| Alternaria helianthi | |
|---|---|
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Fungi |
| Division: | Ascomycota |
| Class: | Dothideomycetes |
| Order: | Pleosporales |
| Family: | Pleosporaceae |
| Genus: | Alternaria |
| Species: | A. helianthi |
| Binomial name | |
| Alternaria helianthi (Hansf.) Tubaki & Nishih., (1969) | |
| Synonyms | |
Helminthosporium helianthiHansf.,(1943) Contents | |
Alternaria helianthi is a fungal plant pathogen causing a disease in sunflowers known as Alternaria blight of sunflower.
Alternaria spp. plant pathogens are found across the world, affecting a variety of species, including sunflowers. It is a major defoliating pathogen in warm humid climates like India and Africa. [1] Farmers and businesses produce sunflowers ( Helianthus spp.) for manufacturing oil, edible seeds, and ornamental flowers displays. There are a couple of diseases that threaten the production of sunflowers.
Leaf blight of sunflowers is one of the most devastating diseases for sunflowers and is caused by Alternaria helianthi (Hansford) Tubaki and Nishihara, a seed-borne pathogenic fungus. It was recorded in Japan and was the same as a fungus collected earlier on sunflower in Argentina, India, Tanzania, Uganda and Zambia. [2] [3] Transportation of infected sunflowers and agricultural practices spread the pathogen worldwide and cause disasters in places, like India, where sunflowers are a main source of oil production. [3] The pathogen that causes this disease is part of the Alternaria genus, it is ubiquitous and abundant and can cause a high mycotoxicological risk during harvest, which causes devastation to entire crop production. [3]
Alternaria helianthi is an ascomycete from the Pleosporaceae family. [4] This pathogen produces simple, meaning rarely branched conidiophores, that bear solitary conidia. These conidia are light brown colored, ellipsoid or broadly ovoid, and rarely form longitudinal septa. [4]
There are eight different species that cause yield loss of sunflowers; however, Alternaria helianthi is the primary causal agent and most widespread. [5] The main hosts are sunflowers (Helianthus annuus); however, it has been proven that safflower (Carthamus tinctorius), noogoora burr (Xanthium pungens), cocklebur (Xanthium strumarium), and Bathurst burr (Xanthium spinosum) can serve as alternative hosts for the pathogen. [4] [5]
Leaf spots start as small, dark, and angular that eventually turn into necrotic areas that result in defoliation. Defoliation is most prevalent starting at lower leaves, where the microclimate is most favorable. [5] Dark brown lesions are found on leaves, stems, petioles, and bracts. Stem lesions are normally narrow (1-3mm) black streaks that get up to 3 cm long. The pathogen may cause linear spots on stems and water-soaked, sunken lesions on the back of the sunflower head. Some spots could have yellow halo around the spots. [4] Infection causes destruction of the flowers and early senescence. [4]
This pathogen overwinters on infected plant residues, but wild sunflowers may also serve as reservoirs. All species, including Alternaria helianthi, may also be seedborne. Alternaria spp. have no sexual or perfect stage. They multiply asexually through the method of sporulation. By producing one or more germ tubes, the conidia are germinated. [6] Disease progression heavily relies on the duration of leaf wetness following initial infection, as the germination of new spores can occur within days. Germination occurs best at temperatures less than 26 degrees C and require a minimum of 4 hours of leaf wetness for sporulation. [3] The pathogen is dispersed and spread via windblown or water-splashed onto lower leaves of the sunflower. [3] Young seedlings are more susceptible, but lower leaves on mature plants frequently are defoliated by Alternaria spp.. [3]
Germ tubes are produced by the conidia and grow across the leaf surface before forming an appressorium. [6] The fungus will then enter the host by penetrating through the cuticle and epidermis. It has also been observed that penetration through wounds and stomates can occur. [6] The conidiophores then develop through the collapsed stomates. Conidiophores are 12 to 50 micrometers long and rise singly or in branches. [7] The conidia will emerge through the stomata and trichomes. [4] At this stage, the conidia produced will cause secondary infection and spread to other healthy plants. [4] Under certain conditions, micro-cyclic conidia can be produced directly from the parent conidia.[ citation needed ]
There are three main types of control for Alternaria helianthi: cultural practices, fungicides, and resistance. Cultural practices include removing wild and volunteer sunflower hosts, minimizing dampness/wetness of leaves, and removal of previous sunflower residues found in the soil. [5] The destruction of the plant residue will eliminate the source of inoculum. [4] Additionally, crop rotation with non-Asteraceae crops or allowing for fallow periods can assist in management. [4] There is an option for seed treatments; however, the use of multiple applications of different fungicides are more effective. [5] Finally, oilseed sunflowers have been found with disease resistance, so there could be a possibility of hybrid sunflowers incorporating the resistance into other sunflower species. [5]
Diplocarpon rosae is a fungus that creates the rose black spot disease. Because it was observed by people of various countries around the same time, the nomenclature for the fungus varied with about 25 different names. The asexual stage is now known to be Marssonina rosae, while the sexual and most common stage is known as Diplocarpon rosae.
Alternaria alternata is a fungus causing leaf spots, rots, and blights on many plant parts, and other diseases. It is an opportunistic pathogen on over 380 host species of plant.
Alternaria triticina is a fungal plant pathogen that causes leaf blight on wheat. A. triticina is responsible for the largest leaf blight issue in wheat and also causes disease in other major cereal grain crops. It was first identified in India in 1962 and still causes significant yield loss to wheat crops on the Indian subcontinent. The disease is caused by a fungal pathogen and causes necrotic leaf lesions and in severe cases shriveling of the leaves.
Stemphylium solani is a plant pathogen fungus in the phylum Ascomycota. It is the causal pathogen for grey leaf spot in tomatoes and leaf blight in alliums and cotton, though a wide range of additional species can serve as hosts. Symptoms include white spots on leaves and stems that progress to sunken red or purple lesions and finally leaf necrosis. S. solani reproduces and spreads through the formation of conidia on conidiophores. The teleomorph name of Stemphyllium is Pleospora though there are no naturally known occurrences of sexual reproduction. Resistant varieties of tomato and cotton are common, though the pathogen remains an important disease in Chinese garlic cultivation.
Diaporthe helianthi is a fungal pathogen that causes Phomopsis stem canker of sunflowers. In sunflowers, Phomopsis helianthi is the causative agent behind stem canker. Its primary symptom is the production of large canker lesions on the stems of sunflower plants. These lesions can eventually lead to lodging and plant death. This disease has been shown to be particularly devastating in southern and eastern regions of Europe, although it can also be found in the United States and Australia. While cultural control practices are the primary method of controlling for Stem Canker, there have been a few resistant cultivars developed in regions of Europe where the disease is most severe.
Ascochyta is a genus of ascomycete fungi, containing several species that are pathogenic to plants, particularly cereal crops. The taxonomy of this genus is still incomplete. The genus was first described in 1830 by Marie-Anne Libert, who regarded the spores as minute asci and the cell contents as spherical spores. Numerous revisions to the members of the genus and its description were made for the next several years. Species that are plant pathogenic on cereals include, A. hordei, A. graminea, A. sorghi, A. tritici. Symptoms are usually elliptical spots that are initially chlorotic and later become a necrotic brown. Management includes fungicide applications and sanitation of diseased plant tissue debris.
Alternaria carthami is a necrotrophic plant pathogen of safflower. The fungus is in the order Pleosporales and family Pleosporaceae. It was first isolated in India, has spread globally and can have devastating effects on safflower yield, and resultant oilseed production. A. carthami is known to be seed-borne and appears as irregular brown lesions on safflower leaves and stems.
Alternaria dauci is a plant pathogen. The English name of the disease it incites is "carrot leaf blight".
Alternaria solani is a fungal pathogen that produces a disease in tomato and potato plants called early blight. The pathogen produces distinctive "bullseye" patterned leaf spots and can also cause stem lesions and fruit rot on tomato and tuber blight on potato. Despite the name "early," foliar symptoms usually occur on older leaves. If uncontrolled, early blight can cause significant yield reductions. Primary methods of controlling this disease include preventing long periods of wetness on leaf surfaces and applying fungicides. Early blight can also be caused by Alternaria tomatophila, which is more virulent on stems and leaves of tomato plants than Alternaria solani.
Didymella bryoniae, syn. Mycosphaerella melonis, is an ascomycete fungal plant pathogen that causes gummy stem blight on the family Cucurbitaceae, which includes cantaloupe, cucumber, muskmelon and watermelon plants. The anamorph/asexual stage for this fungus is called Phoma cucurbitacearum. When this pathogen infects the fruit of cucurbits it is called black rot.
Cercospora sojina is a fungal plant pathogen which causes frogeye leaf spot of soybeans. Frog eye leaf spot is a major disease on soybeans in the southern U.S. and has recently started to expand into the northern U.S. where soybeans are grown. The disease is also found in other soybean production areas of the world.
Botrytis fabae is a plant pathogen, a fungus that causes chocolate spot disease of broad or fava bean plants, Vicia faba. It was described scientifically by Mexican-born Galician microbiologist Juan Rodríguez Sardiña in 1929.
Ascochyta blights occur throughout the world and can be of significant economic importance. Three fungi contribute to the ascochyta blight disease complex of pea. Ascochyta pinodes causes Mycosphaerella blight. Ascochyta pinodella causes Ascochyta foot rot, and Ascochyta pisi causes Ascochyta blight and pod spot. Of the three fungi, Ascochyta pinodes is of the most importance. These diseases are conducive under wet and humid conditions and can cause a yield loss of up to fifty percent if left uncontrolled. The best method to control ascochyta blights of pea is to reduce the amount of primary inoculum through sanitation, crop-rotation, and altering the sowing date. Other methods—chemical control, biological control, and development of resistant varieties—may also be used to effectively control ascochyta diseases.
Southern corn leaf blight (SCLB) is a fungal disease of maize caused by the plant pathogen Bipolaris maydis.
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.
Spilocaea oleaginea is a deuteromycete fungal plant pathogen, the cause of the disease olive peacock spot, also known as olive leaf spot and bird's eye spot. This plant disease commonly affects the leaves of olive trees worldwide. The disease affects trees throughout the growing season and can cause significant losses in yield. The disease causes blemishes on the fruit, delays ripening, and reduces the yield of oil. Defoliation and in severe cases, twig death, can occur, and the disease can have long-term health effects on the trees.
Alternaria black spot of canola or grey leaf spot is an ascomycete fungal disease caused by a group of pathogens including: Alternaria brassicae, A. alternata and A. raphani. This pathogen is characterized by dark, sunken lesions of various size on all parts of the plant, including the leaves, stem, and pods. Its primary economic host is canola. In its early stages it only affects the plants slightly by reducing photosynthesis, however as the plant matures it can cause damage to the seeds and more, reducing oil yield as well.
Botrytis squamosa is a fungus that causes leaf blight on onion that is distinctly characterized by the two stages – leaf spotting followed by blighting. The pathogen is an ascomycete that belongs to the family Sclerotiniaceae in the order Helotiales. The lesions start out as whitish streaks and take on a yellow tinge as they mature. They cause yield losses up to 30%. This fungus is endemic to the USA and has also been reported in Europe, Asia, and Australia. Typical management of this disease includes chemical fungicides with significant efforts being made to establish a means of biological control.
Alternaria brassicicola is a fungal necrotrophic plant pathogen that causes black spot disease on a wide range of hosts, particularly in the genus of Brassica, including a number of economically important crops such as cabbage, Chinese cabbage, cauliflower, oilseeds, broccoli and canola. Although mainly known as a significant plant pathogen, it also contributes to various respiratory allergic conditions such as asthma and rhinoconjunctivitis. Despite the presence of mating genes, no sexual reproductive stage has been reported for this fungus. In terms of geography, it is most likely to be found in tropical and sub-tropical regions, but also in places with high rain and humidity such as Poland. It has also been found in Taiwan and Israel. Its main mode of propagation is vegetative. The resulting conidia reside in the soil, air and water. These spores are extremely resilient and can overwinter on crop debris and overwintering herbaceous plants.
Alternaria leaf spot or Alternaria leaf blight are a group of fungal diseases in plants, that have a variety of hosts. The diseases infects common garden plants, such as cabbage, and are caused by several closely related species of fungi. Some of these fungal species target specific plants, while others have been known to target plant families. One commercially relevant plant genus that can be affected by Alternaria Leaf Spot is Brassica, as the cosmetic issues caused by symptomatic lesions can lead to rejection of crops by distributors and buyers. When certain crops such as cauliflower and broccoli are infected, the heads deteriorate and there is a complete loss of marketability. Secondary soft-rotting organisms can infect stored cabbage that has been affected by Alternaria Leaf Spot by entering through symptomatic lesions. Alternaria Leaf Spot diseases that affect Brassica species are caused by the pathogens Alternaria brassicae and Alternaria brassicicola.
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