Adventitious roots are plant roots that emerge from the other parts of the plant other than the radicle. These are distinguished from primary and sideways roots by this concept. Certain subgroups of the adventitious roots can emerge both naturally during normal development (crown roots on cereals and nodal roots on strawberries) and as a reaction to stressful situations like flooding, nutrient scarcity etc. Several adventitious root types are governed in distinct ways. A mass of adventitious roots along with its branches constitutes an adventitious root system. The adventitious root system differs from the taproot system in such a way that adventitious roots have multiple morphologically identical roots growing from a single node rather than a single primary root from which the branches emerge. Adventitious roots typically appear to develop from a plant’s aerial portions. When planted in the soil, leaf and stem cuttings might produce accidental roots.

They are crucial for human existence and economic growth, as well as for our environment. It’s critical to comprehend how crops establish their adventitious roots in normal and stressful situations in order to increase food production that is environmentally sustainable. Thus, for breeding programmes, it is necessary to understand the physiology and regulation of adventitious root production.

Modifications of the adventitious root system

Adventitious roots are changed to sustain the plant mechanically, store food, and carry out essential tasks.

1. Types of roots for mechanical support:

(a). Prop or pillar adventitious roots- These are adventitious roots that grow while facing downwards from the branches of the trees. These roots get modified in order to support large and chunky branches. The reason why these roots are red in colour is due to the absorption of the water present in the form of moisture in the aerial roots. Because the prop roots nurture the crown of the tree, the tree remains alive even if its trunk has died. A perfect example, that has Prop or pillar adventitious roots, is the Banyan tree.

(b). Stilt roots- These are short and thick and get modified to support the plant. They emerge in slantways from the basal node (located just below or above the soil) of the stem, before penetrating into the soil. Then they mutate into fibrous roots resulting in water and mineral absorption. For example, Sugarcane and maize

(c). Climbing roots- Climber plants have weak stems so they use tendrils to climb on trees. They have climbing roots that penetrate into the cracks. Climbing roots are found in plants like the Money plant (Epipremnum aureum) and vanilla (Vanilla Planifolia) (d). Buttress roots- These roots evolve at the base of the stem and preserve their sturdiness. This type of stem is vertically extended which means that it is bi-directional. For example, the Arjuna Tree has buttress roots.

2. To store food:

(a). Fasciculated roots are modified adventitious roots which are in cluster form that emerges from the base of the stem. Examples are Asparagus and Dahlia

(b). Tuberous roots are shapeless and substantial. These are modified from Taproots. These roots are very fleshy and function as a storage organ in a plant. The Tuberous roots result in root vegetables like Sweet potatoes.

(c). Moniliform roots- Just like Tuberous roots, these roots are modifications of adventitious roots that are swollen in nature. For example, Ross Moss.

(d). Annulated roots- These are modified adventitious roots having disc-like outgrown structures one over the other. For example, Ipecac, a small shrub found in some parts of Central America and Brazil.

(e). Nodulose roots- These are other modified adventurous roots which are oddly swollen at the apex (tip of the root).