How does rust form?

What the evidence shows

Chemical Oxidation

Rust is a complex of oxides and hydroxides of iron². It forms when iron or certain alloys are exposed to oxygen and moisture².

Water molecules can penetrate microscopic pits and cracks in exposed metal². Oxygen atoms then combine with metallic atoms to form the destructive oxide compound².

Fungal Infection

Rust fungi are obligate plant pathogens that only infect living plants⁴. The infection process begins when urediniospores germinate to produce a single germ tube¹.

The germ tube grows across the leaf surface until an appressorium forms¹. Successful infection depends on the availability of moisture on plant surfaces¹.

Biological Growth

Once the fungus invades the plant, it grows into plant mesophyll cells⁴. It produces specialized hyphae known as haustoria to transport nutrients from the plant⁴.

The fungus continues growing and penetrating more plant cells until spore growth occurs⁴. This cycle allows the infection to move from one cereal plant to another³.

What we can't say for sure

The exact start point of the rust fungus life cycle is unknown as it is considered cyclical³.