Colletotrichum kahawae | |
---|---|
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Fungi |
Division: | Ascomycota |
Class: | Sordariomycetes |
Order: | Glomerellales |
Family: | Glomerellaceae |
Genus: | Colletotrichum |
Species: | C. kahawae |
Binomial name | |
Colletotrichum kahawae J.M. Waller & Bridge [1] | |
Colletotrichum kahawae is a fungal plant pathogen that causes coffee berry disease (CBD) on Coffea arabica crops. The pathogen is an ascomycete that reproduces asexually. The asexual spores (conidia) are stored within acervuli. [1] [2] This disease is considered to be one of the major factors hampering C.arabica production in the African continent, which represents the current geographic range of the fungus. [3] Coffee berry disease causes dark necrosis in spots and causes the green berries of the coffee to drop prematurely. High humidity, relatively warm temperatures, and high altitude are ideal for disease formation. [4] Given the severity of the disease and the lack of effective control measures, there is great concern that the fungus may spread to other coffee producing continents, such as South America, which could have catastrophic consequences. [5]
Until recently, the taxonomic description and position of C. kahawae was a subject of great confusion. From the range of Colletotrichum spp. that are isolated from coffee plants, four groups were initially described based on their morphological traits: CCM (C. coffeanum mycelial), CCA (C. coffeanum acervuli), CCP (C. coffeanum pink) and the Coffee berry disease (CBD) strain. [6] The three former groups were later recognized as C. gloeosporioides Penz (CCM and CCA) and C. acutatum Simmonds (CCP), and proved to be non-pathogenic in green coffee berries. [7] Only the fourth group was able to infect both wounded and unwounded green berries and was formerly referred to as C. coffeanum. [7] However, C. coffeanum was described in 1901 based on Colletotrichum isolated from coffee in Brazil, [8] where CBD does not exist, and was probably synonymous with C. gloeosporioides, which occurs as a saprophyte or weak pathogen of ripe berries and damaged coffee tissue worldwide. [9] Several authors attempted to emend this anomaly but it was not until 1993 that Waller and Bridge described C. kahawae as the causal agent of CBD and as a distinct species based on morphological, cultural and biochemical characters [1] and more recently on multi-locus datasets. [3] [10] According to the American Phytopathological Society, C. kahawae is also a causal agent of the bacterial disease Brown Blight [11]
Areca catechu (betelnut palm), Citrus reticulata (mandarin), Coffea arabica (arabica coffee), Coffea canephora (robusta coffee), Coffea liberica (Liberian coffee tree), Cyphomandra betacea (tree tomato), Eruca vesicaria (purple-vein rocket), Liquidambar styraciflua (Sweet gum), and Malus domestica (apple) are all hosts of C. kahawae. [12] Infection can occur on all stages of the plant, from unopened inflorescences to ripe berries and occasionally leaves. The defining characteristic of C. kahawae is its ability to infect green berries; between 4–14 weeks after flowering it is most susceptible. [1] There are two distinct symptoms of berry infections termed "active" and "scab" lesions. The common symptoms of the active lesions are dark brown, slightly sunken spots that begin small and eventually enlarges in area consuming the entire berry to become black. Consequently, the pulp becomes brown, hard, and brittle while the surface of the berry remains smooth (except for the fungal fruiting structures). Under humid conditions, the fruiting structures on the lesions may produce pink spore masses that become white with age. The scab lesions can be found on both young and mature berries in which the lesions are corky, pale tan in color, and slightly sunken. [13] These lesions form stagnantly until the fruit begins to ripen creating a more beneficial environment for the fungus to grow. Secondary inoculum may be produced by the pathogen as seen by concentric rings that are surrounded by emerging black acervuli within the lesion. The active lesions will result in the arrest of berry development depending on favorable weather conditions. This process will in turn result in berry mummification on the branch, and when the berry begins to ripen anthracnose will develop causing the bean to then become infected. [4]
The polycyclic disease cycle of Colletotrichum kahawae is heavily dependent on rain/water for conidial production, dispersion, germination and infection. The timing of infection is regulated by the seasons and rainfall. Coffee growing regions of Africa receive two seasons of rain: long rains and short rains with relatively dry weather in between. The long rains are what induce initial flowering and therefore, initial infection. Short rains induce secondary flowering, but do not contribute to the severe infections of CBD. [14] C. kahawae is an ascomycete that produces conidia from simple hyphae for which its perfect state is still unknown. [1] Mummified berries and twig bark are considered to be primary sources of inoculum for the disease. The spores are covered in a gelatinous coat which expands under wet conditions to facilitate in spore dispersal during rain. [15] [16] Spore movement is downward in tree canopies due to movement being controlled by water films. This characteristic is a reason why coffee crowns are important sources of inoculum in coffee berry disease (CBD). [6] Spores are laterally dispersed between trees and branches by wind and rain, yet localized, downward movement is the prototypical inoculum movement. Common vectors of long and medium-distance dispersal are: Birds, Coffee harvesters, and sometimes insects. [17]
Colletotrichum conidium germination can occur 24 hours after contact with the host plant tissue. Then follows elongation of the germ tube, whose apical section differentiates into a melanised appressorium. This structure will then function to penetrate the plant cell cuticle directly via turgor pressure. [18] C. kahawae is a hemibiotroph that exhibits a transient post-penetrative asymptomatic biotroph phase followed by a necrotrophic phase in which symptoms of CBD are seen. During the biotroph phase, the pathogen invades the host cells without killing them. The fungus then feeds on the living tissue for a period of 48–72 hours post inoculation depending on the isolate aggressiveness. [19] The second phase of feeding, the nectrotrophic phase, involves the increased activity of cell-wall degrading enzymes to function in C. kahawae pathogenicity. The colonization is associated with severe cell wall alterations and death of the host protoplast. [20]
The first report of coffee berry disease caused Colletotrichum kahawae dates back to 1922 in western Kenya when it led to the destruction and abandon of C. arabica plantations in some regions. [16] Soon after, the fungus has quickly spread throughout most of the African continent, being reported in Angola (1930), Democratic Republic of the Congo (1938), Cameroon (1955), Tanzania (1964), Ethiopia (1971), Malawi and Zimbabwe (1985), and eventually most of the Arabic coffee areas in the continent were affected. [5] Until 2018, the disease remained constrained to the African continent, but reported occurrence now includes Colombia and Cuba in the Americas with Hainan island in Asia. [21]
CBD has a high incidence of occurring in highland regions and there is only disease beyond 1000 meters above sea level (m.a.s.l.) (altitude to which C. arabica is grown). The disease is highly dependent upon climatic factors: humidity, rainfall, and temperature. As stated above, rainfall is necessary for spore germination and dispersal for C. kahawae. Temperatures of 20–22 °C (68–72 °F) are optimal for germination and mycelial growth. Appressorium formation occurs at the same temperatures and at a high relative humidity. [4]
Current methods for control of coffee berry disease are resistance and fungicide applications. A study found that there are major genes on three different loci controlling resistance to CBD. The major cultivars being grown with high resistance to the disease are C. arabica L. var. Rume Sudan and the spontaneous hybrid Hibrido de Timor (HdT). [22] [23] Plants bred from these varieties (Catimor, Ruiru 11, etc.) are being used to develop better resistance through gene stacking approaches. This process is made more difficult when a variety that has been bred for high resistance develops undesirable traits ( low yield, poor bean profile, etc.) for commercially produced products, as seen in the Catimor variety. [19] Coffee growing regions outside of Africa are in the process of developing new coffee varieties or increasing the level of resistance in current commercial varieties to CBD as a precaution to the spread of the pathogen. This process is undertaken using artificial methods of screening to detect CBD in young coffee crops (commonly seed hypocotyls) to speed up the resistance screening process. [24] [25]
Fungicide applications are the primary management tactic carried out. Different copper-based fungicides, organic fungicides, as well as mixtures of the two are recommended to control CBD. Copper-based fungicides are used the most due to their low-cost compared to organic fungicides; yet they become expensive when disease intensity requires 7-8 applications per year. This process can become laborious, expensive, and destructive to the soil ecology. CBD's chemical control may account for up to 45% of the annual cost of production in some fields. Despite such elaborate control measures, losses as high as 50% of the potential crop may still occur under unfavorable weather conditions. [26]
Cultural practices are suggested to be interwoven in conventional management tactics. These methods include pruning infected branches, destruction of infected material, removal of mummified berries, [27] minimizing optimal microclimatic conditions for pathogen growth, and the use of competitive and antagonistic microorganisms in the plant phyllosphere. Colletotrichum kahawae has been shown to produce less disease when shaded by fruit trees, as the fruit trees prevent rainfall from falling on berries, thus preventing dispersal of conidia. [28] It has also been noted that the use of the fungus Fusarium stilboides Wollenv and Epicoccum nigrum Link and some yeasts could function in limiting CBD progression. A recent publication has identified and characterized Streptomyces species with strong antagonism towards C. kahwae. [29] These potential biocontrol tactics would then need to be balanced with the use of fungicides due to observations that repeated fungicide applications increased CBD by removal of fungal biocontrols. [20]
There are limited control options once CBD has established on a host. The use of fungicides on susceptible varieties can be extremely costly especially as the disease progresses. In Kenya, it is estimated that it would cost $500 per hectare to manage CBD with chemical control. [30] Because coffee berry disease can become very severe and there is a lack of effective control measures, there is great concern that the fungus may spread to coffee growing areas in other continents, such as South America, which could have catastrophic consequences. Currently, however, the disease is only prevalent in areas Africa at high elevations and with high relative humidity. The disease has been recorded to cause up to 80% yield loss. [10] [31]
Rusts are fungal plant pathogens of the order Pucciniales causing plant fungal diseases.
Botrytis cinerea is a necrotrophic fungus that affects many plant species, although its most notable hosts may be wine grapes. In viticulture, it is commonly known as "botrytis bunch rot"; in horticulture, it is usually called "grey mould" or "gray mold".
Uncinula necator is a fungus that causes powdery mildew of grape. It is a common pathogen of Vitis species, including the wine grape, Vitis vinifera. The fungus is believed to have originated in North America. European varieties of Vitis vinifera are more or less susceptible to this fungus. Uncinula necator infects all green tissue on the grapevine, including leaves and young berries. It can cause crop loss and poor wine quality if untreated. The sexual stage of this pathogen requires free moisture to release ascospores from its cleistothecia in the spring. However, free moisture is not needed for secondary spread via conidia; high atmospheric humidity is sufficient. Its anamorph is called Oidium tuckeri.
Grape black rot is a fungal disease caused by an ascomycetous fungus, Guignardia bidwellii, that attacks grape vines during hot and humid weather. “Grape black rot originated in eastern North America, but now occurs in portions of Europe, South America, and Asia. It can cause complete crop loss in warm, humid climates, but is virtually unknown in regions with arid summers.” The name comes from the black fringe that borders growing brown patches on the leaves. The disease also attacks other parts of the plant, “all green parts of the vine: the shoots, leaf and fruit stems, tendrils, and fruit. The most damaging effect is to the fruit”.
Pyrenophora teres is a necrotrophic fungal pathogen of some plant species, the most significant of which are economically important agricultural crops such as barley. Toxins include aspergillomarasmine A and related compounds.
Hemileia vastatrix is a multicellular basidiomycete fungus of the order Pucciniales that causes coffee leaf rust (CLR), a disease affecting the coffee plant. Coffee serves as the obligate host of coffee rust, that is, the rust must have access to and come into physical contact with coffee in order to survive.
Colletotrichum acutatum is a plant pathogen and endophyte. It is the organism that causes the most destructive fungal disease, anthracnose, of lupin species worldwide. It also causes the disease postbloom fruit drop on many varieties of citrus, especially Valencia and navel oranges in Florida.
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.
Mycosphaerella coffeicola is a sexually reproducing fungal plant pathogen. It is most commonly referred to as the asexual organism Cercospora coffeicola.
Pyrenophora tritici-repentis (teleomorph) and Drechslera tritici-repentis (anamorph) is a necrotrophic plant pathogen of fungal origin, phylum Ascomycota. The pathogen causes a disease originally named yellow spot but now commonly called tan spot, yellow leaf spot, yellow leaf blotch or helminthosporiosis. At least eight races of the pathogen are known to occur based on their virulence on a wheat differential set.
Zymoseptoria tritici, synonyms Septoria tritici, Mycosphaerella graminicola, is a species of filamentous fungus, an ascomycete in the family Mycosphaerellaceae. It is a wheat plant pathogen causing septoria leaf blotch that is difficult to control due to resistance to multiple fungicides. The pathogen today causes one of the most important diseases of wheat.
Diplocarpon earlianum is a species of fungus that causes disease in strawberry plants called strawberry leaf scorch. The disease overwinters in plant debris and infects strawberry plants during the spring season when it is wet. The five main methods to reduce strawberry leaf scorch include: irrigation techniques, crop rotation, planting resistant and disease-free seeds, fungicide use, and sanitation measures. Control of strawberry leaf scorch is important because it is responsible for the majority of disease in strawberries. Diplocarpon earliana affects the fruit quality and yield of the strawberry crop. Losses range from negligible to severe depending on numerous epidemiological factors including cultivar susceptibility, type of cropping system, and weather conditions
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.
Peronospora manshurica is a plant pathogen. It is a widespread disease on the leaves of soybeans and other crop plants. The fungi is commonly referred to as downy mildew, "leafspot", or "leaf-spot".
Colletotrichum capsici is a species of fungus and plant pathogen which causes leaf blight on Chlorophytum borivilianum, basil, chickpea and pepper as well as dieback in pigeonpea and anthracnose in poinsettia.
Colletotrichum coccodes is a plant pathogen, which causes anthracnose on tomato and black dot disease of potato. Fungi survive on crop debris and disease emergence is favored by warm temperatures and wet weather.
Colletotrichum lindemuthianum is a fungus which causes anthracnose, or black spot disease, of the common bean plant. It is considered a hemibiotrophic pathogen because it spends part of its infection cycle as a biotroph, living off of the host but not harming it, and the other part as a necrotroph, killing and obtaining nutrients from the host tissues.
Elsinoë ampelina is a plant pathogen, which is the causal agent of anthracnose on grape.
Colletotrichum coffeanum is a species of fungal plant pathogen affecting mainly the species Coffea arabica and occasionally other species of the genus Coffea. Upon infection, the pathogen can cause coffee berry disease (CBD) which is also known as Brown Blight when it occurs on younger fruits still green in color. The fungus was first reported in Kenya in 1922, and is found throughout most of Africa. C. coffeanum is only found in Africa, but other species of Colletotrichum can be found throughout the rest of the world.
Coffee wilt disease (tracheomycosis) is a common wilt that results in complete death of coffee trees it infects. This vascular disease is induced by the fungal pathogen known by its teleomorph Gibberella xylarioides. In 1927, coffee wilt disease (CWD) was first observed in the Central African Republic where it developed slowly and went on to cause two epidemics between the 1930s and the 1960s. Coffee wilt disease was first seen in Coffea excelsa.