Alternaria leaf spot

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Alternaria leaf spot or Alternaria leaf blight are a group of fungal diseases in plants, that have a variety of hosts. [1] [2] [3] The diseases infects common garden plants, such as cabbage, and are caused by several closely related species of fungi. [4] Some of these fungal species target specific plants, while others have been known to target plant families. [4] 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. [5] 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. [5] Alternaria Leaf Spot diseases that affect Brassica species are caused by the pathogens Alternaria brassicae and Alternaria brassicicola . [6]

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Alternaria leaf spot on quaking aspen leaves Alternaria Leaf Spot of Aspen.png
Alternaria leaf spot on quaking aspen leaves

Hosts and symptoms

A. brassicae and A. brassicicola can infect plant species of the genus Brassica. Hosts include broccoli, cabbage, cauliflower, turnip, kale, rutabaga, Brussels sprout, and mustard. [6] Specifically, plants that have longer periods of leaf wetness are more susceptible to development of the disease. [5] Areas with higher rainfall that experience wet, mild seasons lead to the highest reports of disease incidence. [6] Water promotes disease development as the pathogens only undergo germination and infection after more than nine hours of leaf wetness. [7] A. brassicae and A. brassicicola cause very similar symptoms, with symptoms normally occurring on older leaves, as they are closer to the soil and more likely to be affected by rain splash, which spreads the pathogen. [6] Necrotic lesions bordered by chlorotic halos develop on the leaf surface. These lesions are dark brown to black circular leaf spots with target-like, concentric rings. [5] Shot holing may also occur when lesion centers dry and fall out, similar to the lesions observed in Early Blight caused by Alternaria solani. [8] Symptoms do not usually significantly reduce yields, but they can cause cosmetic issues that reduce marketability of the crop. [6] However, heavy infections of foliage can reduce plant vigor and can result in lower than expected yields.

Disease cycle

A. brassicae and A. brassicicola produce asexual conidia via conidiophores. At optimum temperatures (20-30 C), the average time of sporulation is 13 hours. [6] Conidia are dispersed via water and wind after sporulation. Once they come into contact with a leaf surface under optimal environmental conditions, germination can begin. [9] Germination of conidia occurs most efficiently when temperatures are higher, with germination time increasing as temperature decreases. Germination occurs most quickly at temperatures between 21 and 28 C. The presence of moisture as water or a high relative humidity (at least 95%) is required for germination. [6] After germination, the pathogen begins to infect the host via penetration of the leaf surface using an appressorium and infection peg. Leaf cells are infected, and the symptomatic lesions begin to appear, with conidia-producing conidiophores being produced from mature lesions. [7] Further dispersal of conidia by water or wind occurs from these new conidiophores. This dispersal can be local from one leaf to an adjacent leaf, or it can be long distance from plant to plant. [9] 'The spores can be blown in the wind for distances up to 1.1 miles.'A. brassicae and A. brassicicola survive in the form of microsclerotia and chlamydospores which appear after infected leaves have partially decayed. Both of these survival structures develop best at low temperature (3 C) and they have been found to be resistant to desiccation and freezing. [6] Conidiophores eventually develop from the microsclerotia and chlamydospores, allowing for the production of conidia again and the cycle to repeat. [6]

Management

A. brassicae and A. brassicicola can be chemically controlled by applying fungicides as foliar sprays. These fungicides include iprodione and chlorothalonil. [8] It is recommended to practice crop rotation with non-cruciferous crops. [5] This creates periods of time when no active pathogen is present in the area due to lack of a host. If there are no pathogens present, they cannot produce microsclerotia and chlamydospores that would eventually be input into the surrounding area via plant debris, reducing chances of future infection. It is also recommended to irrigate in the morning when leaves can dry quickly, and to orient rows according to the wind. [5] Morning irrigation promotes shorter periods of leaf wetness, disrupting the pathogens’ germination and infection. Orientation of rows disrupts dispersal of conidia via wind by reducing contact. Application of straw mulch can reduce disease incidence by acting as a barrier against soil-borne inoculum, disrupting dispersal of conidia from conidiophores developed from microsclerotia and chlamydospores. [7] Maintaining control of cruciferous weeds is another important management practice, as this removes potential hosts for the pathogen that can aid in the spread of the disease. [6]

Related Research Articles

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<i>Pseudocercosporella capsellae</i> Species of fungus

Pseudocercosporella capsellae is a plant pathogen infecting crucifers. P. capsellae is the causal pathogen of white leaf spot disease, which is an economically significant disease in global agriculture. P. capsellae has a significant effect on crop yields on agricultural products, such as canola seed and rapeseed. Researchers are working hard to find effective methods of controlling this plant pathogen, using cultural control, genetic resistance, and chemical control practices. Due to its rapidly changing genome, P. capsellae is a rapidly emerging plant pathogen that is beginning to spread globally and affect farmers around the world.

<i>Erysiphe cruciferarum</i> Species of fungus

Erysiphe cruciferarum is a plant pathogen of the family Erysiphaceae, which causes the main powdery mildew of crucifers, including on Brassica crops, such as cauliflower, cabbage, broccoli, and Brussels sprouts. E. cruciferarum is distributed worldwide, and is of particular concentration in continental Europe and the Indian subcontinent. E. cruciferarum is an ascomycete fungus that has both sexual and asexual stages. It is also an obligate parasite that appears to have host specificity; for example, isolates from turnip will not infect Brussels sprout, and vice versa. While being a part of the family Erysiphaceae, it belongs to those members in which the conidia are formed singly and whose haustoria are multilobed.

<i>Mycosphaerella brassicicola</i> Species of fungus

Mycosphaerella brassicicola is a plant pathogen. The pathogen is the teleomorph phase of an ascomycete fungus, which causes the ring spot disease of brassicas. The supplementary anamorph phase Asteromella brassicae produces conidia through its asexual reproduction, however these spores are not confirmed to cause disease in host plants.

<i>Alternaria brassicae</i> Species of fungus

Alternaria brassicae is a plant pathogen able to infect most Brassica species including important crops such as broccoli, cabbage and oil seed rape. It causes damping off if infection occurs in younger plants and less severe leaf spot symptoms on infections of older plants.

Alternaria japonica is a fungal plant pathogen. It is a cause of black spot disease in cruciferous plants. It is not a major source of crop loss, but is considered dangerous for plants during the seedling stage.

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.

<i>Stemphylium solani</i> Species of fungus

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.

Verticillium longisporum, also known as Verticillium Wilt, is a fungal plant pathogen that commonly infects canola. V. longisporum can attack other brassica plants as well as woody ornamentals. A main symptom of the infected plant is wilting. In America, V. longsiporum primarily effects eudicot plants. This pathogen can be very devastating and hard to eradicate, responding only to expensive fumigation or fungal resistant plants.

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Alternaria dauci is a plant pathogen. The English name of the disease it incites is "carrot leaf blight".

<i>Alternaria solani</i> Species of fungus

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.

<i>Mycocentrospora acerina</i> Species of fungus

Mycocentrospora acerina is a deuteromycete fungus that is a plant pathogen.

Peronosclerospora sorghi is a plant pathogen. It is the causal agent of sorghum downy mildew. The pathogen is a fungal-like protist in the oomycota, or water mold, class. Peronosclerospora sorghi infects susceptible plants though sexual oospores, which survive in the soil, and asexual sporangia which are disseminated by wind. Symptoms of sorghum downy mildew include chlorosis, shredding of leaves, and death. Peronosclerospora sorghi infects maize and sorghum around the world, but causes the most severe yield reductions in Africa. The disease is controlled mainly through genetic resistance, chemical control, crop rotation, and strategic timing of planting.

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<i>Cercospora melongenae</i> Fungal disease of eggplant leaves

Cercospora melongenae is a fungal plant pathogen that causes leaf spot on eggplant. It is a deuteromycete fungus that is primarily confined to eggplant species. Some other host species are Solanum aethiopicum and Solanum incanum. This plant pathogen only attacks leaves of eggplants and not the fruit. It is fairly common among the fungi that infect community gardens and home gardens of eggplant. Generally speaking, Cercospora melongenae attacks all local varieties of eggplants, but is most severe on the Philippine eggplant and less parasitic on a Siamese variety.

<span class="mw-page-title-main">Napa cabbage</span> Subspecies of flowering plant

Napa cabbage is a type of Chinese cabbage originating near the Beijing region of China that is widely used in East Asian cuisine. Since the 20th century, it has also become a widespread crop in Europe, the Americas, and Australia. In much of the world, it is referred to as "Chinese cabbage". In Australia, it is sometimes referred to as "wombok".

<i>Botrytis fabae</i> Species of fungus

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.

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.

<i>Alternaria brassicicola</i> Species of fungus

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.

References

  1. ↑ Zhu, Yi; Lujan, Phillip; Dura, Srijana; Steiner, Robert; Zhang, Jinfa; Sanogo, Soum (July 2019). "Etiology of Alternaria Leaf Spot of Cotton in Southern New Mexico". Plant Disease. 103 (7): 1595–1604. doi: 10.1094/PDIS-08-18-1350-RE . PMID   31059384.
  2. ↑ Zhang, Z.; Wei, J. H.; Yang, C. M.; Chen, H. Q.; Sui, C.; Gao, Z. H. (July 2010). "First Report of Alternaria Leaf Blight on Bupleurum chinense Caused by Alternaria alternata in China". Plant Disease. 94 (7): 918. doi: 10.1094/PDIS-94-7-0918A . PMID   30743562.
  3. ↑ Batta, Yacoub (2003-01-01). "Alternaria Leaf Spot Disease on Cucumber: Susceptibility and Control Using Leaf Disk Assay" . Retrieved 2020-01-08.
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