necrotrophs

Necrotrophs are organisms that obtain nutrients from dead or decaying tissue, typically after killing host cells. In plant pathology, they are contrasted with biotrophs, which feed on living tissue, and with hemibiotrophs, which initially colonize living tissue and later switch to a necrotrophic phase. Necrotrophs include many fungi and oomycetes, some bacteria, and various other microorganisms.

Mechanisms typically involve penetration of host tissues through wounds or natural openings, followed by secretion of enzymes that degrade cell walls—such as pectinases, cellulases, and cutinases—and the production of toxins or other factors that induce necrosis. The resulting dead tissue serves as a nutrient-rich substrate for rapid colonization and reproduction. Some necrotrophs cause tissue death directly via toxins, while others contribute to necrosis indirectly by triggering programmed cell death in host cells.

Examples of fungal necrotrophs of agricultural importance include Botrytis cinerea (gray mold) and Sclerotinia sclerotiorum (white mold), which affect fruits, vegetables, and ornamentals; Alternaria and Fusarium species are also necrotrophic. Oomycete necrotrophs include Phytophthora and Pythium species. Bacterial necrotrophs such as Pectobacterium and Erwinia species cause soft rot and tissue maceration.

Ecological and economic significance: necrotrophs contribute to plant disease and tissue decay in natural ecosystems and agriculture, causing yield losses and post-harvest spoilage. Management relies on integrated approaches, including resistant cultivars, sanitation and crop rotation, timely harvest and storage, appropriate chemical controls, and, where suitable, biological control strategies.