Interaction between the root-lesion nematode Pratylenchus vulnus and the mycorrhizal association of Glomus intraradices and Santa Lucia 64 cherry rootstock

The effects of the interaction between Pratylenchus vulnus and the endomycorrhizal fungus Glomus intraradices on growth and nutrition of Santa Lucia 64 cherry rootstock was studied under microplot conditions during one growing season. Fresh top weight, and stem diameter of mycorrhizal plants and high P treatments with and without P. vulnus were significantly higher than those of non-mycorrhizal plants. The lowest shoot length and fresh root weights were recorded in nematode inoculated plants in low P soil. Mycorrhizal infection did not affect the number of nematodes per gram of root in plants infected with P. vulnus. In the presence of the nematode, internal spore production by G. intraradices was significantly reduced. No nutrient deficiencies were detected through foliar analysis, although low levels of Ca, Mn and Fe were detected in nematode treatments. Mycorrhizal plants achieved the highest values for N, P, S, Fe, and Zn, whereas high P treatments increased absorption of Ca and Mn. Early mycorrhizal infection of Santa Lucia 64 cherry rootstock by G. intraradices confers increased growth capacity in the presence of P. vulnus.     

Root Morphology, Stem Growth and Field Performance of Seedlings of Two Mediterranean Evergreen Oak Species Raised in Different Container Types

Outplanting container-grown oak seedlings with undesirable shoot and root characteristics result in poor establishment and reduced field growth. The objective of this study was to determine the influence of container type on both above-and below-ground nursery growth and field performance of one-year old tap-rooted seedlings Quercus ilex L. and Quercus coccifera L. The experiment was conducted in an open-air nursery and the seedlings were grown in three container types. At the end of the nursery, growth period seedlings’ shoot height, diameter (5 mm above root collar), shoot and root biomass, root surface area, root volume and total root length were assessed. Then the seedlings were planted in the field and their survival and growth were recorded for two growing seasons after outplanting. The results showed a difference between the Quercus species in the effect of container type. Q. ilex seedlings raised in paper-pot had significantly greater height, diameter, shoot and root biomass and root volume than those raised in the other two container types. Similarly, Q. coccifera seedlings raised in paper-pot, had significantly greater above-and below-ground growth than those raised in the other two container types. Both oak species showed relatively low survival in the field; the mortality was mainly observed the first year after outplanting, especially after the summer dry period. However, 2 years after outplanting, the paper-pot seedlings of the two oak species showed better field performance.     

Deficit and excess of soil water impact on plant growth of Lotus tenuis by affecting nutrient uptake and arbuscular mycorrhizal symbiosis

The impact of deficit and excess of soil water on plant growth, morphological plant features, N and P plant nutrition, soil properties, Rhizobium nodulation and the symbiosis between arbuscular mycorrhizal (AM) fungi and Lotus tenuis Waldst. & Kit. were studied in a saline-sodic soil. Water excess treatment decreased root growth by 36% and increased shoot growth by 13% whereas water deficit treatment decreased both root and shoot growth (26 and 32%, respectively). Differences between stress conditions on shoot growth were due to the ability of L. tenuis to tolerate low oxygen concentration in the soil and the sufficiency of nutrients in soil to sustain shoot growth demands. Water excess treatment decreased pH, and increased available P and labile C in soil. Water deficit treatment decreased available P and also increased labile C. In general, N and P acquisition were affected more by water excess than water deficit. The number of nodules per gram of fresh roots only increased in water excess roots (97%). Under both stress conditions there was a significant proportion of roots colonized by AM fungi. Compared to control treatment, arbuscule formation decreased by 55 and 14% under water excess and water deficit, respectively. Vesicle formation increased 256% in water excess treatment and did not change under water deficit treatment. L. tenuis plants subjected to water deficit or excess treatments could grow, nodulated and maintained a symbiotic association with AM fungi by different strategies. Under water excess, L. tenuis plants decreased root growth and increased shoot growth to facilitate water elimination by transpiration. Under water deficit, L. tenuis plants decreased root growth but also shoot growth which in turn significant decreased the shoot/root ratio. In the present study, under water excess conditions AM fungi reduced nutrient transfer structures (arbuscules), the number of entry points and spore, and hyphal densities in soil, but increased resistance structures (vesicles). At water deficit, however, AM fungi reduced external hyphae and arbuscules to some extent, investing more in maintaining a similar proportion of vesicles in roots and spores in soil compared to control treatment.     

Physiological and growth responses of Centaurea maculosa (Asteraceae) to root herbivory under varying levels of interspecific plant competition and soil nitrogen availability

Summary Centaurea maculosa seedlings were grown in pots to study the effects of root herbivory by Agapeta zoegana L. (Lep.: Cochylidae) and Cyphocleonus achates Fahr. (Col.: Curculionidae), grass competition and nitrogen shortage (each present or absent), using a full factorial design. The aims of the study were to analyse the impact of root herbivory on plant growth, resource allocation and physiological processes, and to test if these plant responses to herbivory were influenced by plant competition and nitrogen availability. The two root herbivores differed markedly in their impact on plant growth. While feeding by the moth A. zoegana in the root cortex had no effect on shoot and root mass, feeding by the weevil C. achates in the central vascular tissue greatly reduced shoot mass, but not root mass, leading to a reduced shoot/root ratio. The absence of significant effects of the two herbivores on root biomass, despite considerable consumption, indicates that compensatory root growth occurred. Competition with grass affected plant growth more than herbivory and nutrient status, resulting in reduced shoot and root growth, and number of leaves. Nitrogen shortage did not affect plant growth directly but greatly influenced the compensatory capacity of Centaurea maculosa to root herbivory. Under high nitrogen conditions, shoot biomass of plants infested by the weevil was reduced by 30% compared with uninfested plants. However, under poor nitrogen conditions a 63% reduction was observed compared with corresponding controls. Root herbivory was the most important stress factor affecting plant physiology. Besides a relative increase in biomass allocation to the roots, infested plants also showed a significant increase in nitrogen concentration in the roots and a concomitant reduction in leaf nitrogen concentration, reflecting a redirection of the nitrogen to the stronger sink. The level of fructans was greatly reduced in the roots after herbivore feeding. This is thought to be a consequence of their mobilisation to support compensatory root growth. A preliminary model linking the effects of these root herbivores to the physiological processes of C. maculosa is presented.     

Spore production and mycorrhizal development in various tropical crop hosts infected with Glomus clarum

Plant growth, mycorrhizal development and vesicular arbuscular spore production were examined in five tropical crop host species inoculated with Glomus clarum and grown in a glasshouse. In one of the two experiments, sequential harvests of maize, sorghum and chickpea were made in order to study spore production in relation to plant growth and mycorrhizal development. Spore numbers in each of these hosts increased at a fairly constant rate until maximum plant dry weight, when spore production ceased. Sorghum and maize produced considerably more spores than chickpea, with spore numbers being closely correlated with mycorrhizal root length. In the second experiment, Glomus clarum was cultured on each of maize, millet, sorghum, groundnut and chickpea for three consecutive generations before cross-inoculation of the spores from each host onto all five hosts. Sporulation with respect to host size was generally greatest when the inoculum used to infect a host had been produced on that host. The growth-promoting effects of the fungus were not influenced by the source of the inoculum. More spores were produced on the cereals than the legumes. Differences in spore numbers amongst hosts and plant generations were apparently influenced mainly by infected root length and by the growth period.     

Differential responses of three fungal species to environmental factors and their role in the mycorrhization of<Emphasis Type="Italic"> Pinus radiata</Emphasis> D. Don

Three ectomycorrhizal (ECM) isolates of Rhizopogon luteolus, R. roseolus and Scleroderma citrinum were found to differ markedly in their in vitro tolerance to adverse conditions limiting fungal growth, i.e. water availability, pH and heavy metal pollution. S. citrinum was the most sensitive, R. luteolus intermediate and R. roseolus the most tolerant species. Pinus radiata D. Don seedlings were inoculated in the laboratory and in a containerised seedling nursery with spore suspensions of the three ECM species. Colonisation percentage was considerably lower under nursery conditions, probably due to competition by native fungi. The effects of nursery ECM inoculation on seedling growth depended on the fungal species. Only R. roseolus-colonised plants showed a significantly higher shoot growth than non-mycorrhizal plants. All three fungi induced significantly higher root dry weights relative to control plants. Despite the low mycorrhizal colonisation, mycorrhization with all three species improved the physiological status of nursery-grown seedlings, e.g. enhanced root enzyme activity, shoot nutrient and pigment content, net photosynthesis rate and water use efficiency. Of the three fungal species, R. roseolus was the most effective; this species was also the most adaptable and showed the greatest range of tolerance to adverse environmental conditions in pure culture. It is, therefore, proposed as a promising fungal species for ECM inoculation of P. radiata in the nursery.     

Effects of light and nutrient availability on the growth,allocation, carbon/nitrogen balance,phenolic chemistry,and resistance to herbivory of two freshwater macrophytes

Phenotypic responses of Potamogeton amplifolius and Nuphar advena to different light (7% and 35% of surface irradiance) and nutrient environments were assessed with field manipulation experiments. Higher light and nutrient availability enhanced the growth of P. amplifolius by 154% and 255%, respectively. Additionally, biomass was allocated differently depending on the resource: high light availability resulted in a higher root/shoot ratio, whereas high nutrient availability resulted in a lower root/shoot ratio. Low light availability and high nutrient availability increased the nitrogen content of leaf tissue by 53% and 40% respectively, resulting in a 37% and 31% decrease in the C/N ratio. Root nitrogen content was also increased by low light and high nutrient availability, by 50% (P=0.0807) and 77% respectively, resulting in a 20% and 40% decrease in root C/N ratio. Leaf phenolics were significantly increased 72% by high light and 31% by high nutrient availability, but root phenolic concentrations were not altered significantly. None of these changes in tissue constituents resulted in altered palatability to crayfish. N. advena was killed by the same high nutrient treatment that stimulated growth in P. amplifolius, preventing assessment of phenotypic responses to nutrient availability. However, high light availability increased overall growth by 24%, but this was mainly due to increased growth of the rhizome (increased 100%), resulting in a higher root/shoot ratio. High light tended to increase the production of floating leaves (P=0.09) and significantly decreased the production of submersed leaves. High light availability decreased the nitrogen content by 15% and 25% and increased the phenolic concentration by 88% and 255% in floating and submersed leaves, respectively. These differences in leaf traits did not result in detectable differences in damage by herbivores.     

Tillage and N fertilization effects on maize root growth and root:shoot ratio

Two methods for estimating the size of the maize (Zea mays l.) root system from soil cores taken in the field were compared. The spatially weighed block method of estimation accounted for variation in root density by using 18 samples per plant which varied in distance from plant and soil depth. This method was compared to an estimation which averaged all of the 18 samples together. Both methods gave surprisingly similar estimates for total root growth. Increased root growth in the surface soil layers, due to tillage and N fertilization, did not impact on the estimation of total root growth. Total root length remained unchanged or increased with N fertilization, while root weight remained the same or decreased. Root mass per length decreased with N fertilization. The estimated size of the root system was used to calculate root:shoot weight ratios. The largest root:shoot ratio was found in the vegetative stage and decreased throughout the rest of the season. In this field experiment, the estimated size of the root system at 8 weeks after planting was not significantly different from the size at silking or harvest. Nitrogen fertilization significantly decreased the root:shoot weight ratio. However, tillage did not significantly change the ratio.     

油菜素内酯对巨桉组培中不定根诱导、苗木生长和茎基部细胞结构的影响

以巨桉优良无性系EG5和GL1组培苗为材料,在生根培养基中分别加入0、0.005、0.01、0.05、0.10、0.20 mg.L-1的油菜素内酯,研究其对桉树组培苗中不定根的诱导、茎的生长以及茎基部细胞分化的影响。结果表明：油菜素内酯对巨桉无性系EG5的生根率和苗高具有显著影响,无性系EG5在含有0.005 mg.L-1油菜素内酯的生根培养基中达到最高为76.6％的生根率,同时组培苗的苗高随着油菜素内酯浓度的增加而呈现出逐渐降低的趋势。对于巨桉无性系GL1,在生根培养基中添加0.05 mg.L-1油菜素内酯达到最高为88.3％的生根率,不同浓度的油菜素内酯对苗高没有显著影响。同时也发现油菜素内酯明显抑制了无性系EG5不定根的根长,随着其浓度的增加根长逐渐变短;而根条数表现为低浓度时无显著影响,在高浓度时显著性降低,且油菜素内酯对侧根的诱导和分化不起作用。另外通过对无性系EG5生根植株基部的组织切片和化学染色分析表明,油菜素内酯在0.10 mg.L-1时能促进桉树基部的形成层和木质部的分化,这可能是抑制不定根诱导和分化的原因之一。     

Allometric growth, disturbance regime, and dilemmas of controlling invasive plants: a model analysis

Disturbed communities are observed to be more susceptible to invasion by exotic species, suggesting that some attributes of the invaders may interact with disturbance regime to facilitate invasion success. Alternanthera philoxeroides, endemic to South America, is an amphibious clonal weed invading worldwide. It tends to colonize disturbed habitats such as riparian zones, floodplain wetlands and agricultural areas. We developed an analytical model to explore the interactive effects of two types of physical disturbances, shoot mowing and root fragmentation, on biomass production dynamics of A. philoxeroides. The model is based on two major biological assumptions: (1) allometric growth of root (belowground) vs. shoot (aboveground) biomass and (2) exponential regrowth of shoot biomass after mowing. The model analysis revealed that the interaction among allometric growth pattern, shoot mowing frequency and root fragmentation intensity might lead to diverse plant ‘fates’. For A. philoxeroides whose root allocation decreases with growing plant size, control by shoot mowing was faced with two dilemmas. (1) Shoot regrowth can be effectively suppressed by frequent mowing. However, frequent shoot mowing led to higher biomass allocation to thick storage roots, which enhanced the potential for faster future plant growth. (2) In the context of periodic shoot mowing, individual shoot biomass converged to a stable equilibrium value which was independent of the root fragmentation intensity. However, root fragmentation resulted in higher equilibrium population shoot biomass and higher frequency of shoot mowing required for effective control. In conclusion, the interaction between allometric growth and physical disturbances may partially account for the successful invasion of A. philoxeroides; improper mechanical control practices could function as disturbances and result in exacerbated invasion.     

Comparative effects of NaCl and polyethylene glycol on root distribution,growth, and stomatal conductance of sour orange seedlings

An experiment was conducted to study sour orange (Citrus aurantium L.) seedling root density, distribution, and morphological development under NaCl and polyethylene glycol (PEG) stresses in relation to shoot growth and stomatal conductance. Plants were treated with 2 stress levels (– 0.12 and – 0.24 MPa) of NaCl and PEG 4000 for 7 months. Root observation chambers were used to monitor root growth and distribution under stressed and non-stressed conditions. Seedlings receiving NaCl or PEG treatments produced fewer roots and shallower root systems with 46 to 65% of the roots occurring in the top portion of the soil. Fibrous root weight per unit length was increased by 24 to 30% by PEG but was not significantly increased by NaCl.Root growth rate usually alternated with shoot growth in a 2-month cycle. This alternating pattern was not shifted by NaCl and PEG stresses. In all NaCl and PEG treatments, growth was depressed and stomatal conductance was reduced. Compared to controls, plants that received NaCl or PEG had smaller shoot and root dry weights, fewer leaves, shorter height, and fewer roots. Sodium chloride usually caused less damage than PEG to sour orange seedlings suggesting that NaCl and PEG acted through different mechanisms.Florida Agricultural Experiment Station Journal Series No. 9941.     

Seasonal variation of growth and development of the roots of five second year conifer species in the nursery

Every other week over their second growing season, stem height, collar diameter, shoot and root dry masses, number of lateral roots and length of the tap root were measured on nursery grown seedlings ofAbies balsamea L. Mill.,Pinus banksiana Lamb.,Pinus resinosa Ait.,Picea mariana Mill. BSP andPicea glauca Moench Voss. Root elongation, branching and mycorrhizal development were also recorded.Given species showed distinct seasonal growth patterns. The rate and timing of maximum root growth (mg/dry weight/week) differed markedly between species.Except for the increase in height ofPinus banksiana, root and shoot growth were not negatively correlated.The results are discussed in relation to the performance of tree seedlings in the nursery.     

Seedling ecology of two miombo woodland trees

The development of seedlings of two miombo trees, Brachystegia spiciformis Benth. and Julbernardia paniculata (Benth.) Troupin, was studied during two growing seasons (December 1989–April 1991) at a Zambian grassland site. Seed germination rates under laboratory and field conditions were not significantly different although germination in the field was delayed by 1–2 weeks due to insufficient rainfall. After one year of storage J. paniculata seed germination had declined from 67% to 17% while germination of B. spiciformis seeds remained at about 83%.Leaf production was confined to the rainy season. Leaf fall occurred during the dry season and in J. paniculata this was followed by shoot die-back during the hot dry period (August–November). Two-thirds of B. spiciformis seedlings experienced shoot die-back but shoot die-back did not necessarily result in seedling mortality. Seedling deaths occurred during the germination period (6–10 weeks after planting) and in the hot dry period (40–50 weeks after planting) during September–November. Survivorship of B. spiciformis seedlings was 74% at the end of the second growing season while this was 46% for J. paniculata.Shoot growth was negligible during the second growing season. In fact mean maximum leaf area of B. spiciformis decreased significantly from 19.7 cm² (SD=5.7) per plant at the end of the first growing season to 13.3 cm² (SD=5.8) at the end of the second growing season (t=3.31, P<0.01). However, root biomass of B. spiciformis seedlings increased 2.8 times during the second growing season.These results suggest that shoot die-back in seedlings of miombo trees is caused by drought and that the slow shoot growth is the result of allocating most of the biomass to root growth during seedling development.     

Interaction between arbuscular mycorrhizal fungus Glomus mosseae and plant growth promoting fungus Phoma sp. on their root colonization and growth promotion of cucumber (Cucumis sativus L.)

Interaction between arbuscular mycorrhizal fungus Glomus mosseae and plant growth promoting fungus Phoma sp. was studied for its effect on their root colonization and plant growth of cucumber. Two isolates of Phoma sp. (GS8-2 and GS8-3) were tested with G. mosseae. The percent root length colonized by G. mosseae was not adversely affected by the presence of Phoma isolates. In contrast, the root colonization of both isolates GS8-2 and GS8-3 in 4-week-old plants was significantly reduced (80.7% and 84.3%, respectively) by added G. mosseae. Inoculating plants with each Phoma isolate significantly increased the shoot dry weight. However, dual inoculation of each Phoma isolate with G. mosseae had no significant effect on growth enhancement.     

Arbuscular mycorrhiza colonization and development at suboptimal root zone temperature

Temperature has a strong influence on the activity of living organisms. This study, involving two indoor experiments, evaluated the effects of root zone temperature (10, 15 and 23°C) on the formation and development of arbuscular mycorrhizae (AM). In the first trial, greenhouse-grown sorghum [Sorghum bicolor (L.) Moench] was either colonized by Glomus intraradices Schenck & Smith or left non-mycorrhizal. Root length, root and shoot weight and root colonization were measured after 5, 10 and 15 weeks of plant growth. Although suboptimal root zone temperatures reduced growth in both mycorrhizal and non-mycorrhizal plants, mycorrhizal plants were larger than non-mycorrhizal plants after 15 weeks at 15 and 23°C. At suboptimal root zone temperatures, mycorrhizal inoculation sometimes slightly reduced root development. AM colonization was more affected than root growth at suboptimal root zone temperatures. Colonization was markedly reduced at 15°C compared with 23°C, and almost completely inhibited at 10°C. The second experiment was conducted in vitro using transformed carrot (Daucus carota L.) roots supporting G. intraradices. Mycelium length and spore number were measured weekly for 15 weeks. Spore metabolic activity (iodonitrotetrazolium reduction), root length and percentage root colonization were measured after 15 weeks. G. intraradices sporulation was reduced at temperatures below 23°C, while spore metabolic activity was significantly reduced only at 10°C. Root length and in particular percentage colonization were decreased at suboptimal temperatures. A negative interaction between AM hyphal growth and root growth resulting in reduced probability of contact at suboptimal root zone temperatures is proposed to explain the greater reduction observed in root colonization than in root and hyphal growth.     

Root damage and aboveground herbivory change concentration and composition of pyrrolizidine alkaloids of Senecio jacobaea

Thus far not many studies focussed on how herbivory in one plant part affects plant defence in the other. The effects of root damage and a leaf-feeding herbivore (Mamestra brassicae) on pyrrolizidine alkaloid (PA) levels of Senecio jacobaea were investigated in a controlled environment. Three cloned S. jacobaea genotypes, which differed in PA concentrations, received four treatments: (1) no damage, (2) root damage (removing half of the root system), (3) shoot herbivory by M. brassicae larvae, (4) root damage and shoot herbivory.Shoot herbivory did not significantly affect shoot biomass, while root damage decreased both root and shoot biomass. Shoot herbivory decreased PA concentrations in the roots. Conversely, root damage increased PA concentrations in the roots. Alkaloid concentrations in the shoot showed a weak response to root damage, shoot herbivory had no effect on PA levels in the shoot. The effect of damage on the allocation of PAs to shoot and roots depended on genotype. One genotype allocated more PAs to the damaged site, another genotype did not change allocation and the third genotype allocated more PAs to the shoot if the roots were damaged. Changes in PA composition were observed in one genotype. Shoot herbivory increased erucifoline concentrations in the shoot and decreased concentrations of senecionine in the roots. In conclusion, we have shown that even in an alleged constitutively defended plant, damage of one compartment affects secondary metabolite level in the other.     

Phosphorus allocation in P-efficient and inefficient barley cultivars as affected by mycorrhizal infection

A glasshouse experiment was undertaken to investigate the effect of mycorrhizal infection on the allocation of phosphorus (P) in agronomically P-efficient (i.e. high yields at low P supply) and inefficient barley (Hordeum vulgare L.) cultivars. Four barley cultivars differing in agronomic P-efficiency were inoculated or not inoculated with Glomus etunicatum. Cultivars did not differ in percentage of root length infected. The concentration of P in roots of the inefficient cultivars was higher than that of the efficient cultivars. However, because of changes in root to shoot dry weight ratio and below-ground productivity, mycorrhizal infection significantly reduced the percentage of total plant P in roots of the inefficient cultivars. The distribution of P between root and shoot of P-efficient cultivars was not affected by mycorrhizal infection. Root to shoot dry weight ratio of the P-efficient cultivars was lower than that of the inefficient cultivars, and the decrease in the ratio following infection was significant in inefficient but not in P-efficient cultivars. This study indicates that mycorrhizal infection alters the allocation of P in inefficient cultivars and effectively improves the efficiency of P utilization with respect to shoot growth.     

Impact of Bacillus subtilis JA, a biocontrol strain of fungal plant pathogens, on arbuscular mycorrhiza formation in Zea mays

Summary  In the present study, the influence of Bacillus subtilis JA on arbuscular mycorrhizal fungi (AMF) was evaluated by either pot culture or in vitro conditions, respectively. Under the pot culture conditions, the inoculation of B. subtilis JA decreased the frequency (% F) of the root colonization by indigenous arbuscular mycorrhizal fungi and the shoot dry weight of maize (Zea mays L.), but had no apparent effect on the intensity (% I) of AM fungal root colonization. The unknown volatile emitted from the B. subtilis JA in vitro significantly inhibited spore germination and the hyphal growth in the dual-compartment experiments. Moreover, the data from the direct interaction between B. subtilis JA and Glomus etunicatum showed that soluble antifungal lipopeptides influenced the development of AMF. Therefore, the application of antifungal Bacillus strains should take the compatibility with the indigenous beneficial fungi into consideration.     

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.     

Assessment of in vitro growth of apical stem sections and adventitious organogenesis to evaluate salinity tolerance in cultivated tomato

The possible use of in vitro shoot morphogenesis and shoot apex culture to evaluate salt tolerance in cultivated tomato (Lycopersicon esculentum Mill.) has been analyzed, using two cultivars with similar salt tolerance, Pera and Hellfrucht frühstamm (HF). The effect of salt on shoot regeneration was studied by culturing leaf explants on media supplemented with 0, 43, 86, 129 and 172 mM NaCl. The presence of NaCl in the regeneration media at 86 mM strongly inhibited shoot regeneration in the cultivar HF, but not in Pera. However, the substitution of NaCl by mannitol, maintaining the same water potential in the culture media, decreased the regeneration percentage in Pera but did not affect HF. Shoot apices of both cultivars were also subcultured at 6-week intervals, for 4 subcultures, at the same NaCl concentrations as used in the previous experiment, and the shoot growth, leaf and root number, rooted shoot and shoot necrosis were recorded at the end of each subculture. Root formation was the parameter most affected by salt in both cultivars, Pera being more sensitive than HF. The substitution of NaCl by mannitol significantly increased the percentage of rooted shoots in Pera after four subcultures, and slightly decreased this percentage in HF. Shoot necrosis was only observed in the last subculture at NaCl higher than 86 mM, the percentage of necrotic shoots being higher in Pera than in HF (75% and 45%, respectively). The lack of agreement between the results obtained with the in vitro tests, e.g., adventitious shoot formation and growth of apical stem sections, suggests that this approach may not be a reliable tool to evaluate salt tolerance in cultivated tomato. This revised version was published online in June 2006 with corrections to the Cover Date.