The genomic relationships among six wild perennial species of the genus Glycine subgenus Glycine Willd.

Summary Based on meiotic chromosome behavior in intra- and interspecific hybrids, genome symbols were assigned to the following diploid (2n=40) Glycine species: G. canescens = AA; G. clandestina- Intermediate pod (Ip)=A ₁ A ₁; G. clandestina-Short pod (Sp)=BB; G. latifolia = B ₁ B ₁; G. tabacina = B ₂ B ₂; G. cyrtoloba = CC; and G. tomentella = DD. Genome symbol GG was reserved for the soybean, G. max. At metaphaseI, loose chromosome associations were observed in completely sterile interspecific hybrids whose parents differed in their genomes, suggesting some chromosome homologies among species. Although G. clandestina-Sp, G. latifolia and G. tabacina are morphologically distinct species, they differ only by a paracentric inversion. Similar observations were recorded for G. canescens and G. clandestina-Ip. Evidence is presented that demonstrates that G. tabacina (2n=80) and G. tomentella (2n=78, 80) are allotetraploid species complexes. Hybrid weakness, sterility, seedling lethality and seed inviability were found in intra- and interspecific hybrids.This research was supported in part by the Illinois Agricultural Experiment Station and the U.S. Department of Agriculture (Special grant 82-CRSR-2-2007). Travel grants to collect Glycine germplasm were received from the Rockefeller Foundation, the Illinois Soybean Program Operating Board, the National Science Foundation (INT76-14753) and the International Board for Plant Genetic Resources     

雷公藤组培产物的杀虫杀菌活性研究

采用室内生测法研究了雷公藤愈伤组织、悬浮细胞、不定根等组培产物对小菜蛾毒杀、生长发育影响以及不定根提取物对番茄灰霉病等植物病原真菌菌丝生长抑制作用,以明确雷公藤组培产物的生物活性及其应用前景。结果表明,不同雷公藤组培产物对小菜蛾3龄幼虫都具有明显的毒杀作用,悬浮细胞以及不定根的LC50均超过了根皮粉的效果,其中的不定根提取物对小菜蛾3龄幼虫毒杀作用的LC50为根皮粉的1.95倍;不同组培产物提取物对小菜蛾幼虫的生长均有明显的抑制作用,其中不定根提取物处理后每天的小菜蛾体重显著下降,72h后70%左右已经死亡,存活的试虫体重比试验前下降了18.33%;雷公藤不定根提取物对供试的11种植物病原真菌菌丝生长均有一定的抑制作用,有5种的抑制率超过60%,并对番茄灰霉病菌的抑制作用最强,其EC50为10.074mg/mL,且不定根的抑制效果均超过了根皮粉的抑制效果。     

Determination of root biomasses of three species grown in a mixture using stable isotopes of carbon and nitrogen

A method is evaluated that employs variation in stable C and N isotopes from fractionations in C and N acquisition and growth to predict root biomasses of three plant species in mixtures. Celtis laevigata Willd. (C₃), Prosopis glandulosa Torr. (C₃, legume) and Schizachyrium scoparium (Michx.) Nash (C₄), or Gossypium hirsutum L. (C₃), Glycine max (L.) Merr. (C₃ legume), and Sorghum bicolor (L.) Moench (C₄) were grown together in separate, three-species combinations. Surface roots (0–10 cm depth) of each species from each of the two combinations were mixed in various proportions, and the relative abundances of ¹⁵N and ¹⁴N and ¹³C and ¹²C in prepared mixtures, surface roots of single species, and roots extracted from the 80-cm soil profile in which each species combination was grown were analyzed by mass spectrometry. An algebraic determination which employed the δ ¹³C, % ¹⁵N, and C and N concentrations of root subsamples of individual species accounted for more than 95% of the variance in biomass of each species in prepared mixtures with G. max, G. hirsutum, and S. bicolor. A similar analysis demonstrated species-specific differences in rooting patterns. Root biomasses of the C₄ monocots in each combination, S. scoparium and S. bicolor, were concentrated in the upper 20 cm of soil, while those of G. hirsutum and the woody P. glandulosa were largest in lower soil strata. Analyses of stable C and N isotopes can effectively be used to distinguish roots of species which differ in ratios of ¹⁵N to ¹⁴N and ¹³C to ¹²C and thus to study belowground competition between or rooting patterns of associated species with different C and N isotope signatures. The method evaluated can be extended to quantify aboveground and belowground biomasses of component species in mixtures with isotopes of other elements or element concentrations that differ consistently among plants of interest.     

Effect of aluminium on yield and plant chemical concentrations of some temperate legumes

The aluminium (Al) tolerance of 34 temperate legume species (143 genotypes, including 57 from Trifolium repens) was determined in 60 experiments over a 3 year period in a low ionic strength (2.7 × 10^-3 M) solution culture. For each genotype, the relationship between solution Al³⁺ activity (M) and relative yield was determined and the Al³⁺ activity associated with a 50% reduction in yield (Al_RY50) calculated. In addition, plant chemical concentrations were determined in at least one genotype from most species. For white clover, Al_RY50 over all genotypes had an approximately normal distribution with mean of 1.31 M for the tops and 1.51 M for the roots, and a standard deviation of about 0.4. This suggested that Al tolerance had a polygenic inheritance. For the other species tested, Al_RY50 ranged from 0.15 to 4.53 M in the tops and from 0.21 to 4.89 M in the roots. In the tops and roots, 37% and 26% respectively of the genotypes had an Al_RY50 less than 1 M, including all species tested in the genera Melilotus and Medicago. Only 8% or 23% of the genotypes, based on the tops and roots respectively, had an Al_RY50 greater than 2, including all genotypes in the species Lotus pedunculatus. Except for Lotus, there were no consistent differences between genera in plant chemical concentrations. In Lotus, concentrations of Ca, Zn, Mn and Cu in the tops and of all elements except B in the roots were lower than that of the other species. The Al_RY50 of the species was not related to plant chemical concentrations in the absence of Al. Depending on the plant element, increasing solution Al concentrations had no significant effect on plant chemical concentrations for 56–94% of the species. When a significant effect did occur, increasing Al in solution generally decreased S and K concentrations and increased Mn, Zn, Cu Fe, B and Al concentrations in the tops and roots and decreased Ca concentrations in the tops. Plant P concentrations decreased in the tops but increased in the roots. Increasing Al in solution increase plant Al at the average rate of 44 g g^-1 M ^-1 (range 20–87) in the tops and 333 g M ^-1 (range 162–616) in the roots.     

An investigation of morphogenesis within the genus Trifolium

Morphogenic responses within the genus Trifolium were investigated by culturing various explants from seedlings of 72 species. Seedlings from 32 species produced callus alone, 40 produced adventitious shoots and/or roots, of which 25 species produced only shoots and 7 species formed only roots. Seedlings within each species also varied in their response to culture. The section of these seedlings most likely to produce adventitious shoots was the original shoot with the remnants of the surrounding hypocotyl and cotyledons, followed by the excised cotyledons themselves.Inter- and intra-varietal variation was observed in T. repens. Genotypes that produced adventitious buds were selected and crossed. An improvement in the proportion of the population capable of morphogenesis was observed in one cultivar.     

Plant regeneration from seedling explants of perennial Glycine species

More than 5000 cultures, from 30 accessions of six Glycine species, were established to assess the rôle of plant genotype in the response to an agar-solidified culture medium containing B5 salts and vitamins, 3% w/v sucrose, 1.1 mg 1^–1 BAP and 0.005 mg 1^–1 IBA, already known to induce shoot regeneration in callus of G. clandestina. Shoot initiation was obtained in a variety of explants from G. canescens, G. falcata, G. latrobeana and G. tomentella. With the exception of G. latrobeana, development of buds into shoots followed transfer to B5-based medium with 0.2 mg^–1 BAP and 0.005 mg 1^–1 IBA. Shoots readily produced roots in hormone-free half-strength B5 medium. In G. latrobeana, both extension and rooting occurred on this medium. Shoot regeneration was obtained in 12 of 30 accessions evaluated, but one accession of G. canescens, G1171, produced shoots and plantlets at a consistently higher frequency than other accessions, with plantlet recovery in more than 70% of the cultures. Bud formation in callus of G. canescens G1171 also occurred if BAP was replaced by 1.0 mg 1^–1 kinetin, 2i-p or zeatin, albeit at a lower frequency.     

Arbuscular mycorrhizal colonization and nodulation improve flooding tolerance in <Emphasis Type="Italic">Pterocarpus officinalis</Emphasis> Jacq. seedlings

Pterocarpus officinalis (Jacq.) seedlings inoculated with the arbuscular mycorrhizal fungus, Glomus intraradices, and the strain of Bradyrhizobium sp. (UAG 11A) were grown under stem-flooded or nonflooded conditions for 13 weeks after 4 weeks of nonflooded pretreatment under greenhouse conditions. Flooding of P. officinalis seedlings induced several morphological and physiological adaptive mechanisms, including formation of hypertrophied lenticels and aerenchyma tissue and production of adventitious roots on submerged portions of the stem. Flooding also resulted in an increase in collar diameter and leaf, stem, root, and total dry weights, regardless of inoculation. Under flooding, arbuscular mycorrhizas were well developed on root systems and adventitious roots compared with inoculated root systems under nonflooding condition. Arbuscular mycorrhizas made noteworthy contributions to the flood tolerance of P. officinalis seedlings by improving plant growth and P acquisition in leaves. We report in this study the novel occurrence of nodules connected vascularly to the stem and nodule and arbuscular mycorrhizas on adventitious roots of P. officinalis seedlings. Root nodules appeared more efficient fixing N₂ than stem nodules were. Beneficial effect of nodulation in terms of total dry weight and N acquisition in leaves was particularly noted in seedlings growing under flooding conditions. There was no additive effect of arbuscular mycorrhizas and nodulation on plant growth and nutrition in either flooding treatment. The results suggest that the development of adventitious roots, aerenchyma tissue, and hypertrophied lenticels may play a major role in flooded tolerance of P. officinalis symbiosis by increasing oxygen diffusion to the submerged part of the stem and root zone, and therefore contribute to plant growth and nutrition.     

A novel life cycle arising from leaf segments in plants regenerated from horseradish hairy roots

Summary Horseradish (Armoracia rusticana) hairy root clones were established from hairy roots which were transformed with the Ri plasmid in Agrobacterium rhizogenes 15834. The transformed plants, which were regenerated from hairy root clones, had thicker roots with extensive lateral branches and thicker stems, and grew faster compared with non-transformed horseradish plants. Small sections of leaves of the transformed plants generated adventitious roots in phytohormone-free G (modified Gamborg's) medium. Root proliferation was followed by adventitious shoot formation and plant regeneration. Approximately twenty plants were regenerated per square centimeter of leaf. The transformed plants were easily transferable from sterile conditions to soil. When leaf segments of the transformed plants were cultured in a liquid fertilizer under non-sterile conditions, adventitious roots were generated at the cut ends of the leaves. Adventitious shoots were generated at the boundary between the leaf and the adventitious roots and developed into complete plants. This novel life cycle arising from leaf segments is a unique property of the transformed plants derived from hairy root clones.     

Overlapping expression patterns and differential transcript levels of phosphate transporter genes in arbuscular mycorrhizal,P<Subscript>i</Subscript>-fertilised and phytohormone-treated <Emphasis Type="Italic">Medicago truncatula</Emphasis> roots

A microarray carrying 5,648 probes of Medicago truncatula root-expressed genes was screened in order to identify those that are specifically regulated by the arbuscular mycorrhizal (AM) fungus Gigaspora rosea, by P_i fertilisation or by the phytohormones abscisic acid and jasmonic acid. Amongst the identified genes, 21% showed a common induction and 31% a common repression between roots fertilised with P_i or inoculated with the AM fungus G. rosea, while there was no obvious overlap in the expression patterns between mycorrhizal and phytohormone-treated roots. Expression patterns were further studied by comparing the results with published data obtained from roots colonised by the AM fungi Glomus mosseae and Glomus intraradices, but only very few genes were identified as being commonly regulated by all three AM fungi. Analysis of P_i concentrations in plants colonised by either of the three AM fungi revealed that this could be due to the higher P_i levels in plants inoculated by G. rosea compared with the other two fungi, explaining that numerous genes are commonly regulated by the interaction with G. rosea and by phosphate. Differential gene expression in roots inoculated with the three AM fungi was further studied by expression analyses of six genes from the phosphate transporter gene family in M. truncatula. While MtPT4 was induced by all three fungi, the other five genes showed different degrees of repression mirroring the functional differences in phosphate nutrition by G. rosea, G. mosseae and G. intraradices. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Hydrogen peroxide involvement in formation and development of adventitious roots in cucumber

Hydrogen peroxide (H₂O₂), an active oxygen species, is widely generated in many biological systems. The present study demonstrates that H₂O₂ was generated in seedling explants after the primary roots were removed, and it mediates the auxin response prior to adventitious root formation in cucumber (Cucumis sativus L. Ganfeng 8). When compared with the controls, treatment of cucumber seedling explants after primary roots removal with either 20–40 mM H₂O₂ or 10 μM IAA significantly increased the number of adventitious roots, and treatment with 10–50 mM H₂O₂ significantly increased the fresh weight of adventitious roots. The effects of H₂O₂ on promoting the formation and growth of adventitious roots were eliminated by 2 mM ascorbic acid, 100 U CAT or 1 μM DPI, and the effects of IAA were eliminated by 4 mM ascorbic acid, 100 U CAT or 5 μM DPI. Treatment with either 4 mM ascorbic acid or 1–5 μM DPI inhibited the formation and growth of adventitious roots, and these inhibitory effects were partly reversed by exogenous H₂O₂.Furthermore, a higher concentration of endogenous H₂O₂ was detected in seedling explants 3 h after the primary roots were removed. However, in 10 μM DPI-treated seedling explants, the concentration of endogenous H₂O₂ was markedly reduced by DPI. Results obtained suggest that H₂O₂ may function as a signaling molecule, involved in the formation and development of adventitious roots in cucumber.     

培养条件对西洋参不定根诱导的影响

为了提高西洋参不定根的诱导率和生长速度,该研究以西洋参鲜根为外植体,在基本培养基的基础上优化IBA、碳源、氮源和磷源等营养成分。结果表明:西洋参不定根诱导过程可以明显分为外植体脱分化(愈伤化)、再分化(根形成)和根伸长等三个阶段; MS基本培养基更有利于西洋参不定根的诱导,可能与MS培养基中矿质元素含量高有关;当培养基中IBA浓度达到2 mg·L~(-1)时,外植体表面上不定根分布密度大,诱导率达到(96±3.5)%;培养基中添加蔗糖到30 g·L~(-1)时,不定根的诱导效果最好,但继续提高浓度后不定根变短、直径变粗;培养基中NO_3~-∶NH_4~+和PO_4~(3-)浓度分别为20∶10(总氮量30 mmol·L~(-1))和25.0mmol·L~(-1)时,西洋参不定根诱导率达到最大。结果提示优化培养条件可以显著改善西洋参不定根的诱导和生长,为后续西洋参不定根规模化培养提供理论支持。     

Growth responses to waterlogging and drainage of woody Hakea (Proteaceae) seedlings,originating from contrasting habitats in south-western Australia

We investigated the responses of seven woody Hakea (Proteaceae) species (two populations of each), to two months of waterlogging and subsequent drainage, in a controlled glasshouse experiment. The species originated from contrasting environments (winter-wetland versus non-wetland habitats), and differed in abundance (endangered ironstone species versus common species). Waterlogging arrested growth of the main root system, and stimulated the formation of superficial adventitious roots just below the root/shoot junction in all species. Wetland species produced at least twice the amount of adventitious root dry mass of that of non-wetland species, due to differences in number, length or degree of branching. Their adventitious roots also tended to have higher porosities (7–10% versus 5–6% gas spaces). The relative amount of adventitious roots formed was strongly, positively correlated with the maintenance of shoot growth, and only the non-wetland species showed significant shoot growth reductions (19%) upon waterlogging. Dry mass percentage of stems and leaves, and leaf dry mass per area (LMA) increased considerably during waterlogging in all species (averages of 15, 29 and 27%, respectively), returning to the values of continuously drained control plants after drainage. Similarly, upon drainage, a suppression of shoot growth (average 35%) and a stimulation of root growth (average 50%) restored the root mass ratios to those of control plants. We found a negative correlation between the maintenance of growth during waterlogging versus that after waterlogging, suggesting a trade-off in functioning of the superficial adventitious roots between waterlogged and drained conditions. The rare winter-wet ironstone endemics resembled the common winter-wet species in most of their responses to waterlogging and drainage. Therefore, the results presented here cannot offer an explanation for their different distribution patterns. Our results suggest that non-wetland species may be disadvantaged in a wetland environment, due to their lower capacity to form adventitious roots resulting in stronger growth reductions.     

An auxin-inducible gene from loblolly pine (<Emphasis Type="Italic">Pinus taeda</Emphasis> L.) is differentially expressed in mature and juvenile-phase shoots and encodes a putative transmembrane protein

We have isolated a gene from loblolly pine, 5NG4, that is highly and specifically induced by auxin in juvenile loblolly pine shoots prior to adventitious root formation, but substantially down-regulated in physiologically mature shoots that are adventitious rooting incompetent. 5NG4 was highly auxin-induced in roots, stems and hypocotyls, organs that can form either lateral or adventitious roots following an auxin treatment, but was not induced to the same level in needles and cotyledons, organs that do not form roots. The deduced amino acid sequence shows homology to the MtN21 nodulin gene from Medicago truncatula. The expression pattern of 5NG4 and its homology to a protein from Medicago involved in a root-related process suggest a possible role for this gene in adventitious root formation. Homology searches also identified similar proteins in Arabidopsis thaliana and Oryza sativa. High conservation across these evolutionarily distant species suggests essential functions in plant growth and development. A 38-member family of genes homologous to 5NG4 was identified in the A. thaliana genome. The physiological significance of this redundancy is most likely associated with functional divergence and/or expression specificity of the different family members. The exact biochemical function of the gene is still unknown, but sequence and structure predictions and 5NG4::GFP fusion protein localizations indicate it is a transmembrane protein with a possible transport function.Electronic Supplementary Material Supplementary material is available in the online version of this article at Abbreviations ABA Abscisic acid - BA Benzylaminopurine - EST Expressed sequence tag - NAA 1-Naphthaleneacetic acid - GFP Green fluorescent protein - ORF Open reading frame     

Increasing NaCl and CaCl<Subscript>2</Subscript> concentrations in the growth medium of quince leaves: I. Effects on somatic embryo and root regeneration

Summary The effects of increasing concentrations of NaCl and CaCl₂ on quince (Cydonia oblonga Mill. BA 29 clone) somatic embryogenesis and adventitious root regeneration were investigated. Leaves collected from in vitro-grown shoots were used as explants and induced for 2d in liquid Murashige and Skoog medium containing 11.3 μM 2,4-dichlorophenoxyacetic acid. Explants were then cultured on semisolid Murashige and Skoog medium enriched with 4.7 μM kinetin and 0.5 μM naphthaleneacetic acid under red light for 25 d and under white light for another 25 d. Two experiments were performed: in the first, NaCl was used at 0,25, 50, 100, and 200 mM in factorial combination with CaCl₂ at 3, 9, and 27 mM; in the second, NaCl was applied at 0, 5, 10, 20, 40, and 80 mM in combination with CaCl₂ at 0.3, 1.0, and 3.0 mM. Quince leaves revealed the capacity to regenerate somatic embryos and/or adventitious roots. Quantitative and qualitative regeneration from leaves was affected by NaCl treatments: increasing NaCl concentrations, in combination with CaCl₂ at 1 mM, led to an increase in the proportion of leaves producing somatic embryos only, and to a decrease of both leaves regenerating roots only and leaves simultaneously producing somatic embryos and adventitious roots. This suggests a beneficial effect of salt stress on the embryogenic process. The regeneration response decreased with increasing salt concentrations and was almost totally inhibited above 50 mM NaCl and 9 mM CaCl₂. The presence of CaCl₂ in the culture medium apparently mitigated the effects of salt stress, but only when NaCl was applied at 40 mM. NaCl at 5 mM, in the presence of 0.3 or 1 mM CaCl₂, was favorable both to somatic embryo and root production. No value of the ratio Na⁺/Ca²⁺ was found to be optimal for the regeneration processes.     

Drought response of a native and introduced Hawaiian grass

The alien grass, Pennisetum setaceum, dominates many of the lowland arid regions that once supported native Heteropogon contortus grassland on the island of Hawaii. Response to drought in a glasshouse was compared between these C₄ grasses to test if success as an invader is related to drought tolerance or plasticity for traits that confer drought tolerance. Pennisetum produced 51% more total biomass, allocated 49% more biomass to leaves, and had higher net photosynthetic rates (P _n) on a leaf area basis than Heteropogon. Plants of both species under drought produced less total biomass and increased their allocation to roots compared to well-watered plants, but there was no difference between the two species in the magnitude of these responses. The decline in P _n with decreasing leaf water potential (₁) was greater for Pennisetum compared to Heteropogon. Plasticity in the response of P _n to ₁, osmotic potentials, and the water potentials at turgor loss in response to drought were not different between the two species. Stomata were more responsive to w in Heteropogon than in Pennisetum and for well-watered plants compared to droughted plants. Plasticity for the stomatal response to w, however, was not different between the species. There was no evidence that the alien, Pennisetum, had greater plasticity for traits related to drought tolerance compared to the native, Heteropogon. Higher P _n and greater biomass allocation to leaves resulted in greater growth for Pennisetum compared to Heteropogon and may explain the success of Pennisetum as an invader of lowland arid zones on Hawaii.     

Peroxidase isoenzymes as markers for the rooting ability of easy-to-root and difficult-to-root <Emphasis Type="Italic">Grevillea</Emphasis> species and cultivars of <Emphasis Type="Italic">Protea obstusifolia</Emphasis> (Proteaceae)

Summary One easy-to-root and one difficult-to-root species of the ornamental plant Grevillea were investigated for rooting potential in relation to peroxidase activity. In vitro-grown shoot segments of both species started to root 30 d after transplanting to rooting medium containing indole-3-butyric acid (IBA), however, fewer roots were found on fewer segments of the difficult-to-root species G. petrophioides compared to the easy-to-root species G. rondeau. Total peroxidase (POX) activity was measured during the rooting process. G. petrophioides showed higher total POX activity at the time point of adventitious root formation than G. rondeau. Isoelectric focusing electrophoresis showed that G. rondeau contained more acidic isoforms than G. petrophioides, but the basic isoforms were more prominent in the difficult-to-root species, especially at the time point of lateral root emergence. In addition, the ability of different hormones to induced POX activity in upper and lower stem segments of both species was tested. Indole-3-acetic acid (IAA), IBA and α-naphthaleneacetic acid induced POX activity in the upper stem segments of G. rondeau, whereas the same hormones led to the induction of POX activity in the lower stem segments of G. petrophioides. Similar to the results obtained with Grevillea, the difficult-to-root variety of Protea showed higher POX activity, especially in the middle stem part and the leaves. Feeding of radiolabeled IAA to the Grevillea stem segments resulted in the synthesis of three different compounds in both species. After 1h incubation no differences were found in the uptake of IAA and the appearance of other labeled compounds. However, after 2 and 4 h incubation IAA uptake was faster in the easy-to-root species and IAA was also metabolized to a higher extent in G. rondeau. Three metabolites were found, tentatively identified as IAA-aspartate, IBA, and an IBA conjugate.     

Variation for Root Aerenchyma Formation in Flooded and Non-Flooded Maize and Teosinte Seedlings

Morphological and anatomical factors such as aerenchyma formation in roots and the development of adventitious roots are considered to be amongst the most important developmental characteristics affecting flooding tolerance. In this study we investigated the lengths of adventitious roots and their capacity to form aerenchyma in three- and four-week-old seedlings of two maize (Zea mays ssp. mays, Linn.) inbred accessions, B64 and Na4, and one teosinte, Z. nicaraguensis Iltis & Benz (Poaceae), with and without a flooding treatment. Three weeks after sowing and following a seven day flooding treatment, both maize and teosinte seedlings formed aerenchyma in the cortex of the adventitious roots of the first three nodes. The degree of aerenchyma formation in the three genotypes increased with a second week of flooding treatment. In drained soil, the two maize accessions failed to form aerenchyma. In Z. nicaraguensis, aerenchyma developed in roots located at the first two nodes three weeks after sowing. In the fourth week, aerenchyma developed in roots of the third node, with a subsequent increase in aerenchyma in the second node roots. In a second experiment, we investigated the capacity of aerenchyma to develop in drained soil. An additional three teosinte species and 15 maize inbred lines, among them a set of flooding-tolerant maize lines, were evaluated. Evaluations indicate that accessions of Z. luxurians (Durieu & Asch. Bird) and two maize inbreds, B55 and Mo20W, form aerenchyma when not flooded. These materials may be useful genetic resources for the development of flooding-tolerant maize accessions.     

Cooccurring plants forming distinct arbuscular mycorrhizal morphologies harbor similar AM fungal species

Arbuscular mycorrhizal (AM) fungal spores were isolated from field transplants and rhizosphere soil of Hedera rhombea (Miq) Bean and Rubus parvifolius L., which form Paris-type and Arum-type AM, respectively. DNA from the spore isolates was used to generate molecular markers based on partial large subunit (LSU) ribosomal RNA (rDNA) sequences to determine AM fungi colonizing field-collected roots of the two plant species. Species that were isolated as spores and identified morphologically and molecularly were Gigaspora rosea and Scutellospora erythropa from H. rhombea, Acaulospora longula and Glomus etunicatum from R. parvifolius, and Glomus claroideum from both plants. The composition of the AM fungal communities with respect to plant trap cultures was highly divergent between plant species. Analysis of partial LSU rDNA sequences amplified from field-collected roots of the two plant species with PCR primers designed for the AM fungi indicated that both plants were colonized by G. claroideum, G. etunicatum, A. longula, and S. erythropa. G. rosea was not detected in the field-collected roots of either plant species. Four other AM fungal genotypes, which were not isolated as spores in trap cultures from the two plant species, were also found in the roots of both plant species; two were closely related to Glomus intraradices and Glomus clarum. One genotype, which was most closely related to Glomus microaggregatum, was confined to R. parvifolius, whereas an uncultured Glomeromycotan fungus occurred only in roots of H. rhombea. S. erythropa was the most dominant fungus found in the roots of H. rhombea. The detection of the same AM fungal species in field-collected roots of H. rhombea and R. parvifolius, which form Paris- and Arum-type AM, respectively, shows that AM morphology in these plants is strongly influenced by the host plant genotypes as appears to be the case in many plant species in natural ecosystems, although there are preferential associations between the hosts and colonizing AM fungi in this study.     

Influence of pruning management on P and N distribution and use efficiency by N2 fixing and non-N2 fixing trees used in alley cropping systems

Pruning of hedgerow trees is an important management practice for the successful establishment of an alley cropping system. Although pruning affects biomass production, only meager evidence of this management on distribution of nutrients among the different plant organs after tree regrowth is available. This study examined the effect of pruning on the distribution and use efficiency of N and P in a N₂ fixing leguminous tree species, Gliricidia sepium, and two non-N₂ fixing leguminous tree species, Senna siamea and S. spectabilis, grown in a field on an Alfisol (low in P) at Fashola (Guinea Savanna Zone), Southwestern Nigeria. Four P rates, 0, 20, 40 and 80 kg P ha^–1 as single superphosphate were used and management treatments included pruned versus unpruned plants. The ¹⁵N isotope dilution technique was used to measure N₂ fixation in G. sepium. Partitioning of total P among different plant organs was influenced by plant species and pruning management, but was not affected by P application rates. The distribution of total P in the various plant organs followed that of dry matter yield while N partitioning had a different pattern. Pruned plants distributed about 118% more total P to branches and had a higher physiological P use efficiency (PPUE) than unpruned plants. Leaves were the biggest sink for total N and N allocation in the other plant organs was influenced by plant species and pruning management, G. sepium had relatively more of its total N and P partitioned into roots (about double that of the non-N₂ fixing trees) but had a lower PPUE. Unpruned and pruned G. sepium derived 35 and 54% respectively of their total N from atmospheric N2, with about 54% of the fixed N2 being allocated to leaves and roots. Results showed that N and P pools turned over in the branches during plant regrowth after pruning but the causative factors associated with this phenomenon were not clear.     

Karyological studies onGentiana sect.Chondrophyllae (Gentianaceae) from China

Nineteen populations of fifteen species ofGentiana sect.Chondrophyllae from China were observed cytologically.Gentiana alsinoides, G. anisostemon, G. asterocalyx, G. exigua, G. heterostemon, G. intricata, G. praticola, G. pseudoaquatica, G. spathulifolia, andG. subintricata all had the same chromosome number of 2n = 20 (or n = 10), whereasG. piasezkii had 2n = 36,G. squarrosa 2n = 38,G. prattii 2n = 18,G. aristata 2n = 14 (n = 7), andG. heleonastes 2n = 12. All these chromosome numbers are documented here for the first time, except forG. squarrosa, where it is a new number report. The basic numbers of x = 6, x = 7 and x = 19 are new for the section. Karyotype analyses of some species revealed that, except for a few cases, the species examined mainly had metacentric chromosomes. 2n = 20 = 2m(SAT) + 18m was found to be the main type of karyotype for the species with 2n = 20. Chromosomal evolution and its mechanism in this section are also discussed.