Macrophomina phaseolina | |
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Macrophomina phaseolina spores growing on Pinus | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Fungi |
Division: | Ascomycota |
Class: | Dothideomycetes |
Order: | Botryosphaeriales |
Family: | Botryosphaeriaceae |
Genus: | Macrophomina |
Species: | M. phaseolina |
Binomial name | |
Macrophomina phaseolina (Tassi) Goid. (1947) | |
Synonyms | |
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Macrophomina phaseolina is a Botryosphaeriaceae plant pathogen fungus that causes damping off, seedling blight, collar rot, stem rot, charcoal rot, basal stem rot, and root rot on many plant species.
One of the most harmful seed and soil borne pathogens, Macrophomina phaseolina is a fungus that infects nearly 500 plant species in more than 100 families. [2] The hosts include: peanut, cabbage, pepper, chickpea, soybean, sunflower, sweet potato, alfalfa, sesame, potato, sorghum, wheat, and corn, among others. [3] The identification of isolates of M. phaseolina is usually based on morphology and efforts to divide the pathogen into subspecies, but because there are wide intraspecific variations in the phenotype of the isolates, these criteria are often not reliable. [2] The failure to correctly detect and identify M. phaseolina using conventional culture-based morphological techniques has led scientists to develop nucleic acid-based molecular approaches, such as highly sensitive and specific polymerase chain reaction-based methods. [4] [5] Researchers have also recently created species-specific oligonucleotide primers [6] and digoxigenin-labeled probes [6] in hopes of better identifying and detecting M. phaseolina. [5]
The pathogen M. phaseolina affects the fibrovascular system of the roots and basal internodes of its host, impeding the transport of water and nutrients to the upper parts of the plant. [7] As a result, progressive wilting, premature dying, loss of vigor, and reduced yield are characteristic symptoms of M. phaseolina infection. [8] The fungus also causes many diseases like damping off, seedling blight, collar rot, stem rot, charcoal rot, basal stem rot, and root rot. [2] Although brown lesions may form on the hypocotyls or emerging seedlings, many symptoms occur during or after flowering, including grey discoloration of the stem and taproots, shredding of plant tissue in the stem and top of the taproot, and hollowing of the stem. [8] Small black dots may form beneath the epidermis of the lower stem and in the taproot, giving the stems and roots a charcoal-sprinkled appearance. [8] When the epidermis is removed, small and black microsclerotia (a sign of the disease) may be so numerous that they give a greyish-black tint to the plant tissue. [8] In addition, reddish-brown discoloration and black streaks can form in the pith and vascular tissues of the root and stem. [8]
Macrophomina phaseolina has a monocyclic disease cycle.
The M. phaseolina fungus has aggregates of hyphal cells, which form microsclerotia within the taproots and stems of the host plants. [7] The microsclerotia overwinter in the soil and crop residue and are the primary source of inoculum in the spring. [9] They have been shown to survive in the soil for up to three years. [3] They are black, spherical or oblong structures that allow the persistence of the fungus under poor conditions, such as low soil nutrient levels and temperatures above 30 C. [3] However, in wet soils, microsclerotia survival is significantly lower, often surviving no more than 7 to 8 weeks, and mycelium cannot survive more than 7 days. [3] Additionally, infected seeds can carry the fungus in their seed coats. [3] These infected seeds either do not germinate or produce seedlings that die soon after emergence. [3]
Macrophomina phaseolina is a heat- and drought-favoring disease, producing large quantities of microsclerotia under relatively low water potentials and relatively high temperatures. [3] In soybeans especially, charcoal rot typically occurs when the plants are experiencing significant drought stress. [3]
When conditions are favorable, hyphae germinate from these microsclerotia. [10] Germination of the microsclerotia occurs throughout the growing season when temperatures are between 28 and 35 C. [3] Microsclerotia germinate on the roots' surface, and germ tubes on the end of the microsclerotia form appresoria that penetrate the hosts' epidermal cell walls using turgor pressure or through natural openings. [3]
The hyphae infect the roots of the host plant. Initially, the hyphae enter the cortical tissue and grow intercellularly, then infect the roots and the vascular tissue. [3] Within the vascular tissue, mycelia and sclerotia are produced and plug the vessels. [2] This causes the greyish-black color often observed in plants infected by M. phaseolina, and it also prevents water and nutrients from being transported from the roots to the upper parts of the plant. [9] Thus, due to this systemic infection, diseased plants often wilt and die prematurely.
Understanding the monocyclic disease cycle of M. phaseolina can help plant pathologists better understand the pathogen itself, it can help horticulturalists develop disease-resistant crops, and it can help farmers understand at what point during the growing cycle to apply fungicides or implement other management techniques.
There are several techniques currently used to manage M. phaseolina fungal infections. Often, fungicides are used to inhibit mycelial growth. These include thiram, iprodione, carbendazim, pyraclostrobin, fluquinconazol, tolyfluanid, and metalaxyl and penflufen + trifloxystrobin. [5] The active ingredients carbendazim and penflufen + trifloxystrobin were shown to be the most powerful to control M. phaseolina. [5] In this same study, the M. phaseolina isolate showed insensitivity to the active ingredients fluquinconazole, metalaxyl, thiram and tolyfluanid. Thus, fungicides are not necessarily an effective way to manage this fungal pathogen.
However, there are alternatives to fungicides that are especially preferred by organic farmers, such as a combination of soil solarization and organic amendment. [11] Soil solarization is a method of using solar power for controlling pathogens in the soil by mulching the soil and covering it with a large, usually transparent polyethylene tarp to trap solar energy and heat the soil. In studies, this method has proven to be as effective as fungicides. [11] Additionally, crop rotation can be an effective management practice. According to researchers, "Rotation out of soybeans for three years may effectively reduce microsclerotia numbers and is useful for managing charcoal rot" because "corn is not as good of a host to M. phaseolina as soybean so rotation with corn for three years may help reduce populations but not eliminate the pathogen from the soil." [3] Finally, tillage practices can reduce moisture in the soil and make the environment less favorable for the pathogen. [3]
This organism has been reported to cause infection in humans, particularly in immunosuppressed patients. The infection may present as a cutaneous cellulitis or as an ocular keratitis. [12]
Phytophthora sojae is an oomycete and a soil-borne plant pathogen that causes stem and root rot of soybean. This is a prevalent disease in most soybean growing regions, and a major cause of crop loss. In wet conditions the pathogen produces zoospores that move in water and are attracted to soybean roots. Zoospores can attach to roots, germinate, and infect the plant tissues. Diseased roots develop lesions that may spread up the stem and eventually kill the entire plant. Phytophthora sojae also produces oospores that can remain dormant in the soil over the winter, or longer, and germinate when conditions are favourable. Oospores may also be spread by animals or machinery.
Rhizoctonia solani is a species of fungus in the order Cantharellales. Basidiocarps are thin, effused, and web-like, but the fungus is more typically encountered in its anamorphic state, as hyphae and sclerotia. The name Rhizoctonia solani is currently applied to a complex of related species that await further research. In its wide sense, Rhizoctonia solani is a facultative plant pathogen with a wide host range and worldwide distribution. It causes various plant diseases such as root rot, damping off, and wire stem. It can also form mycorrhizal associations with orchids.
Damping off is a horticultural disease or condition, caused by several different pathogens that kill or weaken seeds or seedlings before or after they germinate. It is most prevalent in wet and cool conditions.
Aphanomyces euteiches is a water mould, or oomycete, plant pathogen responsible for the disease Aphanomyces root rot. The species Aphanomyces euteiches can infect a variety of legumes. Symptoms of the disease can differ among hosts but generally include reduced root volume and function, leading to stunting and chlorotic foliage. Aphanomyces root rot is an important agricultural disease in the United States, Europe, Australia, New Zealand, and Japan. Management includes using resistant crop varieties and having good soil drainage, as well as testing soil for the pathogen to avoid infected fields.
Pythium irregulare is a soil borne oomycete plant pathogen. Oomycetes, also known as "water molds", are fungal-like protists. They are fungal-like because of their similar life cycles, but differ in that the resting stage is diploid, they have coenocytic hyphae, a larger genome, cellulose in their cell walls instead of chitin, and contain zoospores and oospores.
Gibberella zeae, also known by the name of its anamorph Fusarium graminearum, is a fungal plant pathogen which causes fusarium head blight (FHB), a devastating disease on wheat and barley. The pathogen is responsible for billions of dollars in economic losses worldwide each year. Infection causes shifts in the amino acid composition of wheat, resulting in shriveled kernels and contaminating the remaining grain with mycotoxins, mainly deoxynivalenol (DON), which inhibits protein biosynthesis; and zearalenone, an estrogenic mycotoxin. These toxins cause vomiting, liver damage, and reproductive defects in livestock, and are harmful to humans through contaminated food. Despite great efforts to find resistance genes against F. graminearum, no completely resistant variety is currently available. Research on the biology of F. graminearum is directed towards gaining insight into more details about the infection process and reveal weak spots in the life cycle of this pathogen to develop fungicides that can protect wheat from scab infection.
Pythium aphanidermatum is a soil borne plant pathogen. Pythium is a genus in the class Oomycetes, which are also known as water molds. Oomycetes are not true fungi, as their cell walls are made of cellulose instead of chitin, they are diploid in their vegetative state, and they form coenocytic hyphae. Also, they reproduce asexually with motile biflagelette zoospores that require water to move towards and infect a host. Sexually, they reproduce with structures called antheridia, oogonia, and oospores.
Sclerotinia sclerotiorum is a plant pathogenic fungus and can cause a disease called white mold if conditions are conducive. S. sclerotiorum can also be known as cottony rot, watery soft rot, stem rot, drop, crown rot and blossom blight. A key characteristic of this pathogen is its ability to produce black resting structures known as sclerotia and white fuzzy growths of mycelium on the plant it infects. These sclerotia give rise to a fruiting body in the spring that produces spores in a sac which is why fungi in this class are called sac fungi (Ascomycota). This pathogen can occur on many continents and has a wide host range of plants. When S. sclerotiorum is onset in the field by favorable environmental conditions, losses can be great and control measures should be considered.
Aphanomyces cochlioides is a plant pathogen that can affect commodity crops like spinach, Swiss chard, beets and related species. In spinach the pathogen is responsible for the black root "rot" that can damage plants.
Phytophthora capsici is an oomycete plant pathogen that causes blight and fruit rot of peppers and other important commercial crops. It was first described by L. Leonian at the New Mexico State University Agricultural Experiment Station in Las Cruces in 1922 on a crop of chili peppers. In 1967, a study by M. M. Satour and E. E. Butler found 45 species of cultivated plants and weeds susceptible to P. capsici In Greek, Phytophthora capsici means "plant destroyer of capsicums". P. capsici has a wide range of hosts including members of the families Solanaceae and Cucurbitaceae as well as Fabaceae.
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Pyrenochaeta terrestris is a fungal plant pathogen that infects maize, sweet potatoes, and strawberries. This plant pathogen causes a disease in onion that is commonly called pink root. P. terrestris is also known to infect shallots, garlic, leeks, chives, cantaloupe, carrots, cauliflower, cowpea, cucumbers, eggplants, lima beans, millet, oats, peas, peppers, potatoes, spinach, sugarcane, and tomatoes.
Sporisorium reilianum Langdon & Full., (1978), previously known as Sphacelotheca reiliana, and Sporisorium reilianum, is a species of biotrophic fungus in the family Ustilaginaceae. It is a plant pathogen that infects maize and sorghum.
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This article summarizes different crops, what common fungal problems they have, and how fungicide should be used in order to mitigate damage and crop loss. This page also covers how specific fungal infections affect crops present in the United States.
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Stromatinia cepivora is a fungus in the division Ascomycota. It is the teleomorph of Sclerotium cepivorum, the cause of white rot in onions, garlic, and leeks. The infective sclerotia remain viable in the soil for many years and are stimulated to germinate by the presence of a susceptible crop.
Gummy stem blight is a cucurbit-rot disease caused by the fungal plant pathogen Didymella bryoniae. Gummy stem blight can affect a host at any stage of growth in its development and affects all parts of the host including leaves, stems and fruits. Symptoms generally consist of circular dark tan lesions that blight the leaf, water soaked leaves, stem cankers, and gummy brown ooze that exudes from cankers, giving it the name gummy stem blight. Gummy stem blight reduces yields of edible cucurbits by devastating the vines and leaves and rotting the fruits. There are various methods to control gummy stem blight, including use of treated seed, crop rotation, using preventative fungicides, eradication of diseased material, and deep plowing previous debris.
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