Allelochemicals released by rice roots and residues in soil

A few rice (Oryza sativa L.) varieties or rice straw produce and release allelochemicals into soil in which interfere with the growth of neighboring or successive plants. Allelopathic rice PI312777 and Huagan-1 at their early growth stages released momilactone B, 3-isopropyl-5-acetoxycyclohexene-2-one-1, and 5,7,4′-trihydroxy-3′,5′-dimethoxyflavone into soil at phytotoxic levels, but non-allelopathic rice Huajingxian did not. Both allelopathic and non-allelopathic rice residues released momilactone B and lignin-related phenolic acids (p-hydroxybenzoic, p-coumaric, ferulic, syringic and vanillic acids) into the soil during residue decomposition to inhibit successive plants. The results indicated that allelochemicals involved in rice allelopathy from living and dead plants are substantially different. Interestingly, the concentrations of the allelochemicals released from the allelopathic rice seedlings in soil increased dramatically when they were surrounded with Echinochloa crus-galli. The concentrations of the allelochemicals were over 3-fold higher in the presence of E. crus-galli than in the absence of E. crus-galli. However, the same case did not occur in non-allelopathic Huajingxian seedlings surrounded with E. crus-galli. In addition to allelochemical exudation being promoted by the presence of E. crus-galli, allelopathic rice seedlings also increased allelochemical exudation in response to exudates of germinated E. crus-galli seeds or lepidimoide, an uronic acid derivative exuded from E. crus-galli seeds. These results imply that allelopathic rice seedlings can sense certain allelochemicals released by E. crus-galli into the soil, and respond by increased production of allelochemicals inhibitory to E. crus-galli. This study suggests that rice residues of both allelopathic and non-allelopathic varieties release similar concentrations and types of allelochemicals to inhibit successive plants. In contrast, living rice plants of certain allelopathic varieties appear to be able to detect the presence of interspecific neighbors and respond by increased allelochemicals.     

Influence of Pluchea lanceolata (Asteraceae) on selected soil properties

Allelopathic interference may operate simultaneously, sequentially, and/or in combination with other mechanisms of interference such as nutrient interference. It is hypothesized that under field conditions, allelopathic plants may cause changes in chemical characteristics of soils in addition to qualitative and quantitative changes in the allelochemical status of soil infested with the allelopathic plant. To test this hypothesis, the perennial allelopathic weed Pluchea lanceolata was selected. A comparative study of P. lanceolata-infested soils, and soils 10, 20, 30, and 40 m away from the weed was undertaken to examine soil characteristics and quantitative and qualitative variation in soil phenolics. Impact of seasonal weather on the biotic and chemical characteristics of P. lanceolata, and quantitative variation in phenolics of weed-infested soils was also studied. Growth experiments were conducted to study the seasonal impact on allelopathic interference of P. lanceolata toward certain crop plants. Results indicate that P. lanceolata influences soil properties in addition to causing variation in soil phenolics. Two-way tests (i.e., analyzing allelopathic and nutrient interference) should be run regardless of whether one is studying allelopathy or nutrient interference and it is important to test allelopathy in all studies dealing with nutrient interference.     

Effects of parental ploidy level and genetic divergence on chromosome elimination and chloroplast segregation in somatic hybrids within Brassicaceae

Summary Chromosome and organelle segregation after the somatic hybridization of related species with different degrees of genetic divergence were studied by comparing the interspecific somatic hybrids Brassica oleracea (CC) (+) B. campestris (AA), B. napus (AACC) (+) B. oleracea (CC) B. napus (AACC) (+) B. nigra (BB) and B. napus (AACC) (+) B. juncea (AABB) with the intergeneric somatic hybrids B. napus (AACC) (+) Raphanus sativus (RR) and B. napus (AACC) (+) Eruca sativa (EE). Within each combination, some hybrids were found whose DNA content was equal to the sum of parental chromosomes, others had a relatively higher DNA content and in most of the cases, some had a relatively lower content. However, the frequency distribution in these three classes differed significantly between the combinations. A positive correlation between the frequency of hybrids with eliminated chromosomes and the genetic distance between the species in each combination was found. Furthermore, by combining species with different ploidy levels we found a significantly higher degree of chromosome elimination compared to combinations of species with the same ploidy level. In the B. napus (+) B. Nigra, B. napus (+) R. sativus and B. napus (+) E. sativa combinations chromosomes from the B, R and E genomes appeared to be preferentially sorted out, as indicated by the fact that some of the nuclear markers from these genomes were missing in 7–46% of the plants, whereas no plants were lacking B. napus nuclear markers. Fertile hybrids were found in all but the B. napus (+) R. sativus fusion combination; the latter hybrids were male sterile, but female fertile. Hybrids between the A and C genomes were more fertile than hybrids obtained between the distantly related AC and B, R or E genomes, respectively. Analysis of the chloroplast RFLP pattern revealed that chloroplasts in the B. oleracea (+) B. campestris hybrids segregated randomly. A slightly biased segregation, favouring B. napus chloroplasts, was found in the B. napus (+) B. oleracea combination, whereas B. napus chloroplasts were strongly selected for in the B. napus (+) B. juncea, B. napus (+) B. nigra, B. napus (+) R. sativus and B. napus (+) E. sativa somatic hybrids.     

Allelopathic interference of alfalfa (<Emphasis Type="Italic">Medicago sativa</Emphasis> L.) genotypes to annual ryegrass (<Emphasis Type="Italic">Lolium rigidum</Emphasis>)

Alfalfa (Medicago sativa L.) genotypes at varying densities were investigated for allelopathic impact using annual ryegrass (Lolium rigidum) as the target species in a laboratory bioassay. Three densities (15, 30, and 50 seedlings/beaker) and 40 alfalfa genotypes were evaluated by the equal compartment agar method (ECAM). Alfalfa genotypes displayed a range of allelopathic interference in ryegrass seedlings, reducing root length from 5 to 65%. The growth of ryegrass decreased in response to increasing density of alfalfa seedlings. At the lowest density, Q75 and Titan9 were the least allelopathic genotypes. An overall inhibition index was calculated to rank each alfalfa genotype. Reduction in seed germination of annual ryegrass occurred in the presence of several alfalfa genotypes including Force 10, Haymaster7 and SARDI Five. A comprehensive metabolomic analysis using Quadruple Time of Flight (Q-TOF), was conducted to compare six alfalfa genotypes. Variation in chemical compounds was found between alfalfa root extracts and exudates and also between genotypes. Further individual compound assessments and quantitative study at greater chemical concentrations are needed to clarify the allelopathic activity. Considerable genetic variation exists among alfalfa genotypes for allelopathic activity creating the opportunity for its use in weed suppression through selection.     

Intertribal somatic hybrids between <Emphasis Type="Italic">Brassica napus</Emphasis> and <Emphasis Type="Italic">Camelina sativa</Emphasis> with high linolenic acid content

Intertribal somatic hybrids of Brassica napus and Camelina sativa were developed by protoplast electrofusion. Hybrid identity of the regenerants was determined using flow cytometric analysis of nuclear DNA content and simple sequence repeat (SSR) marker analysis. Three hybrids exhibited specific bands for B. napus and C. sativa. These hybrids showed intermediate leaf, flower and seed morphology compared with the two parental species. The seeds of these three hybrids had a modified fatty acid profile, indicating higher level of linolenic and eicosanoic acids than those of B. napus. Our results suggest that somatic hybridization offers opportunities for transferring entire genomes between B. napus and C. sativa in improving rapeseed breeding.     

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.     

Novel flowering and fatty acid characters in rapid cycling Brassica napus L. resynthesized by protoplast fusion

Novel rapid cycling Brassica napus lines have been produced by protoplast fusion between rapid cycling B. oleracea and rapid cycling B. rapa. Fusion products were selected based on iodoacetate inactivation and regeneration ability. A total of 36 plants was recovered from 3 regenerating calli. All were confirmed as somatic hybrids by morphological features, flow cytometric estimation of nuclear DNA content, RAPD analysis and/or DNA hybridization. Plants from two of the calli contained chloroplasts from B. rapa, and plants from the third contained B. oleracea chloroplasts. Some plants flowered in vitro, but on average flowering was initiated 22 days after transfer to soil. Although seed set was fairly low after self pollination, more seeds were obtained from pollination of open flowers than from pollination of buds. Seeds of the somatic hybrid B. napus showed novel fatty acid compositions, different from the mean of the two parental lines. Flowering was monitored in plants grown from seeds of the somatic hybrids, rapid cycling B. napus (CrGC 5-1) and the two diploid parental genotypes. Progeny of the somatic hybrids flowered faster and were more vigorous than rapid cycling B. napus (CrGC 5-1). The improved lines contain chloroplasts from B. rapa, unlike rapid cycling B. napus (CrGC 5-1), which has B. oleracea chloroplasts. The somatic hybrid lines produced may be useful for genetic studies or further in vitro manipulations.Abbreviations CrGC Crucifer Genetics Cooperative, University of Wisconsin-Madison - MES 1-morpholino-ethane sulfonate - MS-3,0 Murashige and Skoog medium containing 3% sucrose and no growth regulators - RAPD random amplified polymorphic DNA - RC rapid cycling - RFLP restriction fragment length polymorphism - std standard deviation - TE 10mM Tris, 1 mM EDTA, pH 8     

Effect of Brassica Biofumigant Amendments on Different Stages of the Life Cycle of Phytophthora cinnamomi

The oomycete plant pathogen Phytophthora cinnamomi causes a highly destructive root rot that affects numerous hosts. Integrated management strategies are needed to control P. cinnamomi in seminatural oak rangelands. We tested how biofumigation affects crucial stages of the pathogen's life cycle in vitro, in infested soils under laboratory conditions and in planta. Different genotypes of three potential biofumigant plant species (Brassica carinata, Brassica juncea, Brassica napus) were collected at different phenological stages, analysed for their glucosinolate contents, and subsequently tested. The most effective genotypes against mycelial growth and sporangial production were further tested on the viability of chlamydospores in artificially infested natural soils and in planta on Lupinus luteus, a host highly susceptible to P.cinnamomi. Brassica carinata and B. juncea genotypes inhibited mycelial growth, decreased sporangial production, and effectively inhibited the viability of chlamydospores in soil, but only B. carinata decreased disease symptoms in plants. Effective genotypes of Brassica had high levels of the glucosinolate sinigrin. Biofumigation with Brassica plants rich in sinigrin has potential to be a suitable tool for control of oak root disease caused by P. cinnamomi in Spanish oak rangeland ecosystems.     

<Emphasis Type="Italic">MAM</Emphasis> gene silencing leads to the induction of C3 and reduction of C4 and C5 side-chain aliphatic glucosinolates in <Emphasis Type="Italic">Brassica napus</Emphasis>

Methylthioalkylmalate (MAM) synthases and their associated genes that have been extensively investigated in Arabidopsis control the side-chain elongation of methionine during the synthesis of aliphatic glucosinolates. A Brassica homolog of the Arabidopsis MAM genes was used in this study to analyze the role of MAM genes in B. napus through RNA interference (RNAi). The silencing of the MAM gene family in B. napus canola and B. napus rapeseed resulted in the reduction of aliphatic glucosinolates and total glucosinolate content. The results indicated that RNAi has potential for reducing glucosinolate content and improving meal quality in B. napus canola and rapeseed cultivars. Interestingly, MAM gene silencing in B. napus significantly induced the production of 2-propenyl glucosinolate, a 3-carbon side-chain glucosinolate commonly found in B. juncea mustard. Most transgenic plants displayed induction of 2-propenyl glucosinolate; however, the absolute content of this glucosinolate in transgenic B. napus canola was relatively low (less than 1.00 μmol g⁻¹ seed). In the high glucosinolate content progenies derived from the crosses of B. napus rapeseed and transgenic B. napus canola, MAM gene silencing strongly induced the production of 2-propenyl glucosinolate to high levels (up to 4.45 μmol g⁻¹ seed).     

油菜糖基转移酶BnIRX14基因家族鉴定及遗传转化

糖基转移酶在植物抗逆和发育调控中发挥着重要作用，为发掘糖基转移酶BnIRX14基因家族成员，解析在甘蓝型油菜中的生物学功能，该研究利用前期在甘蓝型油菜中克隆到的BnIRX14基因，采用序列比对和遗传转化的方法，进行BnIRX14基因家族成员鉴定和功能验证，以探讨BnIRX14基因家族在油菜发育中调控机理，为油菜杂交育种和抗逆育种提供理论依据。结果表明：(1)经基因组数据库比对分析在甘蓝型油菜中成功鉴定到3个糖基转移酶不同亚家族的11个BnIRX14家族成员，它们均具有糖基转移酶GT43家族成员结构域特征，其中有8个基因分别被定位在6条不同染色体上，3个亚家族在基因结构和保守元件中具有较大特异性。(2)利用农杆菌介导转化法，获得BnIRX14基因RNA干扰转基因油菜株系20株，经PCR检测，确定5株阳性转化体。(3)表型鉴定发现，有2株阳性转化株的花柱头至花柱中央为一孔状空腔，子房较野生型明显膨大，且柱头表面授粉后不能结实，表现雌性不育；其他3个阳性株花器结构发育正常，但植株茎、枝表皮有液体渗出，呈露珠状粘附在茎、枝表面。(4)实时荧光定量PCR分析显示，转BnIRX14基因油菜阳性植株...     

Valuable New Resistances Ensure Improved Management of Sclerotinia Stem Rot (Sclerotinia sclerotiorum) in Horticultural and Oilseed Brassica Species

Field resistances against Sclerotinia rot (SR) (Sclerotinia sclerotiorum) were determined in 52 Chinese genotypes of Brassica oleracea var. capitata, 14 Indian Brassica juncea genotypes carrying wild weedy Brassicaceae introgression(s) and four carrying B‐genome introgression, 22 Australian commercial Brassica napus varieties, and 12 B. napus and B. juncea genotypes of known resistance. All plants were individually inoculated by securing an agar disc from a culture of S. sclerotiorum growing on a glucose‐rich medium to the stem above the second internode with Parafilm tape. Mean stem lesion length across tested genotypes ranged from <1 to >68 mm. While there was considerable diversity within the germplasm sets from each country, overall, 65% of the B. oleracea var. capitata genotypes from China showed the highest levels of stem resistance, a level comparable with the highest resistance ever recorded for oilseed B. napus or B. juncea from China or Australia. One Indian B. juncea line carrying weedy introgression displayed a significant level of both stem and leaf resistance. However, the vast majority of commercial Australian oilseed B. napus varieties fell within the most susceptible 40% of genotypes tested for stem disease. There was no correlation between expressions of stem versus leaf resistance, suggesting their independent inheritance. A few Chinese B. oleracea var. capitata genotypes that expressed combined extremely high‐level stem (≤1 mm length) and leaf (≤0.5 mean number of infections/plant) resistance will be particularly significant for developing new SR‐resistant horticultural and oilseed Brassica varieties.     

Increased plant growth and copper uptake of host and non-host plants by metal-resistant and plant growth-promoting endophytic bacteria

The effects of inoculation with two metal-resistant and plant growth-promoting endophytic bacteria (Burkholderia sp. GL12 and Bacillus megaterium JL35) were evaluated on the plant growth and Cu uptake in their host Elsholtzia splendens and non-host Brassica napus plants grown in natural Cu-contaminated soil. The two strains showed a high level of ACC deaminase activities. In pot experiments, inoculation with strain GL12 significantly increased root and above-ground tissue dry weights of both plants, consequently increasing the total Cu uptake of E. splendens and Brassica napus by 132% and 48.2% respectively. Inoculation with strain JL35 was found to significantly increase not only the biomass of B. napus, consequently increasing the total Cu uptake of B. napus by 31.3%, but Cu concentration of E. splendens for above-ground tissues by 318% and roots by 69.7%, consequently increasing the total Cu uptake of E. splendens by 223%. The two strains could colonize the rhizosphere soils and root interiors of both plants. Notably, strain JL35 could colonize the shoot tissues and significantly increase the translocation factors and bioaccumulation factors of E. splendens. These results suggested that Burkholderia sp. GL12 and B. megaterium JL35 were valuable bacterial resource which had the potential in improving the efficiency of Cu phytoextraction by E. splendens and B. napus in a natural Cu-contaminated soil.     

The relation between growth inhibition and secretion level of momilactone B from rice root

Abstract

The growth inhibitory activity of seven rice (Oryza sativa L.) cultivars and the secretion level of momilactone B from these rice cultivars were determined to understand chemical basis of the interaction of rice with other plant species. All rice cultivars inhibited the growth of hypocotyls and roots of lettuce (Lactuca sativa L.) seedlings when the lettuce was grown together with the rice, and showed different range of the inhibitory activity. These results suggest that all rice cultivars may possess allelopathic activity and the activity may be cultivar dependent. Momilactone B, which is a potent growth inhibitor, was found in root exudates of all rice cultivars, and the momilactone B concentration was also cultivar-dependent. The allelopathic activity of each rice cultivar was closely correlated with momilactone B concentration in the root exudates. The present results suggest that rice cultivars possess various allelopathic activities and their allelopathic activity may depend on the secretion level of momilactone B. Therefore, momilactone B may play an important role in rice allelopathy and in the chemical interactions of rice with other plant species.     

The EPSPS gene flow from glyphosate-resistant Brassica napus to untransgene B. napus and wild relative species Orychophragmus violaceus

Gene flow from transgenic plants to compatible wild relatives is one of the major impediments to the development of the culture of genetically engineered crop plants. In this work, the flow of EPSPS (conferring resistance to glyphosate) gene of transgene Brassica napus toward the untransgene B. napus and wild relative species Orychophragmus violaceus in an open field (1 ha) was studied. The data related to only the 2004 and 2005 autumn season on one location of southwest of China. Pollen dispersal and fertilization of the target plants were favored and a detailed analysis of the hybrid offspring was performed. In field, the data studied show that the gene flow frequency was 0.16% between GM and non-GM B. napus at a distance of 1 m from the transgenic donor area. The crosspollination frequency was 0.05% between GM and non-GM B. napus at a distance of 5 m from the transgenic donor area. At a distance of 10 m, no crosspollination was observed. According to the results of this study, B. napus transgene flow was low. However, the wild relative species O. violaceus could not be fertilized by the transgenic pollen of B. napus, no matter what the distance was.     

Production and cytogenetic characterization of intertribal somatic hybrids between <Emphasis Type="Italic">Brassica napus</Emphasis> and <Emphasis Type="Italic">Isatis indigotica</Emphasis> and backcross progenies

Intertribal somatic hybrids between Brassica napus (2n = 38, AACC) and a dye and medicinal plant Isatis indigotica (2n = 14, II) were obtained by fusions of mesophyll protoplasts. From a total of 237 calli, only one symmetric hybrid (S2) and five asymmetric hybrids (As1, As4, As6, As7 and As12) were established in the field. These hybrids showed some morphological variations and had very low pollen fertility. Hybrids S2 and As1 possessed 2n = 52 (AACCII), the sum of the parental chromosomes, and As12 had 2n = 66 (possibly AACCIIII). Hybrids As4, As6 and As7 were mixoploids (2n = 48–62). Genomic in situ hybridization analysis revealed that pollen mother cells at diakinesis of As1 contained 26 bivalents comprising 19 from B. napus and 7 from I. indigotica and mainly showed the segregation 26:26 at anaphase I (AI) with 7 I. indigotica chromosomes in each polar group. Four BC₁ plants from As1 after pollinated by B. napus resembled mainly B. napus in morphology but also exhibited some characteristics from I. indigotica. These plants produced some seeds on selfing or pollination by B. napus. They had 2n = 45 (AACCI) and underwent pairing among the I. indigotica chromosomes and/or between the chromosomes of two parents at diakinesis. All hybrids mainly had the AFLP banding patterns from the addition of two parents plus some alterations. B. napus contributed chloroplast genomes in majority of the hybrids but some also had from I. indigotica. Production of B. napus–I. indigotica additions would be of considerable importance for genome analysis and breeding.     

Intergeneric transfer of cytoplasmic male sterility between Raphanus sativus (cms line) and Brassica napus through cytoplast-protoplast fusion

Summary Cytoplasts isolated from hypocotyl protoplasts of Raphanus sativus cv Kosena (cms line) by ultracentrifugation through Percoll/mannitol discontinuous gradient were fused with iodoacetamide(IOA)-treated protoplasts of Brassica napus cv Westar. Seventeen randomly selected regenerated plants were characterized for morphology and chromosome numbers. All of the regenerated plants had morphology identical to B. napus and 10 of them possessed the diploid chromosome number of B. napus. The remaining plants had chimeric or aneuploid chromosome numbers. The mitochondrial genomes in the 10 fusion products possessing the diploid chromosome numbers of B. napus were examined by Southern hybridization analysis. Four of the 10 plants contained mitochondrial DNA showing novel hybridization patterns. Of these 4 plants, 1 was male sterile, and 3 were male fertile. The remaining plants showed mitochondrial DNA patterns identical to B. napus and were male fertile.     

Allelopathic Bacteria and Their Impact on Higher Plants

The impact of allelopathic, nonpathogenic bacteria on plant growth in natural and agricultural ecosystems is discussed. In some natural ecosystems, evidence supports the view that in the vicinity of some allelopathically active perennials (e.g., Adenostoma fasciculatum, California), in addition to allelochemicals leached from the shrub's canopy, accumulation of phytotoxic bacteria or other allelopathic microorganisms amplify retardation of annuals. In agricultural ecosystems allelopathic bacteria may evolve in areas where a single crop is grown successively, and the resulting yield decline cannot be restored by application of minerals. Transfer of soils from areas where crop suppression had been recorded into an unaffected area induced crop retardation without readily apparent symptoms of plant disease. Susceptibility of higher plants to deleterious rhizobacteria is often manifested in sandy or so-called skeletal soils. Evaluation of phytotoxic activity under controlled conditions, as well as ways to apply allelopathic bacteria in the field, is approached. The allelopathic effect may occur directly through the release of allelochemicals by a bacterium that affects susceptible plant(s) or indirectly through the suppression of an essential symbiont. The process is affected by nutritional and other environmental conditions, some may control bacterial density and the rate of production of allelochemicals. Allelopathic nonpathogenic bacteria include a wide range of genera and secrete a diverse group of plant growth-mediating allelochemicals. Although a limited number of plant growth-promoting bacterial allelochemicals have been identified, a considerable number of highly diversified growth-inhibiting allelochemicals have been isolated and characterized. Some species may produce more than one allelochemical; for example, three different phyotoxins, geldanamycin, nigericin, and hydanthocidin, were isolated from Streptomyces hygroscopicus. Efforts to introduce naturally produced allelochemicals as plant growth-regulating agents in agriculture have yielded two commercial herbicides, phosphinothricin, a product of Streptomyces viridochromogenes, and bialaphos from S. hygroscopicus. Many species of allelopathic bacteria that affect growth of higher plants are not plant specific, but some do exhibit specificity; for example, dicotyledonous plants were more susceptible to Pseudomonas putida than were monocotyledons. Differential susceptibility of higher plants to allelopathic bacteria was noted also in much lower taxonomical categories, at the subspecies level, in different cultivars of wheat, or of lettuce. Therefore, when test plants are employed to evaluate bacterial allelopathy, final evaluation must include those species that are assumed to be suppressed in nature. The release of allelochemicals from plant residues in plots of ‘continuous crop cultivation’ or from allelopathic living plants may induce the development of specific allelopathic bacteria. Both the rate by which a bacterium gains from its allelopathic activity through utilizing plant excretions, and the reasons for the developing of allelopathic bacteria in such habitats, are important goals for further research.     

Analysis of plants regenerated from protoplast fusions between Brassica napus and Eruca sativa

Summary Protoplasts from etiolated hypocotyls of Brassica napus stained with carboxyfluorescein were fused with mesophyll protoplasts from Eruca sativa. Hybrid cells could be identified under the light microscope by (1) fully developed chloroplasts derived from E. sativa and (2) the cytoplasmic strands of the B. napus hypocotyl protoplasts, or (3) by the presence of both red and green fluorescence when investigated under UV light. The heterokaryons were selected using either a micro-manipulator or a flow sorter. On average, 5.4% of the calli obtained after selection differentiated into shoots. Regenerated shoots were subjected to isozyme analysis for verification of their hybrid character. Of the 23 hybrids successfully transferred to the greenhouse, 11 were asymmetric according to isozyme analysis. The nuclear DNA content of the hybrids was determined by flow cytometry, which gives an estimate of chromosome number. Most of the hybrids had a DNA content, and thus a chromosome number, that deviated from the expected sum of the parents. Almost all of the hybrids had some degree of fertility and produced seeds. Seed set, expressed as seeds per pollinated flower, was on average 7% of that of B. napus in the case of self-pollination and 26% of that of B. napus when backcrossed to B. napus. The chloroplast genotype was investigated in 13 hybrids. Of these, 11 had chloroplasts derived from B. napus, while only 2 had chloroplasts of E. sativa origin.