Rot is characterized by the deep decomposition of attacked tissues under the action of phytopathogens. These changes are produced by some pathogenic bacteria and fungi. Depending on the climatic conditions and the consistency of the affected organs, rot can be wet or dry.

Potato blackleg disease (Pectobacterium atrosepticum)

The disease can occur both in the field and during storage, with tuber losses reaching 50-60%.

Symptom. Plants from infected tubers remain smaller, with weak stems, erect branches, and bent towards the main axis. Leaflets are twisted towards the lower face, are stiff, yellowish-green with a metallic sheen.

The base of the stems is thin, blackened, and the tissues in this area show a soft rot. The inside of the stem base is brown and soft. The vascular bundles are darker in color. Diseased plants pull off easily, do not produce tubers or the tubers are affected by wet rot.

In sectioning through an attacked tuber, a pinkish-purple discoloration of the vase ring is observed, located a few millimeters below the peel. In a more advanced stage of the disease, starch solubilization begins, forming caverns in the tubers filled with a bacterial mucilage that gives off an unpleasant butyric acid smell. Eventually, the flesh of the tuber breaks down completely.

In damp, unventilated, moderate temperature storage, the disease progresses rapidly causing mass rotting of tubers.

The bacterium is transmitted from one year to the next most often through infected tubers used for planting and through plant debris left in the field after harvesting.

Spread during vegetation is by insects, snails, water from rain or irrigation, tools, etc. Infection is made through wounds, lenticels, or stolons.

Prophylaxis. As prophylactic measures, it is recommended to avoid planting in heavy, wet soils, to respect crop rotation, so that on infected land, potatoes, or other plants for which the pathogen shows affinity, do not return earlier than 4 years.

When planting, only healthy tubers should be used, resistant varieties should be cultivated, soil pests should be controlled, potatoes intended for storage should be harvested at full maturity, and plant remains left on the field after harvesting should be collected and burned.

Before storage, the tubers will be sorted, and the temperature in the storehouses will be maintained at 1-4º C and humidity at 70-80%, ensuring good ventilation.

Damping-off (Pythium debaryanum)

It is one of the most widespread and damaging diseases occurring in seedlings and greenhouses. The pathogen is polyphagous and attacks plants of different botanical families.

Symptom. Mycelial filaments in the soil penetrate through stomata into the hypocotyl region of the seedlings. As a result of infection, brown spots appear on the petiole, spreading to the petiole and the base of the stem, which thins and softens.

The leaves wither and the seedlings fall to the ground and rot. Under high temperature and humidity conditions, the disease is acute, so that in 2-3 days all the seedlings in the seedling can be attacked and destroyed.

The attack is more dangerous as it occurs closer to the germination and budding stage of the seedlings, then as they grow, they become more resistant to the attack of the fungus.

The fungus is transmitted through wounds or active tearing of cell walls. The rotting of the attached tissues is due to a pectolytic enzyme secreted by the phytopathogen.

After destroying plant tissues, the pathogen leads a saprophytic life, by rapidly modifying the enzyme system.

Prophylaxis. Since the critical period of the disease is limited to the seedling stage, preventive measures must ensure that the seedlings are protected from infection until they are panted to the field. Of particular importance is the disinfection of the seedling soil or its replacement with uncontaminated soil.

During sprouting and seedling development, excess moisture should be avoided and good ventilation of the plants should be ensured.

In the chemical control of the phytopathogen, specific fungicides are applied.

Brown rot in pome fruit trees (Monilinia fructigena f.c. Monilia fructigena)

The disease occurs in more than 40 plant species from different families but is most dangerous for apples and pears. Monilliosis causes damage closer to fruit maturity, and late infections that occur during harvest manifest in storage.

Symptom. The attack occurs on branches, leaves, flowers, fruits, the forms of attack taking on different aspects depending on the phase of vegetation and the evolution of climatic conditions.

In spring, during flowering, some young branches begin to wilt, leaves and flowers become brown and dry out.

On the bark of the attacked branches as well as on the flowers, small greyish-yellowish crumbs appear representing the sporodochia of the fungus. Later, when the fruits have reached the size of a peanut, especially on the pear, they blacken and fall off.

The attack on ripe fruit is the most common and the most damaging. At this stage, it can occur in three forms: brown rot, black rot, and mummification.

Brown rot occurs in hot, rainy weather. Brown spots appear on the attacked fruit, spreading over the surface and covering the entire flesh. Sporodochia (mycelia with conidiophores and conidia) arranged in concentric circles appear on the surface of fruit with brown rot. Fruits attacked by brown rot fall off in summer.

Black rot occurs in cool, rainy weather. In this situation, the fruit blackens and rots. They have a shiny epicarp but no sporodochia. This form of attack often occurs in warehouses.

Fruit set occurs in hot, dry weather. In this situation, the attacked fruit dehydrates, hardens, becomes stony, and remains attached to the trees in winter. The sclerotia of the fungus form in these fruits, which are resistance organs of the vegetative apparatus.

The fungus survives in winter, most commonly as mycelial stomata in the fruit and bark of attacked branches.

In spring, under favorable environmental conditions, the mycelium grows and forms sporodochia on which conidiophores with conidia are formed which produce primary infections. Conidia are spread by wind, rainwater, insects. Once on the young fruit, they germinate and produce an infection filament which often penetrates through wounds caused by various abiotic (hail, wind) and biotic (insect bites) factors.

Prophylaxis. It is recommended to destroy by burning the plant debris and the attacked fruits. Treatments during the growing season with specific fungicides are also recommended in treating this disease.

Brown rot in stone fruit trees (Monilinia laxa f.c. Monilia laxa)

It is a widespread and damaging disease, causing damage of 30-50% of fruit production, and can gradually lead to drying of the trees.

Symptom. Both fruit and especially flowers, leaves, and young branches are attacked during spring. Flowers at the top of young branches mostly wilt, brown, and dry out, but do not fall off.

Also, young leaves wither from the tip and hang down. The sporodochia of the fungus appear on the attacked organs as small cushions made of mycelium and spores. This parasitic appearance is characteristic especially on cherry, cherry, peach, and almond trees, and is more dangerous than the attack on the fruit.

On fruit, the disease occurs by brown rot and mummification. Symptoms are similar to those produced by Monilinia fructigena in pome fruit trees, except that the sporodochia formed on the fruit are scattered over the entire surface of the fruit.

The attacked fruit falls off the branches and onto the ground, where it continues to rot. In plum, the sporodochia perforate the epicarp and the sugary juice seeps out, sticking the fruit together. Rotting and mummified fruit bundles remain attached to the branches and are visible in the trees during dormancy.

The fungus overwinters in the form of mycelial stromata in the fruit and bark of attacked branches, and the conidia are 60-70% resistant to low temperatures.

In spring, under favorable environmental conditions (temperature and humidity), the mycelium grows and forms sporodochia or conidia germinate and produce primary infections. In years when the flowering period is long and humidity high, infection occurs. This occurs through the stigma, from where the mycelium enters the style, then the ovary causing wilting of the flowers, often through the fruit stalk the mycelium passes into the branch bark.

In the ripe fruit, the mycelium of the fungus penetrates through the punctures and wounds caused by hail rains.

Prophylaxis. It is recommended to destroy by burning the plant debris and the attacked fruits, avoiding creating wounds on fruits and branches.

Treatments during the growing season with specific fungicides.

White mold (Sclerotinia sclerotiorum)

The disease is one of the most widespread and damaging to sunflower crops, with losses of 60-90% of production in some countries. Among the most frequently attacked species are beet, soybean, alfalfa, carrot, celery, parsley, etc.

Symptom. The disease occurs at all stages of sunflower development. In young plants, browning and rotting of the stem base are observed. Plants attacked at this stage stop growing, fall to the ground and die.

When plants are infected later, around flowering, the attack is located at the base of the stems, in the root ball region, and on the roots, which causes the plants to wilt.

Large portions of tissue appear opaque and are covered in wet weather with a thick, white, cottony-like layer. This layer represents the mycelium of the fungus. Both on the surface of the stem and in the pith, sclerotia can be seen on the surface of the mycelium.

On the leaves, starting from the base of the leaf, there is an alteration and discoloration of the tissues, including the petiole.

The attack on the capitulum starts after its complete development. Brown pigmentation of the tissues appears on the underside, which rots. On the upper, fertile part, abundant white mycelium develops, which changes quite quickly into black sclerotia of various shapes and sizes, generally smaller than those on the stems.

Transmission of the fungus from one year to the next is through sclerotia or mycelium from infected stems and seeds. Sclerotia can retain their germination capacity in the soil for 6-8 years.

During vegetation, the fungus spreads through the dried and flaky mycelium. It can be carried by air currents, insects, birds. Once on healthy plants, under favorable humidity and temperature conditions, the mycelium becomes active and produces new infections. Mycelium in the soil can also pass from one plant to another.

Infection occurs by mycelium penetration through stomata, wounds, or active tearing of plant tissues.

Prophylaxis. As a preventive measure, crop rotation, avoiding excess moisture, deep autumn plowing, cultivation of resistant varieties and hybrids are recommended.

Chemical treatments with specific fungicides are applied during vegetation.

Grey mold of grapes (Botryotinia fuckeliana)

The disease occurs in all countries where vines are grown, destroying a large part of the harvest in autumn, especially in years with abundant rainfall. Significant damage also occurs on grafted stumps.

Symptoms. Grey rot occurs less on leaves, leaf litter, and young bunches, but very frequently on mature berries close to harvest. Yellowish spots appear on the leaves at first, then turn reddish. On both sides of the leaf, a greyish, powdery down develops on the right side, made up of the fruiting bodies of the fungus.

Heavily attacked leaves twist, break off and fall off the leaves. The disease only develops on leaf litter under high humidity conditions. The infection starts at the nodes, where whitish or light yellowish spots appear, which elongate along the internodes.

Attacked tissues are covered with a greyish down, similar to that on leaves. Sometimes small, ovoid, black corpuscles are formed in this down, which are the sclerotia of the fungus.

Grafted seedlings placed in wet sand are attacked at the grafting point, where fungal sclerotia develop, which prevents the graft from being welded to the rootstock.

The most damaging attack is on the berries during ripening.

At first, small spots are visible on their surface, that quickly grow and penetrate into the pulp of the bean.

The patches are yellowish-grey or reddish-purple. Infected berries soften, crack and become covered with a dusty, greyish-brown, powdery down. It spreads from berry to berry, covering the entire cluster, especially in varieties with dense berries. The disease is favored by insect bites, hail damage, and the cracking of fruits epidermis in the vine, a common phenomenon during autumn rains.

The attacked grapes produce weak wines, with low alcohol content and are not suitable for aging and bottling.

In certain areas, on certain soils, on certain varieties, the fungus also produces the so-called “noble rot”. This increases the sugar concentration of the fruit because the fungus mycelium consumes a quantity of water from the berries.

The attacked fruits have a vine color, they are mummified. On their surface, the fungus spores no longer form. The juice obtained has a particularly pleasant aroma, and the high sugar concentration results in liqueur-like, strong wines of outstanding quality.

This “noble rot”, desired by winegrowers, reduces grape production by more than 40%.

The attack of the fungus is favored by high humidity (over 80%) during the ripening period of the grapes and temperatures between 25-28º C. Intense attacks occur after heavy rains accompanied by hail.

On the attacked organs the fungus forms black, rigid, irregularly shaped microsclerotia. The pathogen is transmitted from one year to the next by sclerotia, the resistance mycelium on the attacked cords, and by conidia, which can survive at low temperatures. The pathogen actively penetrates through the epidermis or passively through the wounds of the plant.

Prophylaxis. Cultivation of resistant vine varieties, control of insects that cause fruit injury, early harvesting of vines in rainy and warm autumns are recommended. Fungicide treatments should be made immediately after the falling of petals, when the clusters take on the characteristic shape of the variety, at the entry of the vine and 3 weeks before harvest.

Grey mold (Botrytis cinerea)

It is a disease that is commonly found in tomato crops in greenhouses and solariums and less often in the field.

Symptoms. The attack occurs on all above-ground plant organs. The first symptoms usually appear on the leaves at the base of the plant. Greenish or yellowish-green spots appear on older leaves, which are necrotic and sometimes show concentric zoning.

On the surface of the attacked tissues in a more advanced phase of the disease, an abundant greyish fluff appears, representing the asexual part of the fungus, i.e. conidiophores with conidia. Conidiophores carried by air currents infect other plant organs (stems, fruit).

On stems, the attack is most often seen at the base of the plant, with deep spots appearing in the tissue. If they cover the stem all around, they cause plant death. Similar spots may appear at different levels of the stem and the plants wither above the area of attack.

The most severe form of the attack is on fruit. It looks like a moist, soft rot at the insertion site of the stalk. On its surface, conidiophores and grey conidia develop abundantly. Attacked fruits break off and fall to the ground.

The fungus is transmitted from one year to the next by the resistant mycelium, and during vegetation, it spreads by conidia.

Prophylaxis. As preventive measures, it is recommended to collect and destroy attacked plants, use resistant varieties and hybrids.

During the growing season, specific fungicide treatments are applied.

Fusarium dry rot of potato (Fusarium solani)

It is a very common disease that causes the greatest losses in potatoes during storage.

Symptoms. In the beginning, brown, slightly sunken patches appear on the tubers, of variable size and shape, with soft tissues. The flesh of the tubers rots and turns dark brown, then dries out and hardens.

Gradually the attacked tuber shrivels, shrinks a lot, the flesh turns into a white-yellowish, crumbly mass.

Transmission of the fungus from one year to the next is via conidia, chlamydospores, and resistance mycelium in the attacked plants.

Prophylaxis. Crop rotation over a period of 5-6 years, excluding solanaceous crops, using healthy tubers for planting, sorting tubers before storage, ensuring a temperature between 1-3º C and good ventilation during storage, disinfecting storage rooms before introducing tubers.