Alternaria mali
Encyclopedia
Alternaria mali, also called Alternaria blotch of apple, is a pathogenic fungus
affecting plants. It is prevalent in the southern United States and elsewhere, and damages the leaves of infected apple
trees.
on dead leaves on the ground, in mechanical injuries in twigs, or in dormant buds. Primary infection occurs about one month after petal fall the following year. The disease is favoured by temperatures between 77 and 86 °F (25–30 °C), and by wet conditions. Infection occurs at optimum temperatures with 5.5 hours of wetting, and an outbreak can become serious within two days of infection. The fungus attacks susceptible cultivars using a chemical toxin. Affected plants exhibit circular spots on the leaves that enlarge as the disease advances. Normally, hypha
e cannot adhere to the surface of the host, but under moist conditions light-grey mycelium might be present on the surface. Normally the fungus will not attack fruits except in highly susceptible cultivars; fruit-spotting may occur on the tree or in storage, particularly on fruits with already damaged skin.
on the primary body and the periderm on the secondary body. A. mali can still penetrate the stomates and hydathodes of leaves.
As with most pathogens, Alternaria mali resistance involves a gene-for-gene relationship
. Apple trees can recognize invading pathogens and mount a defense. Often, the plant may be able to resist the pathogen, even though it has no genetic resistance to same. Apple trees seem to have a weak defense to A. mali, base on the fact that no survivors if leaves has been infected.
, Golden Delicious
, Ralls, Toko, Tsugaru, Mutsu
, Jonagold
, Jonathan
. Chemical control uses fungicide
s such as iprodione
, mancozeb and captan
. Disease severity is aggravated by severe mite
infestation; thus good mite management is an important factor in preventing severe disease development.
Pathogenic fungi
Pathogenic fungi are fungi that cause disease in humans or other organisms. The study of pathogenic fungi is referred to as medical mycology. Although fungi are eukaryotic organisms many pathogenic fungi are also microorganisms.-Candida:...
affecting plants. It is prevalent in the southern United States and elsewhere, and damages the leaves of infected apple
Apple
The apple is the pomaceous fruit of the apple tree, species Malus domestica in the rose family . It is one of the most widely cultivated tree fruits, and the most widely known of the many members of genus Malus that are used by humans. Apple grow on small, deciduous trees that blossom in the spring...
trees.
Pathogenesis
A. mali can overwinter as myceliumMycelium
thumb|right|Fungal myceliaMycelium is the vegetative part of a fungus, consisting of a mass of branching, thread-like hyphae. The mass of hyphae is sometimes called shiro, especially within the fairy ring fungi. Fungal colonies composed of mycelia are found in soil and on or within many other...
on dead leaves on the ground, in mechanical injuries in twigs, or in dormant buds. Primary infection occurs about one month after petal fall the following year. The disease is favoured by temperatures between 77 and 86 °F (25–30 °C), and by wet conditions. Infection occurs at optimum temperatures with 5.5 hours of wetting, and an outbreak can become serious within two days of infection. The fungus attacks susceptible cultivars using a chemical toxin. Affected plants exhibit circular spots on the leaves that enlarge as the disease advances. Normally, hypha
Hypha
A hypha is a long, branching filamentous structure of a fungus, and also of unrelated Actinobacteria. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium; yeasts are unicellular fungi that do not grow as hyphae.-Structure:A hypha consists of one or...
e cannot adhere to the surface of the host, but under moist conditions light-grey mycelium might be present on the surface. Normally the fungus will not attack fruits except in highly susceptible cultivars; fruit-spotting may occur on the tree or in storage, particularly on fruits with already damaged skin.
Plant defense
Plants' first lines of defense against A. mali infection are the physical barrier provided by the epidermisEpidermis (botany)
The epidermis is a single-layered group of cells that covers plants' leaves, flowers, roots and stems. It forms a boundary between the plant and the external environment. The epidermis serves several functions, it protects against water loss, regulates gas exchange, secretes metabolic compounds,...
on the primary body and the periderm on the secondary body. A. mali can still penetrate the stomates and hydathodes of leaves.
As with most pathogens, Alternaria mali resistance involves a gene-for-gene relationship
Gene-for-gene relationship
The gene-for-gene relationship was discovered by Harold Henry Flor who was working with rust of flax . Flor was the first scientist to study the genetics of both the host and parasite and to integrate them into one genetic system...
. Apple trees can recognize invading pathogens and mount a defense. Often, the plant may be able to resist the pathogen, even though it has no genetic resistance to same. Apple trees seem to have a weak defense to A. mali, base on the fact that no survivors if leaves has been infected.
Control
Alternaria mali prevention consists of strict quarantine, never importing plants or scions from affected plants and collecting fallen or infected leaves and burning them in winter. Apple cultivars can be ranked in order of increasing resistance as follows: Indo, Red Gold, Raritan, Delicious, FujiFuji (apple)
The Fuji apple is an apple clone developed by growers at the Tohoku Research Station in Fujisaki, Aomori, Japan, in the late 1930s, and brought to market in 1962...
, Golden Delicious
Golden Delicious
The Golden Delicious is a cultivar of apple with a yellow color. It is not closely related to the Red Delicious apple.- Appearance and flavor :...
, Ralls, Toko, Tsugaru, Mutsu
Mutsu (apple)
The apple was introduced in 1948 and is a cross between the Golden Delicious and the Indo apple varieties first grown in Japan, and named after the Mutsu Province of Japan, where it was presumably first grown....
, Jonagold
Jonagold
Jonagold is a cultivar of apple, a cross between Golden Delicious and Jonathan which was developed in 1953 in New York. They form a large sweet fruit with a thin skin. Because of their large size they are now favoured by commercial growers in many parts of the world...
, Jonathan
Jonathan (apple)
The Jonathan apple is a medium-sized sweet apple, with a strong touch of acid and a tough but smooth skin. It is closely related to the Esopus Spitzenburg apple.-History:There are two alternative theories about the origin of the Jonathan apple....
. Chemical control uses fungicide
Fungicide
Fungicides are chemical compounds or biological organisms used to kill or inhibit fungi or fungal spores. Fungi can cause serious damage in agriculture, resulting in critical losses of yield, quality and profit. Fungicides are used both in agriculture and to fight fungal infections in animals...
s such as iprodione
Iprodione
Iprodione is an imidazole fungicide.-Application:Iprodion is used on crops affected by Botrytis bunch rot, Brown rot, Sclerotinia and other fungal diseases in plants. It is currently applied in a variety of crops: fruit, vegetables, ornamental trees and scrubs and on lawns...
, mancozeb and captan
Captan
Captan is the name of a general use pesticide that belongs to the phthalimide class of fungicides. Though it can be applied on its own, Captan is often added as a component of other pesticide mixtures. It is used to control diseases on a number of fruits and vegetables as well as ornamental plants...
. Disease severity is aggravated by severe mite
Mite
Mites, along with ticks, are small arthropods belonging to the subclass Acari and the class Arachnida. The scientific discipline devoted to the study of ticks and mites is called acarology.-Diversity and systematics:...
infestation; thus good mite management is an important factor in preventing severe disease development.