EFFECTS OF RELATIVE HUMIDITY AND TYPE OF CONTAINER ON THE GROWTH OF F1 HYBRID ANNUALS IN CONTROLLED ENVIRONMENTS

The effects of three levels of relative humidity (40%, 65%, and 90%) and two types of containers (clay and plastic) on the seedling growth of three F₁ hybrid annuals were determined after 14 days of controlled-environment treatment. Forty percent relative humidity was severely limiting to the seedling growth of ‘Blue Blazer’ ageratum (Ageratum houstonianum Mill.), ‘Pink Cascade’ petunia (Petunia hybrida Vilm.), and ‘Double Eagle’ marigold (Tagetes erecta L.). Raising the relative humidity to 65% resulted in striking increases in fresh weight, dry weight, and leaf area, especially when clay containers were used. Height of the main shoot was increased significantly at 65% relative humidity but node number was influenced only slightly. Increasing the relative humidity further to 90% had no significant effect on fresh weight, dry weight, or percent dry weight for any of the three species, in either container. Leaf area was increased significantly at 90% only in ageratum seedlings grown in clay pots. Each species responded differently to the type of container used. The fresh weight and dry weight of petunia seedlings were significantly greater in plastic pots at every level of humidity while those of marigold seedlings were unaffected by the type of container used. Ageratum seedlings, on the other hand, had significantly greater fresh weights and dry weights in clay pots only at 90% relative humidity.     

Temporal organization of chilling resistance in cotton seedlings: effects of low temperature and relative humidity

The effect of temperature and relative humidity (RH) on the time course of the rhythmic endogenous changes of chilling resistance was studied in cotton (Gossypium hirsutum L. cv. Deltapine 50) seedlings grown under light-dark cycles of 12:12 h. The resistant phase to 5° C, 85% RH lasted during most of the dark period while to 5° C, 100% RH it was longer and extended into the last half of the light period because a transient phase advance occurred when chilling started at the middle of the light period. Seedlings acclimated by low temperature were resistant throughout the light-dark cycle. A treatment with 100% RH before chilling to acclimated seedlings introduced a sensitive phase that corresponded to that of non-acclimated seedlings. In non-acclimated seedlings, this treatment decreased the resistance but the basic pattern of the rhythm was sustained. Changes in chilling resistance were analyzed under fluctuating temperatures and RHs, and explained taking into consideration the functioning of the circadian clock and environmental induction of resistance.Abbreviations CR chilling resistance - LDC light-dark cycle of 24 h - RH relative humidity     

Rapid Tomato Seedling Assay for Virulent Isolates of Fusarium oxysporum F. sp. Radicis-lycopersici (FORL), the Tomato Crown and Root Rot Pathogen

A rapid tomato seedling assay was developed for determining the relative wilt capacity of isolates of Fusarium oxysporum f. sp. radicis-lyco-persici (FORL), a virulent strain of the tomato pathogen. The procedures for the assay require that 5-day-old cv. Bonny Best tomato seedlings be dipped in 30-day cell-free concentrated culture filtrates of FORL isolates, which were grown in Czapek-Dox medium with 2% Bacto-casamino acids (CDA). The seedlings in the culture filtrates were then incubated at 30 C under artificial light (1200 ftcandles) at 28% relative humidity in a wind stream of 100–150 m min. The relative pathogenicity of the isolates was determined by inoculating the roots of 18-day-old seedlings with cultures of FORL isolates. The pattern of cell-free filtrate wilt among the isolates was the same as that for the disease caused by cultures of the isolates. The seedlings treated with the filtrate from the most virulent isolate (Harrow HRS-182) wilted in 20 min. The filtrates from less virulent isolates took progressively longer. up to 90 min. to cause comparable wilt. Isolate HRS-082 was the first isolate also to induce disease in 10-day-old seedling assay. Both assays indicate three levels of wilt and disease capacities amongthe isolates examined. The utility of the assay in research and breeding for resistance is discussed.     

Effekt und Risiko des Knöllchentests auf Braunfäuleresistenz bei Kartoffelsämlingen im System der Auslese in der Phytophthora-Resistenzzüchtung

The effects and risks involved with the small tuber assay in plant breeding programmes with potato seedlings for resistance to Phytophthora infestans In an assay which involved 838 potato seedlings, the relative resistance to leaf-Phytophthora (KR_G) was tested at the 4–6 leaf growth stage, and the relative tuber resistance to infection was determined on small pot-grown tubers (B_K) and, in the following 2 years, in slices from field-grown potatoes (B_s). The small tuber assay is described and its value as a measure of disease resistance, compared with the potato slice assay, discussed. Among 357 leaf-Phytophthora susceptible clones (KR_G≤ 5) were 10 clones with a good to very good tuber resistance. 18 of 204 leaf-Phytophthora highly resistant idiotypes were extremely susceptible to tuber rot. After discarding those seedlings which showed KR_G-values ≤ 5 and B_X-values ≤ 5, 208 of the remaining 241 (= 86 %) tuber rot resistance carrying seedlings were selected. 14 % of the clones which showed adequate resistance in the potato slice assay were falsely discarded according to the small tuber assay. 80 clones remained as ballast in the field trials (B_K≤ 5, B_s≤ 6.4), 160 (33 % of the idiotypes tested) had been correctly eliminated. The work-intensive small tuber assay presents a possibility by which breeding material can already be reduced in the seedling stage. In this respect there must be a pronounced genetic differentiation present in the potato population and the selection procedure carried out must not be too harsh.     

Morning vs afternoon sun patches in experimental forest gaps: consequences of temporal incongruency of resources to birch regeneration

We investigated whether the timing of high light availability as sun patches within forest gaps, independent of total or peak photosynthetic photon flux (PPF), influences the physiology and growth of four coexisting birch species (Betula alleghaniensis, B. lenta, B. papyrifera, and B. populifolia). Birch seedlings were grown for two years along either the east or west sides of experimental gap structures and at two moisture levels. Seedlings positioned in the west received sun patches earlier in the day than those in the east, and environmental conditions for carbon gain were generally more favorable during the earlier sunpatches in the west; air and leaf temperatures were lower, and relative humidity higher, relative to conditions during sun patches in the cats, simulating patterns observed in natural forest gaps. Seedlings positioned along the west edges of gaps fixed more carbon earlier in the day than those in the east, and in many cases, peak net photosynthetic rates were greater for west positioned seedlings. In year two, leaf-level integrated daily carbon gain was greater for west- than eastpositioned plants, and for the most pioneer species, B. populifolia, differences between west and east seedlings were greatest at lower soil moisture levels. Despite some small effects on leaf gas exchange, the timing of high light availability, and its temporal congruence with other factors critical to carbon gain, had no significant effects on first or second year seedling biomass. The responses of birch seedlings to controlled variations in the timing of high light availability were generally much smaller than birch seedling responses to variations in other components of daily light regimes such as total integrated and peak PPF.     

Different Assessment Techniques of Leaf Blotch (Rhynchosporium secalis (Oud.) J. Davis) in Winter Barley after Artificial Inoculation

Seven winter barley cultivars expressing different field resistance against leaf blotch (Rhynchosporium secalis) and 60 doubled haploid (DH) lines descending from and F₁ hybrid resistant x susceptible were used to develop a test for the quantitative determination of disease severity. Differences in the level of resistance could be measured very precisely after artificial infection of seedlings at the 4-leaf-stage and subseqent incubation at 7 C. The protein of six isolates was usedf, or antiserum production which was subsequently supplied for serological testing (Enzyme-Linked-Immunosorbent-Assay) of infected leaves. The results of visible scoring of the seedlings was significantly correlated with measuring with the ELISA reader. The, results of the seedling test also corresponded to field scores after natural infection.     

Effect of partial drying and desiccation on somatic seedling quality in Norway and Serbian spruce

Somatic embryo quality is still a problem for many researchers. To improve the efficiency of germination, special procedures are used, such as partial drying of somatic embryos at high relative humidity or desiccation in the presence of supersaturated solutions of salt. In this work, cotyledonary somatic embryos of Norway spruce (Picea abies) and Serbian spruce (P. omorika) were placed on culture media (ME or BM-5) to germinate. We found that after 4 weeks of incubation on these media, hypocotyl and radicle growth of control (non-dried) somatic embryos of both species was not adequate to yield seedlings able to acclimatize to greenhouse conditions. Therefore, somatic embryos were partly dried at relative humidity of 97 % or desiccated at relative humidity of 79 %, for 2 or 3 weeks, and then placed on the Margara (ME) medium. Partial drying of somatic embryos at the higher relative humidity (97 %) enabled an improvement of radicle growth of germinating somatic embryos in both species. The highest conversion rate (45 %) was obtained for embryos of Norway spruce maintained for 2 weeks at relative humidity of 97 %. This treatment contributed to the improvement of germination and conversion efficiency of somatic embryos of Norway spruce, regardless of the drying period. Improved radicle growth facilitated development of better quality seedlings of this spruce species. In Serbian spruce, we did not obtain seedlings of sufficient quality, due to poor hypocotyl growth. Desiccation at humidity of 79 % for 3 weeks proved to be lethal to somatic embryos of both species.     

Induced Resistance to Erwinia carotovora ssp. atroseptica, Through the Treatment of Surface Wounds of Potato Tubers with Elicitors

We have investigated the ability of mixed oligogalacturonides, a cell wall hydrolysate from Phytophthora sojae Hildebrand, and chitosan oligomers to induce resistance to Erwinia carotovora ssp. atroseptica in potato tubers (cv. Pentland Squire). Natural infection by Erwinia in stored potatoes generally originates in the surface tissues which have a markedly different biochemical composition to the perimedullary tissue. We therefore investigated the effect of different elicitors in inducing resistance in 2 mm deep wounds made on the surface of potato tubers. When wounded in this way and stored at 20°C and 100% relative humidity, tubers developed a significant level of natural resistance within 24 h. When the potatoes were treated with oligogalacturonides, or Phytophthora cell wall hydrolysate at the time of wounding and challenged with inoculum 8 h later, a significant reduction in disease occurred. Treatment with the chitosan elicitor had no effect on resistance.     

The Expression of Race-Specific Resistance of Wheat Seedlings to Puccinia recondita

A range of wheat cultivars with resistance factors effective against Puccinia recondita f. sp. tritici was studied to investigate the mode of action and expression of resistance at first and third seedling leaf stages. In most cultivars, resistance to isolate 74/2 resulted in extremely low levels of infection, apparently linked with a predominantly hypersensitive response by the host. In seedlings of cultivars Mans Fundin and Sterna, however, race-specific resistance was expressed as increased pathogen latent period and intermediate infection levels.     

Leaf Water Potential and Peroxidase activity in Quercus cerris and Quercus pubescens after Inoculation with Diplodia mutila

Ten-year-old field-grown Quercus pubescens Willd. and Quercus cerris L. individuals were inoculated with Diplodia mutila (teleomorph Botryosphaeria stevensii Shoe-maker) to observe symptom evolution over 2 years. The experiments were carried out for the 3 years: 1991, 1992 and 1993. At the same time, the effect of D. mutila on leaf water potential and peroxidase activity was assessed on the leaves of 2-year-old seedlings from the same two species growing under controlled conditions (18 h day, relative humidity 75%), temperature 24/15°C day/night). Quercus pubescens was more susceptible than Q. cerris, and frequently exhibited dieback of the branch above the inoculation site. On the seedlings, the visible symptoms of infection were much more severe than on the older trees. The infected seedlings showed a lower leaf water potential than healthy seedlings, particularly those of Q. pubescens after the third week. The peroxidase activity was increased in infected Q. pubescens seedlings compared with both groups of control seedlings (wounded but not inoculated, and neither wounded nor inoculated) 14 and 21 days after inoculation. Leaf water potential and peroxidase activity are known indicators of stress which appear even before any visible symptoms; they could therefore serve as early indicators of D. mutila infection.     

Control of Mn status and infection rate by genotype of both host and pathogen in the wheat take-all interaction

Take-all is a world-wide root-rotting disease of cereals. The causal organism of take-all of wheat is the soil-borne fungus Gaeumannomyces graminis var tritici (Ggt). No resistance to take-all, worthy of inclusion in a plant breeding programme, has been discovered in wheat but the severity of take-all is increased in host plants whose tissues are deficient for manganese (Mn). Take-all of wheat will be decreased by all techniques which lift Mn concentrations in shoots and roots of Mn-deficient hosts to adequate levels. Wheat seedlings were grown in a Mn-deficient calcareous sand in small pots and inoculated with four field isolates of Ggt. Infection by three virulent isolates was increased under conditions which were Mn deficient for the wheat host but infection by a weakly virulent isolate, already low, was further decreased. Only the three virulent isolates caused visible oxidation of Mn in vitro. The sensitivity of Ggt isolates to manganous ions in vitro did not explain the extent of infection they caused on wheat hosts. In a similar experiment four Australian wheat genotypes were grown in the same Mn-deficient calcareous sand and inoculated with one virulent isolate of Ggt. Two genotypes were inefficient at taking up manganese and were very susceptible to take-all, one was very efficient at taking up manganese and was resistant to take-all, and the fourth genotype was intermediate for both characters. All genotypes were equally resistant under Mn-adequate conditions.     

Wound-healing in carrot roots in relation to infection by Mycocentrospora acerina

Two ways of examining resistance in apple to Eriosoma lanigerum were assessed. The first method involved a single mass inoculation of young seedlings with first-instar nymphs. This failed to identify many susceptible seedlings and also produced inconsistent results which strongly suggested an uneven distribution of aphids at inoculation. Repeated inoculations were far more efficient in identifying known susceptibles than single inoculations, but they did not discriminate between susceptible and some resistant seedlings. However, the technique would be very useful where the major objective was the identification of higher levels of resistance. To overcome the destructive nature of mass inoculation and the inefficiency in classifying individual seedlings, a second method was devised using clonal material which allowed replication of genotypes. Calibrated inoculations made direct comparisons with controls possible and aphid numbers could be estimated with acceptable accuracy with a volumetric technique. However, comparisons based on approximate colony lengths were adequate, and faster, for routine screening.     

Use of artificial seedlings to estimate damage of forest seedlings due to litterfall and animals

Abstract. The artificial seedling assay method has been used in several tropical and temperate forests to estimate seedling damage and subsequent mortality due to non‐trophic micro‐disturbances such as litterfall and trampling. However, there has been no evidence presented to support the assumption that artificial seedling damage correlates with natural seedling mortality. In this study we evaluated the use of artificial seedlings in five New Zealand forests by comparing damage rates of artificial seedlings with damage and mortality rates of an equal number of selected natural seedlings. A total of 1200 artificial, and 1200 natural seedlings were monitored monthly for two years. Litterfall damage rates of natural seedlings were correlated with those of artificial seedlings. However, there was no relationship found between artificial and natural seedling damage due to animals, or between artificial seedling damage and natural seedling mortality for either cause. Artificial seedlings should not therefore be used to estimate seedling mortality due to non‐trophic microdisturbance. Monitoring natural seedlings enabled non‐trophic animal damage to be readily detected and provided additional information on animal‐plant interactions. The value of using artificial seedlings is that they provide a measure of the litterfall disturbance potential that is independent of the patchy distribution of natural seedlings within safe sites, and independent of species specific resistance to damage. They therefore provide an indication of the selective pressure on seedlings due to litterfall and are useful for comparing the relative ‘safety’ of different forests and microsites. Monitoring natural seedlings provides a measure of the damage and mortality due to litterfall for a specific seedling size class. Concurrently monitoring artificial and natural seedlings for litterfall disturbance provides more information than the same effort expended on either method alone.     

Ultrastructural Effects of Water Stress on Chloroplast Development in Jack Bean (Canavalia ensiformis [L.] DC)

An ultrastructural study has been made to determine to what degree chloroplast differentiation is retarded in leaves of young jack bean (Canavalia ensiformis [L.] DC.) seedlings when they are subjected to mild water stress. Rapid chloroplast differentiation occurred when etiolated seedlings were allowed to green at relative humidities above 85% but not at a relative humidity of 25%. Response to a drop in humidity was rapid. Germination and early development in the dark occurred at 100% relative humidity. At the time of exposure to light, the etioplasts contained well formed prolamellar bodies. Under high relative humidity conditions, transformation of the prolamellar body was well advanced within 2 hours. Under low relative humidity conditions, however, prolamellar body differentiation was extremely retarded for more than 24 hours following the beginning of illumination.     

Effects of environment,seedling age,and seed source on leaf resistance of three species of Chamaecyparis and Tsuga chinensis

Summary The objectives of this study were to determine how stomata of Chamaecyparis spp. react to environmental changes and to determine in what ways leaf resistance patterns may have adaptive value for these confers. Leaf resistances were measured of Chamaecyparis taiwanensis, C. formosensis and C. lawsoniana seedlings in a forest nursery, and of saplings of the first two species and Tsuga chinensis growing in natural forest and clearcuts. Light, temperature, humidity, and sometimes xylem pressure potential were measured concurrently.In the nursery, C. lawsoniana, the species from the driest climate, had the lowest resistance, daily means for well-watered yearold plants being 2–5 s cm^-1. Leaf resistances of well-watered C. formosensis and C. taiwanensis from more humid habitats were two and three times greater. Leaf resistance was more sensitive to environment in those nursery populations of C. formosensis from habitats where a dry season is more severe. There were no clear patterns of variation within the other species. Resistance of scale leaves increased with seedling size and age. Primary leaves of C. formosensis had higher average resistance than its scale leaves, and were more responsive to changes in the environment.In the field, C. taiwanensis had higher resistance than C. formosensis. Leaf resistance of Tsuga chinesis was quite similar to that of C. formosensis. Resistance decreased from winter to spring except during a severe dry spell in March.Changes in leaf resistance were most consistently correlated with humidity, which often increased during the day as humid air rose from the lowlands. Stomata opened as humidity rose even when plant xylem pressure potentials were -15 to -23 bars. Stomatal reaction of Chamaecyparis spp. varies in ways apparently adaptive to their environment.     

RNA Synthesis in Spring and Winter Wheat during Cold Acclimation

The factors responsible for the low transpiration rates of citrus were investigated. Leaf resistance to water vapor exchange by orange seedlings (Citrus sinensis L. cv. Koethen) including a substantial boundary layer resistance, was as low as 1 s cm⁻¹ in humid air. Leaf resistance of well watered plants increased to values as large as 5 s cm⁻¹ when the difference in absolute humidity between leaf and air was increased. Leaf resistance was only slightly influenced by temperature between 20 and 30°C providing the humidity difference between leaf and air was kept constant. Leaf resistance increased when leaf temperature was increased between 20 and 30°C when the absolute humidity external to the leaf was kept constant. Increased humidity differences resulted in greater increases in leaf resistance during initial experiments than when the experiments were repeated with the same leaves indicating acclimation by the plant. It was concluded that the effects of humidity differences on leaf resistance are partially responsible for the low transpiration rates of citrus.     

Parasitism,longevity and progeny production of six indigenous Kenyan trichogrammatid egg parasitoids (Hymenoptera: Trichogrammatidae) at different temperature and relative humidity regimes

Six native Kenyan species/strains of Trichogramma and Trichogrammatoidea, recovered from Helicoverpa armigera were evaluated at six different temperatures (10, 15, 20, 25, 30 and 35°C) and two relative humidity levels (40–50 and 70–80%) with the aim of selecting strains adapted to warmer temperature regimes. The species/strains were collected from low (<700 m), medium (between 700 and 1200 m) and high altitude (>1200 m) locations and were evaluated for parasitism, adult longevity, progeny production and progeny sex ratio at the different environmental regimes. Eggs of the factitious host, Corcyra cephalonica Stainton (Lepidoptera: Pyralidae) were used in the investigations. Temperature and humidity interactions affected parasitism and progeny production. The highest parasitism at the two humidity levels was at 25 and 30°C for all the strains evaluated. Adult longevity was also significantly affected by the interaction of temperature and relative humidity and was longer at the lower than higher relative humidity. Survival followed a type I survivorship curve at lower temperatures and a type III survivorship curve at the higher temperatures. Trichogramma sp. nr. mwanzai from low altitude, Trichogramma sp. nr. mwanzai from medium altitude and Trichogrammatoidea sp. nr. lutea also from medium altitude lived longer than other strains at all the temperatures and relative humidity levels evaluated, including the warmest regimes of 30 and 35°C. These strains appear promising as candidates for augmentative biocontrol of H. armigera in Kenya.     

Genotypic variation in growth and resistance to insect herbivory in silver birch (<Emphasis Type="Italic">Betula pendula</Emphasis>) seedlings

If herbivory is unevenly distributed among different types of plants, or if individual plants differ in their response to herbivory, herbivores may affect seedling growth and survival, and consequently plant population structure. In this study we examined variation in resistance to insect herbivory and in growth responses to feeding among 20 silver birch (Betula pendula Roth) genotypes representing variation within a natural population. Birch seedlings were grown in dense stands in random arrangement so that seedlings of different genotypes competed with each other. On insect exposure plots natural colonization of insects was allowed, and insect removal plots were sprayed with insecticide. Resistance to insect herbivory was measured as the inverse of leaf damage, and growth responses of seedlings to feeding were determined as the change in seedling height relative to the amount of damage. Resistance varied significantly among genotypes, but growth responses to feeding did not. In fertilized seedlings, resistance correlated negatively with height, indicating a trade-off between resistance and growth. The absence of such a correlation in non-fertilized seedlings is a sign of environmental effects on the cost of resistance. Growth responses to feeding did not correlate with either resistance or growth. Nevertheless, different effects of the actual damage on height increase changed the positions of the genotypes in the size hierarchy of the experimental populations. Thus, even moderate levels of insect herbivory can change the outcome of competitive interactions between birch genotypes.Due to an error in the citation line, this revised PDF (published in December 2003) deviates from the printed version, and is the correct and authoritative version of the paper.     

Seedling bank dynamics of Fagus grandifolia var. mexicana before and after a mast year in a Mexican cloud forest

Abstract. Fagus grandifolia var. mexicana seedling dynamics were studied in a relict forest inside the crater of a volcano where it is the only canopy tree species. The objectives of the study were (1) to determine changes in seedling density before and after a mast year, as well as to monitor seedling recruitment, mortality and growth rate in relation to the micro‐environment, and (2) to discuss the impact of masting on seedling dynamics of the population. Before masting, seedling density was 8.8 seedlings m^–2, afterwards seedling density peaked at 51.5 seedlings m^–2, then decreased by 50% in 3 months and by 85% after 8 months, down to levels of before the mast year (9.9 seedlings m^–2) after 16 months. Seedlings in the forest floor before the mast‐seeding event showed a low relative growth rate – 0.14 mm mm^–1 mo^–1 against 1.27 mm mm^–1 mo^–1 for seedlings that emerged immediately after masting. Seed germination was high (83%) and rapid (L₅₀= 7 days) following masting. Seedling growth was positively correlated with soil water content but not with temperatures and relative humidity. Data suggested that seed production in mast years is important in maintaining the seedling bank, and thus the viability of relict Fagus populations.     

Humidity affects genetic architecture of heat resistance in Drosophila melanogaster

Laboratory experiments on Drosophila have often demonstrated increased heritability for morphological and life‐history traits under environmental stress. We used parent–offspring comparisons to examine the impact of humidity levels on the heritability of a physiological trait, resistance to heat, measured as knockdown time at constant temperature. Drosophila melanogaster were reared under standard nonstressful conditions and heat‐shocked as adults at extreme high or low humidity. Mean knockdown time was decreased in the stressful dry environment, but there was a significant sex‐by‐treatment interaction: at low humidity, females were more heat resistant than males, whereas at high humidity, the situation was reversed. Phenotypic variability of knockdown time was also lower in the dry environment. The magnitude of genetic correlation between the sexes at high humidity indicated genetic variation for sexual dimorphism in heat resistance. Heritability estimates based on one‐parent–offspring regressions tended to be higher under desiccation stress, and this could be explained by decreased environmental variance of heat resistance at low humidity. There was no indication that the additive genetic variance and evolvability of heat resistance differed between the environments. The pattern of heritability estimates suggests that populations of D. melanogaster may have a greater potential for evolving higher thermal tolerance under arid conditions.