Strobilurin

Strobilurins are a class of synthetic and natural fungicides that inhibit respiration in fungal cells by targeting the cytochrome bc1 complex of the mitochondrial electron transport chain. The discovery of strobilurin A in 1944 by Japanese mushroom breeder Takehisa Shiku sparked interest, although the first commercial product based on this natural compound, Rward, appeared only in the 1970s. In 1980s the chemistry community identified the active site as the 1,3-bis(phenyl)-4,4-dioxobutene-2,5-diol scaffold. This led to the development of a series of analogues—such as azoxystrobin, kresoxim-methyl, and trifloxystrobin—that were formulated as spray-adjuvants for uses in cereal crops, vineyards, fruit orchards and ornamental horticulture. Strobilurins are broad-spectrum and active against more than 200 phytopathogenic species including Botrytis, Phytophthora, and many powdery mildews. Their mode of action confers long residual activity; application rates are typically lower than for many older systemic fungicides. Resistance management guidelines emphasize alternation with other classes, use of mixtures, and cultivation of resistant crop varieties. The first instances of field resistance arose in the mid-1990s with strains of Botrytis cinerea that possessed secondary mutations in the cytochrome b gene. These mutations diminish binding affinity, resulting in 5-20 fold increases in EC50 values. Regulatory agencies such as the EPA and the European Food Safety Authority accept strobilurins under strict environmental risk assessments, noting their rapid soil degradation (half‑lives of 20–60 days) and low mammalian toxicity. Research continues into next‑generation strobilurins that aim to reduce the potential for resistance and improve safety profiles.