Anthracnose Disease of some Vegetables &Fruits

 Anthracnose Disease of some Vegetables &Fruits

Anthracnose of Strawberry:

Anthracnose has been a very major problem on Strawberry plant when they face winter and spring rains.Anthracnose on strawberry is primarily caused by Colletotrichum acutatum, though the plant is also host to an additional species C. acutatum. Colletotrichum acutatum is not a true soil inhabitant and cannot survive in the soil indefinitely.Studies show that this pathogen, under can remain viable in the soil for about 9 months without a strawberry host.This pathogen is rather unique in that it can infect virtually all parts of the strawberry plant, though some infections are more important than other pathogen. However both the pathogen cause more or less same symptomps.Almost all symptoms on above ­ground parts of plants consist of dark, elongated lesions.Warm weather and wet field condition such lesions contain orange masses of the pathogen's spores.For below-­ground parts, symptoms consist of decayed, darkened roots, discoloration of the internal crown tissue, wilting and collapsing plants.The disease is prominently appear as a fruit or crown rot, both of which severely reduce plant stands and yields. Fruit rot, the most common form of anthracnose, appears as fruit begins to ripen in late spring. Crown rots, on the other hand, can develop in young plants soon after planting or when weather warms in spring. Anthracnose fruit rot can infect green fruit but is found most often on ripe fruit. Round, firm, sunken spots develop on ripening fruit.Spots may range from tan to dark brown. Under rainy or humid conditions, masses of fungal spores develop around the center of spots in a cream to salmon-colored slimy matrix.Spots often enlarge until the entire fruit is affected. Diseased fruit frequently become mummified.

The first visible symptoms of crown rot are sudden leaf wilting and plant death. Crown infections are initiated by spores splashing or washing into central buds from leaves or petioles or by the fungus growing directly into crown tissue.When crowns of wilted plants are split lengthwise, reddish brown streaking/marbling is visible.Although strawberry crowns show discoloration regardless of the cause of death, the reddish marbling pattern is most characteristic of anthracnose. Anthracnose crown rot is active during warm weather but becomes dormant during colder months. However, disease progression resumes when soil warms in spring. Small, dark lesions (dead spots) can appear on stolons and petioles anytime during warm weather. Lesions gradually become black, dry, and sunken. When a lesion girdles a stolon, the unrooted daughter plant beyond the lesion dies. Similarly, a lesion on the petiole often results in death of the attached leaf. Small, round, black to gray spots can appear on expanding leaflets even before petiole or stolon symptoms are noticed. Spores produced in these lesions can wash down into crowns and initiate crown rot.

The disease is favoured by moderate temperatures and wet, humid weather. The development and spread of spores is strongly dependent on sprinkler irrigation and rain.The spores form in a sticky matrix and will only spread through physical contact (such as from passing equipment that brushes against the lesions) or splashing water.Therefore, anthracnose disease on strawberry fruit is very rare unless rains occur during the fruit production season.

 

 Anthracnose of cashew:

Anthracnose of cashew (Anacardium occidentale) was  caused by Colletotrichum gloeosporioides. Disease symptoms manifest in both leaves and young nuts (Freire et al.,2002). Lesions first appear as small, dark spots on stolons and petioles.These enlarge to become dark, elongated, dry, sunken lesions which often girdle the stem.When petioles or runners become girdled, individual leaves or entire daughter plants may wilt and die. Petiole infections occur at the base of the petiole, causing the leaf to bend sharply at the point of attachment and hang down.Lesions on leaves are small, round, and black or light gray, often resembling ink spots. Spots may become numerous on leaflets without causing leaf death and  lesions often appear first on expanding leaves of runner plants.These lesions do not continue to develop in fully expanded leaves but infected leaves may persist on plants for 2-3 months. The fungus sporulates in these lesions and may serve as an inoculum source for flower and fruit. Infection on flower may occur any time after the bud emerges from the crown.Fully open flowers are most susceptible to infection. Flower buds, sepals, pedicels, and peduncles may also become infected.Infected flowers  are characterized by dark lesions spread down the pedicel In the infected flower initially sepals become dry and turn brown and finally the whole flower dry quickly.In fruits symptoms appear as whitish, water soaked lesions.As lesions develop, they turn a light tan to dark brown and eventually become sunken and black with in 2 to 3 days.After several days, lesions may be covered with pink to orange to light salmon-colored spore masses.
Infected fruit eventually dry down to form hard, black, shriveled mummies. Fruit can be infected at any stage of development. Both ripe and unripe fruit can be affected. Infected seeds (achenes) turn black and are slightly sunken. These single seed infections often occur on green fruit;a typical lesion devlops as the fruit ripens. Severe damage on adult plants results in defoliation during shoot development, death of inflorescences and later necrosis and falling of immature nuts (Freire and Cardoso, 2003).

Infected transplants and soil from infected transplants appear to be the primary source of inoculum in most instances, especially in annual production systems.In perennial systems, the fungi may overseason in infected plants and debris, providing inoculum for the following fruiting season.Spores (conidia) may be dispersed in the field by wind-driven rain, splashing water, insects, movement of workers, equipment or animals. Disease development and spread is minimal in most cases under cool, dry conditions. Crown infections often occur in the nursery but do not appear until after planting. The fungus continues to develop in newly planted nursery infected plants, which may suddenly die during warm weather in the fall or early spring of the following year.

 

 

 

2.7.Anthracnose of Pumpkin and other Cucurbit:

 

Anthracnose is a common fungal disease of pumpkin in fields, greenhouses, and high tunnels.It causes a serious economic  losses to growers and became a crucial problem in the cultivation of pumpkin and other cucurbits like cucurmis,gourd etc.The disease can develop on all above ground parts of plants. In cucurbits anthracnose is caused by the fungus Colletotrichum orbiculare i.e., stage or Teleomorph of of an ascomycete fungi stage of Glomerella lagenarium.The symptoms of anthracnose vary somewhat on different hosts. On cucumber leaves the spots start as water soaked areas and expand into brown spots which are roughly circular (Wasilwa et al. 1993).The causal organism of  Cucurbita Anthracnose,Colletotrichum orbiculare is widely distributed in most regions where cucurbits are grown. There are two races of the anthracnose fungus (Colletotrichum orbiculare) are common on cucurbit crops. Race 1 is virulent to cucumber,pulmkin,cucumis etc. On the other hand Race 2 is pathogenic for watermelon. Muskmelon is generally more susceptible to race 1 than to race 2. However all the races cause spots on fruits as well as leaves , petioles etc. On cucurbits, leaf spots are often large and palebrown to gray in color, with distinct margins. Leaf lesions some times tend to be angular The lesions on fruit appear as brownish discolorations that become sunken, wrinkled and dark, with concentric rings of fungal fruiting bodies.

The infections begin by the spores germinating from the acervuli on the fruits, leaves and young shoots.Attacks commonly occur from spores or mycelium under favorable climatic conditions. They are produced in acervuli on infected drupes and are dispersed by rain splash and via wind blown rain droplets.Spores are produced in hyaline, nonseptate, mostly oblong Conidia which measure about 4­6x13­-19 micrometers.The fungus survives non­crop periods on infected plant residue and may be seed borne. Spores are spread by wind, rain, machinery and handling.Warm, wet weather is favorable for anthracnose infection and spread, with optimum temperatures of 26­-32 ^oC. Symptoms develop about 4 days after infection.

 

 

Maize anthracnose:

Anthracnose is one of the most economically important syndromes affecting maize (Zea mays) worldwide.This fungal disease can be present as leaf blight and/or as stalk rot on the plant. One
phase may be present without the other.The causal organism of maize anthracnose is Colletotrichum graminicola (Ces.) G.W.Wills.It is actually an imperfect stage of ascomycete fungi Glomerella graminicola.The fungi is intracellular hemibiotrophic pathogen.It initially colonize their host biotrophically, and then it switch to necrotrophy.In  biotrophy the fungus apparently obtaining nutrients from plant cells that remain alive, whereas in necrotrophy the fungus feeds from dead cells and symptoms develop (Mendgen & Hahn, 2002, Wharton et al., 2001, Wharton & Julian, 1996, Latunde-Dada et al., 1996). The incidence of anthracnose in maize root stalk is favoured by the wounding caused by insects such as the European corn borer. The pathogen has a significant capacity for direct penetration, but this mechanism of infection is much slower and less efficient than penetration through wounds. The fungus breaked the lignified rind fibers by passing through small openings in the cell walls via narrow hyphal connections. Epidermal cells and rind fiber cells do not appear to become rotted. Rotting only occurred once the pathogen had penetrated into the pith parenchyma cells. The pathogen causes reduction in both yield and quality. The foliar infection phase of the fungus is not reported to be of economic importance in maize.The most severe damage is caused by the stalk rot phase. Foliar damage can be observed at different stages of plant development. In the early seedling stage, leaves show irregular, oval-to-elongated lesions with characteristic, yellow-to-reddish-brown margins. In later stages of plant development, similar lesions can be observed in the upper leaves of infected plants, especially in those where stalk rot symptoms have already developed. Lesions are semi-transparent and can originate anywhere on the leaf blade. Fruiting bodies may develop within these dead tissues. Rapid tiring of infected leaves may occur under warm, wet conditions later in the season, referred to as "stop dieback". Two forms of  lesions on the lamina are  commonly found.One of the forms appears as small and restricted  circular to  oval spots,2-4 mm in diameter and having a small pinpoint dark brown centre (acervuli) surrounded by  a light brown areas.On the other hand  in the second form  the lesions appear as  wide and diffused  patches with a number of  black to dark brown spot scattered alover the patches. Due to infection the internal stalk tissue or pith becomes discolored, turning dark brown and, eventually, disintegrates.Late in the season shiny black, linear streaks and blotches appear on the surface of the lower stalk above the brance roots.The fungus travels up the vascular bundles; discolored vascular bundles are often the first symptoms of the advancing edge of disease. At the severity lesionscommonly coalesce causing large leaf areas to shrivel and die and finally causes premature death of plants. Premature death occurs above the ear with the plant tissue below the ear remaining green. The infecting propagules are small, black, oval to elongate acervuli. These acervuli contain numerous black setae (spines) develop on the surface of stems and leaf sheaths. The fungus overwinters as a saprophyte on crop residue in the form of conidia or mycelium.It is also seed borne as stroma or hyphae in the endosperm. Infection usually occurs at the base of the plant or on the roots from the soil borne inoculum. Acervuli that appear on the upper leaves develop from the secondary spread of conidia. Spores from disintegrating debris arecarried by wind or splashing rain to corn leaves where they germinate and penetrate the tissues directly through the epidermis or stomata. Anthracnose occurs over a broad range of environments but is more prevalent in soils that are low in Phosphorus and potash.

 

 

 

Cotton anthracnose:

Anthracnose is a serious problematic disease of Cotton (Gossypium sp.).The yield of cotton fibre is much affected by this disease worldwide.The causal organism of this disease is Colletotrichum gossypii, which is generally considered as anamorph of  an ascomycete fungus Glomerella gossypii. The pathogen Colletotrichum gossypii  occurs on plant as both inter and intra cellular, producing numerous acervuli on the affected leaves, stems and bolls.The infective part of the pathogen is conidia.The conidia bearing structure i.e., conidiophore of the pathogen is more or less hyaline and single celled.Conidia of C. gossypii  ranges between 11-20 X 4-9µ.The pathogen produces thick walled and septate mycelium which are dark coloured at the base and lighter towards the tip.The pathogen is primarily seed-borne, however secondary spread is occured by air and soil-borne conidia.In moist weather the fungus spreads rapidly in the field, causing seedling blight, stem lesions and boll rot. When the bolls are harvested the infected seeds from diseased bolls contaminate the seeds from healthy bolls.An early symptom of infestation is damping off due to the cotyledon's rotting. Infected leaves  have pinkish brown spots that appear especially on their under surfaces. On cotyledons small reddish spots are formed.At collar region elongate reddish brown lesions are formed. All the stages of  cotton bolls are susceptible to the pathogen.Infected immature bolls initially appear as small water soaked, circular, sunken, reddish brown spots and their centres become black as they grow.Then the surface of the boll is coated with thick, grayish to pinkish mycelium which leads to the growth of small black fruiting bodies of the fungus. In infected leaves pinkish brown spots appear mainly on the underside.In case of severe infection, area under necrotic region increases and often results in defoliation.Large areas of the tissues around the veins become yellowish to brownish and eventually dry out.