Pectobacterium carotovorum

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Cereals

The blackleg in cereals caused by the fungus Gaeumannomyces graminis. Especially in this case the winter crops of wheat, barley and rye are affected. The fungus causes the eponymous and typical blackening of cereal roots. After infection of young corn roots vermorschen this and prevent in particularly serious cases, sufficient water and nutrients to the plant. The survival of the fungus in root and stubble residues can be easily countered by good biological activity in the soil and crop rotation on a non- host plant, as its survival is not more than one year.

Potato

The blackleg is a disease that attacks potato plants. The causative agent, the bacterium Erwinia carotovora ( the scientifically correct name is Pectobacterium carotovorum ) caused both blackleg and the " rot ". By blackleg Ertagsminderungen occur when a stock has about 15 % voids. The rot is one of the dreaded storage diseases. Significant problems can also occur in potatoes, especially if losschalige goods are harvested at high temperatures and large temperature differences is suspended for the chain to the consumer ( condensation). Losses only stock may frequently occur in years with a very wet second half of vegetation. Potatoes on heavy soils are more affected than on light soils, particularly high losses occur in waterlogging. The experience, there are problems with individual varieties significantly more frequently ( for example, " Nicola ", " Satina " and " Adretta " ) than in other varieties (eg, " Solara ").

Symptoms

The infection with Erwinia carotovora is a common cause of defects in the inventory. Yellow plants or individual shoots in inventory, care and eventually die. They are easy to pull out of the ground. Destroy the bacteria in the first place, the cells of the supporting tissue of the stem. At the stem base you will find a typical black coloration with a strong tissue destruction of the so-called vascular bundles and a pungent odor. The disease prevents the water supply up and the removal of assimilates produced in the leaves to the tubers. The rot the tubers transformed into a soft lazy, pulpy mass, which is held together only by the thin shell and bursts with light pressure immediately. The typical pungent odor is not triggered by secondary infections with certain other bacteria.

Biology of the pathogen

Understanding the biology of Erwinia is complicated by the different sub- types of bacteria occur, can colonize each with different tissue of the potato plant and also differ in their mode of transmission. In addition to the potato Erwinia carotovora infects a number of other plants such as carrots, cabbage, tomatoes, peppers, pumpkin, onion, bean, pea and turnip.

The main source of distribution for both subspecies deferred ( = not visible ) infestation of the seed, all seed tubers are latently infected. Particularly strong shell and the lenticels (breathing holes ) the tubers are populated. The different seed lots differ only in the extent of colonization. The question of transmission over the ground is still unknown conclusion. A major source of infection appears to be the ground only at very close sequence of hosts ( for example carrots for potatoes or vice versa) to be.

Get the bacteria from the mother tuber directly on the drive and the drive to grow up, they cause there the typical symptoms of blackleg. The formation of voids or of blackleg is especially favored by moist conditions after planting and during early development. Early planted stands, the casserole was delayed by cool, wet weather, are therefore most affected by blackleg. Rainfall and low temperatures lead to increased infestation in spring.

On the Knoll shell adhering germs can not independently access the daughter tuber, therefore, an infection of the tuber tissue only directly from the mother plant, or the soil water on wounds and on the lenticels is possible. A high soil water content creates favorable propagation possibilities and promotes colonization of the lenticels, as they are opened in high humidity. Therefore heavy sites are more affected by soft rot than light. Injury during harvest and grading operations create portals of entry for the bacteria, a contact of the tubers with contaminated material ( rotting tubers, dust, machinery parts ) during the harvesting, processing and storage increases the contamination degree of a tuber or a game. Nassfäuleausbrüche that are triggered by damage as a result of mechanical damage at harvest and storage, however, be limited to the initial phase of the storage period.

Whether after a successful colonization of the tubers a blight actually breaks out, depends on the number of penetrated bacteria, the resistance responses within the tuber and the conditions in the camp. Because with Erwinia environmental conditions (humidity and temperature) play a crucial role. It develops at temperatures above 10 ° C, the optimum temperature is 25-30 ° C. High humidity and low oxygen concentrations in the room air favor an outbreak, since the resistance responses of potato are almost completely inhibited by lack of oxygen. For the formation of decays a certain bacterial density is required ( an average of 10,000 bacteria per gram ). This is explained by the fact that when bacteria to damage or over open and unverkorkte lenticels enter the tuber tissue, this within the short period of time before a new layer of cork forms need to produce a sufficient amount of enzymes that drives the destruction of the tissue to the race to win. For the sufficient production of enzymes a certain amount of bacteria is necessary to jointly overcome the resistance reactions of the tubers. Under optimal conditions for the bacteria (no oxygen, moisture ) range less than 100 bacteria per gram to cause a disease outbreak, while under aerobic conditions, at least one million to 10 million bacterial cells per gram are necessary in the conventional in storage temperatures. Also, a high nitrogen supply increases the risk of Nassfäuleausbrüchen as this corking the lenticels later and provide the bacteria for a longer period a portal of entry.

Control and preventive measures

The fight against this bacterial disease begins with the use of a minimum infested seedlings. Before the emergence of the plants increase rainfall and irrigation, the risk of infestation significantly. Harvesting should be done only after reaching the shell strength in dry soil. The soil conditions at harvest and storage conditions in the first weeks after intercalation are of paramount importance for the occurrence of storage rot. To avoid injury, the Rodearbeiten should be performed at soil temperatures above 10 ° C, the temperature in the soil, however, should not exceed 20 ° C.

A ten to fourteen-day phase of wound healing and careful drying of the tubers after harvest can help to reduce the infestation pressure in Erwinia. An Autumn Sort of tubers - if they can not be avoided - should be done with care. It represents an additional significant burden

Good ventilation during the entire storage period ensures an oxygen supply and prevents the formation of condensation and liquid films on the tuber surface and anaerobic conditions in stock.

A particular problem is also in organic farming is losschalige early potato games, which are very susceptible to injury. The Losschaligkeit causes those batches after harvest at appropriate temperatures to sweat more than fixed -skinned potatoes in the fall. To avoid Nassfäulen potatoes should be as cool as possible taken out of the ground, so that the bacteria in the tubers can not develop so quickly. This means that the Rodearbeiten should be completed early in the morning usually vor 10 clock, because in high summer soil temperatures rise rapidly to 30 ° C and above at. It should also be prevented during temporary storage in the warehouse and in the store, that a water film out forms on the tubers. Particularly at risk are also washed potatoes. These parts should be dried as quickly as possible after washing. In commercial instruments can be purchased, which measure the moisture content in the stack by measuring the electrical resistance.