture to germination without removing the embryo also was unsuccessful. Ovule-embryo culture was essential for recovering interspecific hybrids between diploid alfalfa (2n=2x=16) and the following diploid (2n=2x=16) species: M. hybrida Traut., M. marina L., M. papillosa Boiss., M. rhodopea Velen. and M. rupestris M.B. In addition, trispecies hybrids between M. sativa x M. dzhawakhetica Bordz. F₁ hybrids (2n=3x=24) and either M. cancellata M.B. (2n=6x=48) or M. saxatilis M.B. (2n=6x=48) were obtained from ovuleembryo culture. Media manipulations using M. sativa x M. rupestris F₁ and first backcross generation embryos demonstrated the optimum concentration of 12.5 mM NH₄ ⁺ for successful embryo rescue; ammonium salt formulation (whether chloride, nitrate or sulfate) was not critical. From a few thousand crosses, hybrids between M. sativa and either M. rhodopea or M. rupestris were recovered relatively efficiently with 157 and 66 hybrids, respectively. However, only 13 hybrids between M. sativa and M. papillosa were obtained from more than 2,000 crosses, and just two hybrids each have been recovered from the combinations M. sativa x M. hybrida and M. sativa x M. marina from 2,000 to 3,000 crosses. The predominant chromosome number between diploid alfalfa and the other diploid perennial species was 2n=2x=16. Morphology of the hybrids was generally intermediate. Electrophoretic analysis of the F₁ hybrids and parental clones on uniform or gradient polyacrylamide gels demonstrated that peroxidase phenotypes could be used to confirm hybridity. For all interspecific combinations there was at least one peroxidase isozyme unique to the wild species that was present in the F₁ interspecific hybrid.