Do Conditions During Dormancy Influence Germination of Suaeda maritima?

Background and Aims

Seeds of annual halophytes such as Suaeda maritima experience fluctuating salinity, hydration, hypoxia and temperature during dormancy. Germination then occurs in one flush of 2–3 weeks after about 5 months of winter dormancy during which time the seeds can remain in saline, often waterlogged soil. The aim of this study was to investigate the effect of simulated natural conditions during dormancy on germination and to compare this with germination following the usual conditions of storing seeds dry. The effects of hydration, salinity, hypoxia and temperature regimes imposed during dormancy on germination were investigated. Also looked at were the effects of seed size on germination and the interaction between salinity during dormancy and salinity at the time of germination.

Methods

Various pre-treatments were imposed on samples of seeds that had been stored dry or wet for different periods of time during the 5 months of natural dormancy. Subsequent germination tests were carried out in conditions that simulated those found in the spring when germination occurs naturally. Various salinities were imposed at germination for a test of interaction between storage salinity and salinity at germination.

Key Results

A temperature of about 15 °C was needed for germination and large seeds germinated earlier and better than small seeds. Cold seawater pre-treatment was necessary for good germination; the longer the saline pre-treatment during the natural dormancy period the better the germination. There appeared to be no effect of any specific ion of the seawater pre-treatment on germination and severe hypoxia did not prevent good germination. A short period of freezing stimulated early germination in dry-stored seed. Storage in cold saline or equivalent osmotic medium appeared to inhibit germination during the natural dormancy period and predispose the seed to germinate when the temperature rose and the salinity fell. Seeds that were stored in cold wet conditions germinated better in saline conditions than those stored dry.

Conclusions

The conditions under which seeds of S. maritima are stored affect their subsequent germination. Under natural conditions seeds remain dormant in highly saline, anoxic mud and then germinate when the temperature rises above about 15 °C and the salinity is reduced.Key words: Suaeda maritima, germination, pre-treatment, salinity, temperature     

Diaspore structure and germination ecophysiology of the babassu palm (Attalea vitrivir)

Both germination and seedling establishment in palm trees are strongly influenced by the morphoanatomy of the fruits, although the interactions of these processes with ecophysiological aspects are not yet well understood. The present work evaluated structural and physiological aspects of seed germination in Attalea vitrivir, a species living under the seasonal climate of the Cerrado (Brazilian savanna) biome. We studied morphology, anatomy and histochemistry of the fruits and seedlings, the effects on germination of the pericarp, of diaspore storage conditions, germination temperature, removal of the operculum, and of gibberellic acid (GA3) application, and characterized the imbibition process of the seeds. Germination depends on a series of complex interactions between structures and physiological processes. The pericarp protects the seed and also causes physical dormancy that, when interacting with the temperature regime, can delay germination until subsequent rainy periods. Some seeds demonstrated non-profound physiological dormancy associated with restricted germination imposed by the operculum. Germination and initial development result from the elongation of the cotyledon cells and are affected by the activities of two distinct meristems in the proximal region of the embryo. The haustorium develops an invaginated secretory epithelium and aerenchyma, and actively participates in seed reserve mobilization. The adaptation of A. vitrivir to the Cerrado environment, with a strongly seasonal climate, is favored by its diaspore structure, by the abundance of endosperm reserves that allow the seedlings to survive for a long period above soil level, and by a seedling development pattern that protects the vegetative axis by deep burial.     

Dormancy of Medicago marina (L.) seed

Medicago marina (L.) is a Mediterranean species whose seeds show strong dormancy that prevents germination. We used an integrated approach of physiological analyses and proteomics to investigate the mechanisms that control M. marina dormancy/germination and that underlie stress tolerance. First, we evaluated the effects on dormancy breaking of the following treatments: mechanical scarification, freezing at −20 °C, storage for 4 months and heating at 100 °C for 1 h. Mechanical scarification and freezing were the most effective treatments in overcoming dormancy. The role of abscisic acid (ABA) in M. marina dormancy was studied by ELISA immuno-enzymatic assay. The ABA content of germinated and non-germinated mature (control) and treated seeds was determined. The level of ABA was higher in treated seeds than in control seeds; the most significant increase occurred in the heated seeds. A comparison of the ABA level in the germinated, control and treated seeds suggests that different mechanisms modulate ABA content in response to different stresses, and that a specific ABA-signalling pathway regulates germination. Proteomic analysis revealed 46 proteins differentially expressed between treated and untreated seeds; 14 of these proteins were subsequently identified by mass spectrometry. Several of the proteins identified are important factors in the stress response, and are involved in such diverse functions as lipid metabolism, protein folding and chromatin protection. Lastly, an analysis of the phosphoproteome maps showed that the function of many proteins in seeds subjected to temperature treatment is modulated through post-translational modifications.     

Ecology of seed dormancy and germination in sedges (Carex)

The genus Carex, with its wide distribution and large number of species yet with a rather uniform life history, is a very convenient group for comparative studies of germination ecology at the generic level. The combination of a strict or conditional primary dormancy, a light requirement for germination, low germination at constant temperatures, a positive response to diurnal temperature fluctuations and an induction of secondary dormancy in late spring by increasing environmental temperatures are attributes that were found to be characteristics shared by almost all the Carex species investigated, though there was variation between species in the degree to which these characters were expressed. In almost all species, dormancy was broken by stratification at low temperatures, though few species gained the ability to germinate at temperatures <10 °C. There is evidence that long-term physiological changes and the structure of seed coats can play a decisive role in delaying germination. High dormancy levels were found mainly in Carices with large seeds (>0.9 mg), probably due to a thicker seed coat and hence a higher resistance to germination. Differences in primary dormancy between sedges of various habitats could not be established. However, there was a tendency for temperature limits to be low in forest sedges. Many species of wetlands and open sites showed a greater capability to respond to fluctuating temperatures than species of dry sites. These dormancy and germination traits not only enable the accumulation of seeds in the soil, but also constitute seasonal seed regeneration strategies that rely on the high longevity of seeds and the formation of persistent seed banks. Temperate Carices are mainly adapted to exploit the temporally and spatially infrequent occurrence of canopy gaps that become available only in late spring or early summer, whereas the colonization of gaps at the beginning of the vegetation period is largely prevented by a high temperature requirement for germination. Many of the dormancy and germination characteristics of Carices are important in Cyperaceae generally. A greater diversity of germination responses, however, can be found in the related families, Juncaceae and Poaceae. Our present knowledge is not sufficient to determine unequivocally whether a phylogenetic component contributes significantly to the germination behaviour of the genus Carex, but certain tendencies are clearly indicated.     

Variation within species and inter-species comparison of seed dormancy and germination of four annual Lamium species

In an ecological context, knowledge of intra-species variation in dormancy and germination is necessary both for practical and theoretical reasons. We used four or five seed batches (replicates) of four closely related annuals co-occurring in arable fields in Sweden: Lamium amplexicaule, L. confertum, L. hybridum and L. purpureum. Seeds used for experiments stemmed from plants cultivated on two sites, each site harbouring one population of each species, thereby ensuring similar environmental history of seeds. Seeds were tested for germination when fresh and after three different pre-treatments (cold or warm stratification, or dry storage) for up to 24 weeks. Seeds were also sown outdoors. Despite substantial intra-species variation, there were clear differences between species. The general seed dormancy pattern, i.e. which environmental circumstances that affect dormancy, was similar for all species; dormancy reduction occurred during warm stratification or dry storage. Even though the response to warm stratification indicates a winter annual pattern, successful plants in Sweden were mostly spring emerged. Germination in autumn occurred, but plants survived winters poorly. Consequently, as cold stratification did not reduce dormancy, strong dormancy in combination with dormancy reduction during dry periods might explain spring germination. It is hypothesised that local adaptations occur through changes mainly in dormancy strength, i.e. how much effort is needed to reduce dormancy. Strong dormancy restricts the part of each seed batch that germinate during autumn, and thus reduces the risk of winter mortality, in Sweden.     

Potential for evolutionary change in the seasonal timing of germination in sea beet (<Emphasis Type="Italic">Beta vulgaris</Emphasis> ssp. <Emphasis Type="Italic">maritima</Emphasis>) mediated by seed dormancy

In sea beet (Beta vulgaris ssp. maritima), germination occurs in autumn or spring and is mediated by dormancy which can be released by cold or dry periods. Environmental change such as current climate change may require evolutionary response in seasonal timing. Here, we explore the potential for such evolutionary change. Seed dormancy was studied in a composite population based on seeds from all over the species range in France together with several generations of reciprocal crosses. We found high, repeatable variability for dormancy rate among individuals under greenhouse conditions and confirmed its relevance for germination phenology in the field. Our data fitted best with an exclusively maternal determination of the dormancy phenotype. Narrow-sense heritability, h2 ≈ 0.5 in the composite population and ≈0.4 in the original local populations, was such that rapid evolutionary change in the relative proportions of autumn and spring germination may be possible.     

Comparative analysis of zygospore transcripts during early germination in Chlamydomonas reinhardtii

The unicellular green alga Chlamydomonas reinhardtii has a haplontic life cycle, and forms diploid zygotes for reproduction. The zygospore, a sporulating zygote, begins germination in response to light signals, generating haploid progenies and inducing several cell-biological events; e.g., DNA synthesis and meiotic division, successively. Their regulatory mechanisms remain largely unknown, so we focused on the early stages of germination and analyzed the dynamics of gene expression associated with the germination process. The gene expression levels of zygospores at 1 and 6 h after light exposure were analyzed by a next-generation sequencing platform, the 454 GS Junior. At 6 h, the photosynthesis pathway, including its antenna proteins and two methionine metabolism-related genes (methionine synthase and sulfite reductase), were up-regulated compared to 1 h after light exposure. Meanwhile, three uncharacterized genes that contained an antibiotic biosynthesis monooxygenase domain and an HSP20/alpha crystallin family protein were specifically expressed at 1 h after light exposure. These gene expressions were also verified by quantitative real-time PCR analysis. These results suggest that the photosynthesis and methionine synthesis pathways, both of which occur in the chloroplast, are activated in zygospores at around 6 h after light exposure, and that some polyketides and/or a small heat shock protein may be related to the initiation of zygospore germination.     

Nutritional requirements for conidial germination and hyphal growth of Beauveria bassiana

Nutritional requirements for germination and growth of the entomopathogenic fungus Beauveria bassiana are not complex. For germination to occur, a utilizable source of carbon must be present; however, a nitrogen source is needed for continued hyphal growth, otherwise lysis ensues. Compounds that can serve as utilizable carbon-energy sources for germination include glucose, N-acetylglucosamine, glucosamine, chitin, starch, lanolin, hydrocarbons in crude oil, and some longer-chain fatty acids. Both organic and inorganic sources of nitrogen are readily utilized for growth. Conidia undergo active metabolism soon after being placed in a suitable growth medium, indicating that conidia are released from their state of dormancy several hours before emergence of the germ tube can be observed. Because of the nutritional versatility of B. bassiana, this fungus should be able to survive and be infective in several types of natural environments.     

Seed structure and germination in buriti (Mauritia flexuosa), the Swamp palm

Associations of recalcitrance and dormancy are rare, and little information is available concerning the structure of seeds demonstrating this type of behavior or their ecological implications. Mauritia flexuosa is a palm tree associated with swampy environments in the Amazon rainforest and areas of Cerrado (neotropical savanna), the latter biome having marked climatic seasonality. We describe the structures and physiological aspects of the seeds and seedlings of this species to examine its adaptations to swampy environments and its germination control mechanisms, as well as the relationship between recalcitrance and dormancy in terms of reproductive success. Morphoanatomy and histochemistry of the seeds and seedlings were evaluated using standard methodologies, and the effects of temperature and operculum removal on germination were investigated. Differentiated tracheal elements in the embryo are associated with recalcitrance, and presence of numerous stomata on the embryo and the abundance of secondary metabolite compounds in the seedling indicate their adaptations to swampy environments. The inability of the embryo to overcome the resistance of the adjacent tissues determines dormancy of the physiological type, thus the removal of the operculum is an efficient method for promoting propagation. Cellular elongation in the cotyledon promotes seedling protrusion. Mobilization of endosperm reserves is achieved by symplastic flux and is associated with overcoming of dormancy by weakening the tissues adjacent to the embryo. The association between recalcitrance, which favors adaptation to swampy environments, and dormancy, which favors dispersal, is crucial for the reproductive success of this species and its broad geographical distribution.     

The dual role of temperature in the regulation of the seasonal changes in dormancy and germination of seeds of Polygonum persicaria L.

Summary The role of temperature in the regulation of seasonal changes in dormancy and germination was studied in seeds of Polygonum persicaria. Seeds were buried in the field and under controlled conditions. Portions of seeds were exhumed at regular intervals and germination was tested over a range of conditions. Seeds of P. persicaria exhibited a seasonal dormancy pattern that clearly showed the typical features of summer annuals, i.e. dormancy was relieved at low winter temperatures, the germination peak occurred in spring and dormancy was re-induced in summer. The expression of the dormancy pattern was influenced by the temperature at which germination was tested. At 30°C exhumed seeds germinated over a much longer period of the year than at 20° or 10°C. Nitrate added during the germination test occasionally stimulated germination. The seasonal changes in dormancy of buried seeds were regulated by the field temperature. Soil moisture and nitrate content did not influence the changes in dormancy. The fact that, on the one hand, field temperature determined the changes in dormancy and, on the other hand, germination itself was influenced by temperature, was used to describe the seasonal germination pattern of P. persicaria with a model. Germination of exhumed seeds in Petri dishes at field temperature was accurately described with this model. Germination in the field was restricted to the period where the range of temperatures over which germination could proceed (computed with the model) and field temperature overlapped.     

光和不同打破种子休眠方法对紫茎泽兰种子萌发及幼苗状态的影响

紫茎泽兰是著名的外来入侵植物,作为入侵的第一步,发芽及其幼苗生长应该与其强入侵能力有关.基于此,通过不同光照强度处理和不同打破休眠方法的双因素实验,旨在探讨紫茎泽兰种子是否具有需光萌发特性以及低温、水杨酸、聚乙二醇,硝酸钾等常规打破休眠方法和光照如何共同影响其萌发、幼苗生长等问题.结果表明:在全光照条件下,不同处理的紫茎泽兰种子的萌发率均大于63％,铝箔纸覆盖的遮光条件(0.23％光照)萌发率均大于60％,而在完全黑暗条件下,其萌发率较低(均小于30％),这表明紫茎泽兰种子具有需光萌发的特性.有别于以往对其它植物种子的报道,低温处理、水杨酸处理、聚乙二醇处理和硝酸钾处理不能代替光照打破种子休眠,显示紫茎泽兰种子可能处于一种强迫休眠状态(种子静态).全光照与水杨酸处理、PEG处理对幼苗生长具有交互影响:黑暗下水杨酸处理浓度与幼苗生物量成正相关(P＜0.05),但全光照和加铝箔下不相关(P＞0.05);全光照下PEG处理浓度与根长显著正相关(P＜0.05),而加铝箔和黑暗下不相关(P＞0.05).紫茎泽兰种子需光萌发特征及其幼苗生长特点是人为破坏表土壤、深层土壤种子库地表化导致快速入侵的基础.结果也为通过引入适宜树种造林来控制光照因子对紫茎泽兰进行生态控制提供了理论依据.     

A combined physical and physiological dormancy controls seasonal seedling emergence of Geranium robertianum

Temperate forest herbs with seeds exhibiting both a physical and a physiological dormancy mechanism are rare, and knowledge on the factors regulating germination of these species is fragmentary. The biennial Geranium robertianum L. grows mainly in temperate woodlands, but can also be found in exposed habitats. Seedlings of G. robertianum are known to emerge from spring until autumn, but little is known about the environmental factors regulating germination. In this study, phenology of seedling emergence and of physical dormancy loss was examined for seeds buried at shaded or sunny exposed locations. The role of temperature in regulating dormancy and germination was analysed by incubating seeds in temperature sequences simulating temperatures that seeds experience in nature. The results indicate that most seeds of G. robertianum buried in sunny conditions germinate immediately after physical dormancy loss in summer. Seeds buried in shaded conditions also lose physical dormancy mainly during summer, but remain physiologically dormant and do not germinate until late winter or early spring. Besides physical dormancy, seeds of G. robertianum also initially have a high level of physiological dormancy, which is reduced during dry storage. Physiological dormancy is reduced through chilling in winter, thus enabling the seeds to germinate at low temperatures. We conclude that a complex combination of physical and physiological dormancy ensures that G. robertianum seeds germinate in summer at exposed sites and in early spring at shaded sites.     

Ecological and morphological seed traits of Polygala sardoa and P. sinisica: A comparative study on two endemic species of Sardinia

Polygala sardoa Chodat and P. sinisica Arrigoni (Polygalaceae) are two exclusive endemics to Sardinia and P. sinisica is affiliated under “Critically Endangered” in the IUCN Red Lists. In this work comparative studies on two populations of P. sardoa and in the only one of P. sinisica were carried out. In particular, seed output calculations and morphometric measurements on seed and elaiosome sizes were carried out. The effect of chipping, constant (15 °C) and alternating (25/10 °C) temperature regimes and light (8 h irradiance/day and dark) on germination were investigated. Seedling vigor assessments and a study on seed persistence in the soil were also carried out. P. sinisica had a higher seed output than P. sardoa and P. sinisica seeds were smaller than those of P. sardoa, with lower elaiosome area and elaiosome ratio values. Neither species had alternating temperature or light requirements for germination. P. sardoa achieved high germination percentages (> 80%) at all the tested conditions. P. sinisica had a lower maximum germination (<60%), suggesting the presence of physiological dormancy, and took more than twice as long to reach the maximum germination percentage. Seedlings of P. sardoa were larger than those of P. sinisica, and neither species formed a persistent soil seed bank. These new data may help implement effective conservation measures for these two species and, more generally, for threatened endemic species of this genus.     

Effect of Temperatures on Dormancy and Germination in Three Species in the Lamiaceae Occurring in Northern Wetlands

In the temperate region temperature is the main factor influencing the germination period of plant species. The purpose of this study was to examine effects of constant and fluctuating temperatures on dormancy and germination under laboratory and field conditions in the three wetland species Lycopus europaeus, Mentha aquatica and Stachys palustris. The results should give indications if the temperature-dependent regulation of dormancy and germination is phylogenetically constrained. Tests for germination requirements showed a minimum temperature for germination of 9 °C in Mentha and 12 °C in Lycopus and Stachys, and a maximum temperature of 33 °C for Lycopus and 36 °C for Mentha and Stachys. Fluctuating temperatures promoted germination in all three species but the amplitude required for high germination (>50%) differed: it was 8 °C in Mentha, 10 °C in Stachys and 14 °C in Lycopus (mean temperature 22 °C). The effect of temperatures on the level of dormancy was examined in the laboratory by imbibing seeds at temperatures between 3 °C and 18 °C for periods between 2 and 28 weeks, as well as by a 30-month burial period, followed by germination tests at various temperatures, in light and darkness. In the laboratory only low temperatures (≤12 °C) relieved primary dormancy in seeds of Lycopus, while in Mentha and Stachys also higher temperatures lead to an increase of germination. Dormancy was only induced in Lycopus seeds after prolonged imbibition at 12 °C in the laboratory. Buried seeds of all species exhibited annual dormancy cycles with lower germination in summer and higher germination from autumn to spring. Exhumed seeds, however, showed considerable differences in periods of germination success. Dormancy was relieved when ambient temperatures were below 12 °C. Ambient temperatures that caused an induction of dormancy varied depending on species and test condition, but even low temperatures (8 °C) were effective. At high test temperatures (25 °C) in light, exhumed seeds of all three species showed high germination throughout the year. The three species showed various differences in the effects of temperatures on dormancy and germination. Similarities in dormancy and germination found among the species are in common with other spring-germinating species occurring in wetlands, so it seems that the temperature dependent regulation of dormancy and germination are related to habitat and not to phylogenetic relatedness.     

Proteinbiosynthesen in dormanten und nachgereiften embryonen und samen von Agrostemma githago

Seed germination of Agrostemma githago is prevented by inhibitors of protein and RNA synthesis. Thus protein as well as RNA synthesis are essential prerequisites for germination. Early protein synthesis of Agrostemnia embryos can be completely inhibited by cycloheximide and cordycepin. During the aging of seeds there is a considerable decrease in germination capacity and protein synthesis. In dormant and afterripened embryos of Agrostemma githago¹⁴C-leucine and ¹⁴C-uracil are incorporated in protein and RNA respectively with nearly the same intensity, whereas RNA and protein synthesis of dormant seeds and embryos starts earlier than in those subjected to afterripening. ³H-uracil-labelled RNA from dormant and afterripened embryos are able to hybridize on oligo-dT-cellulose to the same extent. There is a similarity in the protein pattern of dormant and afterripened embryos revealed by electrophoresis in polyacrylamide gels of double-labelled proteins. According to these results dormancy of Agrostemma githago is not caused by a general but by a specific metabolic block.     

The role of temperature in post-dispersal embryo growth and dormancy break in seeds of Aconitum lycoctonum L.

This research was performed to resolve temperature requirement for embryo growth, dormancy break and seed germination of Aconitum lycoctonum, an Eurasian perennial herb growing in deciduous forests. The dormancy strategy of A. lycoctonum was compared with that of other Ranunculaceae species growing in the temperate deciduous forest habitat. Seeds of A. lycoctonum germinate immediately after embryo growth is completed during winter and seedlings subsequently emerge in early spring. Experiments in controlled conditions revealed that (1) embryo growth and germination only occurred at low temperatures (<10 °C), (2) a high-temperature pre-treatment was not required for germination, and (3) application of gibberellic acid did not overcome the chilling requirement. Based on these results, seeds of A. lycoctonum can be classified as having deep complex morphophysiological dormancy. Dormancy breaking requirements of A. lycoctonum are very similar to related species studied before, suggesting stasis in seed dormancy traits has occurred in the Aconitum–Delphinium clade.     

Comparative seed dormancy and germination of eight annual species of ephemeral wetland vegetation in a Mediterranean climate

Ephemeral wetland vegetation (EWV) in the Mediterranean Basin appears in temporary wetlands where favourable hydrological conditions exist only for a short time and year-to-year variability is high. Here, we report results of the seed germination, dormancy and desiccation tolerance of eight annual species living in this vulnerable habitat. Experiments were performed in laboratory conditions under constant and alternating temperatures and using a 12-h daily photoperiod or continuous darkness. Whilst germination and dormancy differed between the species, seeds demonstrated an absolute light requirement and prefer cool temperatures to germinate (mean ≤15 °C). Logistic regression analysis showed significant effects of alternating temperature in all the species except in Tillaea vaillantii whose germination was stimulated by constant temperature. Mean temperature was a significant term in the logistic models for the dormant species Cicendia filiformis, Linum radiola and T. vaillantii for which after-ripening was an effective dormancy-breaking treatment. From these results we infer three strategies of regeneration by seeds: (1) species germinating during the whole vegetative season (2) species germinating in a narrow temperature niche and (3) species requiring flooding (T. vaillantii). Seeds possessed orthodox storage behaviour (tolerating drying to 15 % relative humidity) and may be amenable to seed banking as a means of ex-situ conservation. We conclude that EWV species are adapted to the irregular presence of water with characteristics that are typical of neither truly aquatic nor wetland plants. These EWV species showed a more plastic germination response based on alternating and constant temperature sensitivity and a low proportion of dormant seeds.     

Effects of Stratification, Gibberellic acid and Germination Temperature on the Germination of Betula nana

Experiments were carried out with three seed lots of Betula nana collected in 1967 from different localities in Norway. Seeds were stratified for 0-20 days in dark at +2-+3 °C on filter papers moistened with distilled water, or treated with solution of GA₃ for 24 h at room temperature, and then moved into special germination boxes that were placed in different temperature conditions. All the seed lots had conditional dormancy. Quantitatively, the dormancy was different in the different seed lots (pronenances), but there were no qualitative difference in the reaction to stratification gibberellic acid and to germination temperature. Differences between seed lots may have been due to different stage of seed development. The dormancy was deepest at low temperatures(12 and 15°C) decreasing gradually with increasing temperature (to 24 °C). The dormancy was effectively broken by a short stratification (from 5 to 15 days), and by treatment with gibberellic acid. The deeper the dormancy and the lower the germination temperature the longer the stratification that was needed for maximum germination. Similarly, the concentration of GA₃ needed for maximum germination increased with decreasing temperature and with increasing dormancy.     

Integrated control of the long-tailed mealybug,Pseudococcus longispinus [Hom.: Pseudococcidae], in avocado plantations in Israel

Avocado plantations in Israel neighbouring cotton fields were heavily infested with and damaged by the long-tailed mealybugPseudococcus longispinus Targioni Tozzetti. Drift of pesticides from the aerial sprays of those cotton fields upset the biological equilibrium and resulted in outbreaks of the mealybug population. The honeydew moth,Cryptoblabes gnidiella Mill. is attracted to the honeydew and its larvae gnaw the fruit. Avocado plantations in the vicinity of deciduous fruit trees, vines and citrus orchards treated with non-selective pesticides were also damaged, but to a lesser degree. The annual peak of the long-tailed mealybug population occurs in late spring and early summer, declines from autumn to winter, and is at an ebb usually in April. The parasitic waspHungariella peregrina Compere, the most important natural enemy in Israel of the long-tailed mealybug, was released in the striken areas.Anagyrus fusciventris Girault was introduced from Australia and well established in citrus and avocado plantations. The lady beetleCryptolaemus montrouzieri Muls. did not become established in avocado plantations. Lacewings were less important than parasites as biocontrol agents. Control of ants did not affect markedly the fluctuations in the mealybug populations. As a result of limitations of aerial sprays of cotton near avocado, as well as of release of natural enemies in afflicted plantations, the long-tailed mealybug population and its damage were reduced greatly.     

Ecophysiology of embryo development and seed germination of the European woodland herbaceous perennial Corydalis cava (L.) Schweigg. & Körte subsp. cava (Fumariaceae)

In this study we examined the germination ecology with special reference to the temperature requirements for embryo development and germination of Corydalis cava subsp. cava, under both outdoor and laboratory conditions. Corydalis cava is a spring flowering woodland tuberous geophyte widely distributed across Europe. Germination phenology, including embryo development and radicle and cotyledon emergence, was investigated in a population growing in northern Italy. Immediately after harvest, seeds of C. cava were sown both in the laboratory under simulated seasonal temperatures and naturally. Embryos, undifferentiated at the time of seed dispersal, grew during summer and autumn conditions, culminating in radicle emergence in winter, when temperatures fell to ca 5°C. Cotyledon emergence also occurred at ca 5°C, but first emergence was delayed until late winter and early spring. Laboratory experiments showed that high (summer) followed by medium (autumn) and low temperatures (winter) are needed for physiological dormancy loss, embryo development and germination respectively. Unlike seeds of C. cava that germinated in winter, in other Corydalis species radicle emergence occurred in autumn (C. flavula) or did not depend on a period of high summer temperature to break dormancy (C. solida). Our results suggest that subtle differences in dormancy and germination behavior between Corydalis species could be related to differences in their geographical distribution.