Marginata Seedlings Research Articles

Desenvolvimento in vitro da orquídea ameaça de extinção Laelia marginata Lindl. em meios de cultivo contendo diferentes relações nitrato/amônio

In vitro cultivation is a very important method for the conservation of germplasm and the multiplication of endangered plants; however, studies on the adequacy of the nutrients used for a good development of each species are needed. The objective of this study was to evaluate the in vitro development of Laelia marginata Lindl. in culture media containing different nitrate/ ammonium ratios. Seedlings were obtained from seeds germinated in vitro. The treatments consisted of different nitrate/ ammonium ratios, with five proportions of NO3 - and NH4 + : T1-0/100; T2-25/75; T3-50/50; T4-75/25 and T5-100/0. At 200 days after seedling transplanting, height of the aerial part, root length, number of leaves, number of shoots, leaf length, leaf width, aerial and root dry mass and contents of chlorophyll a, b and carotenoids were evaluated. A completely randomized design was used, with five treatments and ten replicates. The combination of 50/50 nitrate/ammonium resulted in the highest values of aerial part and root length, dry mass of the aerial part and root, as well as leaf length and width. The proportion of 50/50 nitrate/ammonium resulted in the best initial development of L. marginata seedlings.

Phosphite does not stimulate a wounding response in Eucalyptus marginata seedlings

Phosphite is used to protect plants from the soilborne plant pathogen, Phytophthora cinnamomi. While several studies have reported a stimulation of defence mechanisms in response to the infection of plants treated with phosphite, the effect of phosphite on abiotic wound repair is unknown. The aim of this histological study was to detail the effects of phosphite on previously undescribed wound repair in Eucalyptus marginata, an important forest tree of south-western Australia, which responds to phosphite treatment. Clonal lines of young plants of E. marginata without a periderm, considered resistant and susceptible to P. cinnamomi, were sprayed with phosphite and the green stems were wounded with liquid nitrogen, where a small area of the vascular cambium was damaged. Transverse hand sections showed phosphite had no effect and there was no genotypic difference on wound responses in E. marginata. Wound periderm and a ligno-suberised boundary zone formed within 7 days. The generation of new phellogen derivatives occurred and by 14 days the vascular cambium was almost fully restored with wound wood formed by 21 days. In the absence of a pathogen, phosphite did not interfere with the quality and speed of wound repair in the E. marginata clones suggesting that wound repair will not be affected when phosphite is used as a prophylactic treatment.

Effect of phosphite on in planta zoospore production of Phytophthora cinnamomi

The efficacy of phosphite to control the production of zoospores of Phytophthora cinnamomi on infected trees grown in a glasshouse and in a revegetated mined area was examined. Banksia grandis and Eucalyptus marginata seedlings in the glasshouse and E. marginata seedlings in the minepit were sprayed with 0, 5 and 10 g phosphite L−1. In both trials, zoospores were produced from infected tissue of plants treated with all concentrations of phosphite. In the glasshouse, spray application of 5 and 10 g phosphite L−1 significantly reduced the production of zoospores from both B. grandis and E. marginata seedlings. In the mined area there was a similar, though nonsignificant, reduction in the number of zoospores produced from phosphite‐treated and nontreated E. marginata seedlings. However, the average number of zoospores produced was greater in plants not treated with phosphite (1·75 zoospores mL−1) than from plants treated with 5 or 10 g phosphite L−1 (0·04 and 0·09 zoospores mL−1, respectively). Pimelea ferruginea leaves were used to bait the water surrounding the plants in the mined area to determine if zoospores produced from phosphite‐treated plants were able to infect plant material. Significantly more baits were infected by zoospores from plants not treated with phosphite compared with plants treated with 5 or 10 g phosphite L−1. These results suggest that phosphite reduces, but does not prevent, the production of viable zoospores on infected trees. Thus phosphite application may not remove the risk of P. cinnamomi spreading from infested, sprayed areas.

Leaf growth, photosynthesis and tissue water relations of greenhouse-grown Eucalyptus marginata seedlings in response to water deficits.

Leaf growth, rate of leaf photosynthesis and tissue water relations of shoots of Eucalyptus marginata Donn ex Sm. (jarrah) seedlings were studied during a soil drying and rewatering cycle in a greenhouse experiment. Rates of leaf growth and photosynthesis were sensitive to water deficits. The rate of leaf growth decreased linearly with predawn leaf water potential to reach zero at -1.5 MPa. Rate of leaf growth did not recover completely within the first three days after rewatering. Midday photosynthetic rates declined to 40% of those of well-watered seedlings at a predawn leaf water potential of -1.0 MPa and reached zero at -2.2 MPa. Photosynthetic rate recovered rapidly following rewatering and almost fully recovered by the second day after rewatering. All tissue water relations parameters, except the bulk modulus of elasticity, changed significantly as the soil dried and recovered completely by the third day after rewatering. Changes in osmotic pressure at full turgor of 0.4 MPa indicated considerable capacity for osmotic adjustment. However, because there was little osmotic adjustment until predawn leaf water potential fell below -1.5 MPa, this capacity would not have enhanced seedling growth, although it may have increased seedling survival. The sensitivity of photosynthesis and relative water content to water deficits suggests that greenhouse-grown E. marginata seedlings behave like mesophytic plants, even though E. marginata seedlings naturally grow in a drought-prone environment.

Mortality of Eucalyptus marginata (jarrah) seedlings in Mediterranean‐climate forest in response to overstorey, site, seedbed, fertilizer application and grazing

Abstract The effects of overstorey, site, seedbed, seedling density, application of fertilizer and grazing on mortality of Eucalyptus marginata (jarrah) seedlings were studied experimentally in the northern jarrah forest of Western Australia. Rainfall, soil temperature, soil water deficits, leaf water potentials and photosynthetically active radiation (PAR) were monitored. Seedlings on sites with the overstorey removed experienced significantly higher soil temperatures for 9 months of the year (of up to 6°C), smaller soil and leaf water deficits during the dry season (minimum predawn leaf water potentials of ‐0.5 MPa compared to ‐1.6 MPa) and higher intensities of PAR (maximum values of 1900 umol m−2 s1 compared to 900 umol m−2 s−1), compared to seedlings on sites with the overstorey retained. Mortality off. marginata seedlings was greater on sites where the overstorey was retained compared to where the overstorey was removed, on low quality sites than high quality sites, and on undisturbed and lightly disturbed seedbeds compared to heavily disturbed seedbeds. Seedling density, application of fertilizer and grazing by vertebrates did not have a significant effect on percentage mortality. Most of the mortality occurred as water deficits developed in late spring and summer and was attributed to these water deficits. Some mortality that occurred prior to the development of substantial water deficits was probably caused by pathogenic fungi, We conclude that mortality of E. marginata seedlings in the northern jarrah forest of Western Australia can be minimized by reducing the density of the overstorey and by seeding into a seedbed that has had litter and groundcover removed and the soil disturbed.

Emergence of Eucalyptus marginata (jarrah) from seed in Mediterranean‐climate forest in response to overstorey, site, seedbed and seed harvesting

Abstract The effects of overstorey, type of site, seedbed, seeding date and seed harvesting by vertebrates and invertebrates on the emergence of Eucalyptus marginata (jarrah) seedlings were studied experimentally in the northern jarrah forest of Western Australia. Seed harvesting by small vertebrates substantially reduced emergence, whereas invertebrates only slightly reduced emergence. Ninety per cent of seed was removed within 1 day when it was on the soil surface and in the open, whereas seed removal was insignificant when the seed was covered by soil. Vertebrates harvested seed more effectively when the understorey and litter were removed and the seed was more visible on the soil surface. Seed harvesting by small vertebrates had less impact on a site where there had been bauxite mining, possibly because the surrounding area was being revegetated with large numbers of seed and the area afforded poor cover for vertebrates. Emergence was less where the overstorey was removed compared to where it was retained, and on the rehabilitated bauxite mined site compared to the forest sites. There was no difference in emergence between the low and high quality forest sites and so the emergence phase could not fully explain the variation in abundance off. marginata seedlings on different quality sites. Post emergence events are likely to be important in explaining this difference between low and high quality sites.

Mechanisms of resistance to Phytophthora cinnamomi in clonal, micropropagated Eucalyptus marginata

Plants of the eucalypt. Eucalyptus marginata. selected through a glasshouse screening procedure for resistance or susceptibility to Phytophthora cinnamomi, were established in tissue culture and micropropagated. After inoculation with P. cinnamomi, root lesions in clonal lines selected as resistant (RR) to P. cinnamomi were restricted and became contained within four days after inoculation while lesions in roots of those lines susceptible (SS) to P. cinnamomi continued to extend rapidly. Activity of phenylalanine ammonialyase (PAL) was increased above controls in root segments of the RR lines 48 h after inoculation with P. cinnamomi while activity in unselected seedlings and the SS lines was reduced or unchanged. After inoculation, lignin concentration was increased and reached high levels compared with uninoculated control levels in roots of the two RR lines tested. Constitutive levels of phenolics in roots of the RR lines were up to 94% higher than in seedling roots and levels were further increased after inoculation. Levels of phenolics in the other lines and seedlings were unaltered by inoculation. A line derived from resistant seedlings from a susceptible family (RS) had the highest constitutive levels of lignin, which were further increased after inoculation. Resistance to P. cinnamomi in clonally propagated E. marginata seedlings is based on similar mechanisms to those of field resistant species.

Growth of Eucalyptus marginata (Jarrah) seedlings in a greenhouse in response to shade and soil temperature.

The effects of shade and soil temperature on growth of Eucalyptus marginata Donn ex Sm (jarrah) seedlings were studied in greenhouse experiments. Plant dry weight and that of all plant parts declined in response to shade, as did root/shoot ratio. Plant leaf area was less in unshaded plants than in plants grown in shade, and specific leaf area increased with shade. Unshaded seedlings had a higher light-saturated rate of photosynthesis, a higher light compensation point and a higher light saturation point than seedlings grown in 70% shade. The relationship between plant dry weight and leaf dry weight was independent of shading, whereas the relationship between plant dry weight and plant leaf area was dependent on shading. Therefore, leaf dry weight may be a better predictor of biomass production than leaf area in forest stands where shade is likely to affect growth significantly. Soil temperature had a significant effect on the growth of all plant parts except cotyledons. Total plant growth and shoot growth were maximal at a soil temperature of 30 degrees C, but root growth had a slightly lower temperature optimum such that the root/shoot ratio was highest at 20 degrees C. Roots grown at 15 degrees C were about 30% shorter per unit of dry weight than roots grown at 20 to 35 degrees C. We conclude that increases in irradiance and soil temperature as a result of overstory removal in the forest will cause significant increases in growth of E. marginata seedlings, but these increases represent a relatively small component of the growth response to overstory removal.

Interaction between Phytophthora cinnamomi zoospores and micro-organisms on non-mycorrhizal and ectomycorrhizal roots of Eucalyptus marginata

Investigation of the behaviour of Phytophthora cinnamomi zoospores on non-mycorrhizal and ectomycorrhizal roots of Eucalyptus marginata seedlings showed that zoospores encysted and germinated on both root types, but subsequent infection of root tissues was influenced by the type of ectomycorrhizal symbiont and the mycorrhizosphere population associated with the roots. In general, there was little evidence of colonization of P. cinnamomi zoospore cysts or germ tubes by the bacterial and/or actinomycete flora in the rhizoplane of non-mycorrhizal roots of seedlings growing in podsolic soil. On the other hand, there was extensive colonization of the fungus propagules on non-mycorrhizal roots in litter by bacteria and/or actinomycetes. Recovery of the pathogen was also markedly less from these roots than from similar root types growing in soil. Ectomycorrhizas formed by the ascomycete Cenococcum geophilum and the basidiomycete Hysterangium inflation failed to limit root infection in soil and the pathogen was recovered from both root types after 55 d incubation. There was no recovery of the pathogen from ‘white type’ basidiomycete ectomycorrhizas even after 24 h incubation. Micrographs showed zoospores either germinating but failing to penetrate the mantle or being enveloped and parasitized by a range of morphologically distinctive bacteria and a fungus within hours of inoculation of roots with zoospores. The data indicate a specific role for micro-organisms associated with root surfaces in antagonizing and limiting infection of roots by P. cinnamomi zoospores.

A comparison of growth of seedling and micropropagated Eucalyptus marginata (Jarrah) I. Early growth to 2 years

Growth and morphology of Eucalyptus marginata seedlings was compared, in glass-house and field experiments, with micropropagated plantlets derived from the crowns of mature trees. In the glasshouse experiment, the plantlets were shorter and more branched than seedlings; leaf shape and arrangement resembled mature, not juvenile, foliage. The total root length of plantlets was less than seedlings, but diameters were similar. The two soil types used in the glasshouse experiment, a peat/sand mixture and lateritic forest soil, affected the growth of the plants, probably due to the different cation exchange and waterholding capacities of the soils. In the field, after two years growth in lateritic soil, micropropagated plants were taller than seedlings, had no lignotuber and lacked the basal coppice growth which is typical of E. marginata. There is considerable difference between seedlings and micropropagated plants in form, growth and survival.

The relationship of inoculum density of Phytophthora cinnamomi chlamydospores in soil and infection of Eucalyptus marginata seedlings

Chlamydospores of Phytophthora cinnamomi were used as inoculum of known density (ID) in an investigation of the rate of jarrah seed germination and the level of infection of seedlings at the various ID's.Inoculum recovery by soil plating was about 2% of the added density. The germination of the jarrah seedlings was accelerated by the increase of the ID, especially at ID of 250 chlamydospores g −1 soil. The nominal LD 50 value for jarrah seedlings per chlamydospore inoculum was calculated as 13.0 chlamydospores g −1 soil and the number of viable chlamydospores in the rhizosphere at the highest ID was estimated as 9.1.

The Microflora of Unsuberized Roots of Eucalyptus calophylla R.Br. And Eucalyptus marginata Donn ex Sm. Seedlings Grown in Soil Suppressive and Conducive to Phytophthora cinnamomi Rands. I. Rhizosphere Bacteria, Actinomycetes and Fungi

An investigation was made of the microflora associated with unsuberized roots of Eucalyptus marginata and Eucalyptus calophylla raised in different soils. The studies were made for 'conducive' lateritic soil (in which E. marginata is susceptible to infection by Phytophthora cinnamomi but E. Calophylla is resistant); and in 'suppressive' loam soil in which both eucalypt species are unaffected by the pathogen. Lateritic soil in some cases contained natural infection of P. cinnamomi. Rhizospheres of both species contained larger microflora populations (expressed as numbers per g of root) than in the soils. In general, the population of rhizosphere microflora was greater for E. Marginata than E. calophylla seedlings in the uninfected lateritic soil. Qualitative differences were also recorded in populations of bacteria, actinomycetes and fungi, and in particular, fluorescent pseudomonads were more numerous in the rhizosphere of E. marginata seedlings. Eucalypt seedlings raised in loam soil harboured greater microbial populations than in lateritic soil. This could in part be attributed to the higher nutrient and organic matter status of the loam. E. marginata had a greater total rhizosphere population, but actinomycetes were more numerous in the rhizosphere of E. calophylla. Qualitative differences in populations of bacteria, actinomycetes and fungi were also noted. In naturally infected lateritic soil the microflora populations were invariably lower than for the other soils. When the counts of bacteria and actinomycetes were expressed as numbers per mm2 of root surface, E. calophylla had a significantly higher number of propagules per unit area than E. marginata. The loam soil was an exception; there E. marginata had three times as many bacteria per unit area of the root surface as E. calophylla. It is suggested that the microflora population differences recorded for the two eucalypts in lateritic soil may contribute to the differential susceptibility of species to infection by P. cinnamomi; and that the higher populations of microflora in the loam soil contribute to the suppression of P. Cinnamomi in that soil.