Lower Emergence Research Articles

Effect of Larval Competition on Extrinsic Incubation Period and Vectorial Capacity of Aedes albopictus for Dengue Virus.

Despite the growing awareness that larval competition can influence adult mosquito life history traits including susceptibility to pathogens, the net effect of larval competition on human risk of exposure to mosquito-borne pathogens remains poorly understood. We examined how intraspecific larval competition affects dengue-2 virus (DENV-2) extrinsic incubation period and vectorial capacity of its natural vector Aedes albopictus. Adult Ae. albopictus from low and high-larval density conditions were orally challenged with DENV-2 and then assayed for virus infection and dissemination rates following a 6, 9, or 12-day incubation period using real-time quantitative reverse transcription PCR. We then modeled the effect of larval competition on vectorial capacity using parameter estimates obtained from peer-reviewed field and laboratory studies. Larval competition resulted in significantly longer development times, lower emergence rates, and smaller adults, but did not significantly affect the extrinsic incubation period of DENV-2 in Ae. albopictus. Our vectorial capacity models suggest that the effect of larval competition on adult mosquito longevity likely has a greater influence on vectorial capacity relative to any competition-induced changes in vector competence. Furthermore, we found that large increases in the viral dissemination rate may be necessary to compensate for small competition-induced reductions in daily survivorship. Our results indicate that mosquito populations that experience stress from larval competition are likely to have a reduced vectorial capacity, even when susceptibility to pathogens is enhanced.

Effect of Hydro-priming and Priming with Ascorbic and Salicylic Acid on Germination Traits of Dracocephalum moldavica L. Varieties

Information regarding the evaluation of priming treatments on germination traits of Dracocephalum moldavica L. varieties is not available. Therefore, this assay was conducted during 2013 in Islamic Azad University of Sanandaj located in Kurdistan province of Iran. Twelve treatments resulted from a factorial combination of six priming method (factor A) and two varieties of moldavian dragonhead (factor B), arranged in a completely randomized design replicated three times. Factor A included 50 mg L-1 Salicylic acid (SA), 100 mg L-1 SA, 50 mg L-1 Ascorbic acid (AsA), 100 mg L-1 AsA, hydro-priming and control. Factor B included Kurdish landrace and SZK1 cultivar. Results showed that the highest and lowest emergence percentages were 90.1 % in Kurdish SA50 and 52.8 % in SZK1 AsA100 treatments, respectively. Hydro priming treatment increased the emergence rate index more than 100 mg L-1 SA, 100 mg L-1 AsA and control treatments. The highest shoot weight was 9.41 mg for Kurdish SA50 treatment and the lowest length, 1.24 mg was attributed to SZK1 control treatment. The highest (6.56 mg) and lowest (1.74 mg) radicle weight were observed in Kurdish-hydro-priming and SZK1-AsA100 treatments. The Kurdish landrace showed a favorable germination condition compared to SZK1 cultivar.

Effective autodissemination of pyriproxyfen to breeding sites by the exophilic malaria vector Anopheles arabiensis in semi-field settings in Tanzania.

BackgroundMalaria vector control strategies that target adult female mosquitoes are challenged by the emergence of insecticide resistance and behavioural resilience. Conventional larviciding is restricted by high operational costs and inadequate knowledge of mosquito-breeding habitats in rural settings that might be overcome by the juvenile hormone analogue, Pyriproxyfen (PPF). This study assessed the potential for Anopheles arabiensis to pick up and transfer lethal doses of PPF from contamination sites to their breeding habitats (i.e. autodissemination of PPF).MethodsA semi-field system (SFS) with four identical separate chambers was used to evaluate PPF-treated clay pots for delivering PPF to resting adult female mosquitoes for subsequent autodissemination to artificial breeding habitats within the chambers. In each chamber, a tethered cow provided blood meals to laboratory-reared, unfed female An. arabiensis released in the SFS. In PPF-treated chambers, clay pot linings were dusted with 0.2 – 0.3 g AI PPF per pot. Pupae were removed from the artificial habitats daily, and emergence rates calculated. Impact of PPF on emergence was determined by comparing treatment with an appropriate control group.ResultsMean (95% CI) adult emergence rates were (0.21 ± 0.299) and (0.95 ± 0.39) from PPF-treated and controls respectively (p < 0.0001). Laboratory bioassay of water samples from artificial habitats in these experiments resulted in significantly lower emergence rates in treated chambers (0.16 ± 0.23) compared to controls 0.97 ± 0.05) (p < 0.0001). In experiments where no mosquitoes introduced, there were no significant differences between control and treatment, indicating that transfer of PPF to breeding sites only occurred when mosquitoes were present; i.e. that autodissemination had occurred. Treatment of a single clay pot reduced adult emergence in six habitats to (0.34 ± 0.13) compared to (0.98 ± 0.02) in the controls (p < 0.0001), showing a high level of habitats coverage amplification of the autodissemination event.ConclusionThe study provides proof of principle for the autodissemination of PPF to breeding habitats by malaria vectors. These findings highlight the potential for this technique for outdoor control of malaria vectors and call for the testing of this technique in field trials.

The effect of banker plant species on the fitness of Aphidius colemani Viereck and its aphid host (Rhopalosiphum padi L.)

Banker plants, a type of open-rearing unit, are increasingly used in greenhouse crops to sustain natural enemy populations at times of low pest abundance. The most common banker plant system is a non-crop, cereal plant which supports Rhopalosiphum padi L. as an alternative host for Aphidius colemani Viereck. Although bottom-up effects of plants are known to affect natural enemies, this aspect has generally been ignored in previous investigations of banker plant efficacy. Here, we tested four cereal plant species with three varieties each to investigate host plant effects on R. padi and A. colemani. Though limited differences were observed in laboratory experiments spanning one aphid or parasitoid generation, longer greenhouse experiments spanning several generations revealed significant plant effects on both insects. R.padi performed poorly on oats (Avena sativa L.), resulting in wasps with the longest female development time, lowest emergence rates, and the lowest number of wasps produced per unit. Rye (Secale cereal L.) – intermediate in terms of aphid performance – produced a significantly male-biased wasp population with the smallest males. Conversely, R. padi placed onto either wheat (Triticum aestivum L.) or barley (Hordeum vulgare L.) performed consistently well in terms of aphid and parasitoid fitness and abundance, though neither species was obviously superior over the other. Overall, cultivars within each plant species did not significantly affect outcomes. As each plant species tested had different positive effects on aphid and parasitoid phenotypes, the potential benefits of mixing of cereal species is an area for future investigation.

Resistance of Spodoptera litura (Lepidoptera: Noctuidae) to profenofos: Relative fitness and cross resistance

Profenofos, an acetylcholine esterase inhibitor insecticide, has been used for the management of various lepidopteron pests of many crops in Pakistan. In the present study, we investigated the impact of insecticide resistance on fitness cost in Spodoptera litura, and evaluated cross resistance to other insecticides. The effect of profenofos on different life history parameters including survival rate, female ratio, fecundity and hatchability, intrinsic rate of population increase and biotic potential was determined. Significant differences associated with fitness costs were revealed. A field collected S. litura strain was selected by exposure to profenofos in the laboratory (Profen-SEL) and after 14 generations of selection it developed a 52-fold resistance to this insecticide. The Profen-SEL strain showed high cross-resistance to chlorpyrifos (62-fold), but very low to no cross resistance to lambda-cyhalothrin (2.34-fold) or methomyl (0.80-fold), respectively. The resistant strain had a relative fitness of 0.38 with a low larval survival rate, longer larval duration, longer male pupal duration, longer development time, low emergence rate of healthy adults, fecundity and hatchability compared with an unselected strain. The intrinsic rate of natural population increase, mean relative growth rate and biotic potential were lower for the selected strain compared with an unselected strain. Development of resistance may cause fitness costs for the resistant strain. This study provided important information for understanding profenofos resistance and facilitating a better strategy for the management of resistance.

Cultivar Affects Field Emergence, Establishment Rate, and First‐Year Traffic Tolerance of Seeded Bermudagrasses in the Transition Zone

ABSTRACTSlow field emergence and establishment rates of some seeded bermudagrasses [Cynodon dactylon (L.) Pers.] contribute to extreme competition from weeds, sometimes leading to failure of stand establishment. Previous work has also indicated significant differences in tolerance to simulated athletic traffic among some bermudagrass cultivars. This study was conducted in 2010 and 2011 in Lexington, KY, to quantify field emergence rates, establishment rates, and tolerances to simulated traffic applied during the establishment year among seeded bermudagrass cultivars. Nineteen cultivars were evaluated representing all of the seeded bermudagrasses available for purchase from commercial retailers at the beginning of the study. The effect of cultivar was highly significant (P &lt; 0.001) for days to field emergence, days to maximum cover, and traffic tolerance in both years. ‘Riviera’ was equivalent to or very nearly the slowest for field emergence in both years. ‘Casino Royale’ was the fastest or equivalent to the fastest for field emergence in both years. ‘Yukon’ was the slowest to reach maximum cover in both years. ‘Sovereign’ reached maximum cover quickest in 2010. Riviera and Sovereign were equivalent in reaching maximum cover in 2011. Riviera and Yukon ranked highest and lowest, respectively, in tolerance to simulated athletic traffic. We conclude that there are highly significant differences in how cultivars in the upper transition zone should be expected to perform regarding successful establishment and tolerance to simulated athletic traffic applied during the establishment year.

Feasibility of cold-stored Periplaneta americana (Dictyoptera: Blattidae) oothecae for rearing the oothecal parasitoids Aprostocetus hagenowii and Evania appendigaster (Hymenoptera: Eulophidae; Evaniidae): Effect of ootheca age and storage duration

The minimum time of heating (48, 50, and 53°C) required to kill Periplaneta americana (L.) (Dictyoptera: Blattidae) oothecae aged 1, 2, 3 and 4weeks was determined and their suitability as hosts after different storage conditions (live, heat killed and cold stored for 0.5, 1, 2, 3, and 4months at 4°C) for rearing parasitoids Aprostocetus hagenowii (Ratzeburg) and Evania appendigaster (L.) (Hymenoptera: Eulophidae; Evaniidae) was investigated. Heating at 48°C for 45min killed 100% of the oothecae of all ages. Both parasitoids had low emergence in live 4-week-old oothecae but emergence improved after oothecae were heat killed. For A. hagenowii, an interaction effect between ootheca age and storage duration was found for percentage emergence. Emergence rates were reduced in cold-stored 3- and 4-week-old oothecae (1–4 and 3–4months, respectively) but not in 1–2-week-old oothecae. The number of progeny produced in 1–2-week-old and 3–4-week-old oothecae decreased significantly after cold storage for 3–4 and 0.5–4months, respectively. In all conditions, the development time was 34.5–39.9d and the progeny sex ratio was female-biased (88.2–94.3%). E. appendigaster had low parasitism and emergence rates (0–20%) in cold-stored oothecae and took longer to develop in heat-killed and cold-stored oothecae than in live oothecae. In all conditions, the proportion of females was 0.619–0.821. These results illustrate the effects of ootheca age on host treatment and storage and can be used to develop efficient ways to use oothecae for rearing oothecal parasitoids.

Enriquecimento de floresta em restauração por meio de semeadura direta de lianas

Este trabalho objetivou verificar a viabilidade da semeadura direta de lianas no sub-bosque de floresta plantada em restauração. Para isso, sementes das espécies Phanera sp., Macfadyena unguis-cati (L.) A.H. Gentry and Peltastes peltatus (Vell.) Woodson, de lianas foram submetidas a testes de germinação com e sem luz, e com e sem alternância de temperatura. Posteriormente, essas espécies foram semeadas sob a copa de quatro espécies arbóreas em uma Floresta Estacional Semidecidual em restauração no Município de Iracemápolis, SP, Brasil. Em laboratório, apenas Macfadyena unguis-cati apresentou característica de fotoblastismo positivo. As outras espécies não tiveram germinação limitada pela ausência de luz e alternância de temperatura. No sub-bosque, Peltastes peltatus não emergiu; as outras duas espécies não tiveram a emergência alterada em função das espécies arbóreas do dossel sob as quais foram semeadas. Esses resultados sugerem que, apesar da baixa taxa de emergência, é possível o enriquecimento de florestas em processo de restauração a partir da semeadura direta de algumas espécies de lianas.

Temperature during the free-living phase of an ectoparasite influences the emergence pattern of the infective phase

Understanding the population dynamics and co-evolution of host–parasite systems requires detailed knowledge of their phenology which, in turn, requires a deep knowledge of the effect of abiotic factors on the life cycles of organisms. Temperature is known to be a key environmental influence that participates in the regulation of diapause. Yet, not much is known about the effect of temperature on the free-living stages of true parasites and how it may influence host–parasite interactions. Here we experimentally study the effect of ambient temperature on overwintering pupae of Carnus hemapterus (Diptera, Carnidae), an ectoparasitic fly of various bird species. We also test whether chilling is a prerequisite for completion of diapause in this species. In the course of three winter seasons we experimentally exposed carnid pupae from nests of various host species to spring temperatures with and without chilling and recorded the emergence patterns in experimental and control groups. Experimental groups showed an advanced emergence date, a lower emergence rate and, consequently, a protracted emergence period. Chilling had no obvious effect on the start of emergence but it did advance the mean emergence date, shortened the length of the emergence period when compared with the control treatment and increased the emergence rate when compared with the spring treatment. This study identifies an environmental cue, namely temperature during the free-living stage, affecting the emergence of a widespread parasite and demonstrates the plasticity of diapause in this parasite. Our findings are of potential significance in understanding host–parasite interactions.

Seed Size, the Only Factor Positively Affecting Direct Seeding Success in an Abandoned Field in Quebec, Canada

Direct tree seeding is potentially an economical technique for restoring forests on abandoned fields. However, the success of tree establishment depends on many factors related to species and seed characteristics, environmental conditions, competition and predation. We compared seedling emergence, survival and growth of six tree species of different seed sizes in a forest restoration project of abandoned fields. Species were seeded in plots with and without herbaceous vegetation and with and without protection from bird and mammal predation. Yellow birch (Betula alleghaniensis) did not emerge in all treatments, paper birch (Betula papyrifera) and tamarack (Larix laricina) had a seedling emergence rate lower than 1%, and sugar maple (Acer saccharum) had a low overall emergence rate of 6%. Seedling emergence reached 57% for northern red oak (Quercus rubra) and 34% for red pine (Pinus resinosa), but survival of oak after one year was much higher (92%) than pine seedlings (16%). Overall, protection from birds and mammals and elimination of the herbaceous vegetation cover had no detectable effects on seedling emergence, survival and height. Nonetheless, red oak seedlings growing in the presence of vegetation had a smaller diameter and shoot biomass and a larger specific leaf area. We conclude that only large seeded species, such as oak, should be used for forest restoration of abandoned fields by direct seeding in our region.

Testing soybean antibiosis to three clones of soybean aphid, Aphis glycines (Hemiptera: Aphididae) using sprouts and leaflets

Antibiosis of eight soybean cultivars to three clones of soybean aphids (Aphis glycines Matsumura) was evaluated using both soybean sprouts and leaflets. Overall, the performance of soybean aphid was better on sprouts than on leaflets. We confirmed previous reports that Dowling and Jackson cultivars exhibited strong resistance to a clone of soybean aphids from the US, but not to either Japanese or Indonesian clones. The USA clone had delayed development, fewer offspring, and low emergence rates on these two cultivars. However, abnormal offspring were only investigated on the Tachinagaha cultivar. We confirmed that Bay and Himeshirazu cultivars were strongly resistant to the Japanese aphid clone; aphids produced fewer offspring and deformed offspring on Bay and had delayed development and a low rate of emergence on Himeshirazu. None of the eight soybean cultivars were resistant to the Indonesian clone, although abnormal offspring were produced on Jackson, Adams, and Tachinagaha cultivars. These data suggest that there are genetic differences among the three tested clones of soybean aphid and that the characteristics of local soybean aphid clones must be considered when developing resistant soybean cultivars for a given geographic area.

Larval rearing temperature influences the effect of malathion on Aedes aegypti life history traits and immune responses

The effects of anthropogenic chemical contaminants on aquatic organisms are largely influenced by underlying environmental conditions. This study evaluated how larval rearing temperature influences the impact of malathion on the fitness of the yellow fever mosquito Aedes aegypti. Larvae were exposed to water control, and low (0.03mg/L) or high (0.05mg/L) malathion dose at 20°C, 25°C and 30°C and emergence rate, time to emergence, female fecundity and expression of genes encoding two antimicrobial peptides (defensin, cecropin) and an iron-binding protein (transferrin) quantified. High malathion dose at 25°C and 30°C resulted in significantly lower emergence rates compared to control and low malathion dose but this effect was not observed at 20°C. Female time to emergence was inversely proportional to temperature and was significantly shorter in high malathion dose than in control and low malathion dose at 25°C and 30°C but not at 20°C. Regardless of temperature treatment, females from high malathion dose were significantly larger and laid more eggs than their counterparts in control and low malathion dose. Relative to the controls, two immune genes were significantly over-expressed in adult females from malathion-exposed treatments at 20°C (defensin and cecropin) and 25°C (defensin and transferrin) and one gene (defensin) was significantly under-expressed at 30°C. These findings suggest that larval rearing temperature can modify the effect of malathion on fitness traits in mosquitoes.

Effects of mulch practices on fresh ear yield and yield components of sweet corn

The experiment was carried out in the vegetation seasons of 2010 and 2011. The main purpose of the study was to determine the effects of mulch practices (a control-unmulched treatment, a plastic mulch treatment, and a straw mulch treatment) on fresh ear yield and some yield-related traits of sweet corn according to 3 sowing dates: 1 April, 15 April, and 1 May, respectively. The main effects of sowing dates were significant for the harvest period, the emerging rate from soil, the fresh ear yield per hectare, and the yield components of the sweet corn. The emergence rate of sweet corn was decreased on 1 April and 15 April due to the low soil temperature on these sowing dates. Of the mulch practices, the plastic mulch practice resulted in the highest emergence rate, the highest ear length, the highest ear diameter, the highest ear weight, the highest number of kernels per ear, the highest fresh ear yield, and the highest fresh ear number in both 2010 and 2011. The fresh ear yield and yield components were decreased by the straw mulch practice in both 2010 and 2011. The effects of the sowing date × mulch practice interactions on emergence rate, fresh ear yield, and some yield-related traits of sweet corn were statistically (P < 0.05 and P < 0.01) significant in both years. Of the interactions between the sowing dates and the mulch practices, the highest emergence rate (91.2% in 2010 and 93.7% in 2011), highest ear length (18.4 cm in 2010 and 18.5 cm in 2011), highest ear diameter (45.2 mm in 2010 and 46.5 mm in 2011), highest ear weight (229.1 g in 2010 and 227.1 g in 2011), highest number of kernels per ear (562.1 grains in 2010 and 552.3 grains in 2011), highest fresh ear yield (14,952.6 kg ha^{-1} in 2010 and 14,805.2 kg ha^{-1} in 2011), and highest fresh ear numbers (65,781.8 cobs ha^{-1} in 2010 and 65,789.6 cobs ha^{-1} in 2011) were determined from the plastic mulch practices on 1 May, the latest sowing date. The lowest emergence rate, the lowest fresh ear yield, and the lowest yield components were obtained from the straw mulch practice on 1 April, the earliest sowing date, in both 2010 and 2011.

Seedbanks, germination and early survival of bitter cherry (Prunus emarginata) in coastal British Columbia

Early successional species that rely on a seedbank differ in life history from most other species of forested landscapes. Prunus emarginata (bitter cherry) is a shade-intolerant tree that can develop in abundance (>20,000 stems ha−1) from a seedbank after disturbance in forests along the northwest coast of North America. It can inhibit growth of commercially valuable conifers, but also provide habitat diversity and appearance-grade wood. We determined (1) seed populations in soil of 15 stands 1 to 140-plus years old (2) emergence and survival from planted seed, along with environmental conditions, for three years in open clearcut, forest edge, and under closed canopy on mineral soil or organic seedbeds and with and without cages to exclude animals, and (3) effects of light and temperature on germination in controlled environments. There, seeds were cold-stratified (0 or 70days), then exposed to temperature (10, 17, or 25°C) and photoperiod (0, 14h) treatments, which were interrupted with a second (90day) cold period. Population densities of filled seed were greatest in 51–75year-old stands (>106ha−1). Of emergence in the field, 0% was in year 1, 79% in year 2 and 21% in year 3; 81% of emergence occurred in the open, 19% at the edge, and 0% under the canopy. Emergence in the open was greatest in caged, mineral soil plots. Survival of emerged seedlings was 18% in the open, but 0% at the forest edge. Seedling emergence occurred mainly in April. In controlled environments, germination began during the second cold stratification, suggesting alternating warm and cold periods were needed to overcome seed dormancy. Germination was greatest at 17°C, but only in combination with the first cold stratification and light. Midday seedbed temperatures partly explain the timing and location of emergence, but diurnal temperature amplitude may be a more important cue of canopy removal. Large accumulations of seed in soil, combined with low emergence and survival rates, can account for the high population densities of seedlings sometimes observed following disturbance. Canopy removal is necessary to maintaining P. emarginata in the conifer-dominated landscape, and the long-lived seedbank allows it to persist between disturbances.

The effect of time of harvest, irrigation treatments and kilning temperature on Eucalyptus globulus seed germination response to high temperature stress

Low seedling emergence rates of some Eucalyptus globulus seed-lots have been reported and hypothesised to be caused by high temperature stress. This study tested the effects of time of seed harvest, kilning temperature at seed extraction and irrigation treatments applied to E. globulus trees on seed germination traits. Seeds were harvested from three genotypes at 11 months from commencement of flowering (early), 13 months (commercial) and 15 months (late) and kiln dried at 30, 40 or 50°C. Irrigation treatments were full irrigation, half irrigation and no irrigation. Six traits describing the proportion and rate of seed germination and early seedling development were studied. The kilning temperature of capsules and irrigation treatments applied to trees had no effect on the germination traits studied. Time of seed harvest affected the rates of seed germination and normal seedling development. There was little delay in germination rate at 32°C in early-harvested seeds compared with that experienced by the commercial- and late-harvested seeds, suggesting that it has a higher temperature threshold. However, the effect of harvest date on germination was genotype dependent which may be related to different heat sums to which developing seeds are exposed.

Parasitoid and host egg ages have independent impact on various biological traits in a Trichogramma species

Trichogramma (Hymenoptera: Trichogram- matidae) are species used worldwide for the biological control of Lepidopteran pests, notably through inundative releases on millions of hectares. The optimal use of Trichogramma parasitoids in crop protection requires an accurate knowledge of their biology. More specifically, the importance of age factor in parasitoids during the time they forage in crops for host eggs (after initial release) and how the aging of host eggs could impact parasitoid biological traits may be important for overall efficiency in terms of crop protection. In this context, the importance of parasit- oid female and host egg ages on parasitism rate and the development of offspring was studied in laboratory con- ditions on Trichogramma cacoeciae Marchal (Hymenop- tera: Trichogrammatidae) and the eggs of the pest Lobesia botrana Denis and Schiffermuller (Lepidoptera: Tortrici- dae). Host eggs tested were 1-2- and 3-4-day-old, while the ages of T. cacoeciae adult females varied from 1-day- old to 4-day-old post-emergence. When L. botrana eggs were 3-4-day-old, they were less parasitized by T. cacoe- ciae than 1-2-day-old eggs, and this was not linked to the age of T. cacoeciae females. The age of parasitoid females has an effect on parasitism, as 1-day-old females produced fewer parasitized eggs than 2, 3, and 4-day-old females. For the total number of L. botrana eggs killed by T. cacoeciae, the two factors did not show significant effects. When L. botrana eggs were 1-2-day-old, parasitoid emergence increased according to the age of parasitoid females with the highest success observed for 3-day-old females. The lowest emergence rates were obtained with T. cacoeciae females 1-day-old. The development time was also longer with the young 1-day-old parasitoid females. This study demonstrated that both the aging of parasitoids and host eggs play a role in the subsequent development of parasitoid offspring. The importance of these results in the context of biological control programs involving Tricho- gramma parasitoids is discussed.

Native Species Establishment in Tallgrass Prairie Plantings

Prairie restorations are increasingly common throughout the central United States. However, we continue to have little information about which planted species become successfully established, or about the factors potentially limiting establishment. We used a combination of site surveys, field tests and germination testing to examine these issues. We surveyed thirty 4 to 6 y old Conservation Reserve Program (CRP) plantings to quantify the likelihood that planted native species can be found 4–6 y after planting. We then selected a subset of species that had been planted in the CRP sites for use in germination tests and field tests quantifying emergence and seedling survival. We found that nearly one third of the species planted in CRP sites failed to become established and that grasses were more likely to be successful than legumes or nonleguminous forbs. We also found that species with low establishment in the CRP sites often had low emergence rates in the field experiment and low germination rates in germination testing despite differences in seed origin and planting year. Our results suggest that germination may be a major limiting factor in the establishment of some tallgrass prairie species.

Germination response of Eucalyptus globulus seeds exposed to low and high temperature stress

Low seedling emergence rates of some seed lots of genetically elite Eucalyptus globulus Labill have been reported by nursery operators and hypothesized to be caused by high temperature stress. This study has confirmed that germination rate was sensitive to exposure to high temperatures. The optimum temperature for the germination rate of normal seedlings in this species was between 24.8°C and 25.5°C. At 25°C, 96% of seeds produced normal seedlings after 21 days. The cardinal temperatures for development of normal Eucalyptus globulus seedlings were between 9.1°C and 10.5°C at low temperature and between 40.3°C and 41.4°C at high temperature. The optimum temperature for maximum attainment of normal seedlings was between 21.2°C and 24.8°C. Temperatures above 30°C generally delayed commencement of germination, reduced total germination percentage, caused a high proportion of seed death and suppressed the development of normal seedlings. Low temperatures also delayed germination but caused less seed mortality. Despite general consistency in responses there was evidence that seed lots exhibit a differential response to temperature, particularly for normal seedling development at the extremes of temperature tested.

Characteristics of life-form and growth-form of plant species in an alpine ecosystem of North-West Himalaya

The present study was conducted in the alpine pastures of Tungnath (30° 14′ N and 79° 13′ E) to observe life-form and growth-form patterns of alpine plant species under grazed and ungrazed conditions and to work out the plant life form spectrum. Species were categorized as plant habit, height and length of growth-cycle and life-form classes according to Raunkiaer’s system. The results show that in total of 68 species at grazed site, hemicryptophytes (He) accounted for 50.00% species, followed by cryptophytes (26.47%), chamaephytes (16.18%), phanerophytes (4.41%) and therophytes (2.94%). At the ungrazed site in 65 plant species, hemicryptophytes (He) accounted for 49.23% species, cryptophytes (26.15%), chamaephytes (15.38%), phanerophytes (6.15%) and therophytes (3.08 % species). In general, hemicrptophyte are dominant in both sites i.e. graged and ungrazed. Growth form categories were classified as forbs, shrubs, grasses and sedges and undershrubs, according to plant habit and height. On the basis of length of the growth cycle, species were categorized as plant species of short growth cycle, intermediate growth cycle and long growth cycle. The short forbs of plant habit and height, had the highest emergence, and grasses and sedges had the lowest emergence in representative species. Percentage of species with long growth cycle was highest in both sites.

MAIZE (ZEA MAYS) LEAF ANGLE AND EMERGENCE AS AFFECTED BY SEED ORIENTATION AT PLANTING

SUMMARYMaize (Zea mays) seed orientation at planting can influence emerging leaf angle. If leaf angle were consistent among plants without leaf overlap, large numbers of these bilaterally symmetrical plants could be arranged to optimize light interception and possibly increase grain yields or maintain grain yield with a lower population. The objectives were to evaluate the effect of seed orientation in soil on the angle of maize leaves relative to the planted row and on emergence rate. Seeds were planted 2.5 cm deep in diverse combinations of flat, cotyledon down, cotyledon up, on their side, radicle up and radicle down. Each seed orientation was repeated 10 times. Data on days to emergence and leaf angle were collected. In three experiments, maize seeds planted flat with the cotyledon up resulted in homogenous and faster emergence, and maize leaves aligned perpendicular to the direction of the maize row. Similar results were achieved with maize seeds planted parallel to the row with the radicle down. Random placement of maize seeds resulted in random orientation of maize leaves and lower emergence rates. The effects of controlled leaf geometry could facilitate planting higher populations with the potential for increasing grain yield and/or allow the maintenance of grain yields while reducing seed rates.