They release into the plant not toxins that kill cells, but suppressor substances, or effectors that suppress the flow of immune reactions. As a result of this, the plant cells remain alive, but helpless, unable to resist the parasite that attacked them, and the fungus acquires the ability to feed on living cells. Of course, in this case, the infected cells die, but by the time they die, the fungus hyphae will have moved forward and infect new ones. Thus, when a plant is infected with biotrophic fungi, unlike necrotrophic ones, the spread of the parasite in the tissue does not lag behind the necrosis, but precedes it.
Feeding the contents of living cells caused the parasites to change their methods of attack in such a way that the cells of the infected plant retain their vitality as long as possible. And for this, as was said, it is impossible to damage the cytoplasmic membrane (plasmalemma) surrounding the protoplast. Some biotrophic fungi do not infect cells at all, their hyphae spread inside plants (endophyto) through the intercellular spaces and with the help of their metabolites force the plants to secrete nutrients into the intercellular spaces that the parasite uses for itself. But most biotrophs secrete some enzymes from the tip of the hypha that come in contact with the plant cell wall, which locally destroy the cell wall, and through the formed hole in the hypha reaches the plasmalemma, which does not destroy, but gently presses into the cell.haustorium. Since the area of the plasma membrane surrounding the haustorium is not covered by a wall, a signal is sent to the nucleus of the infected cell to seal the gap, and a stream of bubbles containing sugars rush to the site of infection and, instead of going to the wall, are intercepted by haustoria, which use them as food
A huge number of fungi – parasites of plants – has a mixed type of food. Initially, they behave like biotrophs, grow in the intercellular space and are capable of even forming haustoria, but after the death of the plant’s cells, they occupy them and develop as necrotrophs.
The most common symptom of diseases caused by hemibiotrophs is spotting , in which local dark or, on the contrary, light spots are formed on infected organs, sometimes surrounded by a red rim due to accumulation of phenolic pigments as a response to infection. On thick, watered tissues, for example, leaflets of beans or peas, melon or pumpkin, spots can be pressed into the tissue of the fetus and contain mucus on the surface, in which the spores of the fungus are immersed. This kind of disease is called anthracnose.