Risk assessment of outcrossing of transgenic rapessed to related species:

Summary The risk for a gene dispersal is reported for reciprocal crosses between a transgenic rapeseed variety resistant to the herbicide phosphinotricin and five related species. The first stages after pollination were cytologically observed and fertilized ovaries were established in in vitro culture for the production of interspecific hybrids. A similar classification was observed for the index of pollination compatibility and embryo yield. From the 243 embryos produced, 109 plantlets were obtained in a greenhouse. All the interspecific combinations tested were able to produce hybrid plants. A higher number of hybrids was obtained when rapeseed was used as the female parent. The hybrids had the expected triploid structure except for two amphidiploid, B. napus × B. oleracea, and one amphidiploid, B. napus × S. arvensis, plants with 56 chromosomes. The triploid hybrids were sterile or partially fertile but two of the amphidiploid plants, B. napus × B. oleracea, were fully fertile. The cytoplasm source did not seem to affect the fertility of the hybrids.     

Genetic diversity within cultivated teas based on nucleotide sequence comparison of ribosomal RNA maturase in chloroplast DNA

The wild tuber-bearing Solanumspecies represent a genetic pool of enormous diversity, embracing high variability for many agronomic traits. S. kurtzianum (ktz), S. chacoense(chc) and S. ruiz-lealii (rzl) are wild diploid self-incompatible relatives of the common potato, Solanum tuberosumssp. tuberosum, with resistance to adverse biotic and abiotic factors. Pollen-pistil/style compatibility relations and seed set in intra- and interspecific crosses among ktz, chc and rzl were investigated. Pre- and post-zygotic hybridization barriers were detected in the three species, with variable incidence because the percentage of genotypic combinations that produced seeds was15–30% and 7–28% in intra and interspecific crosses, respectively. In pollen-pistil/style incompatible combinations, either pollen grains did not germinate or pollen tube growth was arrested at different sites of the style, but mainly in its upper third. Unilateral incompatibility was detected in both intra-and interspecific crosses, as well as bilateral incompatibility in certain combinations. The incompatibility relations observed could be explained by a genetic model with dominant genes in pistils that interact with corresponding dominant genes in pollen, that are independent of the S-locus. The complex arrangement of compatibility relationships found could not be directly related to taxonomic hypothesis or geographic distribution. These results suggest that divergence between the three species has occurred recently, and that internal barriers of reproductive isolation have not been an important factor in their evolution. This revised version was published online in July 2006 with corrections to the Cover Date.     

Possibility of genetic improvement of pigeonpea (Cajanus cajan (L.)Millsp.) utilizing wild gene sources

Summary Various wild relatives of pigeonpea,Cajanus cajan, namely some species ofAtylosia andRhynchosia, possess desirable characteristics that could be utilized for effecting genetic improvement of this crop. In total 73 cross combinations among two cultivars ofC. cajan and one accession each of eightAtylosia species and one ofRhynchosia were attempted. Twelve hybrids were obtained. Seven of these were analysed for F₁ fertility and their utility for agronomic improvement of theC. cajan. Fertility behaviour of the different F₁ hybrids varied and indicated that potential of gene transfer between the two genera,Atylosia andCajanus, was as good as within the genusAtylosia. From F₂ and F₃ families ofC. cajan × A. scarabaeoides andC. cajan × A. albicans, plants were selected with greater physiological efficiency and agronomic superiority. The prospects of transferring pod borer resistance and higher seed protein content from someAtylosia species to pigeonpea are discussed.     

Crossability and cytology of hybrid progenies in the cross between Brassica campestris and three wild relatives of B. oleracea,B. bourgeaui,B. cretica and B. montana

Summary Crossability and cytology were examined in F₁, F₂, B₁ and hybridsplants of F₁ hybrids of Brassica campestris and three wild relatives of B. oleracea, B. bourgeaui, B. cretica and B. montana, respectively. The F₂ plants were obtained after self-and open pollination of the F₁ hybrids. The B₁ and hybrid plants were produced after the F₁ hybrids backcrosses with B. campestris and crossed with B. napus, respectively. After crossing the F₁ hybrids, many seeds of the F₂, B₁ and hybrid plants were harvested. Multivalent formation was high in the chromsome configuration for the PMCs of F₂, B₁ and hybrid plants, suggesting that crossing over might occur between them. Many different types of aneuploids were obtained in the progenies of the F₂, B₁ and hybrid plants. It is suggested that different types of normal egg cells may be produced by one-by-one or little-by-little chromosome addition. The possibility is discussed of gene transfer from B. bourgeaui, B. cretica and B. montana, to cultivated plants, B. campestris and B. napus.     

Chromosomal structural changes in Capsicum annuum L. and C. chinense Jacq.

Summary Wide hybridizations between M. arvensis and Brassica amphidiploid species (B. napus and B. juncea) were carried out in order to incorporate desirable traits of M. arvensis into Brassica crops. Crossing barriers between them were present without the use of in vitro techniques. F₁ hybrids have been produced through ovary culture, when M. arvensis were used as a female parent. Higher hybrid embryo productivity (3.07 embryos per pollination) was obtained in the cross of M. arvensis x B. napus than in that of M. arvensis x B. juncea (0.79 embryos). The hybridity was confirmed by morphology, cytology, isozyme and Southern analyses. The first backcrossing progenies and open pollinated ones were produced.     

The reproductive biology of three perennial Sesbania species (Leguminosae)

Summary The reproductive biology of Sesbania sesban, S. goetzei and S. keniensis (Leguminosae; Papilionoideae) was studied. Fifty percent flowering was observed at 102 to 153 days after germination for S. sesban accessions; 96 to 146 days for S. goetzei and 131 to 176 days for S. keniensis accessions. Flowers opened in the afternoon and remained fresh for 2–3 days. Bee species including Xylocopa sp., Apis mellifera, Megachile bituberculata and Chalicodoma sp. visited the flowers. Hand pollination experiments showed that all three species were self and cross compatible. The percentage of fully developed seeds was greater in pods formed after cross pollination compared to self pollination. No evidence was found for stigmatic or stylar self incompatibility. Outcrossing is probably the common method of reproduction under natural conditions, although in isolated trees substantial seed set by selfing might occur. Pod production under natural conditions was 34% for S. sesban; 49% for S. goetzei and 39% for S. keniensis. Considerable variation was found in pod production under open pollination between accessions of the same species. Selective abortion was observed within pods, with more mature seeds formed at the distal end of the pod.     

Diversity of penicillarian millets (Pennisetum glaucum and P. purpureum) as for the compatibility between their gynoecia and pollens from some other Poaceae

Summary The compatibility between gynoecia of different penicillarian millets (Pennisetum glaucum and P. purpureum) and pollens from some other Poaceae was evaluated in order to determine whether different penicillarian pistils showed the same pistil-pollen interactions with a same non-penicillarian pollen and to determine whether compatibility was dependent on the genetic divergence or the degree of sympatric evolution of the mating partners. Ten pearl millet lines (P. glaucum subsp. glaucum), six wild pearl millet accessions (P. glaucum subsp. monodii) and one P. purpureum accession were pollinated with five other Pennisetum species: P. pedicellatum, P. polystachyon, P. schweinfurthii, P. squamulatum, P. ramosum, and with three species from other genera: Cenchrus ciliaris, Panicum maximum and Zea mays. Each male species was represented by a unique accession. Pollen grain germination on the stigmata and pollen tube growth in the gynoecia were monitored by means of fluorescence microscopy after aniline blue staining. Significant compatibility differences were observed between a given pollen and gynoecia from different P. glaucum accessions. But there was no evidence of compatibility differences between the three female taxonomic groups. The eight pollen parents can be classified into three groups according to their mean degree of compatibility with the different penicillarian gynoecia. P. ramosum, P. schweinfurthii and P. squamulatum showed a high compatibility: more than 50% of penicillarian gynoecia had pollen tubes at the micropyle, six hours after pollination. Zea mays, Cenchrus ciliaris and Panicum maximum showed a low compatibility: pollen tubes were arrested in the style. P. pedicellatum and P. polystachyon showed nil compatibility: few pollen grains germinated on the stigmata and very rare tubes reached the entry of the style, where they stopped. It must be noted that such a strong gametic barrier has been observed only with pollinator species sympatric to pearl millet.     

Genetic diversity in tef [Eragrostis tef (Zucc) Trotter] and its relatives as revealed by Random Amplified Polymorphic DNAs

Tef is one of the staple cereal crops in Ethiopia. To evaluate genetic diversity of tef and its relatives, 47 accessions of tef, three accessions of E. pilosa, and six accessions of E. curvulawere analyzed using random amplified polymorphic DNA (RAPD) markers. The level of polymorphism among the wild species was extremely high, while low polymorphism was detected among tef accessions. All cultivars and wild species under study could be distinguished with the help of different primers, thereby indicating the potential of RAPD in the genetic fingerprinting of tef. Accessions from E. curvula and E. pilosa can be differentiated by a single selected primer. In spite of low polymorphism within tef, accessions under study could be distinguished by a combination of selected primers. Cluster analysis indicated that tef is a very closely related species to E. pilosa with 45%similarity, supporting the hypothesis that tef originated from E. pilosa based on morphological data. Given that RAPD are relatively quick, simple to use, and are not subjected to environmental influences, they provide a valuable new approach for the genetic fingerprinting and study of genetic diversity in tef. This revised version was published online in July 2006 with corrections to the Cover Date.     

Polygon of crossability between eleven species of Ipomoea: section Batatas (Convolvulaceae)

Summary Crossability within Ipomoea section Batatas is complex because of genetic, cytogenetic and physiological interactions. This complexity is responsible for the fact that knowledge about phylogenetic relationships within this section remains preliminary. Between 1988 and 1991, studies of planting, pollination and evaluation of progenies were carried out at the facilities of CIP in La Molina and San Ramon, Peru. Self-compatibility was found in nine diploid species. Self-incompatibility was found in diploid I. trifida, tetraploid I. tiliacea and both tetraploid and hexaploid I. batatas. Sexual compatibility is though to be related to a multiallelic sporophytic incompatibility system which is expressed in the stigmatic papillae. Altogether, 4,162 cross pollinations were made between 11 species and 76 interspecific combinations of 110 possible combinations in a diallel 11×11 design. From these 76 interspecific combinations only 38 survived, and in these crossability (= proportion between number of fruits harvested/pollinations made) ranged from 0.01 to 1.00 at La Molina. At San Ramon, 11 out of 17 cross combinations were successful, and in these crossability ranged from 0.01 to 0.71. Crossability appeared to be influenced by latitude which is related to flowering synchrony. The early death of seedlings is hypothesized to be related to a genomic imbalance between embryo and endosperm. Maternal effects were found in crosses between diploids and tetraploids which produced triploid and diploid offspring, and in crosses between hexaploids and diploids which gave rise to hexaploid offspring. This study shows that I. trifida and I. x leucantha may act as bridge species for gene flow from wild Ipomoea species to the genepool of the sweetpotato.     

Pollen donor impact on progenies of pseudogamous blackberries (Rubus subgen. Rubus)

A series of intra- and interspecific crosses in Rubus was evaluated with DNA markers to assess the proportion of apomictically vs. sexually derived progeny plants. The species were well separated from each other with these markers and the interspecific hybrids were easy to ascertain. Ten plants each were derived by selfing of R. hartmanni, R. polyanthemus and R. vestitus, and evaluated with RFLP. Of these plants, only one R. hartmanni plant appeared to be sexually derived, whereas the remainder appeared to have arisen by apomixis. Between 10 and 19 progeny plants, derived by open pollination of R. Hartmanni, R. infestus, R. laciniatus and R. vestitus, respectively (total of 63plants), were evaluated with RFLP. Of these, 6 plants (approx. 10%) showed as lightly deviating band pattern, which may indicate sexual seed set but could also result from experimental artefacts. The three species combinations 1) R. hartmanni and R. sprengelii, 2) R. infestus and R. vestitus, and 3)R. laciniatus and R. polyanthemus were cross-pollinated reciprocally and the resulting progenies evaluated with RAPD (combinations 1 and 2)and leaf shape (combination 3). Combination1 produced 20% (3 out of 15 progenies)sexually derived progenies, combination 2produced 100% (26 progenies) and combination 3 produced 64% (16 out of 26progenies), respectively. The hybrid progenies appeared to have been derived through pollination of unreduced as well as reduced egg cells. The ability to produce interspecific hybrid progenies is most probably dependent upon the species combination. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ecological aspects of transgenic sugar beet: transfer and expression of herbicide resistance in hybrids with wild beets

Summary An increasing number of genetically engineered cultivars of several crops is being experimentally released into the environment. In future, crops with new transgenic traits will probably play an important role in agricultural practice. The long-term effect of transgenes on community ecology will depend on the distribution and establishment of transgenic plants in the wild, on the sexual transfer of their new genes to the environment and on the potential ecological impact of the transgenic trait. The starting point was the use of transgenic sugar beet lines, Beta vulgaris subspec. vulgaris var. altissima DÖLL (Helm 1957), with transgenes coding for rhizomania and herbicide (BASTA^®) resistance. The first two questions to answer were: Can the transgenes be transferred via pollen to wild beets, Beta vulgaris subspec. maritima (L.) ARCANG. or cultivated relatives such as red beet or spinach beet and are they expressed in the hybrids? Can transgenes be monitored in young Beta vulgaris-hybrids? The experimental transfer of transgenes was conducted in 1993 at a field location in northern Germany. The beets were hand-pollinated with transgenic pollen. In a non destructive biotest, the hybrid seedlings were tested for herbicide resistance. Transgenic plants showed no noxious phenotypic effects whereas control plants developed leaf necroses. All herbicide resistant hybrids within the biotest were assumed to be transgenic.     

Genotypic variation and polymorphism of 2S albumins of sunflower

Summary An early postfertilization ovule culture technique in Alstroemeria was described in which young ovules were cultured in vitro two days after pollination. This resulted in the direct production of seedlings in a normally incongruous cross combination. A histological study of the in vitro cultured ovules revealed the development of the embryo inside the ovule in the absence of normal endosperm. The in vivo grown ovules showed a total breakdown of the developing seed within four weeks after pollination due to a postfertilization barrier. This ovule culture technique was applied in a diallel cross of seven Alstroemeria species, five from Chile and two from Brazil. The selfings and the reciprocal crosses between the Brazilian species A. inodora and A. brasiliensis were congruous and gave seed set. The cross A. inodora x A. pelegrina gave viable seeds. In all other 39 combinations no viable seeds were harvested. In those cross combinations both pre-and postfertilization barriers were found. After early ovule culture hybrid plants were obtained in 27 of the 39 incongruous species combinations of the diallel.Abbreviations DAP days after pollination - MS medium medium according to Murashige & Skoog (1962)     

Assessment of drought resistance in 20 accessions of Triticum aestivum and related species I. Total dry matter and grain yield stability

Summary Interspecific hybridisation has been suggested to improve the resistance of crops to biotic and abiotic stresses. To identify sources of resistance to drought which could be used in a breeding programme, an assessment of a large number of wheat species was carried out. The evaluation was based on the estimation of a drought susceptibility index and stability in total dry matter and grain yields of various species grown across a range of soil moisture conditions. On the basis of stability in total dry matter yield, T. aestivum was relatively more drought resistant. However, on the basis of grain yield stability, T. sphaerococcum, T. vavilovii and T. aestivum cv. C 306 exhibited better yield stability and drought resistance than the other species tested. It is suggested that the above species could be utilized as parental material in a hybridisation programme aimed at improving the drought resistance of wheat.     

A preliminary genetic analysis of fibre traits and the use of new genomic SSRs for genetic diversity in jute

Jute is one of the most important fibre crops, which is second only to cotton in providing environment-friendly (biodegradable and renewable) ligno-cellulose fibre. In order to improve this largely neglected crop, we conducted a preliminary study involving the following: (i) analysis of nature and extent of the genetic variability for fibre yield and four other related traits in a set of 81 genotypes belonging to two commercially cultivated Corchorus species (45 genotypes of C. olitorius + 36 genotypes of C. capsularis), (ii) development and analysis of a set of simple sequence repeat (SSR) markers from C. olitorius, and (iii) use of a sub-set of SSRs for assessment of genetic diversity in the above set of 81 genotypes. The results suggested quantitative nature of fibre yield and other related traits, with a preponderance of dominance component in genetic variance. A sub-set of 45 SSRs derived from C. olitorius, when used for a study of DNA polymorphism and genetic diversity, showed high transferability of these C. olitorius SSRs to C. capsularis. The average number of alleles for individual SSRs was surprisingly low (3.04 for both species, 2.02 for C. capsularis and 2.51 for C. olitorius), and so was the average polymorphic information content (PIC; 0.23 and 0.24 in two species). In the dendrogram obtained using a similarity matrix, the 81 genotypes were grouped into three clusters, which largely corresponded to the two species, Cluster I belonging mainly to C. capsularis and the other two closely related clusters (clusters II and III) belonging to C. olitorius. It was also shown that a minimum of 15 SSRs could give the same information as 41 SSRs, thus making many SSRs redundant. The SSR markers developed during the present study and to be developed in future will prove useful not only for evaluation of genetic diversity, but also for molecular mapping/QTL analysis, and for comparative genome analysis of the two Corchorus species. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Production of intergeneric hybrids between Brassica juncea and Diplotaxis virgata through ovary culture, and the cytology and crossability of their progenies

The cytogenetic study was investigated in the intergeneric F₁ hybrid, F₂and backcross progenies (BC₁). The plants used were Brassica juncea(2n=36) and Diplotaxis virgata(2n=18). Three intergeneric F₁ hybrids between two species were produced through ovary culture. They showed 36 chromosomes. It might consist one genome of B. juncea and two genomes of D. virgata. The morphology of the leaves resembled that of B. juncea. The color of the petals was yellow that was like in D. virgata. The size of the petal was similar to that of B. juncea. The mean pollen fertility was15.3% and the chromosome associations in the first meiotic division were(0–1)_IV+(0–2)_III+(8–12)_II+(12–20)_I. Many F₂ and BC₁seeds were harvested after open pollination and backcross of the F₁ hybrids withB. juncea, respectively. The F₂seedlings showed different chromosome constitutions and the range was from 28 to54 chromosomes. Most seedlings had 38chromosomes followed by 36, 40 and 54. The BC₁ seedlings also showed different chromosome constitutions and the range was from 29 to 62. Most seedlings had both 40and 54 chromosomes followed by 36, 46 and52. In the first meiotic division of F₂ and BC₁ plants, a high frequency of bivalent associations was observed in all the various kinds of somatic chromosomes. Many F₃ and BC₂ seeds were obtained by self-pollination and open pollination of both F₂ and BC₁ plants, and by backcrossing both F₂ and BC₁plants with B. juncea, respectively,especially, three type progeny with 36, 40or 54 chromosomes. The somatic chromosomes of the F₃ and BC₂ plants were further investigated. The bridge plants between B. juncea and D. virgata with 36 chromosomes may be utilized for breeding of other Brassica crops as well as B. juncea. This revised version was published online in July 2006 with corrections to the Cover Date.     

Pollen germination and pollen tube growth following self-pollination and intra- and interspecific pollination of Medicago species

Summary Pollen germination and pollen tube growth after self- and intra- and interspecific pollinations of annual [M. scutellata (L.) Mill., M. disciformis DC., and M. rigidula (L.) All.] and perennial (M. sativa L.) Medicago species were studied using a Carl Zeiss microscope with a fluorescence filter attachment.Self-pollination of self-fertile annual and intraspecific pollination of cross-fertile perennials were characterized by high pollen germination and rapid normal pollen tube growth. In contrast pollen germination percentages were very low and many pollen tube growth abnormalities occurred following interspecific pollination and self-pollination of self-sterile plants. The time period from pollination to fertilization for interspecific crosses was about double that following self-pollination of the annual species. However, fertilization occurred frequently following interspecific pollinations. Much of the sterility was due to factor(s) operating after fertilization.Cooperative investigations of the Kansas Agricultural Experiment Station, Dept. of Agronomy and the U.S. Department of Agriculture, Agricultural Research Service. Contribution No. 82-582-J- Mention of a trademark name or proprietary product does not constitute a guarantee or warranty by the U.S. Department of Agriculture, and does not imply its approval over other products that also may be suitable.     

Discriminating styles (DS) and pollen-mediated pseudo-self compatibility (PMPSC) in Petunia hybrida hort

Summary Discriminating styles (DS) in Petunia hybrida discriminate among incompatible pollen sources with pollen-mediated pseudo-self compatibility (PMPSC) similarly to those in Nemesia strumosa. Both species exhibit a single-locus gametophytic self-incompatibility system. Correlation of PMPSC to PSC level of the male was not universal and DS/PMPSC operated in heterozygous S genotypes. PSC levels of progenies generated from compatible or incompatible bud pollination were not significantly different from those of open-flower pollination of a DS plant with a given male, suggesting that DS did not select among male gametophytes for increased PSC.Scientific Journal Series Paper Number 13,077 of the Minnesota Agricultural Experiment Station.     

Evolving gene pools in crop plants

Summary The three gene pool system can be applied usefully to the whole range of crop plants. The primary gene pool (GP1) show varying degrees of fragmentation. No morphological discontinuity is apparent between wild and cultivated Lathyrus sativus but clear discontinuities have developed between conspecific wild and cultivated Phaseolus and Vigna species. Further discontinuities can develop in cultigens where disruptive selection has been practiced, as in Beta vulgaris, Linum usitatissimum and Brassica oleracea where more than one distinct crop has evolved within a single biological species. Each such crop has developed its own distinctive gene pool.     

A possible gene source for early,day-length neutral pigeon peas,Cajanus cajan (L.) Millsp.

Summary Atylosia scarabaeoides Benth. and A. platycarpa Benth., close relatives of the species Cajanus cajan (L.) Millsp., were screened for photoperiodic response. Four photoperiods ranging from 12 h 45 min to 19 h were studied in three environments. A. scarabaeoides flowered freely only in the first photoperiod. A. platycarpa not only flowered early (39 to 63 days after planting) in all four photoperiods, but also exhibited a relatively constant vegetative phase up to 16 h of illumination. Cajanus cajan, in which most cultivars-if not all-exhibit a response to photoperiod, was successfully hybridized with the two Atylosia species. It is suggested that genes for earliness and insensitivity to day-length could be transferred from A. platycarpa to C. cajan.     

Screening techniques and sources of resistance to parasitic angiosperms

Parasitic angiosperms cause great losses in many important crops under different climatic conditions and soil types. The most widespread and important parasitic angiosperms belong to the genera Orobanche, Striga, and Cuscuta. The most important economical hosts belong to the Poaceae, Asteraceae, Solanaceae, Cucurbitaceae, and Fabaceae. Although some resistant cultivars have been identified in several crops, great gaps exist in our knowledge of the parasites and the genetic basis of the resistance, as well as the availability of in vitro screening techniques. Screening techniques are based on reactions of the host root or foliage. In vitro or greenhouse screening methods based on the reaction of root and/or foliar tissues are usually superior to field screenings and can be used with many species. To utilize them in plant breeding, it is necessary to demonstrate a strong correlation between in vitro and field data. The correlation should be calculated for every environment in which selection is practiced. Using biochemical analysis as a screening technique has had limited success. The reason seems to be the complex host-parasite interactions which lead to germination, rhizotropism, infection, and growth of the parasite. Germination results from chemicals produced by the host. Resistance is only available in a small group of crops. Resistance has been found in cultivated, primitive and wild forms, depending on the specific host-parasite system. An additional problem is the existence of pathotypes in the parasites. Inheritance of host resistance is usually polygenic and its transfer is slow and tedious. Molecular techniques have yet to be used to locate resistance to parasitic angiosperms. While intensifying the search for genes that control resistance to specific parasitic angiosperms, the best strategy to screen for resistance is to improve the already existing in vitro or greenhouse screening techniques.