Commercial marigold (Tagetes erecta / Tagetes patula) cultivation, grown for loose flower markets, Garland production, and pigment (lutein) extraction, faces heavy economic loss from soil-borne stem rots and foliar flower blights, notably Alternaria Leaf Spot / Flower Blight (Alternaria tagetica), Damping-Off / Collar Rot (Pythium spp. / Rhizoctonia solani), and Phytophthora Stem Rot (Phytophthora nicotianae). Alternaria tagetica causes dark brown circular spots on leaves and petals during humid weather, turning vibrant orange and yellow blooms brown and unmarketable. Applying Bacillus subtilis as a seed treatment, nursery seedling root dip, or weekly foliar spray establishes a dense biological shield across foliage, stems, and flower buds. The bacteria colonize host surfaces, producing cyclic lipopeptides (surfactin, iturin, fengycin) that disrupt fungal spore germination and stop hyphal expansion on flower petals.

Beyond disease control, Bacillus subtilis acts as a valuable plant growth-promoting rhizobacterium (PGPR) in commercial floriculture and intercropping systems. It solubilizes fixed soil phosphorus, secretes siderophores for iron mobilization, and produces natural growth regulators that encourage robust lateral branching and root expansion. Enhanced root health supports heavy flower bud set, increases flower diameter and petiole strength, and improves petal xanthophyll/lutein accumulation. Regular application ensures clean, residue-free marigold flowers with extended post-harvest shelf life for loose flower trading and Garland markets.

Importance of Bacillus subtilis in Marigold Cultivation

Marigold is a fast-growing flowering crop that requires healthy roots and continuous nutrient uptake to support prolonged flowering. Strong root systems encourage vigorous branching and the production of large numbers of marketable flowers.

Bacillus subtilis rapidly colonizes the rhizosphere and competes with harmful fungi and bacteria for nutrients and space. It also produces natural antimicrobial metabolites that suppress disease-causing organisms while encouraging beneficial microbial populations.

Healthy roots support more flowering shoots, larger blooms, improved flower colour, and higher flower yield.