Genetic basis and mapping of the resistance to rice yellow mottle virus. I. QTLs identification and relationship between resistance and plant morphology

 Rice yellow mottle virus (RYMV) resistance QTLs were mapped in a doubled-haploid population of rice, ‘IR64/Azucena’. Disease impact on plant morphology and development, expression of symptoms and virus content were evaluated in field conditions. Virus content was also assessed in a growth chamber. RYMV resistance was found to be under a polygenic determinism, and 15 QTLs were detected on seven chromosomal fragments. For all of the resistance QTLs detected, the favourable allele was provided by the resistant parent ‘Azucena’. Three regions were determined using different resistance parameters and in two environments. On chromosome 12, a QTL of resistance that had already been detected in this population and another indica/japonica population was confirmed both in the field and under controlled conditions. Significant correlations were observed between resistance and tillering ability, as measured on control non-inoculated plants. In addition, the three genomic fragments involved in resistance were also involved in plant architecture and development. In particular, the semi-dwarfing gene sd-1, on chromosome 1, provided by the susceptible parent, ‘IR64’, mapped in a region where resistance QTLs were detected with most of the resistance parameters. In contrast, the QTL of resistance mapped on chromosome 12 was found to be independent of plant morphology. Received: 20 April 1998 / Accepted: 30 April 1998     

Plant biotechnology: the genetic manipulation of plants. * Slater A, Scott N, Fowler M. 2003 Oxford: Oxford University Press. {pound}19.99 (softback). 346 pp.

Few areas of science have progressed as rapidly, or have hadsuch an impact on public consciousness and governments, as recentadvances in plant biotechnology. These exciting scientific discoveriesand their increasing application are continuing to generateconsiderable economic, social and ethical considerations. Particularconcerns have been expressed, however, about potential ‘foodsafety’ and ‘environmental impact’ implications,in particular, of this ‘revolution in biology’ inagriculture and the food     

Black, M. and Pritchard, H.W. (eds). Desiccation and survival in plants. Drying without dying

This excellent volume provides a very readable and comprehensivecoverage of desiccation tolerance in plants. The opening chapter,from which the subtitle ‘Drying without dying’ isdrawn, gives a splendid overview of what desiccation toleranceis and how plants accommodate this potentially lethal stress.It includes a history of research into plant desiccation andthe development of ideas, its occurrence within the plant kingdomand its ecological significance. The subsequent chapters buildmasterfully upon this introduction, in     

Plant roots. Growth, activity and interaction with soils

It is (or should be) self-evident that life on Earth dependsmainly on life in earth, and in this respect soil–plantinteractions are of key importance. This book brings togetherareas that are still often compartmented into fields such aschemical and physical aspects of soil science (where plantsare still sometimes regarded as a ‘black box’ ofuncertain relevance), plant physiology (now sometimes re-badgedas plant functional biology), and soil microbial ecology. Agriculturalscientists have, of course, rarely been guilty of ignoring soilfactors in relation to plant growth and productivity. Plantecologists sometimes have, and to some of them it's the soilthat is the ‘black box’ when it comes to understandingplant population and community ecology. Models of the     

Mendelism, Plant Breeding and Experimental Cultures: Agriculture and the Development of Genetics in France

The article reevaluates the reception of Mendelism in France, and more generally considers the complex relationship between Mendelism and plant breeding in the first half on the 20th century. It shows on the one side that agricultural research and higher education institutions have played a key role in the development and institutionalization of genetics in France, whereas university biologists remained reluctant to accept this approach on heredity. But on the other side, plant breeders, and agricultural researchers, despite an interest in Mendelism, never came to see it as the breeders’ panacea, and regarded it instead as of only limited value for plant breeding. I account for this judgment in showing that the plant breeders and Mendelism designed two contrasting kinds of experimental systems and inhabited distinct experimental cultures. While Mendelian geneticists designed experimental systems that allowed the production of definite ratios of different forms that varied in relation to a few characters, plant breeders’ experimental systems produced a wide range of variation, featuring combinations between hundreds of traits. Rather than breaking this multiple variation down into simple elements, breeders designed and monitored a genetic lottery. The gene was a unit in a Mendelian experimental culture, an “epistemic thing” as Rheinberger put it, that could be grasped by means of statistical regularities, but it remained of secondary importance for French plant breeders, for whom the strain or the variety – not the gene – was the fundamental unit of analysis and manipulation.     

Complementarity effects through dietary mixing enhance the performance of a generalist insect herbivore

The ontogenetic niche concept predicts that resource use depends on an organism’s developmental stage. This concept has been investigated primarily in animals that show differing resource use strategies as juveniles and as adults, such as amphibians. We studied resource use and performance in the grasshopper Chorthippus parallelus (Orthoptera, Acrididae) provided with food plant mixtures of either one, three or eight plant species throughout their development. C. parallelus survival and fecundity was highest in the food plant mixture with eight plant species and lowest in the treatments where only one single plant species was offered as food. C. parallelus’ consumption throughout its ontogeny depended on sex, and feeding on different plant species was dependent on a grasshopper’s developmental stage. To depict grasshopper foraging in food plant mixtures compared to foraging on single plant species, we introduce the term “relative forage total” (RFT) based on an approach used in biodiversity research by Loreau and Hector (Nature 413:548–274, 2001). RFT of grasshoppers in food plant mixtures was always higher than what would have been expected from foraging in monocultures. The increase in food consumption was due to an overall increase in feeding on plant species in mixtures compared to consumption of the same species offered as a single diet. Thus we argue that grasshopper foraging exhibits complementarity effects. Our results reinforce the necessity to consider development-related changes in insect herbivore feeding. Thorough information on the feeding ontogeny of insect herbivores could not only elucidate their nutritional ecology but also help to shed light on their functional role in plant communities. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Effect of certain soil conditions on nodulation ofAcacia spp.

Summary Growth and nodulation ofAcacia spp. in sand increased with increase in soil moisture to an optimum at 15 per cent soil moisture and this agreed with the occurrence of these species in the more moist sites reported by other workers. TheAcacia species grew and produced effective nodules at up to 35°C and this is the highest temperature for nodulation so far recorded. It indicated adaptation of these species to the warm and dry conditions of the fields. Soil reaction affected nodulation more than it affected plant growth. At pH 5–5.5 nodulation was absent while plant growth was as good as at pH 6.5–7.0 which was the optimum level for both growth and effective nodulation. The latter were reduced at pH 8.5–9.0 and therefore the alkaline reaction of the soils in Northern Sudan may be a factor influencing growth of Acacia in that region.     

Genetic dissection of grain yield in bread wheat. I. QTL analysis

Grain yield forms one of the key economic drivers behind a successful wheat (Triticum aestivum L.) cropping enterprise and is consequently a major target for wheat breeding programmes. However, due to its complex nature, little is known regarding the genetic control of grain yield. A doubled-haploid population, comprising 182 individuals, produced from a cross between two cultivars ‘Trident’ and ‘Molineux’, was used to construct a linkage map based largely on microsatellite molecular makers. ‘Trident’ represents a lineage of wheat varieties from southern Australia that has achieved consistently high relative grain yield across a range of environments. In comparison, ‘Molineux’ would be rated as a variety with low to moderate grain yield. The doubled-haploid population was grown from 2002 to 2005 in replicated field experiments at a range of environments across the southern Australian wheat belt. In total, grain yield data were recorded for the population at 18 site-year combinations. Grain yield components were also measured at three of these environments. Many loci previously found to be involved in the control of plant height, rust resistance and ear-emergence were found to influence grain yield and grain yield components in this population. An additional nine QTL, apparently unrelated to these traits, were also associated with grain yield. A QTL associated with grain yield on chromosome 1B, with no significant relationship with plant height, ear-emergence or rust resistance, was detected (LOD ≥2) at eight of the 18 environments. The mean yield, across 18 environments, of individuals carrying the ‘Molineux’ allele at the 1B locus was 4.8% higher than the mean grain yield of those lines carrying the ‘Trident’ allele at this locus. Another QTL identified on chromosome 4D was also associated with overall gain yield at six of the 18 environments. Of the nine grain yield QTL not shown to be associated with plant height, phenology or rust resistance, two were located near QTL associated with grain yield components. A third QTL, associated with grain yield components at each of the environments used for testing, was located on chromosome 7D. However, this QTL was not associated with grain yield at any of the environments. The implications of these findings on marker-assisted selection for grain yield are discussed.     

The Nitrogen Content of Plants and the Self-thinning Rule of Plant Ecology: A Test of the Core-skin Hypothesis

The ‘core-skin’ hypothesis postulates that secondarilythickened plants behave energetically as an inert ‘core’covered by an active ‘skin’, the ‘skin’being two-imensional, the ‘core’ three-dimensional.This would explain the ‘self-thinning ‘or‘–3/2’ rule of plant ecology, that is, the tendencyfor log (dry weight per plant) and log (number of plants perunit area) to progress along a straight line relationship, withslope = – 3/2’. The hypothesis was tested as follows. Plant nitrogen contentwas used as an estimate of the mass of ‘skin’ perplant, and dry weight as an estimate of the mass of the ‘core’.As plants mature the slope of the relationship between y = log(mass of nitrogen per plant) and x = log (mass of dry matterper plant) is expected to decline from an initial value of 1.0towards a final value of 0.66. The intercept of the relationshipis expected to reflect the intrinsic content of ‘skin’per unit of ‘core’. Genotypic variation in thisparameter should cause genotypic differences in the maximumattainable yield of biomass per unit area. The expectations were investigated by fitting the function y= p+qx+r exp – x to 30 sets of data on plant nitrogencontent, plant weight and time in 18 different vegetables. Simplelinear regressions of y on x were fitted to more limited setsof data on weights and nitrogen contents of mature trees. Theexpectations were, with some minor exceptions, confirmed. Nitrogen, yield, plant competition, self-thinning     

Late Transplanting and the Yield of Phaseolus vulgaris L.

The prediction that very high seed yields of dry beans (Phaseolusvulgaris L.) would be produced by the delayed transplantingof large plants has been tested in a factorial experiment withfour dates of transplanting and eight plant populations. Therewere significant differences in yield between transplantingdates and between population densities, and there was a significantdate-density interaction. At low plant densities (up to about30 plants m^–2) the three transplanted treatments yieldedless than the hand-sown controls, and late transplanting yieldedless than early. At the highest density the situation was reversed;all three transplanted treatments out-yielded the controls andlate transplanting tended to out-yield plants transplanted early.The biggest yield was 340 g seed m^–2 from a transplantedcrop grown at 35 plants m^–2. The data on yield fitted a modified rectangular hyperbola ofthe form where y is yield per unit area, p is the number of plants perunit area, t is the number of days between sowing and transplanting,and B_o, n, m, and p are arbitrary parameters. This equationaccounted for 91 per cent of the variation in yield with t andp. It is suggested that late transplanting had adverse effects,due to transplanting ‘shock’ and which were mostmarked at low plant densities; and beneficial effects, ascribableto an effect on plant ‘plasticity’, which were mostmarked at high plant densities. Possible physiological mechanismsof these effects are discussed. Phaseolus vulgaris, yield, density, transplanting     

Mycorrhiza status of Gnetum spp. in Cameroon: evaluating diversity with a view to ameliorating domestication efforts

A field survey was carried out to investigate the diversity of mycorrhizal fungi associated with Gnetum spp. in Cameroon. The extent and variation of ectomycorrhizal colonisation as well as the degree of host specificity were evaluated. Gnetum spp. were found to be almost always ectomycorrhizal in all sites visited. There were just two ectomycorrhizal morphotypes (‘yellow’ and ‘white’) associated with this plant. Such low diversity is unusual for an ectomycorrhizal plant. The yellow morphotype was the most widespread and prevalent and was identified by morphological and molecular methods to have been formed with Scleroderma sinnamariense. Propagules of this fungus were present in soil collected from farm lands, cocoa plantations, Chromolaena and bush fallows, as well as in a relatively undisturbed forest harbouring ectomycorrhizal legumes. The fungus responsible for the white morphotype was identified as also belonging to the genus Scleroderma by ITS sequence similarity. Arbuscular mycorrhizal structures were absent in cleared and stained portions of the roots.     

Studies in the Regeneration of Horseradish: I. A Re-examination of the Morphology and Anatomy of Regeneration

1. Horseradish roots reach a stage of ‘ripeness to regenerate’at the age of 1–2 months, when secondary thickening hasbegun, a phellogen has formed, and the primary cortex has beenshed; provided that they are then detached from the parent plant. 2. New primordia arise (as is already known) only in associationwith the scars of lateral roots; but they are produced, notas previously believed from a callus, but individually as organizedmeristems whose cells are derived only from the phellogen ofthe main root. 3. The primordia appear to be undetermined (‘indifferent’)in nature; their subsequent differentiation into buds or rootsis described.     

Thidiazuron-induced plant regeneration from hypocotyl cultures of St. John's wort (Hypericum perforatum. cv 'Anthos')

 St. John's wort (Hypericum perforatum. cv 'Anthos') is a medicinal plant with evidence of efficacy as an anti-depressant. The present report describes the development of an in vitro regeneration system that utilizes thidiazuron [N-phenyl-N′-(1,2,3-thidiazol-yl)urea] for the induction of de novo shoots on etiolated hypocotyl segments of St. John's wort seedlings. The optimum level of thidiazuron supplementation to the culture medium was 5 μmol·l^–1 for a 9-day induction period followed by subculture of induced hypocotyl explants on basal medium. Other plant growth regulators including benzyladenine and indoleacetic acid were not effective in inducing regeneration on St. John's wort hypocotyls. Histological examination of the cultures revealed that the regenerated plants were derived from de novo developed shoots. Transfer of the regenerated shoots into a liquid medium with no plant growth regulators resulted in the rapid and prolific growth of viable plantlets. The rapid and efficient micropropagation system for St. John's wort may be useful for both the genetic improvement of this crop and the production of high-quality phytopharmaceutical preparations for the treatment of neurological disorders. Received: 19 March 1999 / Revision received: 5 July 1999 · Accepted: 17 August 1999     

Cap Formation during the Elongation of Lateral Roots of Vicia faba L.

Cell proliferation was examined in the cap initials of newly-emerged0·2 and 4·0 cm long lateral roots of Vicia fabafrom an investigation of the passage of labelled cells throughmitosis following a 1-h pulse with tritiated thymidine. Celldoubling time was found to increase in this group of initialcells as the secondary roots elongated, this increase beinga result of a gradual lengthening in the duration of the mitoticcycle of both the fast and slow cycling meristematic cells andof a decrease in the size of both the growth fraction and thoseproliferating cells with a short cycle time. The rate of cellproduction by the cap initials was maximal in the newly emergedsecondary roots and showed a gradual decline with subsequentlateral elongation. This change in the rate of cell proliferationin the cap initials has been shown to be related to the initiationof the quiescent centre following lateral root emergence fromthe tissues of the primary. The number of cells making up the cap of 0·2–4·0cm long secondary roots is known to be constant and thus therate at which cells are sloughed off of the cap into the soilmust be the same as the rate of cap cell formation in theseroots, all of the cap cells being replaced every 6–9 days.The rate of cap cell formation in 0·2–4·0cm long secondary roots was used to calculate that one 11-dayold Vicia plant will have contributed between 56 000 and 85000 cap cells to the rhizosphere from its root system sincegermination.     

Plant form based on the pipe model theory II. Quantitative analysis of ramification in morphology

Ramification in tree structure was investigated by the main axis cutting method, which differs from the ordinary stratified clipping method. An axis running from the arbitrary terminal leader of the shoot to the stem base was termed the “main axis”. Cutting the main axis into pieces of constant length gives the “segment layer”, which consists of segments of the main axis and all branches and leaves diverging from the respective segments. There was a linear relationship between the weight of a main axis segment (in the range where leaves exist) of constant length and that of all the parts above the segment. Since plant form is determined by branches diverging regularly from the mother branch or stem, this linear relationship is considered to support the concept of the pipe model theory. It is also suggested that the proportionality constant of the linear relationship may specify the branching structure or ramifications of plant form.     

In vitro propagation for the conservation of a rare medicinal plant <Emphasis Type="Italic">Justicia gendarussa</Emphasis> Burm. f. by nodal explants and shoot regeneration from callus

Justicia gendarussa is a valuable medicinal plant and various parts of this plant are pharmaceutically used for the treatment of different diseases. In vitro regeneration of shoot buds was obtained from culture of nodal cuttings as well as shoot regeneration from callus. The nodal cuttings differed in shoot proliferation in terms of percentage of explants that responded and average shoot length with various concentrations (4.4, 8.9, 13.3, 17.7, 22.2 μM) of 6-benzyladenine (BA), kinetin (Kn) and thidiazuron. In all treatments, one shoot was invariably present. Optimum 87% of cultures responded with an average shoot length of 4.4 cm on Murashige and Skoog (MS) medium supplemented with 17.7 μM BA. Callus was induced from the mature leaf segments on MS medium supplemented with Kn (4.7, 13.9, 23.2 μM) alone or in combination with 2, 4-dichlorophenoxyacetic acid (2, 4-D; 2.3 μM, 4.5 μM). Optimum callus induction (78%) was obtained on MS medium supplemented with 14 μM Kn and 4.5 μM 2, 4-D. When the callus was subcultured on MS medium fortified with BA (8.9, 17.7, 26.6 μM) or Kn (9.3, 18.6, 27.9 μM) alone or in combination with α naphthalene acetic acid (NAA; 2.7, 5.4 μM), shoot regeneration was obtained. The highest response (92%) was observed on MS medium containing 17.7 μM BA and 5.4 μM NAA. On this medium, an average number of 12.2 shoots were obtained per responding callus. The shoots obtained from callus and nodal cuttings were rooted with a frequency of 73% on MS medium augmented with 9.8 μM indole-3-butyric acid. The rooted shoots were successfully transplanted to soil and sand mixture (1:1) with 90% survival rate. The protocol standardized for shoot proliferation and regeneration in J. gendarussa from nodal cuttings and leaf-derived callus is suitable for micropropagation and conservation of this essential medicinal plant.     

Quantitative trait loci analysis for the developmental behavior of Soybean (Glycine max L. Merr.)

Quantitative trait loci (QTLs) identified so far in soybean were mainly derived in the final stage of plant development, which did not apply to the exploitation of genetic effects that were expressed during a specific developmental stage. Thus, the aim of this study was to identify conditional QTLs associated with yield traits at a specific developmental interval of soybean plant. The 143 recombinant inbred lines developed from the cross of soybean cultivars ‘Charleston’ and ‘Dongnong 594’ were used for the developmental QTLs analysis of pod number in the main stem and plant height by composite interval mapping method combined with mixed genetic model. The results indicated that the number and type of QTLs and their genetic effects for the two agronomic traits were different in a series of measuring stages. A total of 10 unconditional QTLs in 6 linkage groups and 5 conditional QTLs in 3 linkage groups were identified for the pod number of the main stem, while 13 unconditional QTLs in 7 linkage groups and 12 conditional QTLs in 6 linkage groups were identified for plant height. Many QTLs that were detected in the early stages were different from those detected at the later stages. Some QTLs existed only at one stage and others existed across two or three stages. Five marker intervals (satt509-satt251, sat_099-sat_113, sat_113-OPAW19_4, satt457-OPC10_85, sat_095-OPBA08_5) were proven to be associated both with the development of pod number in the main stem and the development of plant height. The present study suggested that the development of pods and plant height in soybean were governed by time-dependent gene expression.     

Are electrostatic forces involved in pollen transfer?

Abstract. The measurements of Yes'kov & Sapozhnikov (1976) suggest that electrostatic potentials on foraging honeybees can reach hundreds of volts. Pollen grains of oilseed rape, Brassica napus L., subjected experimentally to potentials of this order, jumped a distance that increased approximately as the square of the voltage, between two pin electrodes on which, in some experiments, were impaled an anther or stigma of oilseed rape or a freshly-killed honeybee. Most floral surfaces were insulated, but there was a low-impedance path to earth via the stigma, and the electrostatic field due to an approaching charged bee must therefore concentrate there. Thus, if electrostatic potentials of this magnitude occur in nature they may increase the chance that pollen from bees will reach the stigma rather than other floral surfaces, as well as enabling pollen to jump from anther to bee and from bee to stigma across an air gap of the order of 0.5 mm.     

Van der Heijden, M.G.A. and Sanders, I.R. (eds) Microrhizal ecology

In his foreword to the volume, Philip Grime says: ‘Themost significant challenge for ecologists at the present timeis to continue to exploit the many current opportunities forpenetration into detailed mechanisms but simultaneously to activelypromote integration . . . within ecological research.Mycorrhizal ecology is uniquely positioned . . . toprovide a lead.’ The volume, edited by van der Heijdenand Sanders, thus aims to meet the twin needs of scaling up,from detailed molecular science to the ecosystem, and demonstratingthat the plant, as found in nature, is itself a community oforganisms that interact with other such     

Functional Manganese Requirement and its use as a Critical Value for Diagnosis of Manganese Deficiency in Subterranean Clover (Trifolium subterraneum L. cv. Seaton Park)

The effects of manganese supply on plant growth and on photosynthesisand manganese concentrations in young leaves were examined inSeaton Park subterranean clover in three glasshouse water cultureexperiments. Plants werc grown initially with a copious supply of manganese,and transferred to solutions either with or without manganese.Sequential harvests were taken to determine the effects of developingmanganese deficiency on dry matter (DM) yield of whole plantsand selected characteristics [manganese, chlorophyll and photosyntheticoxygen evolution (POE)] of youngest open leaf blades (YOL).In addition, the deffect of leaf age and iron supply on POEwerc examined. Manganese concentrations and POE in YOL declined markedly andrapidly in plants transferred to solutions without manganese,while chlorophyll concentrations of YOL and plant DM yield respondedmore weakly and more slowly. As a result, a level of manganesedeficiency which depressed POE in young leaves by more than50 per cent had no effed on DM production. In youngleaves (YOL, YOL + 1, YOL–1), POE declined whentheir manganese concentrations were < 20 µg g^–1DM. Iron supply did not affect this rdationship. When learnwith < 20 µg Mn g^–1 DM were detached and incubatedfor 24 h in solutions containing high concentrations of manganese,their POE increased to normal rates; leaves with higher manganeseconcentrations did not respond. It is suggested that the valueof 20 µg Mn g^–1 DM is the functional manganese requirementfor POE in young subterranean clover leaves It is also suggestedthat this value may be used as a critical value for indicatingmanganese deficiency in subterranean clover. Functional nutrient requirements determined in this way by correlationof nutrient concentrations in young leaves with their biochemicalor physiological activities appear to offer more accurate andconsistent standards for use an critical values for diagnosisof plant nutrient status than do the critical values determinedin the usual way by correlation with plant dry weight. Trifolium subterraneum L. subterranean clover, manganese, functional requirements, deficiency diagnosis, nutrient requirements, critical values, photosynthetic oxygen evolution