1) By killing nematode  pathogens:

• Dreschler 1937 reported that there are some predacious fungi in the soil. e.g. Arthrobotrys oligospora.
• Fungus grows profusely, producing several minute hyphal loops. These loops form network of threads & are extremely sticky with viscous fluid on their surface.
• While the eelworms wander in the soil. If they come across such a fungal loop, they are at once trapped.
• They may struggle hard to get out themselves from the trap. After about 2 hours, they slow down & finally die soon.
• The fungal hyphae penetrate inside the worm, producing a network of mycelium which feel the body of eelworms. Thus the tissue is utilized as food by the fungus & is disintegrated within one or 2 days after attack.
• In this way crop plant is saved from such nematode infection & grows luxuriantly. Ultimately crop production is increased. Other examples of nematode killing fungi are Dactyllella lobata, D. ellipsospora, Harposporangium spp. etc.

2) By killing fungal pathogens:

• Trichoderma & Gleocladium spp. are present in damp soil.
• They have antagonistic properties or effect on the growth of Pythium mycelium.
• They serve to suppress the growth of pathogens and create favorable environment for plant growth & production.

3) The mycorrhizal association:

• Sometimes fungi grow on the surface or inside the roots of higher plants. They are called mycorrhiza.
• The fungal hyphae in this association functions like root hair & absorbs water & minerals from the soil & supply them to the roots.
• Radioactive labellum studies have shown that N, P & Ca applied in the soil can enter the plants through mycorrhiza & help in the growth of plant & ultimately crop production is increased.
• Inside the infection thread they are released into the cytoplasm of cortical cells where they stimulate the division of cortical cells.
• This division let to the formation of proliferation tissues which finally develops into nodules. The root nodules are made up of tetraploid cells.