VAM is

VAM is fungi.
Vesicular arbuscular mycorrhizal fungi form a symbiotic association with the roots of most terrestrial plants including many crops. It is a type of mycorrhiza in which the symbiont fungus penetrates the cortical cells of the roots of a vascular plant forming arbuscules.
Arbuscular mycorrhizae are characterized by the formation of unique structures, arbuscules and vesicles.
AM fungi help plants to capture phosphorus, sulphur, nitrogen and micronutrients from the soil.