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How does one identify a seed's species & variety, could it be done by some means of DNA or by use of a microscope? Say for example, I had a pumpkin seed, I knew that it was a "small sugar pumpkin" variety, but how would one scientifically identify it to know that it was infact a small sugar pumpkin as well as a pumpkin without going through the process of planting it. Is there some kind of indicator on a DNA level that shows "This is what I am?"
My knowledge regarding biology is extremely basic, but I am very interested in knowing the full process of how this would work.
Yes, their name are "molecular marker". Every gene carrying a phenotype, quantitative or qualitative, is identified as an allele of every gene encoding for proteins. In order to identify a phenotype using just infos gained from DNA, you'll need a previous library made by these gene regions, were every polymorphism between them is associated with a phenotype. For example, a kind of marker used for this kind of work is SSR , or "Simple sequence repeats" : it is made by a simple sequence of DNA interspaced between two other region. The number of repeats of the internal sequence could be associated with a phenotype.
So, by a simple PCR you could amplify this regions:
And by a electrophoresis you could see how much repetitions are in your band, using just the molecular weight. Here is an example of SSR used for phenotype/genotype screening
Woodrats climb readily and are usually active at night. Most species build a large stick den or house on the ground or in trees, but some species live in rocky outcroppings. These houses are typically occupied by one individual or by a female and her young. One animal may inhabit several houses. A nest, usually made of finely shredded plant material, is located within the larger house. Breeding usually occurs in the spring. Woodrats produce 1 to 4 young per litter and may produce more than 1 litter per year in the southern parts of the United States.
Each species of woodrat is generally restricted to a given type of habitat within its range. Woodrats occur from low, hot, dry deserts to cold, rocky slopes above timberline (Table 1).
Woodrats (Neotoma spp.) in North America.
Species: Eastern woodrat (Neotoma floridana)
Description: Total length 14 to 17 inches (36 to 43 cm). Large grayish-brown woodrat with white or grayish belly. Tail shorter than head and body.
Habitat Preference: Rocky cliffs and mountain regions. Usually builds a home of sticks and debris.
Food Preference: Seeds, nuts, and fruits.
Species: Southern plains woodrat (Neotoma micropus)
Description: Total length 13 to 14 inches (33 to 36 cm). Steel-gray woodrat with white hairs on throat, breast, and feet. Blackish tail.
Habitat Preference: Semi-arid brushland, low valleys, and plains.
Food Preference: Cactus, seeds, and acorns.
Species: Whitethroat woodrat (Neotoma albigula)
Description: Total length 13 to 15 inches (33 to 38 cm). Body is gray, belly is white. Hairs on throat and feet white. Tail whitish to brown.
Habitat Preference: Brushlands and rocky cliffs with shallow caves. Builds a house 2 to 3 feet
(0.6 to 0.9 m) high made of sticks and rocks.
Food Preference: Cactus, beans and seeds, leaves of plants, especially new growth.
Species: Desert woodrat (Neotoma lepida)
Description: Total length 10 to 13 inches (25 to 33 cm). Body pale to dark gray washed with fulvous. Belly grayish to fulvous. Slate gray at base of hairs.
Habitat Preference: Desert floors or rocky slopes. House usually on ground or along cliffs.
Food Preference: Seeds, fruits, acorns, and cactus.
Species: Stephens woodrat (Neotoma stephensi)
Description: Total length 10 to 14 inches (25 to 36 cm). Body grayish buff, darker on top, belly washed with buff. Dusky wedge on top hind foot. Tail slightly bushy on end, whitish below, blackish above.
Habitat Preference: Juniper woodlands.
Food Preference: Primarily juniper.
Species: Mexican woodrat (Neotoma mexicana)
Description: Total length 12 to 13 inches (30 to 33 cm). Gray to black in color. Tail distinctly bicolored with white below, black above.
Habitat Preference: Rocks and cliffs in mountains. Does not normally build houses.
Food Preference: Acorns, nuts, seeds, fruits, and cactus plants.
Species: Dusky-footed woodrat (Neotoma fuscipes)
Description: Total length 14 to 18 inches (36 to 46 cm). Body gray-brown above, gray to white below. Tail slightly paler below. Dusky hairs sprinkled on hind feet.
Habitat Preference: Dense chaparral, riparian thickets, deciduous or mixed woodlands. Builds large stick houses on ground or in trees.
Food Preference: Variety of seeds, nuts, acorns, fruits, green vegetation, and fungi.
Species: Bushytail woodrat (Neotoma cinera)
Description: Total length 15 to 16 inches (38 to 41 cm). Body varies from pale gray to nearly black. Has a long, bushy squirrel-like tail.
Habitat Preference: High mountains. Climbs about cliffs easily. Does not normally build houses.
Food Preference: Green vegetation, twigs, and shoots. Feed outside. Trails 3 to 4 inches (8 to 10 cm) wide from the building to the outside may be visible.
Woodrats | Woodrat Overview | Woodrat Damage Assessment | Woodrat Damage Management | Woodrat Resources | Woodrat Acknowledgments | ICWDM | Wildlife Species Information
How does one identify a seed's species & variety? - Biology
Maple Tree Identification
The commercial production of maple products in North America occurs primarily in the northeastern United States and southeastern Canada (Figure 3.1). This is the geographic area of greatest abundance of sugar maple (Acer saccharum) and black maple (Acer nigrum), the two most preferred and most commonly tapped maple species.
There are thirteen native maple species in North America (Table 3-1). While most of these species are probably tapped to some extent, at least by hobbyists, sugar and black maple, along with red maple (Acer rubrum), provide most of the commercial sap. A fourth maple species, silver maple (Acer saccharinum), is sometimes tapped, particularly in roadside operations, and is often confused with red maple.
|Table 3.1. Maple species native to the United States.|
|General Geographic Distribution|
|Sugar Maple||Acer saccharum||Northeast United States & Southern Canada|
|Black Maple||Acer nigrum||Northeast United States & Southeast Canada|
|Red Maple||Acer rubrum||Eastern United States & Southeast Canada|
|Silver Maple||Acer saccharinum||Eastern United States & Southeast Canada|
|Boxelder||Acer negundo||Eastern & Central United States & Canada|
|Mountain Maple||Acer spicatum||Northeast United States & Southeast Canada|
|Striped Maple||Acer pensylvanicum||Northeast United States & Southeast Canada|
|Bigleaf Maple||Acer macrophyllum||Pacific Coast United States & Canada|
|Chalk Maple||Acer leucoderme||Southeast United States|
|Canyon Maple||Acer grandidentatum||U.S. Rocky Mountains|
|Rocky Mountain Maple||Acer glabrum||Western United States|
|Vine Maple||Acer circinatum||Pacific Coast of United States & Canada|
|Florida Maple||Acer barbatum||Southeast United States Coastal Plain & Piedmont|
Table 3-2 contains a descriptive comparison and Figures 3.2 through 3.5 illustrate characteristic leaves, bark, twigs, and fruits of sugar, black, red and silver maple. These four species share several characteristics in common. All have leaves of similar shape: a single leaf blade with the characteristic maple shape, 3-5 lobes radiating out like fingers from the palm of a hand (palmately lobed) with notches (called sinuses) between the lobes. Like all maples, the leaves, buds and twigs of all four are attached in pairs opposite each other along the branches. Also, all four produce a fruit called a samara (or double samara), which is a pair of connected, winged seeds.
margin. Mature leaves have a whitish appearing
|Figure 3.1. Commercial maple syrup production in North America.|
Figure 3.2. Sugar maple bark, fruit, leaf, and twig.
Figure 3.3. Black maple bark, fruit, leaf, and twig.
Figure 3.4. Red maple bark, fruit, leaf, and twig.
Figure 3.5. Silver maple bark, fruit, leaf, and twig.
Species Suitable for Maple Product Production
Sugar and Black Maple
Sugar and black maple are very similar species and unquestionably the most preferred species for producing maple products, primarily because of their high sugar content. Sugar maple occurs naturally throughout most of the northeastern United States and southeastern Canada (Figure 3.6). Black maple, on the other hand, occupies a much smaller natural range (Figure 3.7). Distinguishing between them may be more of an academic exercise than one useful in sugar bush management because (1) they are essentially identical in quality as sugar trees, and (2) they often hybridize producing trees with a range of characteristics, making it difficult to clearly distinguish between them.
Identifying a tree as a sugar or black maple (Table 3.2, Figure 3.2 & 3.3) is easily done from the leaves by observing 5-lobed leaves, the paired opposite attachment of the leaves along the stem and the lack of teeth along the leaf margin from the bark of older trees by observing the long plates that remain attached on one side from the twigs by observing the opposite arrangement of buds and the relatively long, pointed, brownish terminal bud and from the seed by observing its horseshoe shape and size. Distinguishing between sugar and black maple is best done by comparing the leaf structure (particularly the number of lobes, droopiness and presence or absence of stipules along base of petiole) and by the degree of bumpiness of the twigs.
Sugar and black maples are found on a variety of soils and site conditions, but neither tolerates excessively wet or dry sites, and both grow best on moist, deep, well-drained soils. Black maple is more likely to be found along moist river bottoms. Both species can be found growing in pure stands, with each other, or with a wide variety of other hardwood species including American beech, American basswood, yellow birch, black cherry, northern red oak, yellow poplar and black walnut. Both species have been planted extensively as roadside trees which are often tapped as part of a sugaring operation. Plantations of sugar maple have also been established with the intent of developing efficient, productive sugar bushes. Both species are relatively long lived, capable of living well beyond 200 years, with trunk diameters greater than 30 inches and heights greater than 100 feet.
Sugar and black maple both grow in the shade of other trees (they are shade tolerant), and trees of many different ages (sizes) are often found in a forest. Both species are also found in stands composed of trees that are essentially all the same age (size). Healthy sugar and black maple trees growing in overstocked uneven-aged or even-aged stands can be expected to achieve tapable size in 40 to 60 years, depending on overall site quality. Thinning or release cutting dramatically reduces this age-to-tapable-size.
Sugar and black maple are particularly attractive as sugar trees because of their high sap sugar content and the late date at which they begin growth in the spring. Sugar and black maple have the highest sap sugar content of any of the native maples. While the exact sap sugar content of a tree will vary depending on many factors including genetics, site and weather, sugar and black maples generally average between 2.0 and 2.5 percent sap sugar content. It is not unusual to find many trees in a sugar bush well in excess of 3 percent, and occasionally higher. Genetic research on sugar maple suggests that the sap sugar content of planted seedlings can be increased by controlled breeding. Other things being equal, higher sap sugar content translates to lower costs of production and greater profits.
Black and sugar maples begin growth later in the spring than red or silver maple. As maples begin their growth, chemical changes occur in the sap which make it unsuitable for syrup production. The term "buddy sap" is often applied to late season sap which produces syrup with a very disagreeable flavor and odor. Because sugar and black maple resume growth later than red or silver maple, sap may be collected later in the spring.
Red maple is commonly tapped in certain geographic areas, particularly in the southern and western portions of the commercial maple range. Identifying a tree as a red maple (Table 3.2, Figure 3.4) is done from the leaves by observing the 3 lobes (occasionally 5), the paired opposite arrangement of the leaves and the small teeth along the margin from the bark of older trees by the presence of the scaly plates from the twig by observing the paired opposite arrangement of the buds, the relatively short, blunt, rounded, red terminal bud and the lack of an offensive odor when the bark of the twig is bruised or scraped and from the fruit by observing its severe V-shape and size.
Red maple is one of the most abundant and widespread hardwood trees in North America (Figure 3.8). Probably no other species of forest tree, certainly no hardwood, can thrive on a wider variety of soil types and sites. Although it develops best on moderately well-drained to well-drained, moist soils, it commonly grows in conditions ranging from dry ridges to swamps. Because of the wide variety of sites on which red maple will grow, it is found growing naturally in pure stands and with an enormous variety of other tree species ranging from gray birch and paper birch, to yellow poplar and black cherry, and including sugar and black maple. Its rapid growth and ability to thrive on a wide variety of sites have resulted in its widespread planting as ornamental and street trees which are often tapped as part of a sugaring operation.
Compared to sugar and black maple, red maple is a relatively short-lived tree, rarely living longer than 150 years. Mature trees commonly average between 20 and 30 inches in diameter and 60 and 90 feet tall. Like sugar and black maple, red maple is shade tolerant and is found in both even-aged and uneven-aged forests. Thinning or release cutting will substantially shorten the age-to-tapable-size.
From the perspective of producing maple syrup, red maple's most attractive characteristic is its ability to thrive on a wide variety of site conditions. In some areas of the commercial maple range, red maple is the only maple present on many sites. One either taps red maple or they don't sugar. In other areas, red maple may be tapped along with sugar and black maples.
It is important to emphasize that good, high-quality maple syrup can be made from red maple sap. However, for sugaring, red maple does have three important weaknesses. First, the sap sugar content of red maple will be less, on the average, than that of nearby comparable sugar or black maples, perhaps by 1 /2 percent or more. This lower sap sugar content translates to higher costs of production and lower profits. Secondly, red maple begins growth in the spring before sugar and black maples, resulting in a shorter collecting season. In addition, when the sap of some red maples is processed, an excessive amount of sugar sand is produced. Sugar sand or niter is the salt that precipitates during the evaporation process. Sugar sand can cause several problems during the production process.
Silver maple is a rapidly growing maple found throughout much of the eastern United States and extreme southeastern Canada, where it is often tapped (sometimes heavily) in a particular location (Figure 3.9). Throughout much of the commercial maple region, however, most maple producers will not tap silver maple.
Identifying a silver maple (Table 3.2, Figure 3.5) is done from the leaves by observing the 5 lobes with the sides of the terminal lobe diverging toward the tip, the paired opposite arrangement of the leaves, the presence of fine teeth along the margin but not on the inner sides of the sinuses and the silvery white underside from the bark of older trees by the trunk's shaggy appearance from the twigs by observing the paired opposite arrangement of the buds, the relatively short blunt, rounded, red terminal bud and the presence of a fetid or foul odor when the twig is bruised or scraped and from the fruit by observing its V-shape and size.
Under natural conditions, silver maple is primarily a bottomland and floodplain species, where it may occur in pure stands but is more commonly found associated with other bottom species such as American elm, sweetgum, pin oak, swamp white oak, eastern cottonwood, sycamore, and/or green ash. Silver maple is among the fastest growing hardwood species commonly planted in eastern North America, certainly the fastest growing maple. For this reason, it has been widely planted as an ornamental and street tree. Its use as an ornamental and street tree, at least in urban areas, has been discontinued in recent years because the wood of silver maple is very brittle and often breaks in severe wind, snow or ice storms. Nevertheless, large silver maple street trees are numerous in many areas and these are sometimes tapped as part of a sugaring operation.
Like the red maple, silver maple is a relatively short-lived tree when compared to the sugar or black maple, living perhaps
130-150 years. Because of its fast growth rate, however, mature trees can achieve diameters in excess of 3 feet and heights in excess of 100 feet. On good sites with little competition from other trees, silver maple diameter growth may approach 1 /2 inch per year (rates as high as 1 inch per year have been recorded). Silver maple's growth rate often responds dramatically to thinning or release cutting.
When compared to sugar, black and red maple, silver maple is a distinctly fourth choice for sugaring for several reasons. First, its sugar content is usually lower than red maple's, perhaps as much as 1 /2 percent or more, which means even higher production costs and lower profits. Second, like red maple, it begins growth in the spring, earlier than sugar and black maple, resulting in a shorter collecting season. Third, like red maple, the evaporation of sap from some silver maples produces an excessive amount of sugar sand.
Striped maple (Acer pensylvanicum) and mountain maple (Acer spicatum) are two other native maples that are found growing within the commercial maple range (Figures 3.10 and 3.11). Neither of these species is commonly tapped. Striped maple is a small slender tree which rarely attains tapable size. It is most easily identified by the opposite paired arrangement of its leaves and branches, its 3-lobed leaf with fine teeth on the margin, and striping on the branches and young trunks. Mountain maple is essentially a shrub. It is most easily identified by the opposite paired arrangement of its leaves and branches and its 3lobed leaf with coarse teeth. If these species occur in a sugarbush it is important to be able to identify them. They should not be confused with the desirable maple species when performing management practices such as thinning or release cuts.
One exotic maple, Norway maple (Acer platanoides), is commonly planted as an ornamental and street tree and will attain tapable size. It is recognized by the opposite paired arrangements of its leaves and branches, its 7lobed leaf without marginal teeth, and its 1 1 /2 to 2 inch long samara with divergent wings (Figure 3.12). The sap of Norway maple is not commonly used to produce maple syrup.
For fertilization to occur in angiosperms, pollen has to be transferred to the stigma of a flower: a process known as pollination. Gymnosperm pollination involves the transfer of pollen from a male cone to a female cone. When the pollen of the flower is transferred to the stigma of the same flower, it is called self-pollination. Cross-pollination occurs when pollen is transferred from one flower to another flower on the same plant, or another plant. Cross-pollination requires pollinating agents such as water, wind, or animals, and increases genetic diversity. After the pollen lands on the stigma, the tube cell gives rise to the pollen tube, through which the generative nucleus migrates. The pollen tube gains entry through the micropyle on the ovule sac. The generative cell divides to form two sperm cells: one fuses with the egg to form the diploid zygote, and the other fuses with the polar nuclei to form the endosperm, which is triploid in nature. This is known as double fertilization. After fertilization, the zygote divides to form the embryo and the fertilized ovule forms the seed. The walls of the ovary form the fruit in which the seeds develop. The seed, when mature, will germinate under favorable conditions and give rise to the diploid sporophyte.
What benefit do arthropods provide to grassland ecosystems?
What benefits don’t they provide? As the base of the animal food chain in most situations, they directly or indirectly feed most wildlife. They are highly mobile, ubiquitous and regularly interact with plants and animals. As such, they fulfill flowering plants’ need for pollination and seed dispersal. They also control pest populations and consume living and dead organic material — like leaves, bark, fungus and carrion — which is essential for promoting the decomposition and recycling of nutrients in an ecosystem.
Soft rot Enterobacteriaceae (SRE) Pectobacterium atrosepticum (Gardan et al., 2003 ) (formerly Erwinia carotovora subsp. atroseptica (Van Hall) Dye) (Pba), Pectobacterium carotovorum subsp. carotovorum (Gardan et al., 2003 ) [Erwinia carotovora subsp. carotovora (Jones) Bergey et al.] (Pcc), Pectobacterium carotovorum subsp. brasiliense (Erwinia carotovora subsp. brasiliense) (Pcb) (Duarte et al., 2004 ), Pectobacterium wasabiae (Erwinia carotovora subsp. wasabiae) (Pwa) (Pitman et al., 2008 ) and several Dickeya spp. (Erwinia chrysanthemi), including D. dianthicola (Erwinia chrysanthemi pv. dianthicola), Dickeya dadantii, Dickeya zeae (Erwinia chrysanthemi pv. zeae) and the new species Dickeya solani (Toth et al., 2011 van der Wolf et al., 2013 ) are responsible for causing potato blackleg in the field and tuber soft rots in storage and in transit as well as in the field worldwide (Fig. 1). Additionally, some reports suggest that P. carotovorum subsp. odoriferum (Pco) (Waleron et al., 2014 ) and P. betavasculorum (Pbt) (Nabhan et al., 2012 ) can also cause soft rot disease in potato. SRE are recognised among the top 10 most important bacterial pathogens in agriculture limiting crop yield and quality (Mansfield et al., 2012 ).
Of all Pectobacterium spp. infecting potato, Pcc has the widest host range worldwide, whereas Pba is found mainly on potato grown in temperate regions (Pérombelon, 2002 ). In 2004, Pcb, a highly aggressive bacterium, was shown to cause severe infection of potato crops in tropical and subtropical regions (viz. Brazil and South Africa) (Duarte et al., 2004 van der Merwe et al., 2010 ). Pwa which was first associated with horse radish in Japan (Pitman et al., 2008 ) was later found also on potato in New Zealand, South Africa, Canada and various European countries, where it is responsible for severe economic losses (Nykyri et al., 2012 Waleron et al., 2013 ).
In 2005, P. chrysanthemi species was elevated to the genus level and renamed Dickeya which was divided into six genomo-species (D. dianthicola, D. dadantii, D. zeae, D. chrysanthemi, D. dieffenbachia and D. paradisiaca) and nine biovars which largely resembled the initial Erwinia chrysanthemi biovar division (Samson et al., 2005 ). Recently, D. dieffenbachiae was reclassified as a subspecies of D. dadantii (Brady et al., 2012 ).
During the last 50 years different aspects of Pectobacterium and Dickeya species causing blackleg and soft rot diseases have been extensively reviewed. However, procedures used to detect and identify the SRE have not been reviewed as much (Barras et al., 1994 De Boer, 2003 Charkowski, 2012 Czajkowski et al., 2012 Hauben et al., 1998 ). The purpose of this review is to present a comprehensive examination of the available methods. We present methods based on selective growth agar media, biochemical and physiological assays, serological methods and more recently developed nucleic acid sequence-based amplification methods. In addition, methods for species/strain differentiation and identification are examined including biochemical profiling, fingerprinting (REP-PCR), restriction fragment length polymorphism (RFLP), amplified fragment length polymorphism (AFLP), multi locus sequence tagging (MLST), random amplification of polymorphic DNA (RAPD), fatty acid methyl ester (FAME) analyses and full genome sequencing in order to find either major or subtle differences in nucleotide genome sequences. The review also presents less established methods used that could be potentially useful in some situations, namely volatile metabolic profiling, conductometry, flow cytometry, microsphere immunoassays and phage typing.
Finally, using the present literature data on the topic and research experience we would like to propose and recommend set of methods and procedures that in our view would prove useful in the isolation, detection, identification and differentiation of SRE from environmental samples with special emphasis on potato.
Seed potato certification system and visual field inspections
Classification systems were introduced in virtually every country producing seed potato tubers to ensure high quality of the propagation material. These systems and schemes set the levels of tolerance to soft rot and blackleg diseases based on the visual inspections of growing crops as well as on inspections of the harvested tubers after grading and dressing and before sale (Shepard & Claflin, 1975 ). Usually, inspectors visit potato fields at least two times during the season, looking for the presence of symptomatic plants. Records of the blackleg diseased plants provide some indications on the disease incidence and possible infection potential of the progeny tubers (seed) in the next generation but ignore latent progeny tuber contamination which tends to be more closely related to future disease development (Pérombelon & Hyman, 1995 Toth et al., 2011 ).
It is important to point out that the tolerance for blackleg in the European seed potato tubers differs from country to country as there is no uniform policy in the European Union and the rest of the world (Toth et al., 2011 ).
Sampling potato tubers for the presence of soft rot Enterobacteriaceae
A good sampling strategy is crucial for the fool-proof detection and identification of the bacteria present in environmental samples (Pickup, 1991 ). It is worth mentioning that in Europe there is no compulsory testing for Pectobacterium and Dickeya species in potato. In the case of potato seed stocks, we suggest to use a sampling scheme based on the one used to detect quarantine bacteria Ralstonia solanacearum and/or Clavibacter michiganensis subsp. sepedonicus in which routinely 200 tubers are tested per 25 tonne lots in four pooled samples of 50 tubers (alternatively 8 composite samples of 25 tubers each). Although this sampling scheme is not officially accepted, according to the data presented by the Euphresco Phytosanitary ERA-NET ‘Dickeya species in potato and management strategies’ (http://www.euphresco.org/), it allows estimation of infection level in (seed) tubers. This is based on the statistical assumption that there is a 95% probability of detecting at least one infected tuber in a seed lot if 1.5% tubers are infected, according to the Poisson distribution (EPPO, http://www.eppo.int/). This strategy is more suited to high than lower seed grades which can be extensively latently contaminated (Pérombelon, 2002 ).
Isolation of Pectobacterium and Dickeya species
Most methods used for identification and differentiation of soft rot and blackleg causing bacteria require isolation of viable cells from samples, and growth and purification of the bacteria prior to analyses.
Isolation from plant material
From symptomatic tissues, where bacterial densities are often greater than 10 6 cells g −1 , it is best to sample from the advancing front of the rot or from newly diseased tissue to avoid interference and growth suppression by contaminating saprophytes. The sample is usually suspended and diluted in sterile water or buffer and a loopful streaked on a growth medium selective for SRE. To protect bacterial cells from oxidative stress due to the release of the plant compounds during tissue preparation or enrichment, an antioxidant 0.05% DIECA (diethyldithiocarbamic acid) is commonly used (Toth et al., 2011 ).
Plates are incubated at different temperatures as the pathogens have different optimal growth temperatures (Pérombelon & van der Wolf, 2002 ). Depending on the medium, bacterial colonies appear after 24–48 h at 21–37°C.
In latent infection, the bacteria may be found in all tissues, stems, roots, leaves and (progeny) tubers however, their density is usually low, rarely exceeding 10 3 cells g −1 plant tissue. In stems, the bacteria are more frequently found in the first 15–20 cm above ground level (Hélias et al., 2000 ), whereas in tubers they are more commonly present in the stolon end (Czajkowski et al., 2009 ), but are also frequently found in lenticels and suberized wounds (Pérombelon, 2002 ). As the diseases are seed-borne, (seed) tubers are tested in seed certification programmes for the bacteria either qualitatively or quantitatively. Extraction of the bacteria from tubers varies and is either from ground peel strips encompassing the stolon end or the stolon end tuber section of individual or replicated bulked tuber lots (Pérombelon & van der Wolf, 2002 ). However, what has not yet been agreed on is whether it is more useful: (a) to determine the presence or absence of contaminated tubers in a seed lot, (b) the average tuber contamination level of a seed lot or (c) the distribution frequency of individual tuber with different contamination levels, as disease development is related to the latter (Tsror et al., 2012 ). It can be speculated that the number of highly contaminated tubers is more important than the average level of lot contamination, as even relatively small population of heavily infected tubers may already result in diseased plants.
Isolation from soil, rain and irrigation water
Soft rot and blackleg bacteria survive poorly in the environment (Pérombelon & Kelman, 1980 ), and their survival depends mostly on temperature, humidity level and pH. Survival can be longer in potato debris postharvest and in the rhizosphere of certain plants and weeds, but even under favourable conditions, survival is restricted (Pérombelon & Hyman, 1989 ). The detection of low numbers of the bacteria in soil is further hampered by the presence of other (antagonistic) microorganisms that can overgrow the target bacteria during isolation.
In general, soil to be tested for the presence of SRE can be processed by suspending in sterile water or buffer and shaking for a couple of hours, or better still, first enriched by incubating in a selective broth (pectate enrichment broth – PEB see below) (Pérombelon & van der Wolf, 2002 ) before dilution and plating onto agar selective media (see below).
Soft rot and blackleg bacteria can survive for more than 200 days in sterile water (Cother & Gilbert, 1990 ), and have been detected in surface water (Quinn et al., 1980 ). The use of contaminated surface water during irrigation can result in infection of potato crops (Cappaert et al., 1988 ). Because of the low numbers present, often <10 1 cells mL −1 , test samples have to be enriched by incubation in a PEB or the bacteria need to be concentrated by centrifugation prior to plating (Pérombelon & van der Wolf, 2002 ).
Detection, identification and differentiation
For many years, detection and identification of pectinolytic Pectobacterium and Dickeya species bacteria have depended solely on the isolation of viable bacterial cells on (semi-selective) culture agar media followed by serological and biochemical analyses, bioassays and microscopic observations including Gram staining. Later, molecular techniques based on detection of nucleic acids have been introduced, which avoid the need for live cells and now are used routinely due to their high specificity and reproducibility. What is more, they are much faster than traditional methods and allow qualitative and (semi) quantitative detection of bacteria in complex environments.
It is often difficult to discriminate among the methods used exclusively for detection and identification of SRE from those used to differentiate the isolates of Pectobacterium and Dickeya into species and subspecies, as some may be used for both objectives simultaneously. Therefore, we decided, for the purpose of this review, to divide the methods according to their (technical) background (a) morphological and biological methods, (b) serological (immunological) methods, (c) molecular detection methods and (d) other methods. They are critically assessed in terms of their practical applications in detection systems.
Field Biology in Southeastern Ohio
Ah the Asters, could it get more difficult? I want to thank Scott Namestnik of "Get Your Botany On" for reviewing some of these photographs. Both of us will tell you that identifying asters from photos alone can be very unreliable. Even if you're just a photographer, collecting and pressing voucher specimens for detailed observation is often a must to be sure. I have sent these pictures to others, but am still waiting for responses. Should opinions change on anything posted here, I'll be sure to update them. Comments and corrections are welcome.
Asters are part of the Composite family Asteraceae. Their flower heads are yellow-green to red, and the rays range from white to lavender or purple. Once thought to be related to the old world Aster genus, we now know they are different, and have been split into at least three other genera.
Because flower color can vary within the same species, it is critical to have leaf descriptions to narrow down the proper identification. Leaves can vary from serrate to entire, stalked or unstalked, and even clasping the stem. With most species the lower leaves on the plant are often different from the upper leaves.
Making it even a greater challenge are species like this which show both large and small leaves interspersed throughout the stem. Especially confusing are these white asters where people will say "the flowers are more crowded on the stem". Or descriptions like "this species has slightly larger flowers". I'm sorry, but that is a bit vague for me. I suppose if you work with these ALL the time, or are comparing several species growing nearby, that might be okay, but doesn't do much for beginning identification.
Here is an example. Yes, the flowers on the left are a bit larger than the ones on the right, but how often do they all grow side by side? Usually they are out by themselves. What is important on these two is the left one has large broad leaves, and the species on the right has small narrow leaves. Always keep leaves in mind with Asters.
Let's try and make sense of some of the species. Without a doubt, the showiest and easiest species to identify is the New England Aster, Symphyotrichum novae-angliae. They have more rays than other asters.
This is one of our largest flowering species. They grow in any abandoned field, usually in large clumps. You can identify this one just driving by them. They reach four feet in height.
Up close their leaves are entire, but covered in hairs, as is the stem. The leaves are crowded together and clasp around the stem. As I said, this is the one species you need not have to look at this close to be sure.
If while driving around, you see an aster growing in ditches that appears somewhat similar to New England, but seems a bit lighter in color, and has fewer flowers up top, you may be looking at Purple-stemmed Aster, Symphyotrichum puniceum.
Purple-stemmed Aster is a species that likes aquatic environments. Notice the cattails in the background.
The leaves clasp the stem like New England, but not nearly as much. The leaves are more spread out along the stem. The stem can be red to purple and covered with hairs. What's different about this species is the hairs are not soft but stiff.
Another tall species is Smooth Aster, Symphyotrichum laeve. While commonly 3 feet in growth, I have seen them 4-5 feet tall.
The key feature I find on this species is the long leaves that usually have no teeth. They are thick and leathery to the touch. Both the leaves and the stem are smooth and hairless, so the common name is appropriate.
Up close you can see this is another species with very obvious clasping leaves. Look for this plant on the edges of dry woods.
Another showy aster with pale lavender flowers is the Crooked-stemmed Aster, Symphyotrichum prenanthoides. So far I would group New England and Purple-stemmed as having very large flowers as asters go. Smooth and Crooked-stem have medium sized flowers. Oh my, forgive me if I now sound vague as well. After looking at all parts of Crooked-stem Aster, you won't need to worry about flower size anyway.
Continuing our theme of clasping leaved species, here is another. I must admit I didn't plan it that way, as I have these in no particular order. If all you do is look at the leaf base, it probably looks nearly identical to Smooth. Of course we won't limit ourselves to just that. Follow the leaf up the margin. You will see they are always serrate. The stems on this plant are hairy not smooth.
The leaves are broad and sharply toothed at the middle and top, then narrow down to form a wing before clasping the stem.
As with the previous species, the common name tells us what to look for the most. The stem tends to grow crooked or zig-zag at every node, especially further up the plant. Look for this in moist to wet woods and edges.
Departing from the purple species for a moment, here is the Flat-topped Aster, Doellingeria umbellata. The flowers are all located at the top of the plant. They may be on an even plane (flat-topped) or slightly curved or domed like an umbrella (umbellata). The leaves are elongate, narrow and almost willow like. They are distinctly veined and the margins are toothless or weakly serrate. I have seen this plant in open marshes and wet woods.
Another white flowered species is Eurybia divaricata. Common names include White Wood Aster and Heart-leaved Aster. This is a woodland species. I have found it in both wet and dry woods. Either way, it prefers shade.
White Wood Aster tells us where to look for it, Heart-leaved Aster tells us what to look for. Like the previous species, the flower heads are flat-topped, but the leaves are heart shaped with very large coarse teeth on the margin. The flower heads are less numerous than many of the smaller white asters.
The leaves are distinctly stalked, especially lower on the plant. The upper most leaves may sometimes form short wings, as seen in the first photo of this species. The main stem is often twining or somewhat crooked.
Up till now these asters may be considered confusing, but not that tough. Now let's look at the difficult ones. The silhouette of this picture is similar to the previous, with some major differences. The flower cluster is more elongated or panicled, and the rays are blue-purple. This is the Blue Wood or Arrow-leaved Aster, Symphyotrichum cordifolium.
The variability in color makes looking at the flowers alone unreliable. There are similar looking broad leaved species like cordifolium. I have never been able to separate this from sagittifolius or lowrieanus. Turns out, (according to some) they are the same thing, now called urophyllum. Of course it depends whether you are a lumper or splitter. To my understanding S. drummondii is still a valid species. It is much hairier than cordifolium.
In the first of these photos, S. cordifolium usually has long narrow petioles throughout the plant. Whether you consider them different or just varieties, the others have petioles that are broader and form these wings to the stem. Look for these species in dry to mesic woodlands with openings in the canopy.
The jury is still out on this one, but I believe this is Wavy-leaved Aster, Symphyotrichum undulatum (or undulatus). This is another woodland species with light blue flowers.
The leaf shape is key here. The lower leaves are broad, toothed, and with long petioles. The difference with this one is the narrow petioles suddenly enlarge into a wing at the base, and the leaves then clasp the stem. The middle leaves have a shorter petiole that is still winged, and the leaf margin becomes less serrate.
The upper most leaves show no petiole and appear sessile. The margins become entire. These look a little like Smooth aster, but the leaves are rough to the touch, and the stem is hairy. Three different portions of the plant, with this much variation, shows why asters are not easy to identify.
Back to the white asters, this is Panicled Aster, Symphyotrichum lanceolatum. This was formerly known as Aster simplex.
What I look for in this species are the long, narrow or lance shaped leaves. They are weakly toothed to sometimes entire. They do not clasp the stem. Look for small leaves intermingled among the long ones. The stems are angled, and the raised portions are lined in fine hairs.
This is a common species. Considered weedy by many, it's panicled flowers can be quite showy. They are 1/2 to 3/4 of an inch across. Look for it in any wet soils.
Now come the most commonly seen asters in open fields. These are species of "bushy" asters. Most people lump them all into Calico asters, but this is not the case. There are several lookalikes.
Because they form such dense thickets in fields, they are often overlooked or taken for granted they're all the same thing. I have trouble separating them. The leaves on this are very small near the top. They are linear in shape and usually entire, but you have to check the stems. This is the Frost Aster, Symphyotrichum pilosum.
The stems on this plant are covered with silky white hairs. The leaf margins also contain these same hairs. It is said the name Frost Aster comes from the fact the plants look like frozen dew on a cold autumn morning. The hairs stand straight out. Other similar species have hairs that curl or are appressed upward to the twig. If that's the case, everything I come across from Northern to Southern Ohio has been this species. I'd say it's more than common, I'd call it quite abundant.
Now if this one is starting to look more like Symphyotrichum lateriflorum, the Calico Aster, you are correct. Notice the rays on this species number a lot fewer than other asters. The flowers are also much smaller than the other types. It is not really important to count the rays or measure them. As I said earlier, saying things like fewer and smaller when talking about only one species doesn't help much. I only choose those words to COMPARE against other similar species.
It is often noted that Calico can be identified by the red flower centers, but this is not reliable. Early on they are all white. Most if not all the smaller asters will have the flower head turn reddish with time. Size and number of rays are what to look for.
Of course we can't do asters without going back to the leaves. Calico leaves vary in length, but may be several inches long. The larger ones will be coarsely toothed, and the small upper leaves will be entire. The stems will be smooth to slightly hairy. The hairs are usually restricted to thin lines or rows. The green bracts (pic 1 & 4) stay appressed up against the flower head. On others like Frost or Heath Aster, they tend to curve outward. They occur in open fields, but may be more common on the edge of moist woodlands.
Here's another group I can't separate. This is the racemosum/ericoides group. Common names include the Heath Aster, Small White, Smooth White, and Old Field Aster. Superficially they look like any of the white bushy asters. What's different are the leaves. They are reduced in size, tend to look rolled, linear, or awl shaped. Heath plants have leaves like this, but conifers like Fir, Larch or Spruce come to mind when I see these plants. This group of asters tend to hybridize, so I can't be sure which is which.
Key Habitat Considerations
- Habitat can be created in any open space protected from untimely mowing or pesticide application.
- Native milkweeds provide food for monarch caterpillars.
- Native flowers provide food for adult butterflies. A combination of early, middle and late blooming species, with overlap in flowering times, will fuel butterfly breeding and migration and provide beautiful blooms season-long.
- Insecticides should never be used in or surrounding pollinator habitat. Limit use of herbicides within and surrounding the habitat only to control invasive or noxious weeds.
Finding and Selecting Milkweed Seeds and Plants
Information on finding and selecting the right milkweed seeds and plants.
Planting and Growing Milkweed
Information on planting and growing milkweed from seeds or plugs.
Milkweed & Wildflower Vendor Map
Use this map to find local suppliers of native, neonicotinoid-free plants and/or seeds.
Seed Germination, Mobilization of Food Reserves, and Seed Dormancy
6. SOME SEEDS REQUIRE EXPOSURE TO LIGHT
Seeds that have a specific requirement for light for germination are referred to as photoblastic seeds. The phenomenon is common in herbaceous and pioneer species , which produce large numbers of small seeds with relatively little food reserves. Many of these photoblastic seeds require a brief exposure to red light (660 nm) while in a wet state. The photoreceptor in this case is phytochrome, and the response has been well investigated in seeds of Datura ferox (a tropical weed) and lettuce (Lactuca sativa). Indeed, phytochrome was discovered after some remarkable observations on red/far-red reversal of lettuce seed germination (see Chapter 26 ). Light-requiring seeds also show sensitivity to cold temperature, and gibberellins and, in some cases, the light requirement can be bypassed by the exposure of seeds to chilling (2-5°C) or to GA. Both in lettuce and Arabidopsis seeds, it has been shown that red light induces the transcription of genes encoding specific isoforms of 3β-hydroxylase, the enzyme that catalyzes the conversion of GA20 to the biologically active GA1. Thus, the roles of phytochrome and gibberellin in the germination of red light-requiring seeds have been partially clarified.
7 Factors that Affect Seed Germination
I’ve mentioned before that I’m interested in integrating as many permaculture principles into my lifestyle as possible. Agriculture based on permaculture principles should mimic the natural world as much as possible – and natural ecosystems typically include diversity of both species and genetics. Starting plants from seed is not only more economical than purchasing young plants, but it also allows for more genetic diversity (at least with open pollinated species). Knowing what factors could be an issue is the first step to troubleshooting difficult to germinate species.
This one seems obvious but there is more to it than you might think. Seedlings generally need to be kept moist but not wet. This water should also (ideally) be chlorine-free. Urban water supplies are heavily chlorinated, so I let my water stand on the counter for at least 24 hours before I use it to water my seedlings. Also, if seeds are allowed to dry out after they have initially been wet some species will enter a second dormancy that is much harder to break!
This often-neglected factor is actually very important! Most seeds will not germinate in saturated (waterlogged) soil. Seeds and the seedlings they produce need to breath just like we do, so drainage in seed trays is very important!
You might have expected me to say “soil” here, but seedlings actually don’t need soil per-say. Soil, by definition of the NRCS, is “The unconsolidated mineral or organic material on the immediate surface of the Earth that serves as a natural medium for the growth of land plants.” Soil is a limited resource, and it is not the only option.
Seedlings need a substrate to germinate in but that substrate can be partially-decomposed plant matter (such as peat moss or compost), minerals (such as vermiculite or perlite), a combination of these (found in many soilless growing mixes), or just about anything that gives seedlings the structure they need. Generally things to consider when choosing a germination substrate are:
How does one identify a seed's species & variety? - Biology
Also according to the RI Department of Health, there are two other species of ticks that carry Lyme disease: One is I. Pacificus , or the Western Black-Legged Tick which, and is VERY similar to I. Scapularis , the Black-Legged Tick (Deer Tick). The Western Black-Legged Tick is found primarily in the Pacific US and British Columbia.