Role of mycorrhizal infection in the growth and reproduction of wild vs. cultivated plants

Summary We tested the hypothesis that mycorrhizal infection benefits wild plants to a lesser extent than cultivated plants. This hypothesis stems from two observations: (1) mycorrhizal infection improves plant growth primarily by increasing nutrient uptake, and (2) wild plants often possess special adaptations to soil infertility which are less pronounced in modern cultivated plants. In the first experiment, wild (Avena fatua L.) and cultivated (A. sativa L.) oats were grown hydroponically at four different phosphorus levels. Wild oat was less responsive (in shoot dry weight) to increasing phosphorus availability than cultivated oat. In addition, the root: shoot ratio was much more plastic in wild oat (varying from 0.90 in the low phosphorus solution to 0.25 in the high phosphorus solution) than in cultivated oat (varying from 0.44 to 0.17). In the second experiment, mycorrhizal and non-mycorrhizal wild and cultivated oats were grown in a phosphorus-deficient soil. Mycorrhizal infection generally improved the vegetative growth of both wild and cultivated oats. However, infection significantly increased plant lifespan, number of panicles per plant, shoot phosphorus concentration, shoot phosphorus content, duration of flowering, and the mean weight of individual seeds in cultivated oat, while it had a significantly reduced effect, no effect, or a negative effect on these characters for wild oat. Poor positive responsiveness of wild oat in these characters was thus associated with what might be considered to be inherent adaptations to nutrient deficiency: high root: shoot ratio and inherently low growth rate. Infection also increased seed phosphorus content and reproductive allocation.     

Spread of introgressed insect-resistance genes in wild populations of Brassica juncea: a simulated in-vivo approach

Introgression between transgenic, insect-resistant crops and their wild relatives could lead to a progressive increase of the frequency of resistant plants in wild populations. However, few studies help predict the impact on the population dynamics. To simulate the performance of introgressed insect-resistant plants of wild Brassica juncea, independently from the interspecific hybridization cost, healthy plants were cultivated in pure and mixed stands with damaged plants through cutting leaves in field experiments over two field seasons. As expected, resistant (healthy) plants held a competitive advantage when in competition with susceptible (damaged) plants. Individual biomass and seed production of both types of plants decreased as the percentage of resistant plants increased, so that the relative advantage of resistant plants increased. The combined effects of defoliation and competition on the individual performance of B. juncea were additive. Replacement series experiments confirmed this trend but did not show different seed output in pure stand of susceptible versus resistant plots. The total vegetative and reproductive production of mixed populations was not significantly different of that of pure populations. These results suggest that if a transgene for insect-resistance were to colonize wild populations, high herbivory of susceptible plant and low resource availability would facilitate the spread of resistant individuals. However, at the population level, the shift from an insect-susceptible to a predominantly resistant population would not result in exacerbated habitat colonization.     

Foliage Profile, Size Structure and Stem Diameter-Plant Height Relationship in Crowded Plant Populations

The relationships between vertical foliage profile of an individualplant, competition between individuals, size structure and allocationpattern between stem diameter (D) and plant height (H) wereinvestigated using canopy photosynthesis and two-dimensionalcontinuity equation models including D and H as two independentvariables. Broad-leaved type plants (more foliage mass in theupper layer than in the lower layer of the canopy of an individualwhen grown in isolation) showed curvilinear D-H relationshipand bimodal H distribution, and underwent more asymmetric competitionthan coniferous type plants (more foliage mass in the lowerlayer than in the upper layer of the canopy of an individualwhen grown in isolation) under crowded conditions. Coniferoustype plants showed almost linear D-H relationship (i.e. simpleallometry) and unimodal H distribution, and underwent more symmetriccompetition than broad-leaved type plants under crowded conditions.However, in both the cases D distributions were unimodal. Allocationpatterns between D and H affected these features only a little.These simulation results can explain many actual data alreadypublished. The value of     

A COMPARATIVE STUDY OF THE GROWTH OF WILD OATS (AVENA FATUA L. AND A. LUDOVICIANA DUR.) AND OF CULTIVATED CEREALS WITH VARIED NITROGEN SUPPLY

Growth analysis of wild oats ( Avena fatua and A. ludoviciana ) grown in pots with different levels of nitrogen supply showed many similarities to spring barley, winter oats and winter wheat.
Small differences that could affect competition between wild oats and cereals occurred mainly in the seedlings. Wild oat seedlings were smaller than the corresponding cultivated cereals in total dry weight, total nitrogen content, leaf area and number of shoots. However, very young wild oat plants had higher net assimilation rates than the cultivated cereals and soon caught up and passed them. The difference in net assimilation rate did not persist, and in the later stages of growth differences in dry-matter production depended mainly on differences in leaf area. Another important difference between wild oats and cultivated cereals was that 98–100% of the wild oat seeds and none of the crop seeds were dormant 2 months after harvest.
Ear emergence in wild oats spread over a longer period, the range of ear heights was greater and the tallest ears were taller than in the corresponding cultivated cereals. Assimilation in the ear appeared to account for less of the total dry matter of the plants of wild and cultivated oats than of wheat. The wild oats produced more seeds per plant than the cultivated cereals, but the 1000-grain weight, and hence the total dry weight of seeds, was lower in the weeds than in the crop.
Addition of nitrogen to the soil affected the growth of the wild oats in the same ways as the cultivated cereals; they took up the same amount of nitrogen per plant as winter oats and winter wheat but more than spring barley.
It is concluded that wild oats are most susceptible in the seedling stage to competition from the crop and that nitrogenous fertilizer applied to an infested field is unlikely to alter the balance between the yields of crop and of wild oats.     

Reassessment of root competition for P of field-grown maize in pure and mixed cropping

Root competition for phosphate (P) in the field was calculated with maize i) as singly grown plants, ii) in pure cropping and iii) in mixed cropping with lupin. The experimentally determined parameters used for this purpose were thein situ root-distance pattern as registered by autoradiography and the P-depletion cylinder around a maize root as determined autoradiographically under radial diffusional flow. The results do not indicate any competition for P between roots of adjacently grown plants in either pure or mixed cropping. On the other hand, the P-depletion cylinders of approximately one third of the roots of an individual maize plant were found to overlap. However, when allowance was made for the concentration gradients within a depletion cylinder, the actual competition for phosphate was less than 1%.     

Encroachment of Endophyte-infected on Endophyte-free Tall Fescue

Persistence of endophyte-free (E-) tall fescue (Festuca arundinaceaSchreb.)is erratic. Little information exists as to how fast endophyte(Neotyphodium coenophialum)-infected (E+) tall fescue mightencroach on E- tall fescue and whether specific conditions mightinfluence the speed of encroachment. Plots of E+ and E- tallfescue genotypes 7 and 17 were established using a modifiedNelder's design to compare performance of the E+ forms of theplants in pure and mixed communities at different populationdensities. The plots were planted at the USDA Southern PiedmontConservation Research Laboratory in Watkinsville, Georgia, andthe University of Georgia Plant Sciences Farm in Bogart, Georgia.Plants were grown over a 5 year period and dry matter yieldmonitored 1, 3, and 5 years after establishment. Relative crowdingcoefficients were calculated for each to establish trends ofencroachment of the E+ on the E- plants in the mixed communities.Generally, dry matter yields of E+ tall fescue were greaterthan E- tall fescue regardless of whether they were grown inpure or mixed communities. As time progressed, the differencein dry matter yield between E+ and E- tall fescue grown in mixedcommunities was greater than that of the pure communities. Relativecrowding coefficients increased as time progressed. Relativecrowding coefficients at the Watkinsville location were greaterafter 5 years than those at the Plant Sciences Farm. Therefore,site specific conditions exist which affect the competitivenessof E- tall fescue and degree of encroachment by E+ tall fescue.Research is needed to identify which biotic, abiotic and managementvariables exacerbate encroachment of E+ tall fescue to betterdefine the conditions which best suit E- tall fescue.Copyright1998 Annals of Botany Company tall fescue, endophyte,Neotyphodium coenophialum,Festuca arundinacea, competition, population density     

SEED AND VEGETATIVE REPRODUCTION IN RELATION TO DENSITY IN FRAGARIA VIRGINIANA (ROSACEAE)

Transplants of Fragaria virginiana Duchesne, the wild strawberry, from field and woods sites, were studied under controlled laboratory conditions to determine their seed and vegetative reproduction responses under different density conditions. The following results were obtained: (1) Increased competition among high density grown plants resulted in lower total biomass when compared to low density grown plants; (2) Increased shading in high density plots resulted in a greater percentage of biomass in leaves; (3) The percentage of total biomass in reproductive organs (seed and vegetative) was higher in low density grown plants; (4) Vegetative “reproductive effort” was higher in low density plots than in high density plots while seed “reproductive effort” remained constant between the two density treatments; (5) No significant difference between plants from habitats of different successional maturity was observed under the experimental treatments. These results are discussed in relation to reproductive density response models.     

Density Studies on Lupins: I. Flower Development

In an August-sown experiment the pattern of flower developmentwas followed for cv. Ultra (Lupinus albus L.) and cv. Unicrop(L. angustifolius L.) grown at low (10 plants m^–2) andhigh (93 and 83 plants m^–2, Ultra and Unicrop respectively)densities. Dry weight increase of flowers on the main-stem inflorescenceand first lateral below the main-stem were compared at differentfloral stages. Maximum flower weight was reached just priorto the open flower stage and remained constant or declined untila pod formed or abscission occurred. The time period betweenmaximum flower weight and pod formation or abscission was upto 10 days. Emergence of the inflorescence was earlier and thefirst flower of Ultra opened 10 days before Unicrop. Developmentof each terminal raceme (inflorescence) was acropetal, withpods having formed on lower flower nodes when terminal flowerswere still quite immature. Laterals forming the next generationof inflorescences grew from axillary leaf buds below an inflorescencewhile it was in full flower. Sources of competition from connectedreproductive and vegetative metabolic sinks are discussed. Lupinus spp., lupins, flower development, planting density     

Allometric Relationships in Field-grown Soybean

Allometric relationships in plants uncover size-correlated variationsin form and development and characterize the relative growthof a part of a plant in comparison with a whole. Stable allometricrelationships in ontogeny can be used as components of cropmodels and to estimate plant parameters that are difficult tomeasure. Our objective was to discover whether stable allometricrelations exist in ontogeny of field-grown soybeans (GlycinemaxL.). We used field data on vegetative stages, plant height,stem weight, and leaf weight of 16 soybean cultivars measuredon farms and on the experiment station of Mississippi StateUniversity during 1993–1995 growing seasons. The numberof observed crops for each cultivar ranged from one to 14. Stemheights displayed linear log-log dependencies on the vegetativestage, before and after the breakpoint stage, which typicallywas between the ‘fourth node’ and ‘sixth node’vegetative stages. Slopes of the log-log dependencies afterthe breakpoint stage were similar in all cultivars. Stem masshad log-log linear dependencies on stem height. Slopes of thesedependencies differed among cultivars grown under the same conditions,and among crops of the same cultivar grown under different conditions.Water stress could be a modifier of these relationships. Theproportion of leaf weights in the total weight of leaves andstems decreased linearly as the vegetative development progressed.Since allometric relations are stable for a specific crop, theycan be used to forecast vegetative development as soon as theyare established.Copyright 1998 Annals of Botany Soybean,Glycine maxL., allometry, vegetative development.     

FITNESS CONSEQUENCES OF MULTIPLE PATERNITY IN WILD RADISH,RAPHANUS SATIVUS

In natural populations, wild radish plants typically mate with 6–8 pollen donors, and seeds of individual fruits are usually sired by 1–4 fathers. Since radish fruits are indehiscent and gravity-dispersed, progeny are most likely to compete with a mixture of full and half siblings. The fitness consequences of single and multiple paternity were investigated in a greenhouse experiment. Seeds of every possible cross in a 5 times 5 reciprocal diallel mating design were assigned to one of three competition regimes (four full siblings, four maternal half siblings, or four unrelated individuals per pot) or were grown as singletons. After 14 weeks, the aboveground biomass of all plants was harvested and oven-dried. The dry weight of singletons was more than three times that of progeny grown in competition, indicating that intraspecific competition had occurred. Full- and half-sib progenies did not differ in mean dry weight. Thus, there was no evidence that multiple paternity enhances this aspect of maternal fitness. However, the competition regime dramatically affected the coefficient of variation in dry weight of progeny within a pot. Weight hierarchies were much more pronounced in pots of half sibs and unrelated neighbors than in pots of full sibs. Also variance in dry weight attributable to sire was greatest in the half-sib and “unrelated neighbors” competition regimes. These results suggest that weight hierarchies reinforce genetic differences among the offspring.     

Stomatal Response of some Cultivated and Wild Tuber-bearing Potatoes in Warm Tropics as Influenced by Water Deficits

Leaf resistances of 14 cultivated potato genotypes (Solanumspp) and three tuber-bearing wild Solanum species were comparedwhen plants were grown under water stress at two tropical sitesFactors investigated were diurnal changes in leaf resistance,the effect of plant age, transient drought versus well-wateredconditions of potted and field-grown plants These measurementswere carried out in order to determine the stomatal behaviourof tuber-bearing genotypes and species Significant genotypic differences in leaf resistances were notedwithin the cultivated genotypes All genotypes had higher resistanceswhen water-stressed, but LT-7 appeared to have the lowest leafresistances Genetic differences in stomatal behaviour of tuber-bearingSolanum species were confirmed Abaxial stomatal resistancesof water-stressed plants of the species ranged between 1 74and 13 8 s cm^–1 Stomata of S chacoense were less affectedby drought (three-fold) than S tuberosum (four-fold) The greatesteffect was on S jungasense (five-fold) and on S raphanifoliumThese data show that stomata behaviour among tuber-bearing Solanumspecies is sufficiently different to warrant investigationsof drought-resistance in potato species under dry hot conditions Solanum tuberosum L., Solanum raphanifolium, Solanum chacoense, Solanum jungasense, leaf resistance     

Role of Foliage Habit in the Competition Between Differently Sized Plants in Carrot Crops

The length of the tallest leaf on a plant varied considerablywithin each of three carrot crops, and in each crop there wasa high positive correlation between shoot height and root weight.Lowering the petiole angle of carrot leaves greatly reducedthe ability of plants to compete against untreated neighbours,but did not affect growth when all plants were treated similarly.Cutting treatments which produced a more uniform shoot heightfor all plants, allowed small plants temporarily to overcomethe dominance of their larger neighbours. Similar cutting treatmentsapplied in a field experiment reduced crop growth and variationin root weight. These findings support the view that shoot heightdifference is an important component of inter-plant competitionin carrot crops and hence is a source of root-weight variation. Daucus carota L., carrot, foliage habit, competition     

The effect of partial flower removal on the relation betwen root, shootand fruti growth in the indeterminate tomato

The root, vegetative shoot and fruit growth of November and January sown glasshouse tomato plants grown in flowing water culture was followed over 6–7 months. The relationship between vegetative and reproductive growth was examined after two-thirds of the flowers were removed from half the experimental plants. This resulted in larger plants which had fewer, larger fruits and eventually a fruit yield almost as large as the controls. In the control plants, fruit growth increased steadily until it reached 90% of the total incremental fresh weight of the plant 50–60 days after first anthesis. Leaf growth was markedly depressed at this stage and root growth ceased 4 wk after anthesis. Some root death was observed from anthesis onwards. When fruit growth subsequently diminished, vegetative growth recovered but to a lower rate than before fruiting commenced. Following partial flower removal, only 64% or less of the total increment of fresh weight went into the fruit. Although vegetative growth at this stage was thus greater than in the control plants, both shoot and root growth followed the same qualitative pattern with time. The ratio of vegetative shoot to root fresh weight remained essentially constant throughout the fruiting phase in plants of both sowings whether flowers were removed or not. This suggests that the fruit grew in competition with the vegetative organs as a whole, although, for a short period at early fruiting, root growth was more seriously affected. The pattern and amount of fruiting in this indeterminate plant was influenced by the size of the vegetative organs at fruiting, and by the effect of the existing developing fruit on further vegetative and reproductive growth.     

Plant competition for light analyzed with a multispecies canopy model

Summary Competition for light among species in a mixed canopy can be assessed quantitatively by a simulation model which evaluates the importance of different morphological and photosynthetic characteristics of each species. A model was developed that simulates how the foliage of all species attenuate radiation in the canopy and how much radiation is received by foliage of each species. The model can account for different kinds of foliage (leaf blades, stems, etc.) for each species. The photosynthesis and transpiration for sunlit and shaded foliage of each species is also computed for different layers in the canopy. The model is an extension of previously described single-species canopy photosynthesis simulation models. Model predictions of the fraction of foliage sunlit and interception of light by sunlit and shaded foliage for monoculture and mixed canopies of wheat (Triticum aestivum) and wild oat (Avena fatua) in the field compared very well with measured values. The model was used to calculate light interception and canopy photosynthesis for both species of wheat/wild oat mixtures grown under normal solar and enhanced ultraviolet-B (290–320 nm) radiation (UV-B) in a glasshouse experiment with no root competition. In these experiments, measurements showed that the mixtures receiving enhanced UV-B radiation had a greater proportion of the total foliage area composed of wheat compared to mixtures in the control treatments. The difference in species foliage area and its position in the canopy resulted in a calculated increase in the portion of total canopy radiation interception and photosynthesis by wheat. This, in turn, is consistent with greater canopy biomass of wheat reported in canopies irradiated with supplemental UV-B.     

Common Bean (Phaseolus vulgaris L.) Mutants Defective in Root Nodule Formation: I. PHYSIOLOGICAL CHARACTERIZATION

Two ineffectively nodulating, allelic mutants of the commonbean (Phaseolus vulgaris L.) lines RIZ30 and RIZ36 were studied.In both mutants the nodulation phenotype was characterized bythe formation of tumour-like swellings when inoculated withbean Rhizobium strains. Late formation of pink nodules was observedin mutant plants grown in pots with soil or in hydroponic conditionswith perlite. In the absence of mineral nitrogen, mutant growthand nodulation were poor; a low peak of acetylene reductionactivity being detected 45 d after inoculation. Mutant growthin the presence of mineral nitrogen was similar to that of thewild type. The mutants were also characterized by poor pod fertility(seed per pod). The nodulation and pod fertility phenotypesare specifically controlled at the root and shoot levels, respectively,as assessed with grafting experiments. Mutant shoots graftedon wild type, nitrogen-fixing roots produced a number of seedssimilar to the wild type despite the expression of the poorpod fertility phenotype. Nitrogen and seed yields of wild typeshoots, grafted on mutant, ineffectively nodulating roots wereseverely reduced when compared with control wild type plantsalthough nitrogen accumulation during vegetative phase was similar. Key words: Phaseolus valgaris, nitrogen fixation, nodulation mutants, grafting, nitrogen assimilation     

Wild Oat/Barley Interactions: Varietal Differences in Competitiveness in Relation to K+ Supply

Eight cvs of barley (Hordeum vulgare L.) were separately plantedwith Wild Oats (Avena fatua L., genetically pure line CS40)in a sand culture with two external K⁺ concentrations. Substantialdifferences were observed among barley cvs in their abilityto compete with wild oat. The variety Fergus was highly competitiveat both high and low [K⁺]_e, whereas Steptoe was competitiveonly at high [K⁺]_e, and Compana was only weakly competitivewith wild oat. The differences between barley cvs were relatedto their previously reported efficiencies of K⁺ uptake and utilization. Hordeum vulgare L., Avena fatua L., barley, wild oat, competition, K⁺ nutrition, utilization efficiency     

The Effect of Rooting Space on Whole Plant and Leaf Growth in Brussels Sprouts (Brassica oleracea var. gemmifera)

Seedlings of Brassica oleracea var. gemmifera DC. (Brusselssprouts) were grown in four pot sizes over a 4-week period.Whole plant, stem, root and foliage d. wts and foliage area,together with specific leaf area, leaf area ratio and numberof leaves initiated were reduced by restricting rooting space.Individual leaves showed similar reductions in d. wt and area,with the effect being more pronounced in later-formed leaves.Cell counts and measurements on the epidermis and palisade mesophylllayers of the first four leaves showed that the reduction ingrowth was due to reduced cell division. Cell numbers in thefirst-formed leaf were halved over the range of pot sizes used,and there was a progressively greater reduction in cell numbersin later-formed leaves. There was some tendency for cell sizeto decrease with decreasing rooting space, but this was notgeneral and was most marked between plants grown in the twosmallest pot sizes. Brassica oleracea var. gemmifera, Brussels sprouts, rooting space, growth analysis, leaf growth, cell numbers, cell sizes     

Effects of Partial Defoliation on the Growth of Liriodendron tulipifera L. Seedlings

Partial defoliation of Liriodendron tulipifera L. by removalof leaflets as they emerged from the protective buds affecteda variety of growth parameters. Reductions occurred in totaldry weight production, the percentage of new growth devotedto foliage, leaf area ratio, and the increment of leaf areaper unit of leaf weight increment. Increases occurred in unitleaf rate and the rate of production of new leaves. Weight ofleaves near the base of the seedlings was unaffected by treatmentbut leaves developing at the end of the growing season werelarger on defoliated plants. The net effect of removing one-thirdand two-thirds of the developing leaflets was to reduce totaldry weight production by 14 and 42 per cent respectively.     

Effects of Low Oxygen on Photosynthesis, Translocation and Growth in Green Pepper (Capsicum annuum)

Green pepper (Capsicum annuum cv. Bell Boy) plants were exposedin chambers to low (2%) oxygen and controlled carbon dioxideconcentrations. Vegetative and fruiting plants showed short-termincreases in net photosynthesis in low oxygen or elevated carbondioxide (up to 900 µl CO₂ l^–1). Photosynthesis ofyoung vegetative plants increased in low oxygen in the short-termbut there was no long-term benefit. Low oxygen enhancement ofphotosynthesis declined with time and after 10 d, leaf areaand root dry weight were less than in plants grown in normalair. Labelled assimilates were translocated from leaves to otherregions at similar rates in low oxygen and normal air. Low oxygenreduced respiratory losses from leaves and reduced the proportionof soluble carbohydrate converted to polysaccharide in all plantparts. Thus, low-oxygen environments decrease the utilisationof assimilates which then may lead to inhibition of photosynthesis. Capsicum annuum, photosynthesis, photorespiration, translocation, utilization of assimilates     

栽培与野生化血丹不同部位中两种化学成分含量分析

为探讨并分析栽培与野生化血丹植株中不同部位中两种化学成分的含量差异,该研究采用超声法提取、高效液相色谱法(HPLC)测定栽培与野生化血丹根、茎、叶、花、混合样等部位中桃叶珊瑚苷和梓醇的含量,并进行比较。结果表明:(1)桃叶珊瑚苷在栽培与野生化血丹植株内均有分布,含量均以根中最高,其在栽培与野生化血丹植株内的含量表现分别为根叶混合样茎花、根混合样茎花叶,栽培化血丹不同部位中桃叶珊瑚苷的含量均高于野生化血丹。(2)梓醇在栽培化血丹的茎中未检出,在栽培与野生化血丹其他部位均有分布,含量均以叶中最高,其在栽培与野生化血丹植株内的含量分别表现为叶花混合样根、叶混合样茎花根,野生化血丹不同部位中梓醇的含量均高于栽培化血丹。(3)桃叶珊瑚苷和梓醇在栽培和野生化血丹植株不同部位中的含量均存在显著差异(P0.05),栽培与野生同一部位间总体上无显著差异,为该濒危药用植物资源药用部位选择和合理开发利用提供实验参考。