Selection for resistance to Cochliobolus sativus in tall fescue (Festuca arundinacea Schreb.)

Summary Cochliobolus sativus (Ito and Kurib.) Drechsl. ex Dastur is a major foliar pathogen of tall fescue (Festuca arundinacea Schreb.) which can greatly reduce the quantity and quality of forages available for animal consumption. A greenhouse screening program was initiated to determine the inheritance of resistance to C. sativus in tall fescue over several cycles of mass selection. Resistance to C. sativus in four tall fescue cultivars was increased with 2–3 cycles of mass selection. Realized heritabilities were low to moderate (0.04 to 0.58) indicating that environmental influences on the expression of resistance are quite high. Variances were unchanged by selection, indicating that further improvement should be possible. However, progress with mass selection can be expected to be slow. Lesion size was decreased in each cultivar by selecting for lesion coverage. Lesion size, being independent of inoculum load and therefore less subject to environmental variation, should be considered as an additional selection criteria to improve the rate of progress.Journal article No. 6370 of the Mississippi Agricultural and Forestry Experiment Station     

Pollen performance as affected by the pistilar genotype in sweet cherry (Prunus avium L.)

Summary Differences in pollen performance in higher plants can result in significant selective advantages for some particular genotypes leading to both gametophytic and sexual selection. However, the possibility of selection among male gametophytes has been questioned since natural selection could lead to the fixation of alleles for the best competing male genotypes. These two apparently conflicting hypotheses could be reconciled if pollen performance, rather than operating in absolute terms, could be modulated by the pistilar genotype. Thus, pollen performance in vivo and in vitro has been compared in four sweet cherry (Primus avium L.) cultivars. Differences among the cultivars studied have been recorded in the speed and final pollen germination percentages both in vivo and in vitro. The results obtained show that the female genotype also modulates the final result of pollen performance. These two factors are not merely additive but, on the contrary, the interaction between them affects pollen behavior in vivo. This fact has clear implications for gametophytic and sexual selection since the best male-female combinations can be favored and this could explain the variability observed for pollen performance in nature.     

Approaches on vegetative propagation of difficult-to-root <Emphasis Type="Italic">Salix caprea</Emphasis>

In the framework of a willow rust research project, it was necessary to include vegetatively propagated plant material of selected sallow trees (Salix caprea L.) into biotests for identification of pathotypes. Since it was not possible to root sufficient clonal plants by conventional cutting propagation, the applicability of tissue culture methods was tested. From 10 selected donor trees of Salix caprea newly sprouted shoots were harvested and transferred to nutrient media after surface disinfection. The cultures were grown at 20--22 °C, illuminated with warm-white fluorescent tubes. The majority of shoot tips and nodal segments died during the first month, but only with nursery-grown plants this was caused by bacteria contamination. Two clones could be established easily on hormone-free medium. Five clones could be initiated only after repeated subcultures on various media variants. Three clones failed completely. Different basic media compositions were tested and Woody Plant Medium, supplemented with 0.1% activated charcoal, proved to be best for most of the sallow clones. Well developed rooted plantlets were used in vitro for microcutting propagation. The resulting plants were transferred to soil and could be included in the rust screening program after acclimatising. The applicability of micropropagation for selected Salix caprea donor trees was strongly depending on the genotype. But the comparison of results from microcuttings with conventional cutting propagation showed that these methods were successful for different clones each.     

Micropropagation and induction of autotetraploid plants of <Emphasis Type="Italic">Chrysanthemum cinerariifolium</Emphasis> (Trev.) Vis

Rapid propagation technology was established and optimized in vitro for Chrysanthemum cinerariifolium (Trev.) Vis., an important botanical insecticide plant with a huge international market. A large number of buds could be induced directly from epicotyl and hypocotyl explants on Murashige T; Skoog F. J. Plant. Physiol. 15: 473–479; (1962) medium [Murashige and Skoog (MS) medium] supplemented with 0.3 mg l⁻¹ benzyladenine (BA) and 0.3 mg l⁻¹ α-naphthaleneacetic acid (NAA). Root induction and development could be observed within 15 d after inoculation on 1/2 MS medium supplemented with 0.2 mg l⁻¹ indole-3-acetic acid (IAA) and 0.1 mg l⁻¹ rooting powder (ABT). Furthermore, a polyploid breeding study in vitro was reported to obtain superior breeding lines with high yield and good quality. Autotetraploid lines of C. cinerariifolium were obtained by colchicine treatments and identified by root-tip chromosome determination and stoma observation. The chromosome number of the autotetraploid plantlet was 2N = 4x = 36. Obtained autotetraploid lines will be of important genetic and breeding value and be used for further selection and plant breeding.     

Spatial Distribution of Genetic Variation in a Natural Beech Stand (Fagus sylvaticaL.) Based on Microsatellite Markers

The spatial distribution of alleles is described in a naturally regenerated, isolated pure beech (Fagus sylvaticaL.) stand consisting of 99 adult trees. After testing nine microsatellite loci originally developed for F. crenata, each tree was genotyped at four well-scorable microsatellite loci. Specific primers were developed for one locus of F. sylvaticaL. For the characterization of spatial genetic structures, two different statistics were used. One method is based on the mean genetic distance between trees in different spatial distance classes, and the other one is Moran's index I. The results show the same tendency of a strong family structure in the distance classes up to 30m in comparison with that expected for a spatially non-systematic distribution of genotypes. In general, microsatellites are more useful to detect spatial genetic structures than allozymes. Spatial genetic structures are influenced by unpredictable factors such as wind direction at anthesis and can therefore vary from year to year. We recommend that seed collections should cover large areas in order to prevent a preponderance of few families and a reduction of the adaptive potential of the next generation.     

Comparative efficiency of four selection methods for deriving high-yielding lines in mungbean [Vigna radiata (L.) Wilczek]

The comparative efficiency of four selection methods, viz., honeycomb (HC), pedigree selection (PS), single-seed descent (SSD) and the bulk method (BM), was assessed in three crosses of mungbean. The lines derived by each method, along with check varieties, were yield-tested in a compact family block design in F₅ and F₆ generations during summer and kharif of 1990. On the basis of the mean of the lines, the range, the number of superior lines over the best check, and the proportion of the top 10% lines in all the crosses and generations, the honeycomb method exhibited superiority over PS, SSD and BM for yield per plant and its component traits. PS, SSD and BM did not differ from each other. The honeycomb and SSD methods were found suitable for deriving superior lines for seed yield and pods per plant in mungbean.     

The ion concentration of dew condensed on Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.) needles

Summary Dew droplets collected with pipettes from coniferous needles were analysed for their ionic composition. Almost all samples of dew taken from Scots pine trees (Pinus sylvestris) showed significantly higher ion concentrations than those taken from Norway spruce trees (Picea abies). This can be explained by the micromorphology of the needle surface. The higher microscale roughness of the wax layer of a pine needle causes a more efficient flux of atmospheric aerosol particles compared to the spruce needle surface. Dew on coniferous needles is shown to be capable of maintaining pH values below 3 for several hours.     

Early generation yield testing versus visual selection in chickpea (Cicer arietinum L.)

Summary Four F₃ populations of chickpea (Cicer arietinum L.) were simultaneously evaluated for yield in an F₃ yield trial and in single plant progeny rows. Ten high yielding, 10 low yielding and 10 randomly sampled lines, along with 10 lines visually selected for yield from the progeny rows, were retained for further evaluation. The lines from each of the four selection groups in each population were bulked and evaluated in a replicated yield trial at three locations and four environments. The bulk of visually selected lines was not superior in yield to the bulk of randomly sampled lines at all locations. The present results indicate that an early generation yield testing selection procedure is more efficient than visual selection for yield improvements in chickpea.     

Segregation distortion of isozyme loci in cherimoya (Annona cherimola Mill)

The allelic segregation of 13 isozyme loci in hand-fertilized heterozygous cherimoya trees (Annona cherimola Mill.) has been studied. We analyzed 63 locus x progeny combinations and found non-Mendelian segregation in 12 cases. The sequential Bonferroni method revealed only eight cases of non-Mendelian segregation; these have been investigated with several chi-square tests to discover what processes were involved. Gametic selection appears to be the main contributor, although zygotic selection seems also to play a part.     

Mating system and inbreeding depression in whitebark pine (Pinus albicaulis Engelm.)

Mating system and inbreeding depression in quantitative traits of whitebark pine (Pinus albicaulis Engelm.) was determined using isozymes and a seedling common garden experiment. Simultaneous isozyme analysis of embryo and haploid megagametophyes from progeny arrays of families in three distinct geographic regions (Oregon, Montana, and southern British Columbia) was used to estimate parental and progeny inbreeding coefficients, as well as regional and family mean multilocus outcrossing rates (t _m). Quantitative trait family means of seedlings from the same families growing in two temperature treatments in a common garden experiment were regressed on the estimated inbreeding coefficient to determine the presence and magnitude of inbreeding depression. Regional estimates of t _m ranged from 0.73 to 0.93, with a mean over all regions of 0.86. Family mean t _m values indicated predominant outcrossing; however, some individuals experienced substantial inbreeding. The Oregon region had a significant excess of heterozygotes in the parental generation relative to Hardy–Weinberg equilibrium, while both the Oregon and southern BC regions had a heterozygote deficiency in progeny, suggesting selection against inbred individuals. Biomass in the ambient temperature treatment for the southern BC region was the only trait significantly related to inbreeding coefficient. The mean inbreeding coefficient for this region was 0.25, and based on this relationship, mean predicted biomass would be reduced by 19.6% in this region if inbred individuals are not removed by selection. The estimated outcrossing rate of whitebark pine is slightly lower than most wind-pollinated conifers, and while most individuals are highly outcrossing, some experience substantial inbreeding.     

Temporal Changes in the Inequality of Early Growth of Cunninghamia lanceolata (Lamb.) Hook.: A Novel Application of the Gini Coefficient and Lorenz Asymmetry

Growth within tree populations varies among individuals due to changes in biotic and abiotic factors. The degree of such variation, defined as growth inequality, serves as a useful indicator of the uniformity of growth within a population in response to the prevalent environmental conditions. By application of the Gini coefficient (G), an index for inequality, we characterized the early growth inequality of ninety crosses of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) and their open-pollinated parental lines. Tree cumulative height was measured annually for 8 consecutive years. Both the crosses and parental lines exhibited temporal changes in growth inequality. The inequality of total height among the crosses decreased logarithmically with age by nearly 3-fold after 13 growing seasons, suggesting that tree height became less variable among the crosses as trees grew larger. Interestingly, the Lorenz asymmetry, an index reflecting the shape of the Lorenze curve from which G is derived, revealed that the inequality of annual height increment among the crosses resulted from an alternate contribution of the fast-growing and slow-growing trees. Among parental lines, two provenances with the smallest and the largest overall inequality in total height showed a similar pattern of changes in annual growth inequality, and the provenance differences were consistent over time. Compared to the other provinces, a local provenance exhibited less variation in total height among individual trees as reflected by a smaller value of inequality, and was better adapted to the field conditions. Our results demonstrated the sensitivity and usefulness of the Gini coefficient and Lorenz asymmetry for the analysis of growth inequality in non-natural populations. Growth inequality is a potentially useful evaluation criterion for early selection. Given comparable initial growth, provenances/families with lower growth inequality values would likely outperform those with higher growth inequality, and eventually tree size of the latter would be more variable due to greater variations among individual trees. Assessment of growth inequality at early ages will advance our understanding of variability of tree growth within a population, facilitate forest genetics improvement programs, and enhance the efficiency of tree breeding.     

Micropropagation of adult Stone Pine (Pinus pinea L.)

This paper describes a micropropagation protocol for in vitro propagation of mature Stone Pine trees. Axillary bud development was achieved by culturing bud explants in media containing various cytokinins. Experiments were conducted to test the effect of asepsis conditions, type and concentration of cytokinin and rooting protocol. Four cytokinins were tested, namely, benzyladenine, meta-topolin, N-benzyl-9-(2-tetrahydropyranyl)-adenine and thidiazuron (TDZ) of which TDZ gave the best results, as 59% shoot development was obtained following the application of 1 μM TDZ to the culture medium. The shoot development was significantly influenced by the genotype of the tree, but was effective in explants from all 20 genotypes used in the trial. In vitro rooting was, however, difficult to achieve and could only be induced at low rates. This protocol represents the first successful biotechnological approach to the micropropagation of adult Pinus pinea trees. Paloma Moncaleán and Ricardo Javier Ordás contributed equally.     

Pine wilt disease as promising causal agent of the mass mortality of Pinus armandii Franch. var. amamiana (Koidz.) Hatusima in the field

The causal agent of the mass mortality of field populations of Pinus armandii Franch. var. amamiana (Koidz.) Hatusima (PAA) was investigated with special respect to the involvement of pine wilt disease. Wood chips, branches and/or increment cores for detecting the pinewood nematode, feeding marks of the vector insect and environmental stress in the past, respectively, were taken from live and dead PAA trees grown in three locations, Yaku-shima and Tanega-shima Islands and a plantation in Kagoshima City, from 1997 to 1998. Five trees died after the spring of 1996 and, of these, four were inhabited by the pinewood nematode. Feeding marks of the vector insects were found on the branches of all dead trees and most of the live trees investigated. These results suggest that the infection of pine wilt disease in PAA trees occurs in the field. Annual ring growth of the sample trees showed neither intervention nor growth reduction, which implies strong environmental stress that may cause mortality in PAA trees.     

Radial distributions of Cd in stems of oak trees (Quercus robur L.) re-analyzed after 10 years

Radial distribution patterns of Cd were determined in stems of the same oak trees (Quercus robur L.) in 1983 and again in 1994. On both sampling dates the same distribution patterns were generally observed. Highest concentrations of Cd were found at the sapwood-heart-wood transition. A sharp drop over this boundary towards inner parts of the stems occurred in all trees. In the decade between the two investigations the sapwood-heartwood boundaries had shifted outwards by 9–11 annual rings. The Cd peaks at the boundaries were shifted by approximately the same interval. The results suggest that the described Cd peaks are mobile in a radial direction. The present location of such peaks cannot be used to infer the pollution history of the tree's environment. The Cd accumulation at the sapwood-heartwood boundary is probably affected by physiological processes in the wood. Thus it is concluded that radial distributions of Cd in stems of oak trees are no reliable source of information for retrospective monitoring of past time pollution levels.     

Micropropagation of mature wych elm (<Emphasis Type="Italic">Ulmus glabra</Emphasis> Huds.)

Explants of mature vigorous donor trees of wych elm (Ulmus glabra Huds.) that had not been previously exposed to Dutch elm disease were investigated for the influence of phytohormones and media on shoot multiplication rates and organogenic capacity. The regenerates were micropropagated from cultures that originated from 15-year-old progeny of plus trees. Two plus trees aged over 70 years showed recalcitrant responses. Thidiazuron in combination with 6-benzylaminopurine (BAP) induced a significantly higher number of shoots per explant than the most optimal BAP treatment (5.88 vs. 3.05 shoots). Woody plant medium and Dubovský minimal medium had no significant effects on shoot formation and multiplication rates. All plantlets raised in vitro were phenotypically normal and successfully hardened to ex vitro conditions. Two experimental field plots with 3-year-old in vitro-propagated trees were established.Abbreviations DED: Dutch elm disease - BAP: 6-Benzylaminopurine - IBA: Indole-3-butyric acid - TDZ: Thidiazuron - WPM: Woody Plant Medium - DM: Dubovský Minimal Medium Communicated by D. Bartels     

Micropropagation systems for the mexican redbud (Cercis canadensis var. Mexicana L.) and other woody plants of the chihuahuan desert

Summary There are many Chihuahuan desert species that have potential as landscape plants for the arid communities of the southwestern United States [agarita, Berberis trifoliata Moric.; Mexican buckeye, Ungnadia speciosa Endl.; Texas madrone, Arbutus xalapensis var. texana (Buckl.). A. Gray]. Within these plant populations, there are superior genotypes that offer even greater interest for the landscape. However, it is difficult to clonally propagate many of these species with conventional techniques, and the seed-derived populations often do not breed true. Therefore, selection of superior genotypes in wild populations coupled with clonal propagation through tissue culture may offer an attractive option. It is relatively easy to achieve disinfestation of explants from desert plants due to a general lack of natural surface contamination by fungi and bacteria, even though interference from numerous trichomes can impede good contact with disinfesting agents. However, there is only a narrow window of time that is ideal for explant collection, because of the brief, periodic flushes of growth that characterize this unusual plant group. There may be years when, due to the harsh environment, the amount of suitable explant material is severely limited. Phenolics and exudates are also problematic in this group of plants, and acclimatization of ex vitro plantlets to the harsh desert environment is a particular challenge. For these reasons, specific adaptations and modifications were necessary to achieve success with micropropagation of desert plant species such as Mexican redbud (Cercis canadensis var. mexicana L.).     

Interactive effects of mycorrhization and elevated carbon dioxide on growth of young pedunculate oak (Quercus robur L.) trees

Pedunculate oak (Quercus robur L.) was germinated and grown at ambient CO₂ level and 650 ppmv CO₂ in the presence and absence of the ectomycorrhizal fungus Laccaria laccata for a total of 6 month under nutrient non-limiting conditions. Mycorrhization and elevated atmospheric CO₂ each supported the growth of the trees. Stem height, stem diameter, and dry matter accumulation of pedunculate oak were increased by mycorrhization. Elevated atmospheric CO₂ enhanced stem height, stem diameter, fresh weight and dry weight, as well as lateral root formation of the trees. In combination, mycorrhization and elevated atmospheric CO₂ had a more than additive, positive effect on tree height and biomass accumulation, and further improved lateral root formation of the trees. From these findings it is suggested that the efficiency of the roots in supporting the growth of the shoot is increased in mycorrhized oak trees at elevated atmospheric CO₂.Abbreviations DW dry weight - FW fresh weight - RWC relative water content     

Relationship of Pruning and Growth Morphology with Hormone Ratios in Shoots of Pillar and Standard Peach Trees

Genotype and cultural management determine the shape of peach [Prunus persica (L.) Batch] tree canopies in orchards. Not well understood, however, is the relationship between terminal growth, lateral branching, and shoot hormone levels that can fundamentally affect tree canopy development. In this experiment, two peach cultivars with widely differing growth habits (Pillar, KV930479 and Standard, ‘Harrow Beauty’) were budded on ‘Lovell’ rootstock, planted in the field in 1998, and characterized for shoot morphology and hormone concentrations in 2002 and 2003 (the fourth and fifth leaf, respectively). Auxin (indole-3-acetic acid) and cytokinins (largely trans-zeatin riboside, dihydrozeatin riboside, and isopentenyladenosine) were measured in shoot tips (2002) and current-year shoots (2003) using mass spectrometry. In 2002, Pillar trees had less sylleptic branching, more upright growth, and higher auxin and auxin-to-cytokinin ratios than Standard trees. In Pillar trees in 2003, auxin concentrations and shoot growth were highest in current year shoots; in pruned trees, only auxin levels increased. Peach tree growth habits may be the result of altered hormone metabolism. Growth forms leading to superior production efficiency may be developed by selection based on specific target hormone concentrations and ratios.     

Autecological investigations on marine diatoms. 4:Biddulphia aurita (Lyngb.) Brebisson et Godey—A succession of spring diatoms

Comparison of generation times ofBiddulphia aurita (Lyngb.) Brebisson and Godey with other diatoms indicated that the species can reach its best competitive position by growth from –1.5°C to about 6°C. The diatom demonstrates its optimum temperature at about 12°C. Yet, flowerings will occur at the lower temperatures only. Its presence in the early spring plankton is facilitated by its non-adhrence behaviour, that proved to be temperature dependent. At 0°C almost no adherence occurred, whereas at high temperaturesB. aurita adhered completely to the bottom of the glas vessels or pipettes. The importance ofB. aurita in the benthic community is discussed. The mutual differences in growth ofB. aurita, Chaetoceros debilis andThalassiosira nordenskioeldii resulted in a succession comparable with that found in nature.     

Shoot bud regeneration from different explants of Bacopa monniera (L.) Wettst. by trimethoprim and bavistin

A mass in vitro propagation system devoid of growth regulators for Bacopa monniera (L.) Wettst., a traditional Indian medicinal plant, has been developed. Direct shoot bud regeneration was induced by culturing internode and leaf explants on Murashige and Skoog's (MS) medium supplemented with an antibiotic (trimethoprim) or a fungicide (bavistin). Bavistin showed a marked cytokinin-like activity, as evident from high number of shoot buds induced in node, internode and leaf explants. Optimum adventitious shoot buds induction occurred at 300 mg/l bavistin from internode explants. In vitro regenerated shoots were elongated and rooted before transferred to field with 85% survival. The regeneration protocol developed in this study illustrates the usefulness of additives for mass propagation and germplasm conservation of B. monniera.Authors Vaibhav Tiwari and Kavindra Nath Tiwari contributed equally to this work