Many rain forest plants are prone to developing fungal infections on their leaves. Fungi can grow rapidly in moist environments, and a serious infection can kill plants

Resistance plants increase in number whereas non-resistant plants decreases.

Explanation:

The environment of rain forest is suitable for the fungal growth because of the presence of humidity in the environment and we know that fungi needs moist places for its growth. These fungus attached on the leaves and takes nutrients from that plant that leads to the stunted growth and many cases death of the plant occurs. Some plants have no effect of this fungus due to the presence of resistance in them so if the fungus spreads in the whole forest so the plants which are prone to these fungal infections eliminated from that environment and resistant plants are increase in number.