Plant pathology
Plant pathology is the scientific study of diseases in plants caused by pathogens and environmental conditions. Organisms that cause infectious disease include fungi, bacteria, viroids, virus-like organisms, protozoa and parasitic plants. Not included are ectoparasites like insects, vertebrate, or other pests that affect plant health by eating of plant tissues. Plant pathology involves the study of pathogen identification, disease etiology, disease cycles, economic impact, plant disease epidemiology, plant disease resistance, how plant diseases affect humans and animals, pathosystem genetics, management of plant diseases. Control of plant diseases is crucial to the reliable production of food, it provides significant problems in agricultural use of land, water and other inputs. Plants in both natural and cultivated populations carry inherent disease resistance, but there are numerous examples of devastating plant disease impacts such as Irish potato famine and chestnut blight, as well as recurrent severe plant diseases like rice blast, soybean cyst nematode, citrus canker.
However, disease control is reasonably successful for most crops. Disease control is achieved by use of plants that have been bred for good resistance to many diseases, by plant cultivation approaches such as crop rotation, use of pathogen-free seed, appropriate planting date and plant density, control of field moisture, pesticide use. Across large regions and many crop species, it is estimated that diseases reduce plant yields by 10% every year in more developed settings, but yield loss to diseases exceeds 20% in less developed settings. Continuing advances in the science of plant pathology are needed to improve disease control, to keep up with changes in disease pressure caused by the ongoing evolution and movement of plant pathogens and by changes in agricultural practices. Plant diseases cause major economic losses for farmers worldwide; the Food and Agriculture Organization estimates indeed that pests and diseases are responsible for about 25% of crop loss. To solve this issue, new methods are needed to detect diseases and pests early, such as novel sensors that detect plant odours and spectroscopy and biophotonics that are able to diagnose plant health and metabolism.
Most phytopathogenic fungi belong to the Ascomycetes and the Basidiomycetes. The fungi reproduce both sexually and asexually via the production of other structures. Spores may be spread long distances by air or water. Many soil inhabiting fungi are capable of living saprotrophically, carrying out the part of their life cycle in the soil; these are facultative saprotrophs. Fungal diseases may be controlled through the use of other agriculture practices. However, new races of fungi evolve that are resistant to various fungicides. Biotrophic fungal pathogens colonize living plant tissue and obtain nutrients from living host cells. Necrotrophic fungal pathogens infect and kill host tissue and extract nutrients from the dead host cells. Significant fungal plant pathogens include: Fusarium spp. Thielaviopsis spp. Verticillium spp. Magnaporthe grisea Sclerotinia sclerotiorum Ustilago spp. smut of barley Rhizoctonia spp. Phakospora pachyrhizi Puccinia spp. Armillaria spp; the oomycetes are fungus-like organisms.
They include some of the most destructive plant pathogens including the genus Phytophthora, which includes the causal agents of potato late blight and sudden oak death. Particular species of oomycetes are responsible for root rot. Despite not being related to the fungi, the oomycetes have developed similar infection strategies. Oomycetes are capable of using effector proteins to turn off a plant's defenses in its infection process. Plant pathologists group them with fungal pathogens. Significant oomycete plant pathogens include: Pythium spp. Phytophthora spp. including the potato blight of the Great Irish Famine Some slime molds in Phytomyxea cause important diseases, including club root in cabbage and its relatives and powdery scab in potatoes. These are caused by species of Spongospora, respectively. Most bacteria that are associated with plants are saprotrophic and do no harm to the plant itself. However, a small number, around 100 known species, are able to cause disease. Bacterial diseases are much more prevalent in tropical regions of the world.
Most plant pathogenic bacteria are rod-shaped. In order to be able to colonize the plant they have specific pathogenicity factors. Five main types of bacterial pathogenicity factors are known: uses of cell wall–degrading enzymes, effector proteins and exopolysaccharides. Pathogens such as Erwinia species use cell wall–degrading enzymes to cause soft rot. Agrobacterium species change the level of auxins to cause tumours with phytohormones. Exopolysaccharides are produced by bacteria and block xylem vessels leading to the death of the plant. Bacteria control the production of pathogenicity factors via quorum sensing. Significant bacterial plant pathogens: Burkholderia Proteobacteria Xanthomonas spp. Pseudomonas spp. Pseudomonas syringae pv. tomato causes tomato plants to produce less fruit, it "continues to adapt to the tomato by minimizing its recognition by the tomato immune system." Phytoplasma and Spiroplasma are genera of bacteria that lack cell walls and are related to the mycoplasmas, which are human pathogens.
Together they are referred to
Populus
Populus is a genus of 25–35 species of deciduous flowering plants in the family Salicaceae, native to most of the Northern Hemisphere. English names variously applied to different species include poplar and cottonwood. In the September 2006 issue of Science Magazine, the Joint Genome Institute announced that the western balsam poplar was the first tree whose full DNA code had been determined by DNA sequencing; the genus has a large genetic diversity, can grow from 15–50 m tall, with trunks up to 2.5 m in diameter. The bark on young trees is smooth, white to greenish or dark grey, has conspicuous lenticels; the shoots are stout, with the terminal bud present. The leaves are spirally arranged, vary in shape from triangular to circular or lobed, with a long petiole. Leaf size is variable on a single tree with small leaves on side shoots, large leaves on strong-growing lead shoots; the leaves turn bright gold to yellow before they fall during autumn. The flowers are dioecious and appear in early spring before the leaves.
They are borne in long, sessile or pedunculate catkins produced from buds formed in the axils of the leaves of the previous year. The flowers are each seated in a cup-shaped disk, borne on the base of a scale, itself attached to the rachis of the catkin; the scales are obovate and fringed, hairy or smooth, caducous. The male flowers are without calyx or corolla, comprise a group of four to 60 stamens inserted on a disk; the female flower has no calyx or corolla, comprises a single-celled ovary seated in a cup-shaped disk. The style is short, with two to four stigmata, variously lobed, numerous ovules. Pollination is by wind, with the female catkins lengthening between pollination and maturity; the fruit is a two- to four-valved dehiscent capsule, green to reddish-brown, mature in midsummer, containing numerous minute light brown seeds surrounded by tufts of long, white hairs which aid wind dispersal. Poplars of the cottonwood section are wetlands or riparian trees; the aspens are among the most important boreal broadleaf trees.
Poplars and aspens are important food plants for the larvae of a large number of Lepidoptera species. Pleurotus populinus, the aspen oyster mushroom, is found on dead wood of Populus trees in North America. Several species of Populus in the United Kingdom and other parts of Europe have experienced heavy dieback; the genus Populus has traditionally been divided into six sections on the basis of leaf and flower characters. Recent genetic studies have supported this, confirming some suspected reticulate evolution due to past hybridisation and introgression events between the groups; some species had differing relationships indicated by their nuclear DNA and chloroplast DNA sequences, a clear indication of hybrid origin. Hybridisation continues to be common in the genus, with several hybrids between species in different sections known. Populus section Populus – aspens and white poplar Populus adenopoda – Chinese aspen Populus alba – white poplar Populus × canescens – grey poplar Populus spp. X – Pacific albus Populus davidiana – Korean aspen Populus grandidentata – bigtooth aspen Populus sieboldii – Japanese aspen Populus tremula – aspen, common aspen, Eurasian aspen, European aspen, quaking aspen Populus tremuloides – quaking aspen or trembling aspen Populus section Aigeiros – black poplars, some of the cottonwoods Populus deltoides – eastern cottonwood Populus fremontii – Fremont cottonwood Populus nigra – black poplar, placed here by nuclear DNA.
Populus Populus × canadensis – hybrid black poplar Populus × inopina – hybrid black poplar Populus section Tacamahaca – balsam poplars Populus angustifolia – willow-leaved poplar or narrowleaf cottonwood Populus balsamifera – Balsam poplar Populus cathayana – Populus koreana J. Rehnder – Korean poplar Populus laurifolia – laurel-leaf poplar Populus maximowiczii A. Henry – Maximowicz' poplar, Japanese poplar Populus simonii – Simon's poplar Populus suaveolens Fischer – Mongolian poplar Populus szechuanica – Sichuan poplar, placed here by nuclear DNA. Aigeiros Populus trichocarpa – western balsam poplar or black cottonwood Populus tristis, placed here by nuclear DNA.
Frost crack
Frost crack or Southwest canker is a form of tree bark damage sometimes found on thin barked trees, visible as vertical fractures on the southerly facing surfaces of tree trunks. Frost crack is distinct from sun scald and sun crack and physically differs from normal rough-bark characteristics as seen in mature oaks, pines and other tree species; the sloughing or peeling of the bark is a normal process in the spring when the tree begins to grow. The outer layers of the bark are dead tissue and therefore they cannot grow, the outer bark splitting in order for the tree to grow in circumference, increasing its diameter; the inner bark cambium and phloem tissues are living, form a new protective layer of cells as the outer bark pulls apart. Normal furrowed bark has a layer of bark over the wood below, however bark may peel or fall off the tree in sheets, strips or blocks. Frost cracks are the result of some sort of weakness in the bark which occurred to the tree earlier. In late winter and early spring, water in the phloem, known as the inner bark and in the xylem, known as the wood and contracts under significantly fluctuating temperatures.
Wood, in some way damaged does not contract to the same degree as healthy wood. Rapid expansion and contraction of water within the wood and bark under falling night temperatures, can result in a frost crack accompanied by a loud explosive report. Research suggests that the main cause is actually'frost-shrinkage' due to the freezing-out of cell wall moisture into lumens of wood cells. Other causes are the expansion of freezing water in cell lumens, additionally the formation of ice lenses within wood; as stated, previous defects such as healed wounds, branch stubs, etc. in tree trunks function as stress raisers and trigger the frost cracking. In winter when the sun sets or the sky clouds over, the temperature of the tree drops quickly and as the bark cools more and the wood contracts more the bark rips open in a long crack, sometimes with an audible report likened to a rifle crack. Cold, sunny days are the most to result in frost cracking as the heat energy from the low Sun on a Winter day can be higher than any other time of year.
Trees that are growing in poorly drained sites are more subject to frost cracking than are those growing in drier, better drained soils. Trees left exposed by felling are susceptible. Although frost cracks may be up to several metres long, these cracks only become apparent in early spring; these cracks may heal in the summer and be reopen again in the winters, so that successive cracking and healing over a number of years results in the formation of'frost ribs' on the sides of affected trees. The wood beneath the frost crack is damaged; the cracks originate at the base of the trunk and extends from a metre to several metres upwards. Some discoloration is found at the site of the damage. Frost cracks act as sites of entry for wood decay organisms, including insects and bacteria. Timber damaged in this way is unsuitable for use in buildings, etc. Species such as crab-apple, walnut, maples, horse-chestnut and lime are prone to developing frost crack given the right conditions. Avoiding the use of fertilizers late in the growing season can reduce the incidence of splits protecting the bark of young trees from physical damage such as that caused by lawn mowers, car bumpers, grazing animals, strimmers, etc.
Protect young trees in winter with paper tree wrap from ground level to the first main branches. Most tree species try to seal the edges of wounds by forming a callus layer; the wound's edges begin to form this callus during the first growing season after that crack appears and the callus layer will continue to grow and after many years, the wound may close over entirely. Exploding tree Video footage and commentary on Frost Crack
Burl
A burl or bur or burr is a tree growth in which the grain has grown in a deformed manner. It is found in the form of a rounded outgrowth on a tree trunk or branch, filled with small knots from dormant buds. A burl results from a tree undergoing some form of stress, it may be caused by an virus or fungus. Most burls grow beneath the ground, attached to the roots as a type of malignancy, not discovered until the tree dies or falls over; such burls sometimes appear as groups of bulbous protrusions connected by a system of rope-like roots. All burl wood is covered by bark if it is underground. Insect infestation and certain types of mold infestation are the most common causes of this condition. In some tree species, burls can grow to great size; the largest, at 26 ft, can encircle the entire trunk. The world's second-largest burls can be found in British Columbia. One of the largest burls known was found around 1984 in the small town of New South Wales, it stands 6.4 ft tall, with an odd shape resembling a trombone.
In January 2009, this burl was controversially removed from its original location, relocated to a public school in the central New South Wales city of Dubbo. Burls yield a peculiar and figured wood, prized for its beauty and rarity, it is sought after by furniture makers and wood sculptors. There are a number of well-known types of burls; the famous birdseye maple of the sugar maple superficially resembles the wood of a burl but is something else entirely. Burl wood is hard to work with hand tools or on a lathe because its grain is twisted and interlocked, causing it to chip and shatter unpredictably; this "wild grain" makes burl wood dense and resistant to splitting, which made it valued for bowls, mauls and "beetles" or "beadles" for hammering chisels and driving wooden pegs. Burls are harvested with saws or axes for smaller specimens and timber felling chainsaws and tractors for massive ones; because of the value of burls, ancient redwoods in National Parks in Western United States have been poached by thieves for their burls, including at Redwood National and State Parks.
Poachers cut off the burls from the sides of the trunks using chainsaws, which exposes the tree to infection and disease, or fell the entire tree to steal burls higher up. Because of risk of poaching, Jeff Denny, the state park’s redwood coast sector supervisor, encourages those buying burl to inquire where it came from and to ensure it was obtained legally. Legal acquisition methods for burl include trees from private land cleared for new development and from lumber companies with salvage permits. Amboyna burl is a expensive type of burl, much more than bigleaf maple burl, for example, it comes from padauk trees of Southeast Asia. Padauk trees are quite common but burl wood is rare; the amboyna is a deep red, although the more rare moudui burl is the same species but the color is from golden yellow to yellow-orange. The sapwood is creamy white with brown streaks; the common use for amboyna is interiors for luxury vehicles, cabinets and furniture. Canker Forest pathology Gall Corbett, Stephen; the Illustrated Professional Woodworker.
London: Anness Publishing. ISBN 978-0-681-22891-7. Powers, Steven S.. North American Burl Treen: Colonial & Native American. Brooklyn: S. Scott Powers Antiques. ISBN 978-0-9760635-0-6. James, Susanne. "Lignotubers and Burls: Their Structure and Ecological Significance in Mediterranean Ecosystems". Botanical Review. 50: 225–66. Doi:10.1007/BF02862633. JSTOR 4354037. Rankin, William Howard. "Mistletoe Burl and Witches'-Broom". Manual of Tree Diseases. Pp. 214–5. OCLC 1652501. White PR. "A Tree Tumor of Unknown Origin". Proceedings of the National Academy of Sciences of the United States of America. 44: 339–44. Bibcode:1958PNAS...44..339W. Doi:10.1073/pnas.44.4.339. JSTOR 89803. PMC 335423. PMID 16590202. Zalasky, Harry. "Low-temperature-induced cankers and burls in test conifers and hardwoods". Canadian Journal of Botany. 53: 2526–35. Doi:10.1139/b75-277. Funk, A.. "Therrya canker of spruce in British Columbia". Canadian Journal of Plant Pathology. 4: 357–61. Doi:10.1080/07060668209501277. White PR, Millington WF. "The distribution and possible importance of a woody tumor on trees of the white spruce, Picea glauca".
Cancer Research. 14: 128–34. PMID 13126948. Video footage of tree burrs
Bleeding canker of horse chestnut
Bleeding canker of horse chestnut is a common canker of horse chestnut trees, known to be caused by infection with several different pathogens. Infections by the gram-negative fluorescent bacterium Pseudomonas syringae pathovar aesculi are a new phenomenon, have caused most of the bleeding cankers on horse chestnut that are now seen in Britain. Pseudomonas syringae pv. Aesculi is a bacterium; the pathogen can survive in the soil for about a year. It is spread by water and tools that were used on the infected tree, it causes lesions on the bark of the tree that can be near the base of higher. The bleeding from the cankers occurs in the spring and fall. Infection of the tree through lenticels and leaf scars when inoculated in a study occurred most in the spring and summer. In contrast, lesion growth from an artificial wound was less severe in the summer; the lesions developed the most during the dormant period of the tree. Development of the disease occurs throughout the year; the disease starts with local lesions, but becomes systematic when it affects of crown of the tree after several years of infection.
This is a bacterium. The pathogen is spreading across western Europe though movement by wind blown rain. In the past few years, the bacterial pathogen Pseudomonas syringae pv. aesculi has emerged as a new and virulent agent for this disease in Western Europe. Specific to horse chestnut trees, this pathogen infects the bark around main branches; as it spreads, it cuts off the water supply to the crown. This particular infective agent emerged in the past few years, has now spread to infect many trees in Western Europe; the outbreak was attributed to Phytophthora, until DNA tests suggested that a pathovar of Pseudomonas syringae was responsible. The disease has risen markedly in the UK since 2003, now one half of all horse chestnuts in Great Britain are affected and showing symptoms to some degree; the disease is spreading at an alarming rate in the Netherlands, where one third of all horse chestnuts are affected to a greater or lesser extent. A similar upsurge is reported in France. Management of Bleeding Canker of Chestnut is not definitive and treatments are being investigated.
Because the pathogen can be spread by contaminated tools, cultural practices are important to management. Tools should be used with caution after being used on infected trees. Recovery of trees is possible, so management strategies are focused on keeping trees healthy so they can recover. One recommendation is to add fertilizer. Soil de-compaction, providing good drainage, mulching to minimize fluctuation of soil temperature and moisture are all ways to improve or maintain tree health and to manage the pathogen. Chemical methods can be used to help the tree avoid progress of the disease. Management strategies are being developed. A study performed in 2015 examined the infection on trees and found that 41 F1 progeny parent tree source had the most promising lines of viability for resistance. Effective Heat methods: Heating up the bark of the trunk of the Chestnut trees with warm water or heat blankets of Chestnut Tree Treatment. Heat Trial in Station Dordrecht Zuid: established success in the laboratory by Wageningen Plant Research.
After heating up the bacterium for two days at 40° Celsius the bacterium was no longer able to continue to grow and multiply. Seedlings were able to restore their wounds. Packing of chestnut trees with water or heat blankets is used in studies to improve the effectiveness of the Heat treatment to larger chestnut trees. Larger scale tests of the Heat method with electric blankets of Chestnut Tree Treatment are being investigated for public Chestnut Trees in the Dutch Amsterdam Region, see the map here: The Horse Chestnut is considered an economically and important tree, it is estimated. Many are urban, in gardens, they are desirable because they can tolerate many conditions including dry sandy soils, wet clays and chalk. The tree is economically important because it contains aescin which can be used for its anti-inflammatory properties. Wildlife benefit from the nuts the tree provides. UK Forest Research Kew Royal Botanical Gardens- Indian horse chestnut Forestry Commission Website Working group Aesculaap
Willow
Willows called sallows and osiers, form the genus Salix, around 400 species of deciduous trees and shrubs, found on moist soils in cold and temperate regions of the Northern Hemisphere. Most species are known as willow, but some narrow-leaved shrub species are called osier, some broader-leaved species are referred to as sallow; some willows are creeping shrubs. Willows all have abundant watery bark sap, charged with salicylic acid, soft pliant, tough wood, slender branches, large, fibrous stoloniferous roots; the roots are remarkable for their toughness and tenacity to live, roots sprout from aerial parts of the plant. The leaves are elongated, but may be round to oval with serrated edges. Most species are deciduous. All the buds are lateral; the buds are covered by a single scale. The bud scale is fused into a cap-like shape, but in some species it wraps around and the edges overlap; the leaves are simple, feather-veined, linear-lanceolate. They are serrate, rounded at base, acute or acuminate; the leaf petioles are short, the stipules very conspicuous, resembling tiny, round leaves, sometimes remaining for half the summer.
On some species, they are small and caducous. In color, the leaves show a great variety of greens. Willows are dioecious, with male and female flowers appearing as catkins on separate plants; the staminate flowers are without either calyx with corolla. This scale is square and hairy; the anthers are orange or purple after the flower opens. The filaments are threadlike pale brown, bald; the pistillate flowers are without calyx or corolla, consist of a single ovary accompanied by a small, flat nectar gland and inserted on the base of a scale, borne on the rachis of a catkin. The ovary is one-celled, the style two-lobed, the ovules numerous. All willows take root readily from cuttings or where broken branches lie on the ground; the few exceptions include the goat peachleaf willow. One famous example of such growth from cuttings involves the poet Alexander Pope, who begged a twig from a parcel tied with twigs sent from Spain to Lady Suffolk; this twig was planted and thrived, legend has it that all of England's weeping willows are descended from this first one.
Willows are planted on the borders of streams so their interlacing roots may protect the bank against the action of the water. The roots are much larger than the stem which grows from them. Willows have a wide natural distribution from the tropics to the arctic zones and are extensively cultivated around the world. Willows are cross-compatible, numerous hybrids occur, both and in cultivation. A well-known ornamental example is the weeping willow, a hybrid of Peking willow from China and white willow from Europe; the hybrid cultivar'Boydii' has gained the Royal Horticultural Society's Award of Garden Merit. Numerous cultivars of Salix L. have been named over the centuries. New selections of cultivars with superior technical and ornamental characteristics have been chosen deliberately and applied to various purposes. Most Salix has become an important source for bioenergy production and for various ecosystem services; the first edition of the Checklist for Cultivars of Salix L. was compiled in 2015, which includes 854 cultivar epithets with accompanying information.
The International Poplar Commission of the FAO UN holds the International Cultivar Registration Authority for the genus Salix. The ICRA for Salix produces and maintains The International Register of Cultivars of Salix L.. Willows are used as food plants by the larvae of some Lepidoptera species, such as the mourning cloak butterfly. Ants, such as wood ants, are common on willows inhabited by aphids, coming to collect aphid honeydew, as sometimes do wasps. A small number of willow species were planted in Australia, notably as erosion-control measures along watercourses, they are now regarded as invasive weeds which occupy extensive areas across southern Australia and are considered'Weeds of National Significance'. Many catchment management authorities are replacing them with native trees. Substantial research undertaken from 2006 has identified that willows inhabit an unoccupied niche when they spread across the bed of shallow creeks and streams and if removed, there is a potential water saving of up to 500 ML/per year per hectare of willow canopy area, depending on willow species and climate zone.
This water could benefit the environment or provision of local water resources during dry periods. To aid management of willows, a remote sensing method has been developed to map willow area along and in streams a
Fusarium circinatum
Fusarium circinatum is a fungal plant pathogen that causes the serious disease pitch canker on pine trees and Douglas fir. The most common hosts of the pathogen include slash pine, loblolly pine, Monterey pine, Mexican weeping pine, Douglas fir. Like other Fusarium species in the phylum Ascomycota, it is the asexual reproductive state of the fungus and has a teleomorph, Gibberella circinata; this fungus is believed to have originated in Mexico. It by 1986 had reached the western United States, it was first recorded in Japan in the 1980s, in South Africa in 1990, in Chile and Spain in the mid 1990s and in Italy in 2007. In California this canker has been recorded on Douglas fir. In Europe and Asia it has been recorded on over 30 other Pinus species. Monterey pine seems to be the most susceptible species, in California 85% of the native Monterey pine forests were thought to be threatened by the disease; because of the activation of systemic acquired resistance in native Monterey pine trees, the impacts of the disease in California have been mitigated.
F. circinatum infects the branches of pine trees, causing a bark canker. Most infection is by microconidia; the macroconidia are 3-septate, with curved walls and the microconidia are single-celled and borne in false heads on aerial polyphialides. The aerial mycelium is white or pale violet colour and twisted below the proliferation of microconidiophores. In culture, perithecia are produced, they are black and ovoid. Cylindrical asci are released by oozing. There are eight ascospores which are ellipsoidal to fusiform; because peritheca have not been observed in the field, it is not thought that ascospores are an important route for infection. The infection is carried from tree to tree by the rain, the wind or by bark-feeding insects; these including weevils in the genus Pityophthorus and bark beetles in the genera Ips and Conophthorus. These insects infect pine trees and the adults may disperse the pathogen. Additionally, these insects cause a wound when feeding and this may facilitate entry of the infection.
Warmth and moisture encourage the development of the disease whereas cooler drier conditions restrict it. In California it is more severe in coastal areas. Research was undertaken to see whether spores from the telemorph, Gibberella circinata, might be responsible for spread of the fungus, it was found that few vegetative compatibility groups existed among the California strains of the pathogen. This implied that laboratory tests confirmed this; the various symptoms of F. circinatum can help identify and distinguish it from other pathogens or common Pinus diseases. The symptoms are similar to other damping off diseases with seedlings wilting and dying and exuding resin from the root collar areas. Drooping from the resin production and the plant’s resistance mechanism can be observed along with die-back near the apical meristem. A discoloration of the stem and needles is present, with plants exhibiting purple or blue shades. Other symptoms include chlorosis of the needles turning a reddish brown color and lesions on the stems, root collars, tap roots.
Host factors that can trigger infection include plant stress with excessive nitrogen in the soil, unbalanced watering cycles, warmer temperatures, wounds from pruning or insect damage. Numerous plant pathologists have noted F. circinatum as a serious threat to the pine tree species. Due to the high tree mortality rate, reduced growth, degradation of wood quality, the economic and ecological importance are affected by this disease. Not only can the spread of infection go from branch to branch, but infect pine seeds, leading to damping-off of younger seedlings and resulting in death from the fungal infection; the environmental interactions that take place to favor the spread and development of this disease play a large role in transmission. Factors such as soil nutrient ratio, abiotic stressors, air pollution and humidity can all contribute to the spread of this disease. In Chile, the infection was first reported on Pinus radiata in nurseries and was thought to be due to the import of contaminated seed.
Seedlings could be infected by soil-borne contamination. A few years the disease had not spread to mature stands of trees; the same is true in South Africa, where it was reported to infect nursery stock but not forest trees. F. Circinatum is spread locally by wind and insects. Over large distances it can be transported by young plants. Although it could be carried as infected timber, this is considered unlikely if the bark has been removed. If timber had been a significant means of infection, the fungus would have spread more to other parts of the world as there is a considerable trade in pine; the vectors for this disease, such as insects, rely on whether or not the species is indigenous to where the pine is located. There are different ranges of susceptibility that can interact within the environment. Bishop pine has a more extensive range of susceptibility compared to Monterey pine, which serves as a “host bridge” to more northern locations for susceptible Pinus species. Several strategies are being used to help decrease the spread of F. circinatum.
Irrigation water can be chemically treated with a chlorination ozone treatment. Following corrected pH levels in water, it is recommended that 2-3 ppm of chlorine be
