BREEDING SYSTEM OF A HYBRID BETWEEN A SEXUAL AND AN APOMICTIC SPECIES OF AMELANCHIER,SHADBUSH (ROSACEAE,MALOIDEAE)

Amelanchier bartramiana, which has been shown to be sexual and self-incompatible, and A. laevis, in which apospory and self-compatibility occur, grow in a mixed population in western Maine. Also present there is the putative interspecific hybrid, A. × neglecta. Principal components and canonical discriminant analyses of seven morphological characters from 96 parental and putative hybrid individuals substantiate morphological intermediacy of the hybrids. A Nomarski differential interference microscopy study of megasporogenesis and megagametogenesis in five hybrid plants shows a predominantly aposporous mode of reproduction, and controlled pollinations indicate that seed formation between A. bartramiana and A. laevis is possible and that the hybrids are self-compatible. The hybrids, which are tetraploids (n = ca. 34) like both parents in Maine, produce viable pollen and seed, but there is little evidence for backcrossing with either parent.     

THE INCIDENCE AND EFFECTS OF HYBRIDIZATION BETWEEN CULTIVATED RICE AND ITS RELATED WEED RED RICE (ORYZA SATIVA L.)

The objectives of this study were (1) to determine if hybridization occurs naturally between cultivated rice and a closely related weed, red rice (both Oryza sativa L.) and (2) to determine the incidence of hybridization and possible convergence of red rice with cultivated rice. Both morphological and electrophoretic characters were used to confirm the existence of hybrids. A total of 12,000 seeds were collected from red rice plants from fields of six different rice cultivars and sown in a common garden. Hybrids were generally taller and had longer, wider flag leaves than either red rice or cultivated rice. In addition, hybrids produced more tillers than red rice. Overall, hybrids were vegetatively robust plants, demonstrating heterosis and expressing morphological characteristics of both parents. That these plants were hybrids was confirmed by the existence of electrophoretic banding patterns common to both synthetic and natural hybrids. The incidence of hybridization was estimated as the percentage of hybrids found in red rice populations while morphological characteristics were used to test for convergence. Percentage hybridization ranged from 1% in the Lemont cultivar to 52% in the Nortai variety. The greater number of hybrids found in the Nortai variety was attributed to a later flowering time of this variety and the overlap of its flowering time with that of the F₁ hybrids. F₁ hybrids were observed to flower later than either red rice or the early season varieties of cultivated rice. Thus, early season varieties have a temporal separation in flowering time from the F₁ hybrids that prevents back crossing. Unlike the other hybrids that were vegetatively robust, Nortai hybrids were less robust and more similar to the cultivar. These results suggest that later season cultivars may have a higher incidence of hybridization and introgression with red rice and that this may lead to morphological convergence of the weed toward the crop. Convergents were observed in the Nortai variety. Hybridization between cultivated and red rice has the potential to increase the adaptability of red rice populations by promoting genetic diversity.     

Transgenic insect-resistant maintainer line (IR68899B) for improvement of hybrid rice

Heterosis has helped to increase rice yield in F₁ hybrids by 15–20% beyond the level of inbred semidwarf varieties. For stable yield performance rice hybrids must also possess genetic resistance to biotic stresses. One of these, stem borer, reduces the expected yield of hybrid rice. The truncated synthetic cryIA(b) gene from Bacillus thuringiensis is known to be effective in controlling stem borer. The development of transformation techniques has provided the technology for incorporating this bacterial gene into the rice genome, which has not been possible by conventional breeding methods. We have introduced a new approach of using a transgenic maintainer line for developing an insect-resistant hybrid rice. An elite IRRI maintainer line (IR68899B) has been transformed with the cryIA(b) gene driven by the 35S constitutive promoter using the biolistic method. The integration and expression of the cryIA(b) gene could be demonstrated through Southern and Western blot analyses that have been carried out so far up to the T₂ generations. Insect bioassay data showed an enhanced resistance to yellow stem borer in the Bt ⁺ transgenic plants. This is the first report of the development of a transgenic maintainer line for use in hybrid rice improvement. Received: 17 December 1997 / Revision received: 23 June 1998 / Accepted: 25 September 1998     

Analysis of mitochondrial DNA from somatic hybrid cell lines of Saccharum officinarum (sugarcane) and Pennisetum americanum (pearl millet)

Mitochondrial DNA (mtDNA) from cell suspension cultures of two intergeneric somatic hybrids of Pennisetum americanum (pearl millet) + Saccharum officinarum (sugarcane) was examined by restriction endonuclease digestion and hybridization with sorghum mtDNA cosmids. The mtDNA of one somatic hybrid was indistinguishable from that of pearl millet, while the second exhibited a combination of parental mtDNAs, suggesting mitochondrial fusion. Several novel, possibly recombinant, mtDNA restriction fragments were detected in this hybrid, which may have resulted from intergenmic recombination.Florida Agriculture Experiment Station Journal Series No: 8090.     

Field Performance of Transgenic indica Hybrid Rice with Improved Cooking and Eating Quality by Down-regulation of Wx Gene Expression

High amylose content (AC) in rice endosperm is correlated with poor grain quality, particularly in indica hybrid rice. We have generated several homozygous transgenic parent lines of indica hybrid rice carrying an antisense Waxy (Wx) gene and demonstrated that the AC in seeds of these lines decreased dramatically. Two transgenic maintainer lines (L25B and L18B), derived from one of the key maintainer parents of an indica hybrid rice in China, Long-te-fu B (LTF-B), were selected and the antisense Wx gene was subsequently introgressed into the male-sterile counterpart, LTF-A, with the aim to generate improved indica hybrids. The indica hybrids derived from the selected transgenic male-sterile lines and restorer lines were tested for quality and agronomic performance under normal field conditions. Our results demonstrated that the reduction of AC in the homozygous transgenic maintainer lines stably passed down in five successive generations and the improved quality was also found in their relevant transgenic hybrids produced. The other two key characters of rice cooking and eating quality, the gel consistence (GC) and gelatinization temperature (GT), were also improved in the grains of both the transgenic maintainer lines and their relevant hybrids. In addition, no change was observed for most of the agronomic characters of the transgenic maintainer lines and the relevant transgenic hybrids. Although the grain weight of the transgenic line was reduced, the grain yield of the homozygous transgenic parent lines and the transgenic hybrids was similar when compared with that of the wild-type controls. These results suggest that transgenic approaches are an effective way to obtain rice lines with both improved qualities and high yield, especially for indica hybrid rice.     

Acrylamide gel electrophoresis of seed proteins from someSolanum (sectionSolanum) species

Polyacrylamide gel electrophoresis was used to investigate the seed proteins of 36 accessions belonging toSolanum sect.Solanum (Solanaceae). These accessions represented 20 species, of four differing ploidy levels, and included infraspecific morphological variants. The resultant band patterns tended to reflect the morphological differences and genetical isolation displayed by many of the species. The most variable band patterns were encountered in the taxa with the greatest infraspecific variation, while many of the more morpho-genetically distinct taxa seemed to have species-specific band patterns.Good matches were found between the band patterns of artificial hybrids, those of their known parents, and mixtures of the parental protein extracts. This illustrates the potential use of such a technique for pinpointing possible genome donors of natural hybrids, and especially of polyploids. These comparative band patterns confirmed experimental work on the origin of the hexaploidS. nigrum from the diploidS. americanum and the tetraploidS. villosum, and also supported the suggestion thatS. nigrum contains two genomes from the diploidS. sarrachoides, but not four genomes of the diploidS. americanum.     

Molecular mapping and candidate gene identification of the Rf2 gene for pollen fertility restoration in sorghum [Sorghum bicolor (L.) Moench]

The A1 cytoplasmic–nuclear male sterility system in sorghum is used almost exclusively for the production of commercial hybrid seed and thus, the dominant genes that restore male fertility in F₁ hybrids are of critical importance to commercial seed production. The genetics of fertility restoration in sorghum can appear complex, being controlled by at least two major genes with additional modifiers and additional gene–environment interaction. To elucidate the molecular processes controlling fertility restoration and to develop a marker screening system for this important trait, two sorghum recombinant inbred line populations were created by crossing a restorer and a non-restoring inbred line, with fertility phenotypes evaluated in hybrid combination with three unique cytoplasmic male sterile lines. In both populations, a single major gene segregated for restoration which was localized to chromosome SBI-02 at approximately 0.5 cM from microsatellite marker, Xtxp304. In the two populations we observed that approximately 85 and 87% of the phenotypic variation in seed set was associated with the major Rf gene on SBI-02. Some evidence for modifier genes was also observed since a continuum of partial restored fertility was exhibited by lines in both RIL populations. With the prior report (Klein et al. in Theor Appl Genet 111:994–1012, 2005) of the cloning of the major fertility restoration gene Rf1 in sorghum, the major fertility restorer locus identified in this study was designated Rf2. A fine-mapping population was used to resolve the Rf2 locus to a 236,219-bp region of chromosome SBI-02, which spanned ~31 predicted open reading frames including a pentatricopeptide repeat (PPR) gene family member. The PPR gene displayed high homology with rice Rf1. Progress towards the development of a marker-assisted screen for fertility restoration is discussed.     

Morphological and genetic evidence of contemporary intersectional hybridisation in Mediterranean Helichrysum (Asteraceae,Gnaphalieae)

Hybridisation is considered an important evolutionary phenomenon in Gnaphalieae, but contemporary hybridisation has been little explored within the tribe. Here, hybridisation between Helichrysum orientale and Helichrysum stoechas is studied at two different localities in the islands of Crete and Rhodes (Greece). Using three different types of molecular data (AFLP, nrDNA ITS sequences and cpDNA ndhF sequences) and morphological data, the aim is to provide simultaneous and direct comparisons between molecular and morphological variation among the parental species and the studied hybrid populations. AFLP profiles, ITS sequences and morphological data support the existence of hybrids at the two localities studied, shown as morphological and genetic intermediates between the parental species. Chloroplast DNA sequences show that both parental species can act either as pollen donor or as maternal parent. Fertility of hybrids is demonstrated by the viability of seeds produced by hybrids from both localities, and the detection of a backcross specimen to H. orientale. Although there is general congruence of morphological and molecular data, the analysis of morphology and ITS sequences can fail to detect backcross hybrids.     

Yield and morpho-agronomical evaluation of food-grade white sorghum hybrids grown in Southern Italy

Abstract

Grain sorghum [Sorghum bicolor (L.) Moench] is a gluten-free grain that is gaining attention as a food crop that can be used in the management of celiac disease. At present, sorghum is widely grown in many semiarid regions of the world. New food-grade sorghum cultivars are of particular interest in Mediterranean countries due to improved quality characteristics and gluten-free status of the grains. Until now very few studies have examined the grain yield (GYLD) and agronomic performance characteristics of food-grade sorghum hybrids in Italy. A 2 year study was conducted to evaluate the agronomic performance of eight food-grade sorghum hybrids representing different maturity classes in trials conducted in Southern Italy. The results showed wide variation in adaptation of these hybrids as measured by differences in GYLD (2.35–8.50 t ha^?1) and other pheno-morphological characteristics. Of particular interest was the fact that many of the early-flowering hybrids (e.g. SP-X303) performed better than the later-flowering hybrids (e.g. ArchX-02). These results demonstrated that flowering time of hybrid and crop cycle length are important factors to consider in selecting cultivars for production in the Mediterranean region.     

Establishment of somatic hybrid cell lines between Zea mays L. (maize) and Triticum sect,trititrigia MacKey (trititrigia)

Summary Somatic hybrid cell lines were constructed by the fusion of protoplasts isolated from cell suspensions of Zea mays L. (maize, 2n = 20) and Triticum sect, trititrigia MacKey (trititrigia, 2n = 35), a perennial hybrid of T. durum Desf. and Elytrigia intermedium (Host) Nevski. Iodoacetamide-inactivated protoplasts of maize were fused with trititrigia protoplasts, which were sensitive to the PEG/DMSO fusion treatment at high pH and high calcium. Based on physiological complementation, approximately 0.002% of the total protoplasts cultured following fusion treatment developed into cell colonies, and 79 lines of them, almost a half, were singled out and subcultured. Among the subcultured lines three were, in comparison with the parents, identified as somatic hybrids by their coupled XbaI restriction patterns of total DNAs probed with the ribosomal DNA of rice. Southern analysis of the digested total DNAs with a mitochondrial gene, atpA., from pea, or a chloroplast gene, trnK, from rice, revealed that all the hybrids carried only the organellar DNAs of trititrigia, which excluded the possibilities of a chimeric callus or any DNA contamination. Cytogenetically, one hybrid was mixoploid with a 2n of 46–67 in which chromosomal endoreduplication, characterized by the appearance of diplochromosomes, was occasionally observed. Its hybridity was reconfirmed by the fact that it bore the satellite chromosomes of both maize and trititrigia, which were distinguishable from each other by size. In contrast, the other two hybrids were aneuploids. The potential of gene transfer between Zea and Triticum species was thus conclusively established.     

Identification of larch species (Larix decidua, Larix kaempferi and Larix X eurolepis) and estimation of hybrid fraction in seed lots by RAPD fingerprints

Species-specific RAPD markers were used to identify the different larch species (Larix decidua and Larix kaempferi) and their interspecific hybrid (Larix X eurolepis). Although morphological differences between pure species and the hybrids exist, differentiation is not always possible, especially at an early stage (seed or plantlet). Eleven RAPD markers differentiated the two larch species, and 4 species-specific markers were sufficient to estimate the F₁ hybrid fraction in a seed lot. The species-specific markers were tested on individual trees of European and Japanese larches of diverse geographic origins and on several seed lots of different origins (F₁, F₂ hybrids and pure species). The 4 specific markers found for the European larch and the Japanese larch were monomorphic and present in all provenances and in all F₁ hybrid trees tested. Polymorphic SCAR fragments were obtained for 3 of the 11 fragments originally selected for the RAPD screening phase. For 2 of them, the sequence had some homology with the mitochondrial genome of other organisms and is thus mitochondrial. The two mitochondrial fragments and the OPF-13₁₀₀₀ fragment exhibited one polymorphic band, thereby maintaining its species-specific identity: OPF-13₁₀₀₀ is specific to the European larch. The 4 RAPD primers selected in this study offer a reliable, quick and cheap tool for the identification of different larch species (Larix decidua and Larix kaempferi) and their interspecific hybrid (Larix X eurolepis). Received: 28 February 1999 / Accepted: 29 April 1999     

Nitrate Reductase Activity: A Biochemical Criterion of Hybrid Vigour in Sorghum bicolor (L.) Moench

F₁ hybrids of Sorghum bicolor (L.) Moench and their inbred parentswere analysed for NADH-nitrate reductase activity during theearly stages of seedling growth. In all the hybrids both mid-parentaland better parental heterosis were discernible in shoots whereasin roots two hybrids out of the three tested, showed heteroticlevels. It is suggested that in sorghum nitrate reductase activityduring seedling stages can be used as a biochemical criterionfor evaluating hybrid vigour. Sorghum bicolor (L.) Moench, sorghum, hybrid vigour, nitrate reductase     

Natural and experimental hybridization inArmeria (Plumbaginaceae):A. villosa subsp.carratracensis

An experimental crossing program was carried out in order to test the hypothesis thatArmeria villosa subsp.carratracensis, a serpentine endemic from Southern Spain, is of hybrid origin. Fruit-set and mainly pollen stainability data in artificial hybrids demonstrate that internal interspecific barriers are weak. Two generations of backcrossing with the two putative parents —A. colorata andA. villosa subsp.longiaristata— can restore pollen stainability to an average of 83.2 and 68.7, respectively. A morphometric analysis of 148 specimens belonging to parental species, different artificial hybrid generations and wild putative hybrid race shows that (1) morphological characters have a strong genetic basis and thus are good markers in identifying hybrids and introgression inArmeria; (2) artificial backcrossing produces in morphometrical characters a variation which conforms in both trend and magnitude to what is commonly attributed in the wild to introgression; (3) the position of the putative hybrid race is intermediate between the two parental species used in the program. These results are in accordance with the hypothesis of hybrid origin ofA. villosa subsp.carratracensis. Natural and experimental hybridization inArmeria, I     

Interspecific hybridization in natural populations ofCyrtandra (Gesneriaceae) on the Hawaiian Islands: Evidence from RAPD markers

Interspecific hybridization among Hawaiian species ofCyrtandra (Gesneriaceae) was investigated using randomly amplified polymorphic DNA (RAPD) markers. Thirty-three different primers were used to investigate interspecific hybridization for 17 different putative hybrids based on morphological intermediacy and sympatry with putative parental species. RAPD data provided evidence for the hybrid origin of all putative hybrid taxa examined in this analysis. However, the patterns in the hybrid taxa were not found to be completely additive of the patterns found in the parental species. Markers missing in the hybrid taxa can be attributed to polymorphism in the populations of the parental species and the dominant nature of inheritance for RAPD markers. Unique markers found within hybrid taxa require further explanation but do not necessarily indicate that the taxa are not of hybrid origin. The implications suggest that these interspecific hybridization events had, and continue to have, an effect on the adaptive radiation and conservation biology ofCyrtandra.     

Molecular and morphological evidence of hybridization between newts Triturus vulgaris and T. montandoni (Caudata: Salamandridae) in Slovakia

Natural hybridization and introgression is recorded between the newt species Triturus vulgaris and T. montandoni in Slovakia. To confirm a hybrid status of two putative hybrids, morphological and Randomly Amplified Polymorphic DNA (RAPD) markers specific for T. vulgaris and T. montandoni were used. The individuals found in Zbojská (Veporské vrchy Mts, Slovakia; analyzed morphologically and genetically) and Zubrohlava (Oravská kotlina basin, Slovakia; analyzed only morphologically) possessed markers of both species. Segregation of RAPD markers together with a model-based Bayesian analysis revealed that the specimen from Zbojská belonged to later generation hybrids.     

Associations between host plant concentrations of selected biochemical nutrients and Mexican rice borer,Eoreuma loftini,infestation

The Mexican rice borer, Eoreuma loftini (Dyar) (Lepidoptera: Crambidae), is an economic pest of sugarcane (Saccharum spp. hybrids) and other graminaceous host crops, and it attacks grassy weeds. Oviposition preference has been known to be for plants with leaves that form folds. This study is the first to associate the nutritional quality of crop and forage plant hosts with Mexican rice borer injury. Three experiments were conducted to determine the levels of selected biochemical nutrients, including free amino acids and sugars, in four grass weeds [barnyardgrass, Echinochloa crus‐galli (L.); broadleaf signalgrass, Urochloa platyphylla (Munro ex C. Wright); johnsongrass, Sorghum halepense (L.) Pers.; and Vasey's grass, Paspalum urvillei Steud.], a forage grass [sudangrass, Sorghum bicolor (L.) Moensch spp. drummondi (Nees ex Steud.) de Wet & Harlan], three crop species [maize, Zea mays L.; sorghum, Sorghum bicolor (L.) Moench; and sugarcane, Saccharum spp.], and a sorghum‐sudangrass forage hybrid (all Poaceae). Of 16 free amino acids detected among plants in the first two experiments, only high accumulations of free histidine in sudangrass and maize were associated with increased infestations by Mexican rice borer larvae. In all three experiments, high levels of fructose were associated with heightened Mexican rice borer infestation. Ramifications of these findings on the potential dispersal of this invasive pest in the USA and possible applications of fructose in baits are discussed.     

Morphological and molecular evidence of natural hybridization in Shorea (Dipterocarpaceae)

Shorea (Dipterocarpaceae) is a large genus in which many closely related species often grow together in Southeast Asian lowland tropical rain forests. Many Shorea species share common pollinators, and earlier studies suggested occurrence of interspecific hybridization and introgression. Here, we show morphological and molecular evidence of hybridization between Shorea species. In the census of all the trees of Shorea curtisii, Shorea leprosula, and Shorea parvifolia (>30 cm dbh) within the 164-ha area of Bukit Timah Nature Reserve in Singapore, we found 21 morphologically recognizable hybrid individuals. All of the putative hybrids could be distinguished obviously from the parental species on the basis of vegetative characters. Population genetic analysis of DNA sequences of two nuclear (GapC and PgiC) and chloroplast (trnL-trnF) regions demonstrated that each of the three species had several species-specific mutations. The nuclear sequences of the putative hybrids were heterozygote at all the species-specific sites between two parental species. Hybrid between S. curtisii and S. leprosula was found most, while S. curtisii × S. parvifolia and S. leprosula × S. parvifolia hybrids were also found. Almost no shared polymorphism between populations of the parental species suggests rarity of introgression. The study indicated that natural hybridization between sympatric Shorea species should not be uncommon, but all of the hybrid individuals were F₁, and the post-F₁ hybrids were considerably rare.     

Classification of rice germplasm: III. High-resolution fingerprinting of cytoplasmic genetic male-sterile (CMS) lines with AFLP

 The cytoplasmic genetic male-sterile (CMS) lines developed at the International Rice Research Institute are valuable in producing tropical rice hybrids. Efficient use of CMS lines in hybrid rice production will depend on their level of genetic diversity. Aside from morphological characterization, molecular analysis based on DNA markers can provide information on the genetic diversity of the germplasm. The Amplified Fragment Length Polymorphism (AFLP) technique was used to fingerprint 71 CMS lines and four rice cultivars, ‘IR64’, ‘Azucena’, ‘IR74’, and ‘FR13A’. Eleven primer pair combinations specific to the enzymes PstI and MseI were used to generate 530 AFLP markers, 176 of which were polymorphic. Each CMS line revealed a distinct fingerprint. The AFLP marker-based dendrogram depicted genetic variation among the CMS lines. The CMS lines developed in japonica background grouped with ‘Azucena’, a japonica cultivar. None of the CMS lines clustered with ‘FR13A’, a flood-tolerant traditional indica variety. ‘IR64’ was found to be distinct from the other indica CMS lines and clustered with lines developed in its background. The grouping of CMS lines into a few groups is useful for breeders in selecting genetically diverse CMS lines for hybrid rice production and in avoiding test crossing every CMS line empirically. This study demonstrated that AFLP is a powerful and reliable tool in determining the genetic relationships and in producing distinct fingerprints of rice cultivars. Received: 20 December 1996 / Accepted: 9 October 1997     

A new hybrid horsetail Equisetum×lofotense (E. arvense×E. sylvaticum,Equisetaceae) from Norway

On the Island of Austvågøya (Lofoten, Norway), a new hybrid horsetail (E. arvense×E. sylvaticum) was found, which is described as E.×lofotense. Its macro‐ and micro‐morphological characters are discussed and compared with the similar hybrid E.×mildeanum (E. pratense×E. sylvaticum) with which it shares the E. sylvaticum parentage. The hybrid nature is verified by its completely aborted spores, and the micro‐morphology of the stem ridges and stomata, illustrated by SEM images, confirm the proposed origin. An overview of all known hybrids in the genus Equisetum is given and critically commented. It becomes evident that in subgenus Equisetum E. arvense is the species most frequently involved in hybridization events.     

EVIDENCE FOR SELECTION AGAINST HYBRIDS IN THE FAMILY CYPRINIDAE (GENUS NOTROPIS)

Notropis cornutus and N. chrysocephalus are two cyprinid fishes which hybridize extensively in the midwest. In this paper, statistical analysis was used to determine if the deficiency of Notropis cornutus × N. chrysocephalus hybrids can be attributed partly to selection against hybrids. Principal component analysis was used to construct a folded hybrid index (FHI) using morphological and electrophoretic characters which distinguish N. cornutus, N. chrysocephalus, and their hybrids. A Wilcoxon signed-rank test comparing mean FHI between successive age classes within cohorts and regression analysis of FHI on age supported the conclusion that hybrids are less fit than parentals in nature; however, this analysis did not include a test of selection at zygotic and larval life history stages or partial infertility of hybrids. Selection eliminated hybrids at a rate of 9.2% per year. Considering the intensity of selection and the age of hybridization, it is surprising that premating reproductive isolating mechanisms have not been perfected by selection against gametic wastage as predicted by classical speciation theory. It appears that the reinforcement of premating isolating mechanisms is an extremely slow process, if it occurs at all, despite apparently intense selection against hybrids.