Fungal resistance to sterol biosynthesis inihitors: a new challenge

Yield losses caused by plant pathogens have threatened the security and efficiency of crop production since agriculture became the main source of the human food supply. Fortunately, agriculture has made tremendous progress during the last century, and part of this progress has been the development of modern means of plant disease control. In particular, the introduction of chemical disease control agents has contributed to a substantial increase in c r o p p roduc t ion , t o a smoothing of annual undulations in crop yields, and, ultimately, to today's high level of food security. T h e f i rs t mi les tone in fungic ide development was the introduction of ino rgan ic fungic ides such a s sul fur , copper, or mercury compounds, followed by the development of organic fungicides such as dithiocarbamates (e.g., maneb) and phthalimides (e.g., captan). These two classes of protective compounds have been used extensively for decades without development of field resistance. D u r i n g the s a m e pe r iod , o rgan ic insect ic ides had a l r eady encoun te red cumbersome drawbacks. Gordon (16) introduced his 196 1 review on insecticide resistance with a clear statement: "The number of insect species or populations resistant t o one or more of the synthetic organic insecticides has increased every year since 1947, and there is yet no indication that this trend can be halted or reversed." The conclusion on fungicide res is tance d r a w n 6 years l a t e r by Georgopoulos and Zaracovitis (14) was clearly different: "Tolerance to organic fungicides used in the control of fungal diseases of plants or storage rot has created practical difficulties in only a few instances."The future prospects, however, sounded less optimistic, and the authors must have seen the dawn of a major change: "If future fungicides must be selective, interfering with the metabolism