A new family of dispersed repeats from Brassica nigra: characterization and localization

The 459-bp HindIII (pBN-4) and the 1732-bp Eco RI (pBNE8) fragments from the Brassica nigra genome were cloned and shown to be members of a dispersed repeat family. Of the three major diploid Brassica species, the repeat pBN-4 was found to be highly specific for the B. nigra genome. The family also hybridized to Sinapis arvensis showing that B. nigra had a closer relationship with the S. arvensis genome than with B. oleracea or B. campestris. The clone pBNE8 showed homology to a number of tRNA species indicating that this family of repeats may have originated from a tRNA sequence. The species-specific 459-bp repeat pBN-4 was localized on the B. nigra chromosomes using monosomic addition lines. In addition to the localization of pBN-4, the chromosomal distribution of two other species-specific repeats, pBN34 and pBNBH35 (reported earlier), was studied. The dispersed repeats pBN-4 and pBNBH35 were found to be present on all of the chromosomes, whereas the tandem repeat pBN34 was localized on two chromosomes.     

Intergeneric (intersubtribe) hybridization between Moricandia arvensis and Brassica A and B genome species by ovary culture

Summary Intergeneric hybrids between Moricandia arvensis (C₃–C₄ intermediate species) and Brassica A and B genome species (B. campestris and B. nigra) were produced via ovary culture. When M. arvensis was used as a female parent, the hybrid embryo yield (0.25–0.45 embryo per pollination) was similar between two genomes, regardless of the male parent. The reciprocal hybrid using B. campestris as a female was also obtained, although yield of embryo was lower (0.02 embryo per pollination). On the other hand, no hybrids were obtained without the in vitro technique. As most hybrid embryos could not develop normal shoots, plants were regenerated by inducing shoots on the cultured hypocotyl. The hybrid nature of the regenerated plant was confirmed morphologically and cytogenetically. A certain amount of bivalents (2.52-2.71) in the hybrids indicated the existence of partial chromosome homology between two genera. The present results indicate that ovary culture is an effective technique for overcoming the crossing barrier between M. arvensis and Brassica cultivated species.     

Genetic variation within and among different cultivars and landraces of Brassica campestris L. and B. oleracea L. based on isozymes

Genetic variation based on isozymes was studied in 43 landraces and cultivars of Brassica campestris from China, 4 cultivars of B. campestris from Sweden and 1 from India, and 5 cultivars of B. oleracea from Sweden and 1 from China (B. alboglabra). A total of 17 isozyme loci was studied, 10 of these were polymorphic in B. campestris and 6 were polymorphic in B. oleracea. The level of heterozygosity seemed to be reduced in the Swedish cultivars compared to the Chinese landraces and cultivars of B. campestris. The level of heterozygosity in B. oleracea was even lower than that in the Swedish cultivars of B. campestris. A phylogeny of the cultivars and landraces of B. campestris showed that the B. campestris var yellow sarson cultivar, originating from India, deviated significantly from the other cultivars of B. campestris. A phylogeny of the cultivars of B. oleracea confirmed the expectations that the cultivar B. alboglabra was not closely related to the cultivated forms of B. oleracea.     

Host plant derived feeding deterrence towards ants in the turnip sawfly Athalia rosae

Larvae of the sawfly Athalia rosae ruficornis Jakovlev (Hymenoptera: Tenthredinidae) feed on several glucosinolate-containing plants and have been shown to sequester the main glucosinolates of different hosts, namely sinalbin (p-hydroxybenzylglucosinolate) from Sinapis alba L., sinigrin (allylglucosinolate) from Brassica nigra (L.) Koch, and glucobarbarin ((S)-2-hydroxy-2-phenylethylglucosinolate) from Barbarea stricta Andrz. (Brassicaceae). These plant metabolites are stored in the haemolymph, which is readily released when larvae are attacked by predators. In a dual-choice bioassay the bio-activity of sawfly haemolymph collected from larvae reared on different host plants (S. alba, B. nigra, and B. stricta) was tested against the ant Myrmica rubra L. (Hymenoptera: Formicidae). The haemolymph had a stronger deterrence effect when the corresponding sawfly larvae were reared on S. alba than when reared on B. nigra and B. stricta. Haemolymph of caterpillars of Pieris rapae L. (Lepidoptera: Pieridae) that had fed on S. alba was not deterrent to the ants. No sinalbin could be detected in their haemolymph. The glucosinolates sinalbin and sinigrin, offered in a concentration comparable to that in the sawfly haemolymph, were deterrent to the ants, but not as strongly as the corresponding haemolymph samples. This suggests, that glucosinolates are not the only compounds involved in the chemical defence of A. rosae. However, the presence of sequestered glucosinolates is already a sufficient defence towards predators such as ants, and their effectiveness is modulated by the host plant chemistry.     

Brassica taxonomy based on nuclear restriction fragment length polymorphisms (RFLPs)

Summary RFLPs were used to study genome evolution and phylogeny in Brassica and related genera. Thirtyeight accessions, including 10 accessions of B. rapa (syn. campestris), 9 cultivated types of B. oleracea, 13 nine-chromosome wild brassicas related to B. oleracea, and 6 other species in Brassica and allied genera, were examined with more then 30 random genomic DNA probes, which identified RFLPs mapping to nine different linkage groups of the B. rapa genome. Based on the RFLP data, phylogenetic trees were constructed using the PAUP microcomputer program. Within B. rapa, accessions of pak choi, narinosa, and Chinese cabbage from East Asia constituted a group distinct from turnip and wild European populations, consistent with the hypothesis that B. rapa had two centers of domestication. A wild B. rapa accession from India was positioned in the tree between European types and East Asian types, suggesting an evolutionary pathway from Europe to India, then to South China. Cultivated B. oleracea morphotypes showed monophyletic origin with wild B. oleracea or B. alboglabra as possible ancestors. Various kales constitute a highly diverse group, and represent the primitive morphotypes of cultivated B. oleracea from which cabbage, broccoli, cauliflower, etc. probably have evolved. Cauliflower was found to be closely related to broccoli, whereas cabbage was closely related to leafy kales. A great diversity existed among the 13 collections of nine-chromosome wild brassicas related to B. oleracea, representing various taxonomic states from subspecies to species. Results from these studies suggested that two basic evolutionary pathways exist for the diploid species examined. One pathway gave rise to B. fruticulosa, B. nigra, and Sinapis arvensis, with B. adpressa or a close relative as the initial ancestor. Another pathway gave rise to B. oleracea and B. rapa, with Diplotaxis erucoides or a close relative as the initial ancestor. Raphanus sativus and Eruca sativus represented intermediate types between the two lineages, and might have been derived from introgression or hybridization between species belonging to different lineages. Molecular evidence for an ascending order of chromosome numbers in the evolution of Brassica and allied genera was obtained on the basis of RFLP data and phylogenetic analysis.     

Pollen selection for Alternaria resistance in oilseed brassicas: responses of pollen grains and leaves to a toxin of A. brassicae

Summary The effects of destruxin B, a host-specific toxin of Alternaria brassicae that causes black spot disease in oilseed brassicas, were studied on in vitro pollen germination and pollen-tube growth of Brassica campestris var brown sarson, B. juncea, B. napus cvs Westar and Cresor, B. nigra and Sinapis alba. Pollen grains of B. nigra, B. juncea and B. campestris were the most sensitive and those of S. alba the least sensitive to the toxin. Effects of the toxin were also studied on the leaves of these species, and the degree of sensitivity of leaves of different species was comparable to that of their pollen grains. The results on the responses of pollen grains as well as leaves to the toxin are in agreement with the degree of susceptibility/resistance of these species to A. brassicae reported in the literature, indicating that the genes imparting susceptibility/restistance are expressed in the pollen, a prerequisite for pollen selection. Results are also presented which show that the toxin fed to the cut end of isolated inflorescence axis is readily taken up by the developing pollen and results in the inhibition of germination of susceptible pollen. This technique offers a simple and effective method for application of selection pressure to eliminate pollen grains susceptible to the toxin from effecting fertilization.     

Production of hybrids, amphiploids and backcross progenies between a cold-tolerant wild species, Erucastrum abyssinicum and crop brassicas

Three intergeneric hybrids were produced between a cold-tolerant wild species, Erucastrum abyssinicum and three cultivated species of Brassica, B. juncea, B. carinata and B. oleracea, through ovary culture. The hybrids were characterized by morphology, cytology and DNA analysis. Amphiploidy was induced in all the F₁ hybrids through colchicine treatment. Stable amphiploids and backcross progenies were obtained from two of the crosses, E. abyssinicum x B. juncea and E. abyssinicum x B. carinata. The amphiploid, E. abyssinicum x B. juncea was successfully used as a bridge species to produce hybrids with B. napus, B. campestris and B. nigra. These hybrids and backcross progenies provide useful genetic variability for the improvement of crop brassicas.     

Pollen beetle (Meligethes aeneus) oviposition and feeding preference on different host plant species

The oviposition and feeding preferences of the pollen beetle, Meligethes aeneus, were determined in choice and no-choice tests in field, semi-field and greenhouse trials. Plant species used were Brassica napus, B. campestris, B. juncea, B. nigra, B. carinata, Sinapis alba and Crambe abyssinica. With respect to number of eggs laid, S. alba and C. abyssinica were inferior to the other species. Pollen beetles laid fewer eggs on B. nigra than on the other Brassica spp. in no-choice tests, however this difference was partly due to fewer eggs laid per bud rather than fewer buds used for oviposition. Most eggs, for all plant species, were deposited in buds sized 2–3 mm. Feeding damage on all plant species was relatively similar. Pollen beetles seem to have a wider host range for feeding than for oviposition. There was good agreement in plant species ranking as oviposition hosts between the field, semi-field and greenhouse trials.     

Analysis of chloroplast and mitochondrial segregation in three different combinations of somatic hybrids produced within Brassicaceae

Summary Mitochondrial and chloroplast DNA were characterized in three different combinations of somatic hybrids produced between different species within Brassicaceae. The fusions were made between B. campestris and B. oleracea, B. napus and B. nigra and between B. napus and Eruca sativa. The combinations represent interspecific hybridizations, but the phylogenetic distance between the species used in each instance is different. Whereas the B. campestris (+) B. oleracea and the B. napus (+)B. nigra hybrids are both examples of intrageneric hybrids, B. campestris is more closely related to B. oleracea than B. napus is to B. nigra. The fusion of B. napus and E. sativa represents an intergeneric hybridization. Since hybrids were produced with reproducible and uniform fusion and culture methods, a comparison of chloroplast and mitochondrial segregation and mitochondrial DNA (mt-DNA) rearrangements could be made between the combinations. The segregation of both chloroplasts and mitochondria was biased in the B. napus (+)B. nigra and the B. napus (+)E. sativa combination. The nonrandom segregation of chloroplasts and mitochondria could be due to the different ploidy levels of the fusion partners and/or reflect differences in organelle replication rate. Furthermore, segregation of mitochondria was correlated to the differences in phylogenetic distance between the species used in the fusions. However, mitochondrial segregation, in contrast to chloroplast segregation, could in all combinations also have been affected by the cell type used as protoplast source in the fusions. All different chloroplast types could be established within each combination. Hybrids containing chloroplast from one parent together with mitochondria from the other parent were found in two of the combinations, although the majority of the hybrids had mt-DNA that was altered compared to the parental species. The rearranged mt-DNA found in most hybrids was an effect of the heteroplasmic state following protoplast fusion rather than of the tissue culture methods, since no mt-DNA rearrangements were found in B. napus plants regenerated from protoplast culture. The mtDNA restriction patterns of the hybrids with rearranged mt-DNA indicated that specific regions of the mt-DNA were involved in the rearrangements following protoplast fusion.     

Molecular systematics of Brassica and allied genera (Subtribe Brassicinae,Brassiceae) —chloroplast genome and cytodeme congruence

Summary Chloroplast DNA restriction sites for 20 endonucleases were mapped using cpDNA probes from Brassica juncea and site variation was surveyed in 33 diploid taxa of the Subtribe Brassicinae. A total of 419 mutations was observed, including both site (i.e., gain/ loss) and fragment length (i.e., insertions or deletions); 221 (53%) mutations showed variation at the interspecific level. Phylogenetic analysis indicated a clear division of the subtribe into two ancient evolutionary lineages. These were (I) the Nigra lineage: Brassica nigra, B. fruticulosa, B. tournefortii, Sinapis pubescens, S. alba, S. flexuosa, S. arvensis, Coincya cheiranthos, Erucastrum canariense, and Hirschfeldia incana, and (II) the Rapa/ Oleracea lineage: Brassica rapa, B. oleracea ssp. oleracea and ssp. alboglabra, B. rupestris-villosa complex (B. rupestris, B. drepanensis, B. macrocarpa, B. villosa), B. barrelieri, B. deflexa, B. oxyrrhina, B. gravinae, Diplotaxis erucoides, D. tenuifolia, Eruca sativa, Raphanus raphanistrum, R. sativus, and Sinapis aucheri. In the Nigra lineage, Brassica nigra was most closely related to the annual Sinapis species, S. arvensis and S. alba. In the Rapa/Oleracea lineage, the Brassica rapa and B. oleracea genomes formed a distinct group whose closest relatives were the wild species of the B. oleracea (n=9) complex (i.e., B. rupestris-villosa complex). Species with n=7 chromosomes exist in both lineages. Hirschfeldia incana (n=7), in the Nigra lineage, was most closely related to Sinapis pubescens. In the Rapa/Oleracea lineage three taxa with n=7 — B. deflexa, D. erucoides, and S. aucheri — were closely related, advanced in the lineage, and were the closest apparent relatives (particularly D. erucoides) to B. rapa, B. oleracea, and its wild relatives. Levels of genetic divergence suggested by the cpDNA data were consistent with cytodeme recognition in the subtribe, but provided evidence for inconsistencies in the current generic delimitations based on morphology. Very low levels of genetic divergence were evident among taxa/accessions within a cytodeme. Raphanus was closely related to the Brassica rapa and B. oleracea genomes and clearly belongs in Subtribe Brassicinae. Several cytoplasmic genetic markers of potential use in plant breeding programs were identified for each of the cytodemes.     

Glucosinolate profile and oviposition behavior in relation to the susceptibilities of Brassicaceae to the cabbage seedpod weevil

Understanding how host‐plant characteristics affect behavioral and physiological responses of insect herbivores is of considerable importance in the development of resistant crop germplasm. Feeding, oviposition preference, larval development, and oviposition behavior of the cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham) (= Ceutorhynchus assimilis Payk.) (Coleoptera: Curculionidae), were investigated on eight Brassicaceae species that differed in their glucosinolate profiles. The least preferred host plants for feeding and oviposition were the Sinapis alba L. lines while the Brassica carinata L. line was most preferred. Larval development occurred most rapidly on Brassica rapa L. and slowest on S. alba. Larval weight was highest on B. napus L. and lowest on S. alba. Total glucosinolate levels did not influence C. obstrictus larval growth or development; however high levels of specific glucosinolates such as p‐hydroxybenzyl and 3‐butenyl glucosinolate were associated with increased developmental time or reduced weight. The time required for oviposition behavioral events was measured on different host‐plant species: B. rapa, B. napus, B. napus×S. alba, B. tournefortii Gouan., B. juncea (L.) Czern, B. carinata, B. nigra (L.) Koch., and S. alba. The early steps in the sequence were completed faster on more susceptible host plants (B. carinata, B. napus, and B. rapa) than on relatively resistant ones (B. tournefortii and B. juncea). Females explored pods of B. nigra and S. alba, but oviposition occurred only rarely on these species. There was no significant difference in the location on the pod on which oviposition occurred among the different plant species. Mean eggs laid per female weevil were highest on the B. napus×S. alba hybrid and lowest on B. nigra and S. alba.     

Molecular and cytological characterization of repetitive DNA sequences in Brassica

Summary We isolated three different repetitive DNA sequences from B. campestris and determined their nucleotide sequences. In order to analyze organization of these repetitive sequences in Brassica, Southern blot hybridization and in situ hybridization with metaphase chromosomes were performed. The sequence cloned in the plasmid pCS1 represented a middle repetitive sequence present only in B. campestris and not detected in closely related B. Oleracea. This sequence was localized at centromeric regions of six specific chromosomes of B. campestris. The second plasmid, pBT4, contained a part of the 25S ribosomal RNA gene, and its copy number was estimated to be 1,590 and 1,300 per haploid genome for B. campestris and B. oleracea, respectively. In situ hybridization with this sequence showed a clear signal at the NOR region found in the second largest chromosome of B. Campestris. The third plasmid, pBT11, contained a 175-bp insert that belongs to a major family of tandem repeats found in all the Brassica species. This sequence was detected at centromeric regions of all the B. campestris chromosomes. Our study indicates that in situ hybridization with various types of repetitive sequences should give important information on the evolution of repetitive DNA in Brassica species.     

Characteristics of oviposition behaviour of the pollen beetle, Meligethes aeneus on four different host plants

Oviposition behaviour of Meligethes aeneus F. (Coleoptera: Nitidulidae) is characterised and quantified on four different plant species. Six behavioural components are identified: W—walking, WA—walking with abdomen on surface, R—resting, B—biting, AOH—placing abdomen over the bite hole and OVI—oviposition. Comparison of host acceptance behaviours on Brassica napus L., Brassica juncea (L.) Czern, Brassica nigra (L.) Koch and Sinapis alba L. showed that S. alba was accepted as a host only after a long exposure to the plant. Behaviour on the Brassica species was similar, however on B. nigra beetles spent a high proportion of time actually ovipositing. We conclude that important cues for oviposition are located both on the bud surface and inside the bud.     

Pollen-pistil interactions in Populus: β-galactosidase activity associated with pollen-tube growth in the crosses P. nigra x P. nigra and P. nigra x P. alba

Summary In order to understand the nature of interspecific barriers in Populus, we have explored pollen/pistil interactions in intra- and interspecific crosses Populus nigra x P. nigra and P. nigra x P. alba. The kinetics of pollen-tube growth demonstrated that P. nigra and P. alba pollen tubes have distinct behavioral patterns inside P. nigra pistils. P. alba pollen tubes exhibit an unique S-shaped growth curve and an arrested growth site near the sylodium. P. nigra pollen tubes exhibit two growth phases, in the stigmatic tissues and in the ovarian cavity respectively. P. nigra and P. alba curves diverge 5 h after controlled pollination and could be related to a change in the physiology of the P. nigra pollen tube, which shifts from an autotrophic to a heterotrophic type of nutrition. Protein analysis of pollinated stigmatic extracts (0,6 and 20 h after pollination) revealed qualitative and quantitative differences that are related to the presence of either P. nigra or P. alba pollen tubes inside the stigmatic tissues. Increasing numbers of protein bands were detectable from 0 to 20 h after pollination only in intraspecific cross. Glycoproteins were detected, and the differences observed were dependent of the cross. -Galactosidase activity was found in pollinated stigmas, but an increase in its activity (one isozyme of pHi 4.2) between 6 h and 20 h after pollination was detected only in the intraspecific cross. This enzyme could play a role in heterotrophic pollen-tube nitrition, and its activity could be the final result of a series of interactions started by the initial pollen-stigma dialog.     

The role of glucosinolates and their hydrolysis products in oviposition and host-plant finding by cabbage webworm, Hellula undalis

The cabbage webworm, Hellula undalis (Fabricius) (Lepidoptera: Pyralidae), a tropical pest on crucifers (Brassicaceae), differentiated among host-plant species for oviposition in laboratory and field tests. White mustard, Sinapis alba (L.) var. Selinda, was the preferred host-plant, followed by Brassica juncea (L.) Czern. et. Coss var. Canadian brown mustard, and pak-choi, Brassica campestris L. ssp. chinensis var. Joi Choi, Black Behi and Bai Tsai. Glucosinolates (GS), secondary plant compounds characteristic to the Cruciferae plant family, and their breakdown products were analyzed by using HPLC and GC-MS-techniques. Species differed in GS composition and concentration. Content of GS was highest in S. alba with progressively lower contents detected in B. juncea and B. chinensis. The aromatic GS, 4-hydroxybenzyl-GS and benzyl-GS, were detected in S. alba. In B. juncea the alkenyl GS, allyl-GS, dominated, whereas in varieties of B. chinensis indolyl and alkenyl GS predominated. Oviposition of H. undalis females on the non-host-plant Vigna unguiculata ssp. sesquipedalis (L.) Fruwirth was stimulated by application of GS extracts from the crucifer species; the extract from S. alba was preferred, followed by extracts from B. juncea and B. chinensis. Hydrolysis of GS in the plant extract from B. chinensis causes loss of the oviposition stimulatory effect of the extract. Application of the GS, allyl-GS, and benzyl-GS also stimulated oviposition by H. undalis. Significantly more eggs were laid on leaves treated with the aromatic GS, benzyl-GS, than with the alkenyl GS, allyl-GS. Host-plant odor attracted H. undalis females but not males, in behavioral assays conducted in a Y-tube olfactometer. Low concentrations of the GS hydrolysis product, allyl-isothiocyanate, induced anemotaxis of females, but a high concentration of allyl-isothiocyanate was repellent. Oviposition by H. undalis females was not stimulated by host-plant volatiles. Females laid eggs on inserted traps and the walls of the Y-tube regardless of presence or absence of host-plant odor. The relevance of these results in the context of crucifer-insect interactions is discussed.     

Oviposition and larval performance of Rabdophaga terminalis on Salix spp. with special consideration to bud size of host plants

Females of the gall midge Rabdophaga terminalis (H. Loew) (Diptera: Cecidomyiidae) are very selective in their choice of host plants at oviposition. In preference trials, eggs were laid almost exclusively on S. alba and S. fragilis. One single oviposition occurred on S. viminalis but none on S. triandra, S. daphnoides or S. smithiana. Significantly more eggs were laid on S. alba than on S. fragilis. No differences were detected between clones of the same species regarding oviposition in laboratory trials. Within the species of S. alba, larger buds were preferred. However, this did not explain the preference of S. alba to S. fragilis. There was agreement between plant species selected by the females and survival of the larvae. No galls developed when eggs were transferred to species that were not oviposited on. There was no difference between S. alba and S. fragilis in larval growth, but after two weeks of development there was a significantly higher proportion of larvae in cocoons and pupae on S. alba. There was a negative linear relationship between weight of larvae and larval number per gall, indicating larval competition. The negative slope was steeper for S. alba than for S. fragilis when larvae were weighed after two weeks of development. There were some discrepancies between laboratory and field data on infestation of S. alba and S. fragilis. Higher infestation levels were related to denser stands in the field.

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Résumé Etude de la ponte et des performances larvaires de Rabdophaga terminalis (Diptera; Cecidomyiidae) sur plusieurs espèces de saules avec examen particulier de l'influence de la taille des bourgeons.La ponte et les performances larvaires de la cécidomyie galliforme, Rabdophaga terminalis (H. Loew) ont été étudiées sur plusieurs espèces et clones de saules cultivés en Suède. Les femelles sélectionnent avec soin les plantes hôtes lors de la ponte. Dans des essais préférentiels, les oeufs ont été pondus presque exclusivement sur S. alba et S. fragilis; une ponte a été observée sur S. viminalis et aucune sur S. triandra, S. daphnoïdes ou S. smithiana. Significativement plus d'oeufs ont été pondus sur S. alba que sur S. fragilis. Les essais au laboratoire n'ont pas permis de déceler des différences entre clones de la même espèce. Chez S. alba, les plus gros bourgeons étaient préférés, mais ceci ne permet pas d'expliquer la préférence pour S. alba par rapport à S. fragilis. Il y a coïncidence entre les plantes choisies par les femelles et al survie des larves; il n'y avait pas développement de galles quand des oeufs étaient transférés sur des espèces qui n'avaient pas reçu de pontes. La croissance larvaire sur S. alba et S. fragilis ne présentait pas de différences, mais après 2 semaines de développement il y avait significativement plus de larves en cocons et pupes sur S. alba. La corrélation entre le poids des larves et le nombre de larves par cellule était linéaire et négative, ce qui indique une compétition larvaire; la pente était plus raide pour S. alba que pour S. fragilis quand les larves étaient pesées au bout de 2 semaines de développement. Il y a eu quelques discordances entre les résultats au laboratoire et les données de terrain sur la contamination de S. alba et S. fragilis. Les plus fortes contaminations étaient observées à l'extérieur sur pépinières denses.

     

Sinapis phylogeny and evolution of glucosinolates and specific nitrile degrading enzymes

Levels of sinalbin (4-hydroxybenzylglucosinolate) and 28 other glucosinolates were determined in leaves and roots of 20 species that were either phylogenetically close to Sinapis alba, Sinapis arvensis, or Sinapis pubescens (tribe Brassiceae, Brassicaceae), or were expected to contain arylalkyl nitrilase activity. Comparison with a molecular phylogenetic tree based on ITS DNA sequences identified two separate occurrences of sinalbin. The first in a group of species related to S. alba (including members of the genera Coincya and Kremeriella); and the second in S. arvensis, nested among sinalbin deficient species. Significant 4-hydroxyphenylacetonitrile degrading enzyme activity was found in both S. alba and S. arvensis, but in S. alba the major product was the corresponding carboxylic acid, while in S. arvensis the major product was the amide. Both investigated enzyme activities, nitrilase and nitrile hydratase, were specific, accepting only certain arylacetonitriles such as 4-hydroxy and 4-methoxyphenylacetonitrile. Only the S. alba enzyme required an oxygen in para position of the substrate, as found in sinalbin. Indole-3-acetonitrile, arylcyanides, and arylpropionitriles were poor substrates. The nitrilase activity of S. alba was quantitatively comparable to that reported in the monocot Sorghum bicolor (believed to be involved in cyanogenic glycoside metabolism). Glucosinolates derived from methionine were found in all Sinapis clades. Glucosinolate patterns suggested a complex evolution of glucosinolates in the investigated species, with several apparent examples of abrupt changes in glucosinolate profiles including chain length variation and appearance of glucosinolates derived from branched-chain amino acids. NMR data for desulfated homosinalbin, 9-methylsulphonylnonylglucosinolate, 3-methylpentylglucosinolate and related glucosinolates are reported, and a facultative connection between sinalbin and specific nitrilases is suggested.     

Intergeneric hybrids between Enarthrocarpus lyratus,a wild species,and crop brassicas

Summary Attempts were made to produce intergeneric hybrids between Enarthrocarpus lyratus, a wild species, and several species of crop brassicas: B. campestris, B. nigra, B. oleracea, B. juncea, B. napus and B. Carinata. Hybrids using E. lyratus as female parent were realized by means of embryo rescue in four combinations — E. lyratus x B. campestris, E. lyratus x B. oleracea, E. lyratus x B. napus and E. lyratus x B. carinata. Reciprocal crosses showed strong pre-fertilization barriers and yielded no hybrids except in one combination — B. Juncea x E. Lyratus — in which a single hybrid could be realized. All of the hybrids were multiplied in vitro through the multiplication of axillary shoots. Morphological and cytological studies confirmed hybridity. All hybrids were completely pollen sterile except for E. lyratus x B. carinata, which showed 2% pollen fertility. Attempts to double the chromosome number through the in vitro application of colchicine to axillary meristems of F₁ hybrids were successful in only one hybrid, E. lyratus x B. oleracea. Cytological studies of the hybrids indicated the presence of a partial homology between the genomes of E. lyratus and crop brassicas. Backcross progenies were raised from all of the five F₁ hybrids to develop malesterile alloplasmic lines.     

Construction of Brassica B genome synteny groups based on chromosomes extracted from three different sources by phenotypic, isozyme and molecular markers

The three B genomes of Brassica contained in B. nigra, B. carinata and B. juncea were dissected by addition in B. napus. Using phenotypic, isozyme and molecular markers we characterized 8 alien B-genome chromosomes from B. nigra and B. carinata and 7 from B. juncea by constructing synteney groups. The alien chromosomes of the three different sources showed extensive intragenomic recombinations that were detected by the presence of the same loci in more than one synteny group but flanked by different markers. In addition, intergenomic recombinations were observed. These were evident in euploid AACC plants of the rapeseed phenotype derived from the addition lines carrying a few markers from the B genome due to translocations and recombinations between non-homoeologous chromosomes. The high plasticity of the Brassica genomes may have been an powerful factor in directing their evolution by hybridization and amphiploidy.     

Low Allozymic Variation in the Bidens pilosa L. Complex (Asteraceae)

Bidens alba, B. subalternans, and B. pilosa form a complex group based on their morphological similarities. Bidens pilosa L. and B. subalternans DC. are herbs with a wide distribution in agricultural and disturbed areas. Bidens alba (L.) DC. varies in size from herb to subshrub and has a coastal distribution. Enzyme electrophoresis was used to evaluate genetic diversity in 12 populations of Bidens. All but three loci (Lap-1, Est, and Got) were monomorphic. Est-1 and Got were polymorphic only in B. alba. Lap-1 was polymorphic only in B. pilosa and B. subalternans. The estimates of genetic variability were low for all three taxa and all of the populations studied. Genetic diversity varied from 0.01 to 0.03. Mean genetic identities were high among populations of each species (0.99 for B. alba and 1.00 for B. pilosa and B. subalternans) and among the three species (1.00). Bidens pilosa and B. subalternans could be considered a single species if the taxonomy of the group were based solely on isozyme data.