Agricultural Fungicides Targeting the Cytochrome bc1 Complex

The cytochrome bc 1 complex of the mitochondrial respiratory chain is a proven target for agricultural fungicides. The complex possesses two substrate/inhibitor binding pockets, termed Q o site and Qi site. Their inhibitors are classified as Q o Is (Q o site binding inhibitors) and QiIs (Qi site binding inhibitors), with a few rare compounds targeting both sites. Several tools are available to determine the mode of action of bc 1 complex inhibitors, which include spectroscopic methods and mutational analysis. Most of the agrifungicides bind at the Q o site of the complex. 338 They share the same binding mode as the same resistance mutation in the Q o site, namely G143A, confers cross-resistance to these Q o Is, with the exception of metyltetraprole, a new compound still in development. Until recently, only three agrifungicides targeting the Q i site were available. They are active only against oomycetes. By contrast, the newly marketed fenpicoxamid is active against a broad range of ascomycetes. Novel compounds that can counter the problem of the widespread resistance mutation G143A, such as metyltetraprole and fenpicoxamid, are likely to be useful tools for the control of pathogenic fungi. However, the possible occurrence of resistance mutations, especially target site mutations, remains an issue.