**2. Chemicals alternative to conventional fungicides**

The continuing development of fungicide resistance in plant and human pathogens necessitates the discovery and development of new fungicides. Several preharvest and postharvest pathogens have developed resistance to commonly used fungicides. Hence, a wide range of chemicals has been evaluated for their potential for use as alternative to the current fungicides, e.g. plant extracts and some compounds obtained from plants. Discovery and evaluation of natural product based fungicides for agriculture is largely dependent upon the availability of miniaturized antifungal bioassay. Essentials for natural product bioassays include sensitivity to very small quantities, selectivity to determine optimum target pathogens, and adaptability assays should be relevant to potential pathogen target sites in the natural infection process of the host and applicable to the agrochemical industry. Bioassays should take advantage of current high throughput technology available to evaluate dose-response relationships, commercial fungicides standards, modes of action, and structure activity studies (Wedge & Smith, 2006).

Since the early 1970s, agriculture worldwide has struggled with the evolution of pathogen resistance to disease control agents. Increased necessities for repeated chemical applications, development of pesticide cross-resistance and disease resistance management strategies have characterized the use of agricultural chemicals to-date. As a consequence, producers are currently attempting to control agricultural pests with a decreasing arsenal of effective crop protection chemicals. In addition, the desire for safer pesticides with less environmental impact has become a major public concern. Particularly desirable is the discovery of novel pesticide agents from new chemical classes that are able to operate using different modes of action and, consequently, against plant pathogens with resistance to currently used chemistries. In this regard, evaluating natural products and extracts as a source of new pesticides is one strategy for the discovery of new chemical moieties that have not previously been created by synthetic chemists (Wedge & Smith, 2006).

In January 2009, European Parliament agreed the text of a Regulation to replace 91/414/EC which Plant Protection Products have been regulated up to now. The new Regulation, originally proposed in July 2006, maintained risk assessment but also introduced the concept of hazard assessment or 'cut-off criteria' for the approval of active substances. In addition it proposed the concept of comparative assessment and substitution for those active substances meeting certain 'less stringent' hazard criteria. According to this Regulation, the potential impact in terms of percentage reductions in available active fungicides from 31 to 43% not approved (Richardson, 2009).

fruit or within its tissues following fungicidal treatment and the 1986 report from the US National Academic of Sciences (Research Council, Board of Agriculture, 1987) indicating that fungicide residues on food pose a great health risk to the consumer, led to the search for safe alternatives to synthetic fungicides. The fact that the effectiveness of synthetic fungicides has been reduced by the frequent development of resistance by the pathogens further highlighted the need for new substances and methods for the control of storage diseases. Naturally occurring plant products are important sources of antifungal compounds with low toxicity to mammals and safe to the environment which may serve as substitutes for synthetically produced fungicides. It was later suggested that these compounds might be developed either as products by themselves or used as starting point

The continuing development of fungicide resistance in plant and human pathogens necessitates the discovery and development of new fungicides. Several preharvest and postharvest pathogens have developed resistance to commonly used fungicides. Hence, a wide range of chemicals has been evaluated for their potential for use as alternative to the current fungicides, e.g. plant extracts and some compounds obtained from plants. Discovery and evaluation of natural product based fungicides for agriculture is largely dependent upon the availability of miniaturized antifungal bioassay. Essentials for natural product bioassays include sensitivity to very small quantities, selectivity to determine optimum target pathogens, and adaptability assays should be relevant to potential pathogen target sites in the natural infection process of the host and applicable to the agrochemical industry. Bioassays should take advantage of current high throughput technology available to evaluate dose-response relationships, commercial fungicides standards, modes of action,

Since the early 1970s, agriculture worldwide has struggled with the evolution of pathogen resistance to disease control agents. Increased necessities for repeated chemical applications, development of pesticide cross-resistance and disease resistance management strategies have characterized the use of agricultural chemicals to-date. As a consequence, producers are currently attempting to control agricultural pests with a decreasing arsenal of effective crop protection chemicals. In addition, the desire for safer pesticides with less environmental impact has become a major public concern. Particularly desirable is the discovery of novel pesticide agents from new chemical classes that are able to operate using different modes of action and, consequently, against plant pathogens with resistance to currently used chemistries. In this regard, evaluating natural products and extracts as a source of new pesticides is one strategy for the discovery of new chemical moieties that have

In January 2009, European Parliament agreed the text of a Regulation to replace 91/414/EC which Plant Protection Products have been regulated up to now. The new Regulation, originally proposed in July 2006, maintained risk assessment but also introduced the concept of hazard assessment or 'cut-off criteria' for the approval of active substances. In addition it proposed the concept of comparative assessment and substitution for those active substances meeting certain 'less stringent' hazard criteria. According to this Regulation, the potential impact in terms of percentage reductions in available active

not previously been created by synthetic chemists (Wedge & Smith, 2006).

fungicides from 31 to 43% not approved (Richardson, 2009).

for synthesis (Knight et al., 1997).

**2. Chemicals alternative to conventional fungicides** 

and structure activity studies (Wedge & Smith, 2006).

Under this situation there have been investigated new methods to control plant diseases as an alternative way to chemical fungicide application either eliminating these synthetic compounds from agriculture or meanly controlling their use together with natural fungicide substances in an unique strategy plan called Integrated Plant Management (IPM).
